Here comes the fun!
(Note the noteworthy submissions from Dr. Luke O'Dell in this wrap-up.)
These are the journals that were exhaustively combed (three times over. Honestly.) to procure the following entries:
Advanced Mater. (Wiley)
Chem. Phys. Lett. (Elsevier)
Chem. Commun. (RSC)
Dalton Trans. (RSC)
***
Chemical Physics Letters
Vol: 458, Issue: 4-6, June 17, 2008
pp. 368-372
Title: Intermolecular multiple-quantum coherences between spin 1/2 and quadrupolar nuclei in liquid nuclear magnetic resonance
Authors: Chen, S.; Cai, S.; Chen, Z.
Abstract (English): The features of the NMR signals from intermolecular multiple-quantum coherences between spin 1/2 and quadrupolar nuclei were investigated theoretically and experimentally.
***
Chemical Physics Letters
Vol: 458, Issue: 4-6, June 17, 2008
pp. 391-395
Title: Improving resolution in proton solid-state NMR by removing nitrogen-14 residual dipolar broadening
Authors: Stein, R.S.; Elena, B.; Emsley, L.
Abstract (English): Improved resolution is obtained for 1H solid-state NMR spectra by removing residual broadening due to interactions with neighboring 14N nuclei.
***
Chemical Physics Letters
Vol: 459, Issue: 1-6, June 27, 2008
pp. 188-193
Title: Solid-state single-scan 2D NMR under magic-angle-spinning
Authors: Gal, M.; Melian, C.; Demco, D.E.; Blumich, B.; Frydman, L.
Abstract (English): 2D NMR rubber spectrum collected within a single-scan (27ms total time) using a 2ms mixing time and magic-angle-spinning at 17kHz.
***
Chemical Physics Letters
Vol: 460, Issue: 1-3, July 20, 2008
pp. 278-283
Title: MIRROR recoupling and its application to spin diffusion under fast magic-angle spinning
Authors: Scholz, I.; Huber, M.; Manolikas, T.; Meier, B.H.; Ernst, M.
Abstract (English): A new second-order recoupling experiment under MAS NMR conditions is introduced. It allows measurement of proton-driven spin-diffusion spectra even at fast MAS conditions.
***
Chemical Physics Letters
Vol: 460, Issue: 4-6, July 30, 2008
pp. 531-535
Title: Simultaneous adiabatic spin-locking cross polarization in solid-state NMR of paramagnetic complexes
Authors: Peng, W.K.; Samoson, A.; Kitagawa, M.
Abstract (English): 13C NMR spectrum of Cu(II)(d,l-alanine)2.H2O, observed with different techniques, (a) SADIS cross polarization, (b) RAMP cross polarization, and (c) direct excitation of 13C. The signal-to-noise ratios (SNRs) are denoted besides its peaks.
***
Chemical Physics Letters
Vol: 461, Issue: 1-3, August 8, 2008
pp. 33-37
Title: From correlation-consistent to polarization-consistent basis sets estimation of NMR spin-spin coupling constant in the B3LYP Kohn-Sham basis set limit
Author: Kupka, T.
Abstract (English): Based on recently B3LYP calculated spin-spin coupling constants (SSCC) of several small molecules with cc-pVxZ, cc-pCVxZ, cc-pCVxZ-sd and cc-pCVxZ-sd+t basis sets, a reasonably fit, using the two-parameter formula, to the complete basis set limit (CBS) is shown. Calculation of water's ^1J(OH) using B3LYP/cc-pCVxZ and B3LYP/pcJ-n significantly improved the FC term and its total convergence.
***
Chemical Physics Letters
Vol: 462, Issue: 1-3, September 1, 2008
pp. 125-128
Title: Quantification of cross polarization with relaxation compensated reciprocity relation in NMR
Authors: Shu, J.; Chen, Q.; Zhang, S.
Abstract (English): Computer simulated reciprocity relation between the dynamics of cross polarization (CP) and cross depolarization (CDP) for a powder sample under fast magic angle spinning (MAS=40kHz). The symmetrical pattern between CP(t) and CDP(t) manifests the quantification of cross polarization under fast MAS. In the simulation, the dipolar coupling constant for a 1H-13C spin pair is d=25.37kHz and the RF spin-locking fields f1I and f1S are 140 and 100kHz, respectively.
***
Chemical Physics Letters
Vol: 463, Issue: 4-6, October 1, 2008
pp. 418-421
Title: Determination of transverse relaxation rates of individual spins while quenching echo modulations due to homonuclear scalar couplings
Authors: Aeby, N.; Bodenhausen, G.
Abstract (English): When spin-echo modulations are quenched, individual transverse relaxation rate constants R2(I)=1/T2(I) can be determined for each spin I individually site by site.
***
Chemical Physics Letters
Vol: 464, Issue: 1-3, October 13, 2008
pp. 97-102
Title: QCPMG using adiabatic pulses for faster acquisition of ultra-wideline NMR spectra
Authors: O'Dell, L.A.; Schurko, R.W.
Abstract (English): A QCPMG-like pulse sequence utilizing adiabatic (WURST) pulses. This sequence allows broadband excitation of ultra-wideline solid-state NMR spectra, combined with a significant increase in signal per scan. The sequence has been successfully used to acquire 71Ga and 91Zr spectra over 500kHz in width without any frequency or field adjustment. It can also be used to observe satellite transitions.
***
Chemical Physics Letters
Vol: 464, Issue: 1-3, October 13, 2008
pp. 42-48
Title: New perspectives on calcium environments in inorganic materials containing calcium-oxygen bonds: A combined computational-experimental ^4^3Ca NMR approach
Authors: Gervais, C.; Laurencin, D.; Wong, A.; Pourpoint, F.; Labram, J.; Woodward, B.; Howes, A.P.; Pike, K.J.; Dupree, R.; Mauri, F.; Bonhomme, C.; Smith, M.E.
Abstract (English): The potential of a combined experimental-computational 43Ca solid state NMR approach for the structural analysis of inorganic compounds is presented.
***
Chemical Physics Letters
Vol: 464, Issue: 4-6, October 23, 2008
pp. 235-239
Title: Irreducible spherical tensor analysis of quadrupolar nuclei
Authors: Chandra Shekar, S.; Rong, P.; Jerschow, A.
Abstract (English): Selection of a specific spherical tensor term from the density matrix of a spin=7/2 particle, demonstrated experimentally as a function of evolution time.
***
Chemical Physics Letters
Vol: 466, Issue: 1-3, November 24, 2008
pp. 95-99
Title: Homonuclear dipolar decoupling at magic-angle spinning frequencies up to 65kHz in solid-state nuclear magnetic resonance
Authors: Leskes, M.; Steuernagel, S.; Schneider, D.; Madhu, P.K.; Vega, S.
Abstract (English): Experimental aspects of the implementation of homonuclear dipolar decoupling schemes for 1H spectroscopy in solid-state NMR at high magic-angle spinning frequencies of up to 65kHz are demonstrated.
***
Chemical Physics Letters
Vol: 466, Issue: 4-6, December 4, 2008
pp. 227-234
Title: Application of static microcoils and WURST pulses for solid-state ultra-wideline NMR spectroscopy of quadrupolar nuclei
Authors: Tang, J.A.; O'Dell, L.A.; Aguiar, P.M.; Lucier, B.E.G.; Sakellariou, D.; Schurko, R.W.
Abstract (English): The uses of microcoils and WURST pulses for acquiring ultra-wideline (UW) NMR spectra of half-integer quadrupolar nuclei are explored.
***
Chemical Physics Letters
Vol: 466, Issue: 4-6, December 4, 2008
pp. 247-251
Title: Efficient heteronuclear decoupling by quenching rotary resonance in solid-state NMR
Authors: Weingarth, M.; Tekely, P.; Bodenhausen, G.
Abstract (English): We propose efficient heteronuclear decoupling by quenching rotary resonance in fast MAS solid-state NMR
***
Chem. Commun.
2008, 5568 - 5570,
DOI: 10.1039/b812928b
Title: Quantifying the fraction of glycine and alanine in -sheet and helical conformations in spider dragline silk using solid-state NMR
Authors: Gregory P. Holland, Janelle E. Jenkins, Melinda S. Creager, Randolph V. Lewis and Jeffery L. Yarger
Abstract: Solid-state two-dimensional refocused INADEQUATE MAS NMR experiments resolve distinct helical and -sheet conformational environments for both alanine and glycine in Nephila clavipes dragline silk fibers; the fraction of alanine and glycine in -sheet structures is determined to be 82% ± 4% and 28% ± 5%, respectively.
***
Chem. Commun.
2008, 5722 - 5724
DOI: 10.1039/b812905c
Title: Deuterated polymer gels for measuring anisotropic NMR parameters with strongly reduced artefacts
Authors: Grit Kummerlöwe, Sebastian Knör, Andreas O. Frank, Thomas Paululat, Horst Kessler and Burkhard Luy
Abstract: Perdeuterated poly(styrene) is introduced as an almost artefact-free and arbitrarily scalable alignment medium for measuring residual dipolar couplings and other anisotropic NMR parameters; the spectral quality achievable in this new medium is demonstrated for HSQC spectra leading to the conformational analysis of staurosporine and homonuclear TOCSY-type experiments.
***
Chem. Commun.
2008, 5933 - 5935
DOI: 10.1039/b814326a
Title: Solid-state 115In NMR study of indium coordination complexes
Authors: Fu Chen, Guibin Ma, Ronald G. Cavell, Victor V. Terskikh and Roderick E. Wasylishen
Abstract: The feasibility of solid-state 115In NMR studies is demonstrated by an examination of four different coordination complexes: indium(III) acetylacetonate, indium(III) tris(tropolonato), indium(III) triiodide bis(tris(4-methoxyphenyl)phosphine oxide) and indium(III) trichloride tris(2,4,6-trimethoxyphenyl)phosphine. The results provide information about the electric field gradients and magnetic shielding at the indium nuclei through the nuclear quadrupolar and chemical shift parameters, respectively. The CQ values in these four complexes range between 106.0 ± 2.0 and 200.0 ± 4.0 MHz, while the magnetic shielding anisotropies fall in the range from 85 ± 15 to 550 ± 60 ppm. Finally, this research demonstrates that solid-state 115In NMR studies are facilitated by performing experiments at the highest possible magnetic-field strengths, and that NMR offers a promising tool for the characterization of indium compounds.
***
Chem. Commun.
2008, 5981 - 5983
DOI: 10.1039/b813237b
Title: Revealing molecular self-assembly and geometry of non-covalent halogen bonding by solid-state NMR spectroscopy
Authors: Markus Weingarth, Noureddine Raouafi, Benjamin Jouvelet, Luminita Duma, Geoffrey Bodenhausen, Khaled Boujlel, Bernd Schöllhorn and Piotr Tekely
Abstract: We report a new spectroscopic fingerprint of intermolecular contacts in halogen bond-driven self-assembling aggregates and a precise determination of intermolecular NI distances in microcrystalline samples.
***
Chem. Commun.
2009, 186 - 188
DOI: 10.1039/b817017g
Title: A natural abundance 33S solid-state NMR study of layered transition metal disulfides at ultrahigh magnetic field
Authors: Andre Sutrisno, Victor V. Terskikh and Yining Huang
Abstract: Using a series of layered transition metal disulfides we demonstrate that the wide-line natural abundance solid-state NMR spectra of 33S in a less symmetric environment can readily be obtained at ultrahigh magnetic field of 21.1 T and that surprisingly these closely related materials display a wide range of 33S quadrupole coupling constant and chemical shift anisotropy values.
***
Dalton Trans.
2008, 3723 - 3728
DOI: 10.1039/b802496k
Title: Structural, 197Au Mössbauer and solid state 31P CP/MAS NMR studies on bis (cis-bis(diphenylphosphino)ethylene) gold(I) complexes [Au(dppey)2]X for X = PF6, I
Authors: Peter C. Healy, Bradley T. Loughrey, Graham A. Bowmaker and John V. Hanna
Abstract: 197Au Mössbauer spectra for the d10 gold(I) phosphine complexes, [Au(dppey)2]X (X = PF6, I; dppey = (cis-bis(diphenylphosphino)ethylene), and the single crystal X-ray structure and solid state 31P CPMAS NMR spectrum of [Au(dppey)2]I are reported here. In [Au(dppey)2]I the AuP4 coordination geometry is distorted from the D2 symmetry observed for the PF6- complex with Au–P bond lengths 2.380(2)–2.426(2) Å and inter-ligand P–Au–P angles 110.63(5)–137.71(8)̊. Quadrupole splitting parameters derived from the Mössbauer spectra are consistent with the increased distortion of the AuP4 coordination sphere with values of 1.22 and 1.46 mm s-1 for the PF6- and I- complexes respectively. In the solid state 31P CP MAS NMR spectrum of [Au(dppey)2]I, signals for each of the four crystallographically independent phosphorus nuclei are observed, with the magnitude of the 197Au quadrupole coupling being sufficiently large to produce a collapse of 1J(Au–P) splitting from quartets to doublets. The results highlight the important role played by the counter anion in the determination of the structural and spectroscopic properties of these sterically crowded d10 complexes.
***
Dalton Trans.
2008, 3782 - 3790
DOI: 10.1039/b719526e
Title: Perspectives in paramagnetic NMR of metalloproteins
Authors: Ivano Bertini, Claudio Luchinat, Giacomo Parigi and Roberta Pierattelli
Abstract: NMR experiments and tools for the characterization of the structure and dynamics of paramagnetic proteins are presented here. The focus is on the importance of 13C direct-detection NMR for the assignment of paramagnetic systems in solution, on the information contained in paramagnetic effects observed both in solution and in the solid state, and on novel paramagnetism-based tools for the investigation of conformational heterogeneity in protein–protein complexes or in multi-domain proteins.
***
Dalton Trans.
2008, 4965 - 4974
DOI: 10.1039/b803510p
Title: Nitrogen-15 NMR spectroscopy of N-metallated nucleic acids: insights into 15N NMR parameters and N–metal bonds
Authors: Yoshiyuki Tanaka and Akira Ono
Abstract: It was recently demonstrated spectroscopically that RNA/DNA nucleobases can bind to metal cations in aqueous solution through coordination bonds and covalent bonds. Nitrogen-15 (15N) NMR spectroscopy was employed and shown to be a powerful tool for determining the mode of metal ion binding to nitrogen atoms in RNA/DNA molecules. This review describes 15N NMR spectroscopic characteristics in accordance with the mode of metal ion binding to nitrogen atoms. The general rules for 15N chemical shift changes, which are applicable to the determination of the metal ion binding mode of N-metallated compounds, are also described.
***
Dalton Trans.
2008, 5296 - 5301
DOI: 10.1039/b809062a
Title: Effect of oxygen content on the 29Si NMR, Raman spectra and oxide ion conductivity of the apatite series, La8+xSr2-x(SiO4)6O2+x/2
Authors: A. Orera, E. Kendrick, D. C. Apperley, V. M. Orera and P. R. Slater
Abstract: 29Si NMR data have been recorded for the apatite series La8+xSr2-x(SiO4)6O2+x/2 (0 x 1.0). For x = 0, a single NMR peak is observed at a chemical shift of -77 ppm, while as the La:Sr ratio and hence interstitial oxygen content is increased, a second peak at a chemical shift of -80 ppm is observed, which has been attributed to silicate groups neighbouring interstitial oxide ions. An increase in the intensity of this second peak is observed with increasing x, consistent with an increase in interstitial oxide ion content, and the data are used to estimate the level of interstitial oxide ions, and hence Frenkel-type disorder in these materials. The increase in second 29Si NMR peak intensity/interstitial oxide ion content is also shown to correlate with an increase in conductivity. The effect of interstitial oxygen content can also be studied by means of Raman spectroscopy, with a new mode at 360 cm-1 appearing for samples with x > 0 in the symmetric bending mode energy region of the SiO4 group. The intensity of this mode increases with increasing oxygen content, yielding results comparable to those from the NMR studies, showing the complementarities of the two techniques.
***
Dalton Trans.
2008, 6150 - 6158
DOI: 10.1039/b810863c
Title: Structure determination of -Pb2ZnF6 by coupling multinuclear solid state NMR, powder XRD and ab initio calculations
Authors: Charlotte Martineau, Franck Fayon, Christophe Legein, Jean-Yves Buzaré, Monique Body, Dominique Massiot and François Goutenoire
Abstract: The results from one-dimensional multinuclear (19F, 207Pb and 67Zn) magic-angle spinning nuclear magnetic resonance experiments combined with the use of the ISODISPLACE program allow for the space group determination of -Pb2ZnF6 (no. 138 P42/ncm). The structure was refined from X-ray powder diffraction data (a = 5.633 (1) and c = 16.247 (1) , Z = 4). -Pb2ZnF6 has one six-fold coordinated Zn, one eleven-fold coordinated Pb and five F non-equivalent crystallographic sites and is built from alternated layers parallel to the (a, b) plane; tilted ZnF42- layers of corner sharing ZnF64- octahedra and FPb+ layers of edge sharing FPb47+ tetrahedra. The structure of -Pb2ZnF6 was then optimized using the ab initio code WIEN2k and the calculated 67Zn EFG is in agreement with the NMR results. 19F–19F proximities and 19F–207Pb connectivities were evidenced using through-space and through-bond NMR correlation experiments, respectively, and support the proposed structure. 19F–207Pb J-coupling was also used to select fluorine resonances depending on the number of neighbouring lead ions, leading to an unambiguous assignment of the different 19F resonances.
***
Thursday, January 08, 2009
Macromolecules August 2008 (Volume 41, Issue 16) to January 2009 (Volume 42, Issue 1)
Segmental Dynamics of Bulk Poly(vinyl acetate)-d3 by Solid-State 2H NMR: Effect of Small Molecule Plasticizer
Rakesh R. Nambiar† and Frank D. Blum*‡
Macromolecules, 2008, 41 (24), pp 9837–9845
Abstract: The effect of dipropyleneglycol dibenzoate, a plasticizer, on the glass-transition temperature (Tg) of poly(vinyl acetate) was studied using deuterium solid-state NMR and modulated differential scanning calorimetry (MDSC) from 0 to 20% plasticizer content. Quadrupole-echo 2H NMR spectra were obtained for methyl deuterated PVAc-d3 samples with different plasticized amounts. The Tgʼs of different plasticized samples were determined from NMR as the temperatures at which the deuterium powder patterns collapsed. It was found that the Tgʼs decreased by approximately 6 °C for every 5% increment in the plasticizer content and that the trends in the NMR-determined Tgʼs, that is, Tg(NMR), were consistent with those determined by modulated differential scanning calorimetry (MDSC). The Tg(NMR) values were about 36 °C above those of the Tg(DSC) values. This difference in the Tgʼs was due to the different time scales of the two experiments which could be accounted for on the basis of time−temperature superposition principles. The experimental NMR line shapes were fitted using a set of simulated spectra generated from the MXQET simulation program. The spectra were based on a model of nearest-neighbor jumps on a truncated icosahedron (soccer ball). The resulting average correlation times were also found to fit a time−temperature superposition with the same parameter. While the Tg was decreased by the amount of plasticizer, it was found that the breadth of the transitions from either the NMR line shapes or the MDSC thermograms did not seem to change much with the amount of added plasticizer.
Segmental Dynamics of Poly(ethylene oxide) Chains in a Model Polymer/Clay Intercalated Phase: Solid-State NMR Investigation
Cédric Lorthioir*†, Françoise Lauprêtre†, Jérémie Soulestin‡ and Jean-Marc Lefebvre‡
Macromolecules, 2009, 42 (1), pp 218–230
DOI: 10.1021/ma801909s
Abstract: A model poly(ethylene oxide) (PEO)/laponite hybrid material, characterized by a high silicate content, was used to probe the dynamical behavior of polymer chains at the surface with clay platelets. Such a system mimics the intercalated phases that may occur in polymer/clay nanocomposites with usual silicate amounts of 5 wt %. The segmental motions underlying the α-relaxation of fully amorphous PEO chains confined within the nanometer-thick laponite galleries were monitored over the tens of microseconds time scale by means of 13C and 1H solid-state NMR. A significant slowing down of these motions was mostly observed, as compared to the local dynamics in the amorphous phase of neat PEO. Strong dynamical heterogeneities among the intercalated PEO monomer units remain even at room temperature, i.e., more than 50 K above the temperature at which the frequency of the segmental motions displayed by a significant part of the PEO chain segments gets above 52 kHz. Such heterogeneities are related to a pronounced extension of the α-relaxation process toward the low-frequency side. The slowing down of the PEO segmental motions was assigned to ion-dipole interactions between the PEO oxygen atoms and the Na+ counterions located in the laponite galleries. The domains formed by PEO monomer units characterized by a reduced segmental mobility were found to display rather long lifetime, about 13 ms at room temperature.
2H NMR Studies of Polymer Multilayer Capsules, Films, and Complexes
Blythe Fortier-McGill and Linda Reven*
Macromolecules, 2009, 42 (1), pp 247–254
DOI: 10.1021/ma801929g
Abstract: The chain dynamics of aqueous suspensions of polyelectrolyte complexes, supported multilayers deposited on submicron silica colloids, and hollow capsules were characterized by wide-line 2H NMR spectroscopy (DNMR) as a function of layer number, temperature, and ionic strength. The strong polyelectrolytes, poly(diallyldimethyl ammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were employed with selective deuteration of the PDADMAC methyl group. DNMR line-shape analyses showed that there is enhanced chain mobility in the systems with excess positive monomer units, that is, supported multilayers and capsules capped with PDADMAC. Selective deuteration of the first, fifth, and ninth layers confirms that the alternation in chain mobility with the capping layer is a through-film effect. Differential scanning calorimetry (DSC)-detected phase transitions were found to occur between 32 and 45 °C for the PSS/PDADMAC complexes, supported multilayers, and capsules. Whereas the glass transitions of bulk-state polymers are detected by DNMR typically 30 to 40° above the DSC-detected Tg, the onset of fast chain motion for the water-saturated polyelectrolyte complexes and supported multilayers coincides with calorimetric transitions.
Anisotropic Diffusion and Morphology in Perfluorosulfonate Ionomers Investigated by NMR
Jing Li, Kyle G. Wilmsmeyer and Louis A. Madsen*
Macromolecules, 2009, 42 (1), pp 255–262
DOI: 10.1021/ma802106g
Abstract:Anisotropy in ionomer membranes represents a powerful interaction for modulating properties such as mechanical moduli, thermal expansions, and small molecule transport, all tunable via controlled processing. We observe uniform hydrophilic channel alignment in three perfluorosulfonate ionomer membrane types, quantified by 2H NMR spectroscopy of absorbed D2O molecules. Our measurements show biaxial or uniaxial in-plane alignment for extruded membranes, but uniaxial through-plane alignment for dispersion-cast membranes, and further demonstrate affine swelling with both water uptake and thermal expansion. In order to correlate alignment data with a quantity relevant to proton transport, we measure the anisotropy of water self-diffusion using pulsed-field-gradient NMR along different membrane directions. Extruded membranes with stronger alignment exhibit 18% faster in-plane diffusion than through-plane diffusion, while diffusion anisotropy is minimal for weakly aligned membranes. These results should lead to a more quantitative understanding of and control over membrane properties via manipulation of molecular order.
Rakesh R. Nambiar† and Frank D. Blum*‡
Macromolecules, 2008, 41 (24), pp 9837–9845
Abstract: The effect of dipropyleneglycol dibenzoate, a plasticizer, on the glass-transition temperature (Tg) of poly(vinyl acetate) was studied using deuterium solid-state NMR and modulated differential scanning calorimetry (MDSC) from 0 to 20% plasticizer content. Quadrupole-echo 2H NMR spectra were obtained for methyl deuterated PVAc-d3 samples with different plasticized amounts. The Tgʼs of different plasticized samples were determined from NMR as the temperatures at which the deuterium powder patterns collapsed. It was found that the Tgʼs decreased by approximately 6 °C for every 5% increment in the plasticizer content and that the trends in the NMR-determined Tgʼs, that is, Tg(NMR), were consistent with those determined by modulated differential scanning calorimetry (MDSC). The Tg(NMR) values were about 36 °C above those of the Tg(DSC) values. This difference in the Tgʼs was due to the different time scales of the two experiments which could be accounted for on the basis of time−temperature superposition principles. The experimental NMR line shapes were fitted using a set of simulated spectra generated from the MXQET simulation program. The spectra were based on a model of nearest-neighbor jumps on a truncated icosahedron (soccer ball). The resulting average correlation times were also found to fit a time−temperature superposition with the same parameter. While the Tg was decreased by the amount of plasticizer, it was found that the breadth of the transitions from either the NMR line shapes or the MDSC thermograms did not seem to change much with the amount of added plasticizer.
Segmental Dynamics of Poly(ethylene oxide) Chains in a Model Polymer/Clay Intercalated Phase: Solid-State NMR Investigation
Cédric Lorthioir*†, Françoise Lauprêtre†, Jérémie Soulestin‡ and Jean-Marc Lefebvre‡
Macromolecules, 2009, 42 (1), pp 218–230
DOI: 10.1021/ma801909s
Abstract: A model poly(ethylene oxide) (PEO)/laponite hybrid material, characterized by a high silicate content, was used to probe the dynamical behavior of polymer chains at the surface with clay platelets. Such a system mimics the intercalated phases that may occur in polymer/clay nanocomposites with usual silicate amounts of 5 wt %. The segmental motions underlying the α-relaxation of fully amorphous PEO chains confined within the nanometer-thick laponite galleries were monitored over the tens of microseconds time scale by means of 13C and 1H solid-state NMR. A significant slowing down of these motions was mostly observed, as compared to the local dynamics in the amorphous phase of neat PEO. Strong dynamical heterogeneities among the intercalated PEO monomer units remain even at room temperature, i.e., more than 50 K above the temperature at which the frequency of the segmental motions displayed by a significant part of the PEO chain segments gets above 52 kHz. Such heterogeneities are related to a pronounced extension of the α-relaxation process toward the low-frequency side. The slowing down of the PEO segmental motions was assigned to ion-dipole interactions between the PEO oxygen atoms and the Na+ counterions located in the laponite galleries. The domains formed by PEO monomer units characterized by a reduced segmental mobility were found to display rather long lifetime, about 13 ms at room temperature.
2H NMR Studies of Polymer Multilayer Capsules, Films, and Complexes
Blythe Fortier-McGill and Linda Reven*
Macromolecules, 2009, 42 (1), pp 247–254
DOI: 10.1021/ma801929g
Abstract: The chain dynamics of aqueous suspensions of polyelectrolyte complexes, supported multilayers deposited on submicron silica colloids, and hollow capsules were characterized by wide-line 2H NMR spectroscopy (DNMR) as a function of layer number, temperature, and ionic strength. The strong polyelectrolytes, poly(diallyldimethyl ammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were employed with selective deuteration of the PDADMAC methyl group. DNMR line-shape analyses showed that there is enhanced chain mobility in the systems with excess positive monomer units, that is, supported multilayers and capsules capped with PDADMAC. Selective deuteration of the first, fifth, and ninth layers confirms that the alternation in chain mobility with the capping layer is a through-film effect. Differential scanning calorimetry (DSC)-detected phase transitions were found to occur between 32 and 45 °C for the PSS/PDADMAC complexes, supported multilayers, and capsules. Whereas the glass transitions of bulk-state polymers are detected by DNMR typically 30 to 40° above the DSC-detected Tg, the onset of fast chain motion for the water-saturated polyelectrolyte complexes and supported multilayers coincides with calorimetric transitions.
Anisotropic Diffusion and Morphology in Perfluorosulfonate Ionomers Investigated by NMR
Jing Li, Kyle G. Wilmsmeyer and Louis A. Madsen*
Macromolecules, 2009, 42 (1), pp 255–262
DOI: 10.1021/ma802106g
Abstract:Anisotropy in ionomer membranes represents a powerful interaction for modulating properties such as mechanical moduli, thermal expansions, and small molecule transport, all tunable via controlled processing. We observe uniform hydrophilic channel alignment in three perfluorosulfonate ionomer membrane types, quantified by 2H NMR spectroscopy of absorbed D2O molecules. Our measurements show biaxial or uniaxial in-plane alignment for extruded membranes, but uniaxial through-plane alignment for dispersion-cast membranes, and further demonstrate affine swelling with both water uptake and thermal expansion. In order to correlate alignment data with a quantity relevant to proton transport, we measure the anisotropy of water self-diffusion using pulsed-field-gradient NMR along different membrane directions. Extruded membranes with stronger alignment exhibit 18% faster in-plane diffusion than through-plane diffusion, while diffusion anisotropy is minimal for weakly aligned membranes. These results should lead to a more quantitative understanding of and control over membrane properties via manipulation of molecular order.
Chem. Mater., Article ASAP
Sc2(WO4)3 and Sc2(MoO4)3 and Their Solid Solutions: 45Sc, 17O, and 27Al MAS NMR Results at Ambient and High Temperature
Namjun Kim* and Jonathan F. Stebbins
Abstract
The mobilities of trivalent ions are generally considered to be low in solid oxides and thus trivalent ionic conductors are rare. Sc2(WO4)3 and related compounds have been described as Sc3+ ionic conductors. However, there has not been conclusive experimental evidence whether Sc3+ is the major or the only mobile species. Here, we report 45Sc, 17O, and 27Al MAS NMR studies at ambient and high temperature of Sc2(WO4)3-type compounds including Sc2(WO4)3, Sc2(MoO4)3 (scandium tungstate and scandium molybdate), and their solid solutions, as well as aluminum-doped Sc2(WO4)3. 45Sc MAS NMR spectra at ambient temperature of the Sc2(WO4)3−Sc2(MoO4)3 binary are consistent with random mixing of W6+ and Mo6+ on tetrahedral sites. 17O spectra show that the details of the end-member short-range structure are preserved throughout this solid solution, indicating that lattice distortion is minimized by the close similarity of the radii of the hexavalent cations. Al3+ substitutes only into the octahedral sites. At high temperatures (600−700 °C), only the 17O high spectra show noticeable line shape changes, whereas 45Sc high-temperature spectra maintain a constant peak width and shift in position only, suggesting that the oxide anion may be a more mobile species but not excluding the possibility of a minor number of mobile scandium ions. 17O high-temperature NMR data also suggest that oxide ions bonded to molybdenum ions may be more mobile than those in tungstate groups.
Namjun Kim* and Jonathan F. Stebbins
Abstract
The mobilities of trivalent ions are generally considered to be low in solid oxides and thus trivalent ionic conductors are rare. Sc2(WO4)3 and related compounds have been described as Sc3+ ionic conductors. However, there has not been conclusive experimental evidence whether Sc3+ is the major or the only mobile species. Here, we report 45Sc, 17O, and 27Al MAS NMR studies at ambient and high temperature of Sc2(WO4)3-type compounds including Sc2(WO4)3, Sc2(MoO4)3 (scandium tungstate and scandium molybdate), and their solid solutions, as well as aluminum-doped Sc2(WO4)3. 45Sc MAS NMR spectra at ambient temperature of the Sc2(WO4)3−Sc2(MoO4)3 binary are consistent with random mixing of W6+ and Mo6+ on tetrahedral sites. 17O spectra show that the details of the end-member short-range structure are preserved throughout this solid solution, indicating that lattice distortion is minimized by the close similarity of the radii of the hexavalent cations. Al3+ substitutes only into the octahedral sites. At high temperatures (600−700 °C), only the 17O high spectra show noticeable line shape changes, whereas 45Sc high-temperature spectra maintain a constant peak width and shift in position only, suggesting that the oxide anion may be a more mobile species but not excluding the possibility of a minor number of mobile scandium ions. 17O high-temperature NMR data also suggest that oxide ions bonded to molybdenum ions may be more mobile than those in tungstate groups.
Cryst. Growth Des., Article ASAP
Solid-State NMR Analysis of Organic Cocrystals and Complexes
Frederick G. Vogt*†, Jacalyn S. Clawson†, Mark Strohmeier†, Andrew J. Edwards‡, Tran N. Pham‡ and Simon A. Watson‡
Abstract
Solid-state NMR (SSNMR) is capable of providing detailed structural information about organic and pharmaceutical cocrystals and complexes. SSNMR nondestructively analyzes small amounts of powdered material and generally yields data with higher information content than vibrational spectroscopy and powder X-ray diffraction methods. These advantages can be utilized in the analysis of pharmaceutical cocrystals, which are often initially produced using solvent drop grinding techniques that do not lend themselves to single crystal growth for X-ray diffraction studies. In this work, several molecular complexes and cocrystals are examined to understand the capabilities of the SSNMR techniques, particularly their ability to prove or disprove molecular association and observe structural features such as hydrogen bonding. Dipolar correlation experiments between spin pairs such as 1H−1H, 1H−13C, and 19F−13C are applied to study hydrogen bonding, intermolecular contacts, and spin diffusion to link individual molecules together in a crystal structure and quickly prove molecular association. Analysis of the principal components of chemical shift tensors is also utilized where relevant, as these are more sensitive to structural effects than the isotropic chemical shift alone. In addition, 1H T1 relaxation measurements are also demonstrated as a means to prove phase separation of components. On the basis of these results, a general experimental approach to cocrystal analysis by SSNMR is suggested.
Frederick G. Vogt*†, Jacalyn S. Clawson†, Mark Strohmeier†, Andrew J. Edwards‡, Tran N. Pham‡ and Simon A. Watson‡
Abstract
Solid-state NMR (SSNMR) is capable of providing detailed structural information about organic and pharmaceutical cocrystals and complexes. SSNMR nondestructively analyzes small amounts of powdered material and generally yields data with higher information content than vibrational spectroscopy and powder X-ray diffraction methods. These advantages can be utilized in the analysis of pharmaceutical cocrystals, which are often initially produced using solvent drop grinding techniques that do not lend themselves to single crystal growth for X-ray diffraction studies. In this work, several molecular complexes and cocrystals are examined to understand the capabilities of the SSNMR techniques, particularly their ability to prove or disprove molecular association and observe structural features such as hydrogen bonding. Dipolar correlation experiments between spin pairs such as 1H−1H, 1H−13C, and 19F−13C are applied to study hydrogen bonding, intermolecular contacts, and spin diffusion to link individual molecules together in a crystal structure and quickly prove molecular association. Analysis of the principal components of chemical shift tensors is also utilized where relevant, as these are more sensitive to structural effects than the isotropic chemical shift alone. In addition, 1H T1 relaxation measurements are also demonstrated as a means to prove phase separation of components. On the basis of these results, a general experimental approach to cocrystal analysis by SSNMR is suggested.
J. Phys. Chem. C vol. 112, iss. 51
Two Kinds of Framework Al Sites Studied in BEA Zeolite by X-ray Diffraction, Fourier Transform Infrared Spectroscopy, NMR Techniques, and V Probe
Redouane Hajjar†‡, Yannick Millot*†‡, Pascal P. Man†‡, Michel Che§∥⊥ and Stanislaw Dzwigaj*§∥
J. Phys. Chem. C, 2008, 112 (51), pp 20167–20175
Abstract: The dealumination of BEA zeolite by treatment with concentrated nitric acid is evidenced by X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Two-dimensional 27Al 3Q and 5Q magic-angle-spinning (MAS) NMR allow the detection of two kinds of tetrahedral Al atoms whose relative amounts depend on the Si/Al ratio and which correspond to two specific T-sites. 29Si MAS NMR and 1H MAS NMR measurements confirm these results. 29Si MAS NMR spectra evidence two resonances at around −114 and −111 ppm ascribed to Si sites of the Si(OSi)4 environment of two different crystallographic sites. Moreover, the presence of Si atoms associated with hydroxyl groups is confirmed by a resonance at −102 ppm when 1H−29Si CP is applied. The Brønsted and Lewis acidic sites in dealuminated BEA zeolites are evidenced by FTIR spectra of adsorbed pyridine which show two kinds of bridging hydroxyl groups (Si−O(H)−Al) of different acid strength. 51V MAS NMR confirms the incorporation of vanadium atoms into vacant T-atom sites of a fully dealuminated SiBEA zeolite leading to two kinds of tetrahedral V(V) sites (δiso = – 708 and – 766 ppm), with a V=O double bond and linked by V−OSi bonds to the framework. The two types of tetrahedral V(V) sites are in line with the two kinds of tetrahedral Al sites initially present in the zeolite. Moreover, the two bands at 3620 and 3645 cm−1 suggest that VSiBEA also contains V(V) sites with V(V)O−H groups, which exhibit Brønsted acidic character as shown by FTIR of adsorbed pyridine. Possible ways for the formation of tetrahedral V(V) in the BEA structure are proposed.
Direct Correlation between the 31P MAS NMR Response and the Electronic Structure of Some Transition Metal Phosphides
E. Bekaert†, J. Bernardi‡, S. Boyanov‡, L. Monconduit‡, M.-L. Doublet*‡ and M. Ménétrier*†
J. Phys. Chem. C, 2008, 112 (51), pp 20481–20490
Abstract: A series of binary transition metal phosphides (Ni3P, Ni12P5, Ni2P, Ni5P4, NiP, NiP2, FeP, FeP2, FeP4, VP2, CoP) were investigated by solid state 31P MAS NMR, leading to rather different lineshapes, shifts, relaxation times, and temperature dependences. The electronic structures of these compounds were computed using various DFT codes, based either on plane wave PAW potentials (VASP) or on all-electron basis sets in the FPLAPW formalism (Wien2K). Depending on the electronic features of the phosphide, self-interaction corrected formalisms (DFT+U or PBE0 hybrid functional) were also used to reach a better description of the electronic ground state and to establish a correlation with the shape and the nature of the NMR signals. As a result of the analysis, the main categories are diamagnetic compounds (FeP4, NiP2) and metallic ones, either real (VP2) or with some electronic localization in band tails (Ni12P5, Ni2P, Ni5P4, NiP) or with spin-polarized conduction bands (CoP, FeP). FeP2 appears somewhat ambiguous, both based on the various computational results and on the NMR characteristics. Besides, FeP4 is the only compound for which very clear J couplings resulting from P−P bonds were observed
Redouane Hajjar†‡, Yannick Millot*†‡, Pascal P. Man†‡, Michel Che§∥⊥ and Stanislaw Dzwigaj*§∥
J. Phys. Chem. C, 2008, 112 (51), pp 20167–20175
Abstract: The dealumination of BEA zeolite by treatment with concentrated nitric acid is evidenced by X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Two-dimensional 27Al 3Q and 5Q magic-angle-spinning (MAS) NMR allow the detection of two kinds of tetrahedral Al atoms whose relative amounts depend on the Si/Al ratio and which correspond to two specific T-sites. 29Si MAS NMR and 1H MAS NMR measurements confirm these results. 29Si MAS NMR spectra evidence two resonances at around −114 and −111 ppm ascribed to Si sites of the Si(OSi)4 environment of two different crystallographic sites. Moreover, the presence of Si atoms associated with hydroxyl groups is confirmed by a resonance at −102 ppm when 1H−29Si CP is applied. The Brønsted and Lewis acidic sites in dealuminated BEA zeolites are evidenced by FTIR spectra of adsorbed pyridine which show two kinds of bridging hydroxyl groups (Si−O(H)−Al) of different acid strength. 51V MAS NMR confirms the incorporation of vanadium atoms into vacant T-atom sites of a fully dealuminated SiBEA zeolite leading to two kinds of tetrahedral V(V) sites (δiso = – 708 and – 766 ppm), with a V=O double bond and linked by V−OSi bonds to the framework. The two types of tetrahedral V(V) sites are in line with the two kinds of tetrahedral Al sites initially present in the zeolite. Moreover, the two bands at 3620 and 3645 cm−1 suggest that VSiBEA also contains V(V) sites with V(V)O−H groups, which exhibit Brønsted acidic character as shown by FTIR of adsorbed pyridine. Possible ways for the formation of tetrahedral V(V) in the BEA structure are proposed.
Direct Correlation between the 31P MAS NMR Response and the Electronic Structure of Some Transition Metal Phosphides
E. Bekaert†, J. Bernardi‡, S. Boyanov‡, L. Monconduit‡, M.-L. Doublet*‡ and M. Ménétrier*†
J. Phys. Chem. C, 2008, 112 (51), pp 20481–20490
Abstract: A series of binary transition metal phosphides (Ni3P, Ni12P5, Ni2P, Ni5P4, NiP, NiP2, FeP, FeP2, FeP4, VP2, CoP) were investigated by solid state 31P MAS NMR, leading to rather different lineshapes, shifts, relaxation times, and temperature dependences. The electronic structures of these compounds were computed using various DFT codes, based either on plane wave PAW potentials (VASP) or on all-electron basis sets in the FPLAPW formalism (Wien2K). Depending on the electronic features of the phosphide, self-interaction corrected formalisms (DFT+U or PBE0 hybrid functional) were also used to reach a better description of the electronic ground state and to establish a correlation with the shape and the nature of the NMR signals. As a result of the analysis, the main categories are diamagnetic compounds (FeP4, NiP2) and metallic ones, either real (VP2) or with some electronic localization in band tails (Ni12P5, Ni2P, Ni5P4, NiP) or with spin-polarized conduction bands (CoP, FeP). FeP2 appears somewhat ambiguous, both based on the various computational results and on the NMR characteristics. Besides, FeP4 is the only compound for which very clear J couplings resulting from P−P bonds were observed
J. Phys Chem B Vol 112, Issue 51
Dynamic Solvophobic Effect and Its Cooperativity in the Hydrogen-bonding Liquids Studied by Dielectric and Nuclear Magnetic Resonance Relaxation
Tsuyoshi Yamaguchi*, Hiroki Furuhashi, Tatsuro Matsuoka and Shinobu Koda
J. Phys. Chem. B, 2008, 112 (51), pp 16633–16641
Abstract: The reorientational relaxation of solvent molecules in the mixture of nonpolar solutes and hydrogen-bonding liquids including water, alcohols, and amides are studied by dielectric and 2H-nuclear magnetic resonance (NMR) spin−lattice relaxations. The retardation of the reorientational motion of the solvent by weak solute−solvent interaction is observed in all the solvent systems. On the other hand, no clear correlation between the strength of the solute−solvent interaction and the slowing down of the solvent motion is found in N,N-dimethylacetamide, which suggests the importance of the hydrogen bonding in the dynamic solvophobic effect. The cooperativity of the reorientational relaxation is investigated by the comparison between the collective relaxation measured by the dielectric spectroscopy and the single-molecular reorientation determined by NMR. The modification of the dielectric relaxation time caused by the dissolution of the solute is larger than that of the single-molecular reorientational relaxation time in all the solvents studied here. The effect of the static correlation between the dipole moments of different molecules is calculated from the static dielectric constant, and the effect of the dynamic correlation is estimated. The difference in the effects of the solutes on the collective and single-molecular reorientational relaxation is mainly ascribed to the dynamic cooperativity in the cases of water and alcohols, which is consistent with the picture on the dynamic solvophobicity derived by our previous theoretical analysis (Yamaguchi, T.; Matsuoka, T.; Koda, S. J. Chem. Phys. 2004, 120, 7590). On the other hand, the static correlation plays the principal role in the case of N-methylformamide.
Richard Weber*†‡, Sabyasachi Sen§, Randall E. Youngman∥, Robert T. Hart⊥ and Chris J. Benmore‡
J. Phys. Chem. B, 2008, 112 (51), pp 16726–16733
DOI: 10.1021/jp807964u
Abstract: The structure of binary aluminosilicate glasses containing 60−67 mol % Al2O3 were investigated using high-resolution 27Al NMR and X-ray and neutron diffraction. The glasses were made by aerodynamic levitation of molten oxides. The 67% alumina composition required a cooling rate of ∼1600 °C s1− to form glass from submillimeter sized samples. NMR results show that the glasses contain aluminum in 4-, 5-, and 6-fold coordination in the approximate ratio 4:5:1. The average Al coordination increases from 4.57 to 4.73 as the fraction of octahedral Al increases with alumina content. The diffraction results on the 67% composition are consistent with a disordered Al framework with Al ions in a range of coordination environments that are substantially different from those found in the equilibrium crystalline phases. Analysis of the neutron and X-ray structure factors yields an average bond angle of 125 ± 4° between an Al ion and the adjoining cation via a bridging oxygen. We propose that the structure of the glass is a “transition state” between the alumina-rich liquid and the equilibrium mullite phase that are dominated by 4- and 6-coordinated aluminum ions, respectively.
Ultrahigh Resolution Characterization of Domain Motions and Correlations by Multialignment and Multireference Residual Dipolar Coupling NMR
Charles K. Fisher, Qi Zhang, Andrew Stelzer and Hashim M. Al-Hashimi*
J. Phys. Chem. B, 2008, 112 (51), pp 16815–16822
DOI: 10.1021/jp806188j
Abstract: Nuclear magnetic resonance (NMR) residual dipolar couplings (RDCs) provide a unique opportunity for spatially characterizing complex motions in biomolecules with time scale sensitivity extending up to milliseconds. Up to five motionally averaged Wigner rotation elements, ⟨D0k2(αβ)⟩, can be determined experimentally using RDCs measured in five linearly independent alignment conditions and applied to define motions of axially symmetric bond vectors. Here, we show that up to 25 motionally averaged Wigner rotation elements, ⟨Dmk2(αβγ)⟩, can be determined experimentally from multialignment RDCs and used to characterize rigid-body motions of chiral domains. The 25 ⟨Dmk2(αβγ)⟩ elements form a basis set that allows one to measure motions of a domain relative to an isotropic distribution of reference frames anchored on a second domain (and vice versa), thus expanding the 3D spatial resolution with which motions can be characterized. The 25 ⟨Dmk2(αβγ)⟩ elements can also be used to fit an ensemble consisting of up to eight equally or six unequally populated states. For more than two domains, changing the identity of the domain governing alignment allows access to new information regarding the correlated nature of the domain fluctuations. Example simulations are provided that validate the theoretical derivation and illustrate the high spatial resolution with which rigid-body domain motions can be characterized using multialignment and multireference RDCs. Our results further motivate the development of experimental approaches for both modulating alignment and anchoring it on specifically targeted domains.
Structure, Orientation, and Dynamics of the C-Terminal Hexapeptide of LRAP Determined Using Solid-State NMR
Wendy J. Shaw* and Kim Ferris
J. Phys. Chem. B, 2008, 112 (51), pp 16975–16981
DOI: 10.1021/jp808012g
Abstract: Amelogenin is the predominant protein found during enamel development and has been shown to be essential to proper enamel formation. Leucine-rich amelogenin peptide (LRAP) is a naturally occurring splice variant that preserves the charged N- and C-termini of full length amelogenin, regions thought to be crucial in interacting with hydroxaypatite. Particularly, the highly charged C-terminal hexapeptide (KREEVD) is thought to be the region most intimately interacting with hydroxyapatite (HAP). The structure of this charged region was investigated, along with the proximity to the surface and the mobility of two of the residues. The structure was found to be consistent with a random coil or more extended structure, as has been seen for more internalized residues in the C-terminus. The backbone K54(13C′), V58(13C′), and V58(15N) were all found to be close to the surface of HAP, ∼ 6.0 Å from the nearest 31P atom, suggesting a strong interaction and emphasizing the importance of these residues in interacting with HAP. However, both ends of the hexapeptide at residues K54 and V58 experience significant mobility under hydrated conditions, implying that another portion of the protein helps to stabilize the strong LRAP-HAP interaction. Interestingly, the backbone of the C-terminal third of the protein is consistently 6.0 Å from the HAP surface, providing a model in this region of the protein lying flat on the surface with no three-dimensional folding. The combination of these features, that is, a random coil structure, a significant mobility, and a lack of three-dimensional folding in this region of the protein, may have an important functional role, possibly allowing maximum crystal inhibition at low protein concentrations.
Tsuyoshi Yamaguchi*, Hiroki Furuhashi, Tatsuro Matsuoka and Shinobu Koda
J. Phys. Chem. B, 2008, 112 (51), pp 16633–16641
Abstract: The reorientational relaxation of solvent molecules in the mixture of nonpolar solutes and hydrogen-bonding liquids including water, alcohols, and amides are studied by dielectric and 2H-nuclear magnetic resonance (NMR) spin−lattice relaxations. The retardation of the reorientational motion of the solvent by weak solute−solvent interaction is observed in all the solvent systems. On the other hand, no clear correlation between the strength of the solute−solvent interaction and the slowing down of the solvent motion is found in N,N-dimethylacetamide, which suggests the importance of the hydrogen bonding in the dynamic solvophobic effect. The cooperativity of the reorientational relaxation is investigated by the comparison between the collective relaxation measured by the dielectric spectroscopy and the single-molecular reorientation determined by NMR. The modification of the dielectric relaxation time caused by the dissolution of the solute is larger than that of the single-molecular reorientational relaxation time in all the solvents studied here. The effect of the static correlation between the dipole moments of different molecules is calculated from the static dielectric constant, and the effect of the dynamic correlation is estimated. The difference in the effects of the solutes on the collective and single-molecular reorientational relaxation is mainly ascribed to the dynamic cooperativity in the cases of water and alcohols, which is consistent with the picture on the dynamic solvophobicity derived by our previous theoretical analysis (Yamaguchi, T.; Matsuoka, T.; Koda, S. J. Chem. Phys. 2004, 120, 7590). On the other hand, the static correlation plays the principal role in the case of N-methylformamide.
Richard Weber*†‡, Sabyasachi Sen§, Randall E. Youngman∥, Robert T. Hart⊥ and Chris J. Benmore‡
J. Phys. Chem. B, 2008, 112 (51), pp 16726–16733
DOI: 10.1021/jp807964u
Abstract: The structure of binary aluminosilicate glasses containing 60−67 mol % Al2O3 were investigated using high-resolution 27Al NMR and X-ray and neutron diffraction. The glasses were made by aerodynamic levitation of molten oxides. The 67% alumina composition required a cooling rate of ∼1600 °C s1− to form glass from submillimeter sized samples. NMR results show that the glasses contain aluminum in 4-, 5-, and 6-fold coordination in the approximate ratio 4:5:1. The average Al coordination increases from 4.57 to 4.73 as the fraction of octahedral Al increases with alumina content. The diffraction results on the 67% composition are consistent with a disordered Al framework with Al ions in a range of coordination environments that are substantially different from those found in the equilibrium crystalline phases. Analysis of the neutron and X-ray structure factors yields an average bond angle of 125 ± 4° between an Al ion and the adjoining cation via a bridging oxygen. We propose that the structure of the glass is a “transition state” between the alumina-rich liquid and the equilibrium mullite phase that are dominated by 4- and 6-coordinated aluminum ions, respectively.
Ultrahigh Resolution Characterization of Domain Motions and Correlations by Multialignment and Multireference Residual Dipolar Coupling NMR
Charles K. Fisher, Qi Zhang, Andrew Stelzer and Hashim M. Al-Hashimi*
J. Phys. Chem. B, 2008, 112 (51), pp 16815–16822
DOI: 10.1021/jp806188j
Abstract: Nuclear magnetic resonance (NMR) residual dipolar couplings (RDCs) provide a unique opportunity for spatially characterizing complex motions in biomolecules with time scale sensitivity extending up to milliseconds. Up to five motionally averaged Wigner rotation elements, ⟨D0k2(αβ)⟩, can be determined experimentally using RDCs measured in five linearly independent alignment conditions and applied to define motions of axially symmetric bond vectors. Here, we show that up to 25 motionally averaged Wigner rotation elements, ⟨Dmk2(αβγ)⟩, can be determined experimentally from multialignment RDCs and used to characterize rigid-body motions of chiral domains. The 25 ⟨Dmk2(αβγ)⟩ elements form a basis set that allows one to measure motions of a domain relative to an isotropic distribution of reference frames anchored on a second domain (and vice versa), thus expanding the 3D spatial resolution with which motions can be characterized. The 25 ⟨Dmk2(αβγ)⟩ elements can also be used to fit an ensemble consisting of up to eight equally or six unequally populated states. For more than two domains, changing the identity of the domain governing alignment allows access to new information regarding the correlated nature of the domain fluctuations. Example simulations are provided that validate the theoretical derivation and illustrate the high spatial resolution with which rigid-body domain motions can be characterized using multialignment and multireference RDCs. Our results further motivate the development of experimental approaches for both modulating alignment and anchoring it on specifically targeted domains.
Structure, Orientation, and Dynamics of the C-Terminal Hexapeptide of LRAP Determined Using Solid-State NMR
Wendy J. Shaw* and Kim Ferris
J. Phys. Chem. B, 2008, 112 (51), pp 16975–16981
DOI: 10.1021/jp808012g
Abstract: Amelogenin is the predominant protein found during enamel development and has been shown to be essential to proper enamel formation. Leucine-rich amelogenin peptide (LRAP) is a naturally occurring splice variant that preserves the charged N- and C-termini of full length amelogenin, regions thought to be crucial in interacting with hydroxaypatite. Particularly, the highly charged C-terminal hexapeptide (KREEVD) is thought to be the region most intimately interacting with hydroxyapatite (HAP). The structure of this charged region was investigated, along with the proximity to the surface and the mobility of two of the residues. The structure was found to be consistent with a random coil or more extended structure, as has been seen for more internalized residues in the C-terminus. The backbone K54(13C′), V58(13C′), and V58(15N) were all found to be close to the surface of HAP, ∼ 6.0 Å from the nearest 31P atom, suggesting a strong interaction and emphasizing the importance of these residues in interacting with HAP. However, both ends of the hexapeptide at residues K54 and V58 experience significant mobility under hydrated conditions, implying that another portion of the protein helps to stabilize the strong LRAP-HAP interaction. Interestingly, the backbone of the C-terminal third of the protein is consistently 6.0 Å from the HAP surface, providing a model in this region of the protein lying flat on the surface with no three-dimensional folding. The combination of these features, that is, a random coil structure, a significant mobility, and a lack of three-dimensional folding in this region of the protein, may have an important functional role, possibly allowing maximum crystal inhibition at low protein concentrations.
Wednesday, January 07, 2009
J. Chem. Phys. 130, 014504 (2009)
Proton-proton homonuclear dipolar decoupling in solid-state NMR using rotor-synchronized z-rotation pulse sequences
J. Chem. Phys. 130, 014504 (2009)
Olivier Lafon, Qiang Wang, Bingwen Hu, Julien Trébosc, Feng Deng, and Jean-Paul Amoureux
Abstract:
We present a theoretical analysis of rotor-synchronized homonuclear dipolar decoupling schemes that cause a z-rotation of the spins. These pulse sequences applicable at high spinning rates (vr > 30 kHz) yield high-resolution proton NMR spectra that are free of artifacts, such as zero lines and image peaks. We show that the scaled isotropic chemical-shift positions of proton lines can be calculated from the zero-order average Hamiltonian and that the scaling factor does not depend on offset. The effects of different adjustable parameters (rf field, spinning rate, pulse shape, offset) on the decoupling performance are analyzed by numerical simulations of proton spectra and by 1H solid-state NMR experiments on NaH2PO4 and glycine.
J. Chem. Phys. 130, 014504 (2009)
Olivier Lafon, Qiang Wang, Bingwen Hu, Julien Trébosc, Feng Deng, and Jean-Paul Amoureux
Abstract:
We present a theoretical analysis of rotor-synchronized homonuclear dipolar decoupling schemes that cause a z-rotation of the spins. These pulse sequences applicable at high spinning rates (vr > 30 kHz) yield high-resolution proton NMR spectra that are free of artifacts, such as zero lines and image peaks. We show that the scaled isotropic chemical-shift positions of proton lines can be calculated from the zero-order average Hamiltonian and that the scaling factor does not depend on offset. The effects of different adjustable parameters (rf field, spinning rate, pulse shape, offset) on the decoupling performance are analyzed by numerical simulations of proton spectra and by 1H solid-state NMR experiments on NaH2PO4 and glycine.
Solid-State NMR Review in Analytical Chemistry
Solid-State NMR Spectroscopy
Hi-Res PDF[88 KB]
PDF w/ Links[204 KB]
Cecil Dybowski* and Shi Bai
Anal. Chem., 2008, 80 (12), pp 4295–4300
Solid-state NMR is a mature field with many applications. This review covers the period from early 2005 to March, 2008. A search of the literature showed that there were at least 3100 articles published that contain some emphasis on solid-state NMR. We do not pretend to make a complete or exhaustive review of all of these; rather we have attempted to highlight some reports that seem to indicate the broad sweep of solid-state NMR at this time. In this review, therefore, you should expect the choice of examples to be incomplete, and it is quite possible that another reviewer could have chosen other equally appropriate examples. With a field as wide as this one has become, there are multiple special reviews. One may find published reviews on subjects as diverse as applications of solid-state NMR to material science, polymer chemistry, biomolecular solids, and inorganic solids (1-4). In addition, there are always reviews in such series as Specialist Periodical Reports and Progress in Nuclear Magnetic Resonance Spectroscopy that may cover the solid-state techniques.
Hi-Res PDF[88 KB]
PDF w/ Links[204 KB]
Cecil Dybowski* and Shi Bai
Anal. Chem., 2008, 80 (12), pp 4295–4300
Solid-state NMR is a mature field with many applications. This review covers the period from early 2005 to March, 2008. A search of the literature showed that there were at least 3100 articles published that contain some emphasis on solid-state NMR. We do not pretend to make a complete or exhaustive review of all of these; rather we have attempted to highlight some reports that seem to indicate the broad sweep of solid-state NMR at this time. In this review, therefore, you should expect the choice of examples to be incomplete, and it is quite possible that another reviewer could have chosen other equally appropriate examples. With a field as wide as this one has become, there are multiple special reviews. One may find published reviews on subjects as diverse as applications of solid-state NMR to material science, polymer chemistry, biomolecular solids, and inorganic solids (1-4). In addition, there are always reviews in such series as Specialist Periodical Reports and Progress in Nuclear Magnetic Resonance Spectroscopy that may cover the solid-state techniques.
Tuesday, January 06, 2009
J Phys Chem B Vol. 113 Issue 1
Li-Ion Diffusion in the Equilibrium Nanomorphology of Spinel Li4+xTi5O12
Marnix Wagemaker*†, Ernst R. H. van Eck‡, Arno P. M. Kentgens‡ and Fokko M. Mulder*†
J. Phys. Chem. B, 2009, 113 (1), pp 224–230
DOI: 10.1021/jp8073706
Abstract: Li4Ti5O12 spinel as Li-ion electrode material combines good capacity, excellent cycleability with a high rate capability. Although the potential of about 1.56 V vs Li is relatively high, these features make it the anode of choice for state of the art high power Li-ion batteries. Although the flat voltage profile reflects a two-phase reaction during lithiation, the small change in lattice parameters upon lithiation (“zero-strain” property) leads to a solid solution in equilibrium, as recently demonstrated with diffraction. In this study, the morphology and Li-ion mobility is studied by NMR spectroscopy leading to a more detailed picture, showing that the solid solution in Li4+xTi5O12 spinel should actually be described as domains with sizes less than 9 nm having either tetrahedral (8a) Li occupation or octahedral (16c) Li occupation. The abundant domain boundaries and the associated disorder appear to be responsible for the facile diffusion through the lattice, and hence these nm-sized domains are most likely the origin of the relative high rate capability of this material as electrode for Li-ion batteries. The small domain size, smaller than typical Debye lengths, makes that the material electrochemically behaves as a solid solution. As such, the results give insight in the fundamental properties of the “zero-strain” Li4Ti5O12 spinel material explaining the favorable Li-ion battery electrode properties on an atomic level.
Utilizing the Charge Field Effect on Amide 15N Chemical Shifts for Protein Structure Validation
Reto Bader*
J. Phys. Chem. B, 2009, 113 (1), pp 347–358
Abstract: Of all the nuclei in proteins, the nuclear magnetic resonance (NMR) chemical shifts of nitrogen are the theoretically least well understood. In this study, quantum chemical methods are used in combination with polarizable-continuum models in order to show that consideration of the effective electric field, including charge screening due to solvation, improves considerably the consistencies of statistical relationships between experimental and computed amide 15N shifts between various sets of charged and uncharged oligopeptides and small organic molecules. A single conversion scheme between shielding parameters from first principles using density functional theory (DFT) and experimental shifts is derived that holds for all classes of compounds examined here. This relationship is then used to test the accuracy of such 15N chemical shift predictions in the cyclic decapeptide antibiotic gramicidin S (GS). GS has previously been studied in great detail, both by NMR and X-ray crystallography. It adopts a well-defined backbone conformation, and hence, only a few discrete side chain conformational states need to be considered. Moreover, a charge-relay effect of the two cationic ornithine side chains to the protein backbone has been described earlier by NMR spectroscopy. Here, DFT-derived backbone amide nitrogen chemical shifts were calculated for multiple conformations of GS. Overall, the structural dynamics of GS is revisited in view of chemical shift behavior along with energetic considerations. Together, the study demonstrates proof of concept that 15N chemical shift information is particularly useful in the analysis and validation of protein conformational states in a charged environment.
Marnix Wagemaker*†, Ernst R. H. van Eck‡, Arno P. M. Kentgens‡ and Fokko M. Mulder*†
J. Phys. Chem. B, 2009, 113 (1), pp 224–230
DOI: 10.1021/jp8073706
Abstract: Li4Ti5O12 spinel as Li-ion electrode material combines good capacity, excellent cycleability with a high rate capability. Although the potential of about 1.56 V vs Li is relatively high, these features make it the anode of choice for state of the art high power Li-ion batteries. Although the flat voltage profile reflects a two-phase reaction during lithiation, the small change in lattice parameters upon lithiation (“zero-strain” property) leads to a solid solution in equilibrium, as recently demonstrated with diffraction. In this study, the morphology and Li-ion mobility is studied by NMR spectroscopy leading to a more detailed picture, showing that the solid solution in Li4+xTi5O12 spinel should actually be described as domains with sizes less than 9 nm having either tetrahedral (8a) Li occupation or octahedral (16c) Li occupation. The abundant domain boundaries and the associated disorder appear to be responsible for the facile diffusion through the lattice, and hence these nm-sized domains are most likely the origin of the relative high rate capability of this material as electrode for Li-ion batteries. The small domain size, smaller than typical Debye lengths, makes that the material electrochemically behaves as a solid solution. As such, the results give insight in the fundamental properties of the “zero-strain” Li4Ti5O12 spinel material explaining the favorable Li-ion battery electrode properties on an atomic level.
Utilizing the Charge Field Effect on Amide 15N Chemical Shifts for Protein Structure Validation
Reto Bader*
J. Phys. Chem. B, 2009, 113 (1), pp 347–358
Abstract: Of all the nuclei in proteins, the nuclear magnetic resonance (NMR) chemical shifts of nitrogen are the theoretically least well understood. In this study, quantum chemical methods are used in combination with polarizable-continuum models in order to show that consideration of the effective electric field, including charge screening due to solvation, improves considerably the consistencies of statistical relationships between experimental and computed amide 15N shifts between various sets of charged and uncharged oligopeptides and small organic molecules. A single conversion scheme between shielding parameters from first principles using density functional theory (DFT) and experimental shifts is derived that holds for all classes of compounds examined here. This relationship is then used to test the accuracy of such 15N chemical shift predictions in the cyclic decapeptide antibiotic gramicidin S (GS). GS has previously been studied in great detail, both by NMR and X-ray crystallography. It adopts a well-defined backbone conformation, and hence, only a few discrete side chain conformational states need to be considered. Moreover, a charge-relay effect of the two cationic ornithine side chains to the protein backbone has been described earlier by NMR spectroscopy. Here, DFT-derived backbone amide nitrogen chemical shifts were calculated for multiple conformations of GS. Overall, the structural dynamics of GS is revisited in view of chemical shift behavior along with energetic considerations. Together, the study demonstrates proof of concept that 15N chemical shift information is particularly useful in the analysis and validation of protein conformational states in a charged environment.
Monday, January 05, 2009
Al's Journal Update
Superadiabaticity in magnetic resonance
J. Chem. Phys. 129, 204110 (2008)
Michaël Deschamps, Gwendal Kervern, Dominique Massiot, Guido Pintacuda, Lyndon Emsley, and Philip J. Grandinetti
Abstract:
Adiabaticity plays a central role in modern magnetic resonance experiments, as excitations with adiabatic Hamiltonians allow precise control of the dynamics of the spin states during the course of an experiment. Surprisingly, many commonly used adiabatic processes in magnetic resonance perform well even though the adiabatic approximation does not appear to hold throughout the process. Here we show that this discrepancy can now be explained through the use of Berry's superadiabatic formalism, which provides a framework for including the finite duration of the process in the theoretical and numerical treatments. In this approach, a slow, but finite time-dependent Hamiltonian is iteratively transformed into time-dependent diagonal frames until the most accurate adiabatic approximation is obtained. In the case of magnetic resonance, the magnetization during an adiabatic process of finite duration is not locked to the effective Hamiltonian in the conventional adiabatic frame, but rather to an effective Hamiltonian in a superadiabatic frame. Only in the superadiabatic frame can the true validity of the adiabatic approximation be evaluated, as the inertial forces acting in this frame are the true cause for deviation from adiabaticity and loss of control during the process. Here we present a brief theoretical background of superadiabaticity and illustrate the concept in the context of magnetic resonance with commonly used shaped radio-frequency pulses.
Proton assisted recoupling and protein structure determination
J. Chem. Phys. 129, 245101 (2008)
Gaël De Paëpe, Józef R. Lewandowski, Antoine Loquet, Anja Böckmann, and Robert G. Griffin
Abstract:
We introduce a homonuclear version of third spin assisted recoupling, a second-order mechanism that can be used for polarization transfer between 13C or 15N spins in magic angle spinning (MAS) NMR experiments, particularly at high spinning frequencies employed in contemporary high field MAS experiments. The resulting sequence, which we refer to as proton assisted recoupling (PAR), relies on a cross-term between 1H–13C (or 1H–15N) couplings to mediate zero quantum 13C–13C (or 15N–15N recoupling). In particular, using average Hamiltonian theory we derive an effective Hamiltonian for PAR and show that the transfer is mediated by trilinear terms of the form C1‡C2‡ HZ for 13C–13C recoupling experiments (or N1‡N2‡ HZ for 15N–15N). We use analytical and numerical simulations to explain the structure of the PAR optimization maps and to delineate the PAR matching conditions. We also detail the PAR polarization transfer dependence with respect to the local molecular geometry and explain the observed reduction in dipolar truncation. Finally, we demonstrate the utility of PAR in structural studies of proteins with 13C–13C spectra of uniformly 13C, 15N labeled microcrystalline Crh, a 85 amino acid model protein that forms a domain swapped dimer (MW=2×10.4 kDa). The spectra, which were acquired at high MAS frequencies ( r2 >20 kHz) and magnetic fields (750–900 MHz 1H frequencies) using moderate rf fields, exhibit numerous cross peaks corresponding to long (up to 6–7 Å) 13C–13C distances which are particularly useful in protein structure determination. Using results from PAR spectra we calculate the structure of the Crh protein.
Neutron Powder Diffraction, Multinuclear, and Multidimensional NMR Structural Investigation of Pb5Ga3F19
Inorg. Chem., 2008, 47 (23), pp 10895–10905
Charlotte Martineau, Franck Fayon, Christophe Legein, Jean-Yves Buzaré, François Goutenoire and Emmanuelle Suard
Abstract:
The room temperature structure of Pb5Ga3F19 is investigated by combining neutron diffraction and multinuclear 19F, 71Ga, and 207Pb one-dimensional and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments. Two models built in space group I4cm are reported for the description of the crystalline structure of Pb5Ga3F19. The structure is built from a network of both opposite corner-sharing Ga2F63− octahedra forming infinite chains along the c-axis and isolated Ga1F63− octahedra. The two models present two slightly different views of the strong static disorder of the fluorine ions belonging to the Ga2F63− octahedra. 71Ga NMR results show that the local environment of all Ga2 ions is identical, which indicates a tilt of the Ga2F63− octahedra within the chains. 207Pb NMR experiments confirm that the environment of only one of the two lead sites, Pb1, is strongly affected by the disorder, which gives rise to three broad distinct 207Pb NMR lines for this site. All 19F NMR lines are assigned using the 19F DQ-SQ MAS experiment. 19F−207Pb through-bond and through-space heteronuclear correlation experiments are carried out for the first time, supporting assignment of both the 19F and 207Pb NMR spectra. These correlation experiments also show that both models correctly describe the medium-range order of the structure of Pb5Ga3F19.
Investigation of Silver-Containing Layered Materials and Their Interactions with Primary Amines Using Solid-State 109Ag and 15N NMR Spectroscopy and First Principles Calculations
Inorg. Chem., 2008, 47 (23), pp 11245–11256
Hiyam Hamaed, Andy Y. H. Lo, Leslie J. May, Jared M. Taylor, George H. Shimizu and Robert W. Schurko
Abstract:
Silver-containing layered networks of the form [Ag(L)] (L = 4-pyridinesulfonate or p-toluenesulfonate) were treated with primary amines in different ratios. The structures of the parent supramolecular networks are well-known; however, their interactions with primary amines lead to the formation of new layered materials for which single-crystal X-ray structures cannot be obtained. Solid-state 109Ag, 15N, and 13C cross-polarization magic-angle spinning (CP/MAS) NMR experiments, in combination with powder X-ray diffraction experiments and ab initio calculations, are utilized to investigate the interactions between the primary amines and the parent materials, and to propose structural models for the new materials. 109Ag chemical shift (CS) tensor parameters are extremely sensitive to changes in silver environments; hence, 1H-109Ag CP/MAS NMR experiments are used to distinguish and characterize silver sites. The combination of 109Ag and 15N NMR experiments on starting materials and samples prepared with both 15N-labeled and unlabeled amines permits the accurate measurements of indirect 1J(109Ag,15N) and 1J(109Ag,14N) spin−spin coupling constants, providing further information on structure and bonding in these systems. First principles calculations of silver CS tensors and 1J(109Ag,14N) coupling constants in model complexes aid in formulating the proposed structural models for the new materials, which are largely comprised of layers of silver-diamine cations.
The Kagomé Topology of the Gallium and Indium Metal-Organic Framework Types with a MIL-68 Structure: Synthesis, XRD, Solid-State NMR Characterizations, and Hydrogen Adsorption
Inorg. Chem., 2008, 47 (24), pp 11892–11901
Christophe Volkringer, Mohamed Meddouri, Thierry Loiseau, Nathalie Guillou, Jérôme Marrot, Gérard Férey, Mohamed Haouas, Francis Taulelle, Nathalie Audebrand and Michel Latroche
Abstract:
The vanadium-based terephthalate analogs of MIL-68 have been obtained with gallium and indium (network composition: M(OH)(O2C−C6H4−CO2), M = Ga or In) by using a solvothermal synthesis technique using N,N-dimethylformamide as a solvent (10 and 48 h, for Ga and In, respectively, at 100 °C). They have been characterized by X-ray diffraction analysis; vibrational spectroscopy; and solid-state 1H and 1H−1H radio-frequency-driven dipolar recoupling (RFDR), 1H−1H double quantum correlation (DQ), and 13C{1H} cross polarization magic angle spinning (CPMAS) NMR spectroscopy. The three-dimensional network with a Kagomé-like lattice is built up from the connection of infinite trans-connected chains of octahedral units MO4(OH)2 (M = Ga or In), linked to each other through the terephthalate ligands in order to generate triangular and hexagonal one-dimensional channels. The presence of DMF molecules with strong interactions within the channels as well as their departure upon calcination (150 °C under a primary vacuum) of the materials has been confirmed by subjecting MIL-68 (Ga) to solid-state 1H MAS NMR. The 1H−1H RFDR and 1H−1H DQ spectra revealed important information on the spatial arrangement of the guest species with respect to the hybrid organic−inorganic network. 13C{1H} CPMAS NMR of activated samples provided crystallographically independent sites in agreement with X-ray diffraction structure determination. Brunauer−Emmett−Teller surface areas are 1117(24) and 746(31) m2 g−1 for MIL-98 (Ga) and MIL-68 (In), respectively. Hydrogen adsorption isotherms have been measured at 77 K, and the storage capacities are found to be 2.46 and 1.98 wt % under a saturated pressure of 4 MPa for MIL-68 (Ga) and MIL-68 (In), respectively. For comparison, the hydrogen uptake for the aluminum trimesate MIL-110, which has an open framework with 16 Å channels, is 3 wt % under 4 MPa.
NMR evidence of LiF coating rather than fluorine substitution in Li(Ni0.425Mn0.425Co0.15)O2
Journal of Solid State Chemistry 181 (2008) 3303–3307
M. Menetrier, J. Bains, L. Croguennec, A. Flambard, E. Bekaert, C. Jordy, Ph. Biensan, C. Delmas
Abstract:
A series of “Li1+z/2(Ni0.425Mn0.425Co0.15)1−z/2O2−zFz” materials was prepared by a coprecipitation route and their structure was characterized using X-ray diffraction (XRD), as well as 7Li and 19F Magic Angle Spinning (MAS) NMR spectroscopy. Two hypotheses were considered: (i) formation of layered oxyfluoride materials and (ii) formation of a mixture between the layered material and LiF. Structural parameters were refined by the Rietveld method, using XRD diffraction data. The refinement results did not allow us to choose between these two hypotheses: no significant change in crystallinity and structural parameters was observed irrespective of the fluorine ratio. 7Li and 19F MAS NMR analyses showed signals with isotropic positions characteristic of LiF, but envelopes characteristic of very strong dipolar interactions with the electron spins of the material, demonstrating that LiF was not incorporated into the layered oxide structure but was instead present as a coating.
Modulation of the crystallinity of hydrogenated nitrogen-rich graphitic carbon nitrides
Journal of Solid State Chemistry 182 (2009) 165–171
Denis Foy, GerardDemazeau, PierreFlorian, DominiqueMassiot, Christine Labrugere, GraziellaGoglio
Abstract:
An hydrogenated nitrogen-rich graphitic carbon nitride, structurally related to the theoretical graphitic phase of C3N4, has been synthesized in a bulk well-crystallized form. This new material was prepared by thermal decomposition of thiosemicarbazide up to 600 °C at ambient pressure under nitrogen flow. Its composition was determined by elemental combustion analysis. Powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and C13 MAS NMR characterizations were performed. This material can be schematically described with a two-dimensional framework and a composition close to C3N4.17H1.12. In this nitrogen-rich material, C3N3 voids are fully occupied by water molecules which are strongly trapped into the material. A loss of crystallinity associated with a modification of the thermal behavior is observed when the amount of trapped molecules decreases in the graphitic material, order being damaged both between and in the graphitic planes.
J. Chem. Phys. 129, 204110 (2008)
Michaël Deschamps, Gwendal Kervern, Dominique Massiot, Guido Pintacuda, Lyndon Emsley, and Philip J. Grandinetti
Abstract:
Adiabaticity plays a central role in modern magnetic resonance experiments, as excitations with adiabatic Hamiltonians allow precise control of the dynamics of the spin states during the course of an experiment. Surprisingly, many commonly used adiabatic processes in magnetic resonance perform well even though the adiabatic approximation does not appear to hold throughout the process. Here we show that this discrepancy can now be explained through the use of Berry's superadiabatic formalism, which provides a framework for including the finite duration of the process in the theoretical and numerical treatments. In this approach, a slow, but finite time-dependent Hamiltonian is iteratively transformed into time-dependent diagonal frames until the most accurate adiabatic approximation is obtained. In the case of magnetic resonance, the magnetization during an adiabatic process of finite duration is not locked to the effective Hamiltonian in the conventional adiabatic frame, but rather to an effective Hamiltonian in a superadiabatic frame. Only in the superadiabatic frame can the true validity of the adiabatic approximation be evaluated, as the inertial forces acting in this frame are the true cause for deviation from adiabaticity and loss of control during the process. Here we present a brief theoretical background of superadiabaticity and illustrate the concept in the context of magnetic resonance with commonly used shaped radio-frequency pulses.
Proton assisted recoupling and protein structure determination
J. Chem. Phys. 129, 245101 (2008)
Gaël De Paëpe, Józef R. Lewandowski, Antoine Loquet, Anja Böckmann, and Robert G. Griffin
Abstract:
We introduce a homonuclear version of third spin assisted recoupling, a second-order mechanism that can be used for polarization transfer between 13C or 15N spins in magic angle spinning (MAS) NMR experiments, particularly at high spinning frequencies employed in contemporary high field MAS experiments. The resulting sequence, which we refer to as proton assisted recoupling (PAR), relies on a cross-term between 1H–13C (or 1H–15N) couplings to mediate zero quantum 13C–13C (or 15N–15N recoupling). In particular, using average Hamiltonian theory we derive an effective Hamiltonian for PAR and show that the transfer is mediated by trilinear terms of the form C1‡C2‡ HZ for 13C–13C recoupling experiments (or N1‡N2‡ HZ for 15N–15N). We use analytical and numerical simulations to explain the structure of the PAR optimization maps and to delineate the PAR matching conditions. We also detail the PAR polarization transfer dependence with respect to the local molecular geometry and explain the observed reduction in dipolar truncation. Finally, we demonstrate the utility of PAR in structural studies of proteins with 13C–13C spectra of uniformly 13C, 15N labeled microcrystalline Crh, a 85 amino acid model protein that forms a domain swapped dimer (MW=2×10.4 kDa). The spectra, which were acquired at high MAS frequencies ( r2 >20 kHz) and magnetic fields (750–900 MHz 1H frequencies) using moderate rf fields, exhibit numerous cross peaks corresponding to long (up to 6–7 Å) 13C–13C distances which are particularly useful in protein structure determination. Using results from PAR spectra we calculate the structure of the Crh protein.
Neutron Powder Diffraction, Multinuclear, and Multidimensional NMR Structural Investigation of Pb5Ga3F19
Inorg. Chem., 2008, 47 (23), pp 10895–10905
Charlotte Martineau, Franck Fayon, Christophe Legein, Jean-Yves Buzaré, François Goutenoire and Emmanuelle Suard
Abstract:
The room temperature structure of Pb5Ga3F19 is investigated by combining neutron diffraction and multinuclear 19F, 71Ga, and 207Pb one-dimensional and two-dimensional solid-state nuclear magnetic resonance (NMR) experiments. Two models built in space group I4cm are reported for the description of the crystalline structure of Pb5Ga3F19. The structure is built from a network of both opposite corner-sharing Ga2F63− octahedra forming infinite chains along the c-axis and isolated Ga1F63− octahedra. The two models present two slightly different views of the strong static disorder of the fluorine ions belonging to the Ga2F63− octahedra. 71Ga NMR results show that the local environment of all Ga2 ions is identical, which indicates a tilt of the Ga2F63− octahedra within the chains. 207Pb NMR experiments confirm that the environment of only one of the two lead sites, Pb1, is strongly affected by the disorder, which gives rise to three broad distinct 207Pb NMR lines for this site. All 19F NMR lines are assigned using the 19F DQ-SQ MAS experiment. 19F−207Pb through-bond and through-space heteronuclear correlation experiments are carried out for the first time, supporting assignment of both the 19F and 207Pb NMR spectra. These correlation experiments also show that both models correctly describe the medium-range order of the structure of Pb5Ga3F19.
Investigation of Silver-Containing Layered Materials and Their Interactions with Primary Amines Using Solid-State 109Ag and 15N NMR Spectroscopy and First Principles Calculations
Inorg. Chem., 2008, 47 (23), pp 11245–11256
Hiyam Hamaed, Andy Y. H. Lo, Leslie J. May, Jared M. Taylor, George H. Shimizu and Robert W. Schurko
Abstract:
Silver-containing layered networks of the form [Ag(L)] (L = 4-pyridinesulfonate or p-toluenesulfonate) were treated with primary amines in different ratios. The structures of the parent supramolecular networks are well-known; however, their interactions with primary amines lead to the formation of new layered materials for which single-crystal X-ray structures cannot be obtained. Solid-state 109Ag, 15N, and 13C cross-polarization magic-angle spinning (CP/MAS) NMR experiments, in combination with powder X-ray diffraction experiments and ab initio calculations, are utilized to investigate the interactions between the primary amines and the parent materials, and to propose structural models for the new materials. 109Ag chemical shift (CS) tensor parameters are extremely sensitive to changes in silver environments; hence, 1H-109Ag CP/MAS NMR experiments are used to distinguish and characterize silver sites. The combination of 109Ag and 15N NMR experiments on starting materials and samples prepared with both 15N-labeled and unlabeled amines permits the accurate measurements of indirect 1J(109Ag,15N) and 1J(109Ag,14N) spin−spin coupling constants, providing further information on structure and bonding in these systems. First principles calculations of silver CS tensors and 1J(109Ag,14N) coupling constants in model complexes aid in formulating the proposed structural models for the new materials, which are largely comprised of layers of silver-diamine cations.
The Kagomé Topology of the Gallium and Indium Metal-Organic Framework Types with a MIL-68 Structure: Synthesis, XRD, Solid-State NMR Characterizations, and Hydrogen Adsorption
Inorg. Chem., 2008, 47 (24), pp 11892–11901
Christophe Volkringer, Mohamed Meddouri, Thierry Loiseau, Nathalie Guillou, Jérôme Marrot, Gérard Férey, Mohamed Haouas, Francis Taulelle, Nathalie Audebrand and Michel Latroche
Abstract:
The vanadium-based terephthalate analogs of MIL-68 have been obtained with gallium and indium (network composition: M(OH)(O2C−C6H4−CO2), M = Ga or In) by using a solvothermal synthesis technique using N,N-dimethylformamide as a solvent (10 and 48 h, for Ga and In, respectively, at 100 °C). They have been characterized by X-ray diffraction analysis; vibrational spectroscopy; and solid-state 1H and 1H−1H radio-frequency-driven dipolar recoupling (RFDR), 1H−1H double quantum correlation (DQ), and 13C{1H} cross polarization magic angle spinning (CPMAS) NMR spectroscopy. The three-dimensional network with a Kagomé-like lattice is built up from the connection of infinite trans-connected chains of octahedral units MO4(OH)2 (M = Ga or In), linked to each other through the terephthalate ligands in order to generate triangular and hexagonal one-dimensional channels. The presence of DMF molecules with strong interactions within the channels as well as their departure upon calcination (150 °C under a primary vacuum) of the materials has been confirmed by subjecting MIL-68 (Ga) to solid-state 1H MAS NMR. The 1H−1H RFDR and 1H−1H DQ spectra revealed important information on the spatial arrangement of the guest species with respect to the hybrid organic−inorganic network. 13C{1H} CPMAS NMR of activated samples provided crystallographically independent sites in agreement with X-ray diffraction structure determination. Brunauer−Emmett−Teller surface areas are 1117(24) and 746(31) m2 g−1 for MIL-98 (Ga) and MIL-68 (In), respectively. Hydrogen adsorption isotherms have been measured at 77 K, and the storage capacities are found to be 2.46 and 1.98 wt % under a saturated pressure of 4 MPa for MIL-68 (Ga) and MIL-68 (In), respectively. For comparison, the hydrogen uptake for the aluminum trimesate MIL-110, which has an open framework with 16 Å channels, is 3 wt % under 4 MPa.
NMR evidence of LiF coating rather than fluorine substitution in Li(Ni0.425Mn0.425Co0.15)O2
Journal of Solid State Chemistry 181 (2008) 3303–3307
M. Menetrier, J. Bains, L. Croguennec, A. Flambard, E. Bekaert, C. Jordy, Ph. Biensan, C. Delmas
Abstract:
A series of “Li1+z/2(Ni0.425Mn0.425Co0.15)1−z/2O2−zFz” materials was prepared by a coprecipitation route and their structure was characterized using X-ray diffraction (XRD), as well as 7Li and 19F Magic Angle Spinning (MAS) NMR spectroscopy. Two hypotheses were considered: (i) formation of layered oxyfluoride materials and (ii) formation of a mixture between the layered material and LiF. Structural parameters were refined by the Rietveld method, using XRD diffraction data. The refinement results did not allow us to choose between these two hypotheses: no significant change in crystallinity and structural parameters was observed irrespective of the fluorine ratio. 7Li and 19F MAS NMR analyses showed signals with isotropic positions characteristic of LiF, but envelopes characteristic of very strong dipolar interactions with the electron spins of the material, demonstrating that LiF was not incorporated into the layered oxide structure but was instead present as a coating.
Modulation of the crystallinity of hydrogenated nitrogen-rich graphitic carbon nitrides
Journal of Solid State Chemistry 182 (2009) 165–171
Denis Foy, GerardDemazeau, PierreFlorian, DominiqueMassiot, Christine Labrugere, GraziellaGoglio
Abstract:
An hydrogenated nitrogen-rich graphitic carbon nitride, structurally related to the theoretical graphitic phase of C3N4, has been synthesized in a bulk well-crystallized form. This new material was prepared by thermal decomposition of thiosemicarbazide up to 600 °C at ambient pressure under nitrogen flow. Its composition was determined by elemental combustion analysis. Powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and C13 MAS NMR characterizations were performed. This material can be schematically described with a two-dimensional framework and a composition close to C3N4.17H1.12. In this nitrogen-rich material, C3N3 voids are fully occupied by water molecules which are strongly trapped into the material. A loss of crystallinity associated with a modification of the thermal behavior is observed when the amount of trapped molecules decreases in the graphitic material, order being damaged both between and in the graphitic planes.
Tuesday, December 23, 2008
J. Am. Chem. Soc., 2008, 130 (51), pp 17502–17508
2H Solid-State NMR of Ruthenium Complexes
Bernadeta Walaszek, Anna Adamczyk, Tal Pery, Xu Yeping†, Torsten Gutmann, Nader de Sousa Amadeu, Stefan Ulrich†, Hergen Breitzke, Hans Martin Vieth, Sylviane Sabo-Etienne§, Bruno Chaudret§, Hans-Heinrich Limbach† and Gerd Buntkowsky
Abstract
The 2H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT)2 (1a), Tp*RuD(D2)(THT) (1b), Tp*RuD(D2)2 (1c), Cp*RuD3(PPh3) (2) and RuD2(η2-D2)2(PCy3)2 (3) have been measured in a wide temperature range. These compounds were chosen as potential model systems for hydrogen surface species in Ru-nanoparticles. The deuterium quadrupolar coupling constants Qcc and asymmetry parameters were extracted by 2H NMR line-shape analysis. The Qcc values of the deuterons bound to the metal vary between 13 kHz and 76 kHz. In addition all spectra show that some of the deuterium is incorporated into carbon positions exhibiting quadrupolar coupling constants in the range of 134 kHz to 192 kHz. The room temperature spectra contain an additional weak very narrow line which was assigned to deuterons exhibiting a high mobility. These deuterons are attributed to crystallographic impurity and partially to D2 molecules which lost by the complexes. The temperature where their motion is quenched and the types of these motions depend on the chemical structure. We propose to use the values of the quadrupolar coupling constants measured in order to characterize different hydrogen species on the surface of Ru-nanoparticles.
Bernadeta Walaszek, Anna Adamczyk, Tal Pery, Xu Yeping†, Torsten Gutmann, Nader de Sousa Amadeu, Stefan Ulrich†, Hergen Breitzke, Hans Martin Vieth, Sylviane Sabo-Etienne§, Bruno Chaudret§, Hans-Heinrich Limbach† and Gerd Buntkowsky
Abstract
The 2H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT)2 (1a), Tp*RuD(D2)(THT) (1b), Tp*RuD(D2)2 (1c), Cp*RuD3(PPh3) (2) and RuD2(η2-D2)2(PCy3)2 (3) have been measured in a wide temperature range. These compounds were chosen as potential model systems for hydrogen surface species in Ru-nanoparticles. The deuterium quadrupolar coupling constants Qcc and asymmetry parameters were extracted by 2H NMR line-shape analysis. The Qcc values of the deuterons bound to the metal vary between 13 kHz and 76 kHz. In addition all spectra show that some of the deuterium is incorporated into carbon positions exhibiting quadrupolar coupling constants in the range of 134 kHz to 192 kHz. The room temperature spectra contain an additional weak very narrow line which was assigned to deuterons exhibiting a high mobility. These deuterons are attributed to crystallographic impurity and partially to D2 molecules which lost by the complexes. The temperature where their motion is quenched and the types of these motions depend on the chemical structure. We propose to use the values of the quadrupolar coupling constants measured in order to characterize different hydrogen species on the surface of Ru-nanoparticles.
Friday, December 19, 2008
Special Issue Coordination Chemistry Reviews: Applications of NMR to Inorganic and Organometallic Chemistry
Volume 252, Issues 21-22, Pages 2155-2444 (November 2008)
Applications of NMR to Inorganic and Organometallic ChemistryEdited by P.S. Pregosin
1.
Editorial BoardPage CO2 Preview PDF (38 K) Related Articles
Preface
2.
PrefacePage 2155Paul S. Pregosin Preview PDF (55 K) Related Articles
Reviews
3.
31P and 13C NMR studies on metal complexes of phosphorus-donors: Recognizing surprisesPages 2156-2170Paul S. Pregosin Preview PDF (2512 K) Related Articles
4.
Applications of 31P NMR spectroscopy in development of M(Duphos)-catalyzed asymmetric synthesis of P-stereogenic phosphines (M = Pt or Pd)Pages 2171-2179David S. Glueck Preview PDF (1203 K) Related Articles
5.
19F NMR in organometallic chemistry: Applications of fluorinated arylsPages 2180-2208Pablo Espinet, Ana C. Albéniz, Juan A. Casares, Jesús M. Martínez-Ilarduya Preview PDF (3272 K) Related Articles
6.
Vanadium NMR of organovanadium complexesPages 2209-2223Dieter Rehder Preview PDF (782 K) Related Articles
7.
NMR investigation of non-covalent aggregation of coordination compounds ranging from dimers and ion pairs up to nano-aggregatesPages 2224-2238Gianfranco Bellachioma, Gianluca Ciancaleoni, Cristiano Zuccaccia, Daniele Zuccaccia, Alceo Macchioni Preview PDF (831 K) Related Articles
8.
Applications of heteronuclear NMR spectroscopy in biological and medicinal inorganic chemistryPages 2239-2277Luca Ronconi, Peter J. Sadler Preview PDF (2201 K) Related Articles
9.
Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistryPages 2278-2291Simon B. Duckett, Nicholas J. Wood Preview PDF (876 K) Related Articles
10.
Solution structure, dynamics and speciation of perfluoroaryl boranes through 1H, 11B and 19F NMR spectroscopyPages 2292-2313Tiziana Beringhelli, Daniela Donghi, Daniela Maggioni, Giuseppe D’Alfonso Preview PDF (2401 K) Related Articles
11.
NMR spectroscopy in coordination supramolecular chemistry: A unique and powerful methodologyPages 2314-2345Aurelia Pastor, Eloísa Martínez-Viviente Preview PDF (4472 K) Related Articles
12.
Ligand exchange and complex formation kinetics studied by NMR exemplified on fac-[(CO)3M(H2O)]+ (M = Mn, Tc, Re)Pages 2346-2361Lothar Helm Preview PDF (1718 K) Related Articles
13.
Multinuclear NMR studies of the interaction of metal ions with adenine-nucleotidesPages 2362-2380Zoltán Szabó Preview PDF (1337 K) Related Articles
14.
Dihydrogen, dihydride and in between: NMR and structural properties of iron group complexesPages 2381-2394Robert H. Morris Preview PDF (283 K) Related Articles
15.
NMR: A good tool to ascertain σ-silane or σ-borane formulations?Pages 2395-2409Gilles Alcaraz, Sylviane Sabo-Etienne Preview PDF (1209 K) Related Articles
16.
Linkers and catalysts immobilized on oxide supports: New insights by solid-state NMR spectroscopyPages 2410-2423Janet Blümel Preview PDF (1555 K) Related Articles
17.
Metal containing nanosized systems for MR-Molecular Imaging applicationsPages 2424-2443Daniela Delli Castelli, Eliana Gianolio, Simonetta Geninatti Crich, Enzo Terreno, Silvio Aime Preview PDF (3094 K) Related Articles
Applications of NMR to Inorganic and Organometallic ChemistryEdited by P.S. Pregosin
1.
Editorial BoardPage CO2 Preview PDF (38 K) Related Articles
Preface
2.
PrefacePage 2155Paul S. Pregosin Preview PDF (55 K) Related Articles
Reviews
3.
31P and 13C NMR studies on metal complexes of phosphorus-donors: Recognizing surprisesPages 2156-2170Paul S. Pregosin Preview PDF (2512 K) Related Articles
4.
Applications of 31P NMR spectroscopy in development of M(Duphos)-catalyzed asymmetric synthesis of P-stereogenic phosphines (M = Pt or Pd)Pages 2171-2179David S. Glueck Preview PDF (1203 K) Related Articles
5.
19F NMR in organometallic chemistry: Applications of fluorinated arylsPages 2180-2208Pablo Espinet, Ana C. Albéniz, Juan A. Casares, Jesús M. Martínez-Ilarduya Preview PDF (3272 K) Related Articles
6.
Vanadium NMR of organovanadium complexesPages 2209-2223Dieter Rehder Preview PDF (782 K) Related Articles
7.
NMR investigation of non-covalent aggregation of coordination compounds ranging from dimers and ion pairs up to nano-aggregatesPages 2224-2238Gianfranco Bellachioma, Gianluca Ciancaleoni, Cristiano Zuccaccia, Daniele Zuccaccia, Alceo Macchioni Preview PDF (831 K) Related Articles
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Applications of heteronuclear NMR spectroscopy in biological and medicinal inorganic chemistryPages 2239-2277Luca Ronconi, Peter J. Sadler Preview PDF (2201 K) Related Articles
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Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistryPages 2278-2291Simon B. Duckett, Nicholas J. Wood Preview PDF (876 K) Related Articles
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Thursday, December 18, 2008
J Phys Chem C Issue 50
Methane Activation over Zn-Modified MFI Zeolite: NMR Evidence for Zn−Methyl Surface Species Formation
Yuriy G. Kolyagin†, Irina I. Ivanova*†, Vitaly V. Ordomsky†, Antoine Gedeon‡ and Yuri A. Pirogov§
J. Phys. Chem. C, 2008, 112 (50), pp 20065–20069
Abstract: The early stages of methane activation over Zn-modified H-MFI catalysts obtained by high-temperature reaction with zinc vapor have been studied by 13C MAS NMR in situ. Methane 99.9% enriched with 13C was used as labeled reactant. The spectroscopic data pointed to formation of zinc methyl species at ambient temperature just after methane adsorption onto the zeolite sample. The results suggest that methane activation occurs via dissociative adsorption over acid−base Zn−O pairs involving Zn2+ cations and negatively charged oxygen atoms of the zeolite framework. The nature of the sites responsible for the dissociation is discussed.
Yuriy G. Kolyagin†, Irina I. Ivanova*†, Vitaly V. Ordomsky†, Antoine Gedeon‡ and Yuri A. Pirogov§
J. Phys. Chem. C, 2008, 112 (50), pp 20065–20069
Abstract: The early stages of methane activation over Zn-modified H-MFI catalysts obtained by high-temperature reaction with zinc vapor have been studied by 13C MAS NMR in situ. Methane 99.9% enriched with 13C was used as labeled reactant. The spectroscopic data pointed to formation of zinc methyl species at ambient temperature just after methane adsorption onto the zeolite sample. The results suggest that methane activation occurs via dissociative adsorption over acid−base Zn−O pairs involving Zn2+ cations and negatively charged oxygen atoms of the zeolite framework. The nature of the sites responsible for the dissociation is discussed.
Wednesday, December 17, 2008
European Journal of Pharmaceutical Sciences, Volume 34, Issues 2-3, 3 July 2008, Pages 140-148
Anticancer cisplatin interactions with bilayers of total lipid extract from pig brain: A 13C, 31P and 15N solid-state NMR study
Magnus Jensena and Willy Nerdal
Abstract
Cisplatin (cis-diamminedichloroplatinum(II)) is used in chemotherapy and it is well established that cisplatin forms platinum-DNA adducts that initiate tumor cell death. Drawbacks are side effects such as neurotoxicity and cellular cisplatin resistance and it is possible that part of these effects are linked to cisplatin interaction with lipids and the phospholipid bilayer. 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of total lipid extract from pig brain with and without cisplatin show that the phosphatidylserine (PS) carboxyl resonance disappears in presence of cisplatin and that a new resonance of similar intensity appears at 185.5 ppm. Thus, indicating cisplatin interaction with the PS head-group. Static and MAS 31P NMR spectra of lipid extract with and without cisplatin show that the phospholipids to a large extent reside in a bilayer environment in pure lipid extract, and that the presence of cisplatin promotes isotropic and/or hexagonal lipid phases.
Magnus Jensena and Willy Nerdal
Abstract
Cisplatin (cis-diamminedichloroplatinum(II)) is used in chemotherapy and it is well established that cisplatin forms platinum-DNA adducts that initiate tumor cell death. Drawbacks are side effects such as neurotoxicity and cellular cisplatin resistance and it is possible that part of these effects are linked to cisplatin interaction with lipids and the phospholipid bilayer. 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra of total lipid extract from pig brain with and without cisplatin show that the phosphatidylserine (PS) carboxyl resonance disappears in presence of cisplatin and that a new resonance of similar intensity appears at 185.5 ppm. Thus, indicating cisplatin interaction with the PS head-group. Static and MAS 31P NMR spectra of lipid extract with and without cisplatin show that the phospholipids to a large extent reside in a bilayer environment in pure lipid extract, and that the presence of cisplatin promotes isotropic and/or hexagonal lipid phases.
Monday, December 15, 2008
J. Am. Chem. Soc., 2008, 130 (50), pp 17148–17153
Competition Saturation Transfer Difference Experiments Improved with Isotope Editing and Filtering Schemes in NMR-Based Screening
Krisztina Fehér†, Patrick Groves‡§, Gyula Batta⊥, Jesús Jiménez-Barbero§, Claudia Muhle-Goll†◼ and Katalin E. Kövér
Abstract
Competition binding experiments are used in NMR-based screenings to match up to the binding site with that of a known ligand and to determine the strength of the interaction, thus providing a ranking of hits according to receptor affinity. These competition titration experiments must use a reference ligand for which the binding site on the receptor and the affinity of the interaction is known. These experiments rely on the observation of separate signals of the reference and hit compounds, which is very often hampered by signal overlap. Here, we present a combination of isotope editing and filtering schemes with saturation transfer difference (STD) experiments that allows the separation of the STD signals of the labeled reference ligand from that of the natural abundance hit compound even in the case of severe signal overlap. Thus, the measurement of well-defined titration curves in competition STD titration experiments is feasible and allows the quantitative determination of binding constants. Note that the method requires the availability of the reference ligand in an NMR-active, stable-isotope-labeled form.
Krisztina Fehér†, Patrick Groves‡§, Gyula Batta⊥, Jesús Jiménez-Barbero§, Claudia Muhle-Goll†◼ and Katalin E. Kövér
Abstract
Competition binding experiments are used in NMR-based screenings to match up to the binding site with that of a known ligand and to determine the strength of the interaction, thus providing a ranking of hits according to receptor affinity. These competition titration experiments must use a reference ligand for which the binding site on the receptor and the affinity of the interaction is known. These experiments rely on the observation of separate signals of the reference and hit compounds, which is very often hampered by signal overlap. Here, we present a combination of isotope editing and filtering schemes with saturation transfer difference (STD) experiments that allows the separation of the STD signals of the labeled reference ligand from that of the natural abundance hit compound even in the case of severe signal overlap. Thus, the measurement of well-defined titration curves in competition STD titration experiments is feasible and allows the quantitative determination of binding constants. Note that the method requires the availability of the reference ligand in an NMR-active, stable-isotope-labeled form.
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