Friday, August 31, 2007

J. Am. Chem. Soc.,
An Exchange-Free Measure of 15N Transverse Relaxation: An NMR Spectroscopy Application to the Study of a Folding Intermediate with Pervasive Chemical Exchange
D. Flemming Hansen, Daiwen Yang, Haniqiao Feng, Zheng Zhou, Silke Wiesner, Yawen Bai, and Lewis E. Kay

A series of experiments are presented that provide an exchange-free measure of dipole-dipole 15N transverse relaxation, Rdd, that can then be substituted for 15N R1 or R2 rates in the study of internal protein dynamics. The method is predicated on the measurement of a series of relaxation rates involving 1H-15N longitudinal order, anti-phase 1H and 15N single-quantum coherences, and 1H-15N multiple quantum coherences; the relaxation rates of all coherences are measured under conditions of spin-locking. Results from detailed simulations and experiments on a number of protein systems establish that Rdd values are independent of exchange and systematic errors from dipolar interactions with proximal protons are calculated to be less than 1-2%, on average, for applications to perdeuterated proteins. Simulations further indicate that the methodology is rather insensitive to the exact level of deuteration so long as proteins are reasonably highly deuterated (>50%). The utility of the methodology is demonstrated with applications involving protein L, ubiquitin, and a stabilized folding intermediate of apocytochrome b562 that shows large contributions to 15N R1 relaxation from chemical exchange.

J. Am. Chem. Soc.,
Proton-Detected Solid-State NMR Spectroscopy of Fully Protonated Proteins at 40 kHz Magic-Angle Spinning

Donghua H. Zhou, Gautam Shah, Mircea Cormos, Charles Mullen, Dennis Sandoz, and Chad M. Rienstra*

Remarkable progress in solid-state NMR has enabled complete structure determination of uniformly labeled proteins in the size range of 5-10 kDa. Expanding these applications to larger or mass-limited systems requires further improvements in spectral sensitivity, for which inverse detection of 13C and 15N signals with 1H is one promising approach. Proton detection has previously been demonstrated to offer sensitivity benefits in the limit of sparse protonation or with ~30 kHz magic-angle spinning (MAS). Here we focus on experimental schemes for proteins with ~100% protonation. Full protonation simplifies sample preparation and permits more complete chemical shift information to be obtained from a single sample. We demonstrate experimental schemes using the fully protonated, uniformly 13C,15N-labeled protein GB1 at 40 kHz MAS rate with 1.6-mm rotors. At 500 MHz proton frequency, 1-ppm proton line widths were observed (500 ± 150 Hz), and the sensitivity was enhanced by 3 and 4 times, respectively, versus direct 13C and 15N detection. The enhanced sensitivity enabled a family of 3D experiments for spectral assignment to be performed in a time-efficient manner with less than a micromole of protein. CANH, CONH, and NCAH 3D spectra provided sufficient resolution and sensitivity to make full backbone and partial side-chain proton assignments. At 750 MHz proton frequency and 40 kHz MAS rate, proton line widths improve further in an absolute sense (360 ± 115 Hz). Sensitivity and resolution increase in a better than linear manner with increasing magnetic field, resulting in 14 times greater sensitivity for 1H detection relative to that of 15N detection.

Monday, August 27, 2007

Hiyam's Journal Update

J. Am. Chem. Soc.,

Molecular Dynamics Computational Study of the 199Hg-199Hg NMR Spin-Spin Coupling Constants of [Hg-Hg-Hg]2+ in SO2 Solution
Jochen Autschbach* and Mariusz Sterzel

The isotropic one-bond and two-bond 199Hg-199Hg nuclear magnetic spin-spin coupling constants (J-couplings) of [Hg-Hg-Hg]2+ were calculated using density functional theory, the zeroth-order regular approximation (ZORA) to treat relativistic effects, and Born-Oppenheimer molecular dynamics (BOMD) including SO2 molecules explicitly for the description of solvent effects. The final BOMD average of 150 kHz for 1J (199Hg-199Hg) agrees well with the experimental spin-spin coupling of 140 kHz measured in liquid SO2, while computations not considering explicit solvation at the quantum-mechanical level yielded one-bond coupling constants between 230 and 260 kHz. The two-bond coupling is similarly strongly affected by solvent effects. An analysis of the BOMD data shows that the effect is mainly due to close contacts between the terminal Hg atoms of [Hg-Hg-Hg]2+ and the solvent's oxygen atoms. The results highlight the importance of solvent effects for the NMR parameter of heavy metals and demonstrate the usefulness of treating such solvent effects with the help of molecular dynamics-based averaging.

Hiyam's Journal Update

J. Am. Chem. Soc.,

Characterization of Polymorphs and Solid-State Reactions for Paramagnetic Systems by 13C Solid-State NMR and ab Initio Calculations
Medhat A. Shaibat, Leah B. Casabianca, Nalinda P. Wickramasinghe, Stephen Guggenheim, Angel C. de Dios, and Yoshitaka Ishii*

Despite its importance in drug and material science, spectroscopic characterization of polymorphs or supramolecular structures of paramagnetic systems often poses challenges, particularly for noncrystalline solids. This work demonstrates that 13C solid-state NMR (SSNMR) of paramagnetic systems under very fast magic angle spinning (VFMAS) (spinning speed of 20 kHz or higher) provides exceptionally sensitive means to probe small structural difference among polymorphs of paramagnetic complexes in noncrystalline solids, including drugs and materials containing paramagnetic metal ions. 13C VFMAS SSNMR experiments and corresponding ab initio shift calculations for Cu(II)(8-quilinolinol)2, anticancer agents, show that - and -forms of this compound can be easily distinguished by notable difference in paramagnetic relaxation times and hyperfine shifts. It is also shown that applications of the present technique allow for quantitative and chemical characterization of solid-state reactions for Cu(8-quilinolinol)2 and Cu(imidazole)2 in a noninvasive manner.

J. Am. Chem. Soc.

Residual Dipolar Couplings by Off-Magic-Angle Spinning in Solid-State Nuclear Magnetic Resonance Spectroscopy

Giuseppe Pileio, Ying Guo, Tran N. Pham, John M. Griffin, Malcolm H. Levitt,* and Steven P. Brown*

A solid-state NMR analogue of the solution-state residual dipolar coupling effect is demonstrated. A small misset of the spinning axis by less than 0.5 changes the modulation frequency of spin-echoes, allowing the estimation of internuclear dipole-dipole couplings and hence internuclear distances.

J. Am. Chem. Soc.,

Phosphate-Mediated Arginine Insertion into Lipid Membranes and Pore Formation by a Cationic Membrane Peptide from Solid-State NMR
Ming Tang, Alan J. Waring, and Mei Hong*

The insertion of charged amino acid residues into the hydrophobic part of lipid bilayers is energetically unfavorable yet found in many cationic membrane peptides and protein domains. To understand the mechanism of this translocation, we measured the 13C-31P distances for an Arg-rich -hairpin antimicrobial peptide, PG-1, in the lipid membrane using solid-state NMR. Four residues, including two Arg's, scattered through the peptide were chosen for the distance measurements. Surprisingly, all residues show short distances to the lipid 31P: 4.0-6.5 Å in anionic POPE/POPG membranes and 6.5-8.0 Å in zwitterionic POPC membranes. The shortest distance of 4.0 Å, found for a guanidinium C at the -turn, suggests N-H···O-P hydrogen bond formation. Torsion angle measurements of the two Arg's quantitatively confirm that the peptide adopts a -hairpin conformation in the lipid bilayer, and gel-phase 1H spin diffusion from water to the peptide indicates that PG-1 remains transmembrane in the gel phase of the membrane. For this transmembrane -hairpin peptide to have short 13C-31P distances for multiple residues in the molecule, some phosphate groups must be embedded in the hydrophobic part of the membrane, with the local 31P plane parallel to the -strand. This provides direct evidence for toroidal pores, where some lipid molecules change their orientation to merge the two monolayers. We propose that the driving force for this toroidal pore formation is guanidinium-phosphate complexation, where the cationic Arg residues drag the anionic phosphate groups along as they insert into the hydrophobic part of the membrane. This phosphate-mediated translocation of guanidinium ions may underlie the activity of other Arg-rich antimocrobial peptides and may be common among cationic membrane proteins.

Friday, August 24, 2007

Joel's Journal Update

13C-13C Chemical Shift Correlation in Rotating Solids without 1H Decoupling During Mixing.
C. Herbst, K. Riedel, J. Leppert, O. Ohlenschlager, M. Gorlach,R. Ramachandran.
Adiabatic RF pulse schemes using inversion pulses with low power factor are difficult to implement but are shown to be feasible and advantageous for generating 13C-13C MAS solid-state NMR chemical shift correlation spectra via longitudinal magnetisation exchange without 1H decoupling during mixing.

Quenching and Recoupling of Echo Modulations in NMR Spectroscopy.
K. Gopalakrishnan, N. Aeby, G. Bodenhausen
Trains of spin echoes are normally modulated by homonuclear scalar couplings. It has long been known that echo modulations are quenched when the pulse-repetition rates are much larger than the offsets of the coupling partners, because the spin systems behave as if they consisted of magnetically equivalent spins when the offsets are suppressed. This type of quenching of the echo modulations can occur when the radio-frequency (RF) pulses are ideal, that is, when they are perfectly homogeneous, properly calibrated to induce rotations through an angle, p, and have an RF amplitude, w1=-gB1, that is strong compared to the largest offset, WS=w0S-wRF, with respect to the carrier frequency. Recently, it was discovered that echo modulations can also be quenched when the RF pulses are nonideal, that is, when they are too weak to bring about an ideal rotation of the magnetization of the coupling partners, so that the effective fields associated with the RF pulses are tilted in the rotating frame. This phenomenon typically occurs when the pulse-repetition rates are much slower than the offset of the coupling partner. Under such conditions, it turns out, however, that for certain offsets, when the phase, fS (which arises from a free precession of the magnetization of the coupling partner, S, in the pulse interval, 2t, and the pulse length, tp), approaches a multiple of 2p, the echo modulations are restored. However, the frequencies of these echo modulations are not simply determined by the homonuclear scalar coupling, JIS. The Fourier transforms of the echo trains (the so-called J spectra) reveal surprising multiplet patterns, and the amplitudes of the echo modulations depend on the offsets of the coupling partners. Herein, we present a unified theory, based on an average-Hamiltonian approach, to describe these effects for two-spin systems. Experimental evidence of echo modulations in a system of two spins is presented. Experiments with three and more spins, backed up by extensive numerical simulations, will be presented elsewhere.

NMR Studies of Double Proton Transfer in Hydrogen bonded cyclic N,N'-diarylformamidine Dimers: Conformational Control, Kinetic HH/HD/DD Isotope Effects and Tunneling.
J.M Lopez, F. Mannle, I. Wawer, G. Buntkowsky, and H.H. Limbach.
Using dynamic NMR spectroscopy, the kinetics of the degenerate double proton transfer in cyclic dimers of polycrystalline 15N,15N-di-(4-bromophenyl)-formamidine (DBrFA) have been studied including the kinetic HH/HD/DD isotope effects in a wide temperature range. This transfer is controlled by intermolecular interactions, which in turn are controlled by the molecular conformation and hence the molecular structure. At low temperatures, rate constants were determined by line shape analysis of 15N NMR spectra obtained using cross-polarization (CP) and magic angle spinning (MAS). At higher temperatures, in the microsecond time scale, rate constants and kinetic isotope effects were obtained by a combination of longitudinal 15N and 2H relaxation measurements. 15N CPMAS line shape analysis was also employed to study the non-degenerate double proton transfer of polycrystalline 15N,15N-diphenyl-formamidine (DPFA). The kinetic results are in excellent agreement with the kinetics of DPFA and 15N,15N-di-(4-fluorophenyl)-formamidine (DFFA) studied previously for solutions in tetrahydrofuran. Two large HH/HD and HD/DD isotope effects are observed in the whole temperature range which indicates a concerted double proton transfer mechanism in the domain of the reaction energy surface. The Arrhenius curves are non-linear indicating a tunneling mechanism. Arrhenius curve simulations were performed using the Bell–Limbach tunneling model. The role of the phenyl group conformation and hydrogen bond compression on the barrier of the proton transfer is discussed.

Selectivity of guest-host interactions in self-assembled hydrogen-bonded nanostructures observed by NMR.
G. Brunklaus, A. Koch, D. Sebastiani, H.W. Spiess
We studied the incorporation of various small guest molecules into calix[4]hydroquinone nanotubes and nanoclusters using solid-state proton NMR spectroscopy in combination with quantum chemical calculations. While the molecules exhibit different types of hydrogen bonding and van der Waals interactions, they show different affinities to the nanotube host structures. As the guest molecules are located inside the complexes, they experience a shift in the NMR resonance line caused by screening effects from the aromatic electrons of the host superstructure. The abilities to fill the otherwise empty space within the tubes can hence be measured indirectly by the displacement of the NMR lines relative to the free molecules. In this way, we can probe which guest molecules are recognized by the calix[4]hydroquinones as suitable for filling their nanoporous superstructures. Selective guest–host interactions have been successfully achieved for the three component mixture of water and acetone with either 2-methyl-2-propanol or 2-propanol. In both cases, the alcohols were superior to acetone in filling the CHQ tubes.

Friday, August 17, 2007

Hiyam Journal Update

J. Am. Chem. Soc., 129 (33), 10195 -10200, 2007.

Differential Line Broadening in MAS Solid-State NMR due to Dynamic Interference
Veniamin Chevelkov, Katja Faelber, Anna Schrey, Kristina Rehbein, Anne Diehl, and Bernd Reif

Many MAS (magic angle spinning) solid-state NMR investigations of biologically relevant protein samples are hampered by poor resolution, particularly in the 15N chemical shift dimension. We show that dynamics in the nanosecond-microsecond time scale in solid-state samples can induce significant line broadening of 15N resonances in solid-state NMR experiments. Averaging of 15NH/ multiplet components due to 1H decoupling induces effective relaxation of the 15N coherence in case the N-H spin pair undergoes significant motion. High resolution solid-state NMR spectra can then only be recorded by application of TROSY (Transverse Relaxation Optimized Spectroscopy) type techniques which select the narrow component of the multiplet pattern. We speculate that this effect has been the major obstacle to the NMR spectroscopic characterization of many membrane proteins and fibrillar aggregates so far. Only in very favorable cases, where dynamics are either absent or very fast (picosecond), high-resolution spectra were obtained. We expect that this approach which requires intense deuteration will have a significant impact on the quality and the rate at which solid-state NMR spectroscopic investigations will emerge in the future.

Chem. Mater., 19 (17), 4166 -4173, 2007. 10.

DFT Modeling of NMR Contact Shift Mechanism in the Ideal LiNi2O4 Spinel and Application to Thermally Treated Layered Li0.5NiO2
Cédric Chazel, Michel Ménétrier,* Dany Carlier, Laurence Croguennec, and Claude Delmas

LiNi2O4 spinel-type phases were prepared by thermal treatment of electrochemically deintercalated layered Li~0.5NiO2. The phase transformation was followed by 7Li NMR, showing a gradual change of the signal from the layered compound. The characteristic signal of the latter (related to local Li/vacancy and Ni3+/Ni4+ ordering) vanishes after heating to 150 C and is replaced by a new signal showing faster exchange kinetics (originating from Ni3+/Ni4+ hopping around Li), which progressively transforms into a broad distribution of signals. Around 200 C, a set of three positively shifted signals is observed, corresponding to the appearance of the spinel phase as seen from XRD; these signals disappear after heating to 240 C, corresponding to the beginning of decomposition of the spinel into a disordered Rm type phase with oxygen evolution as previously shown by Guilmard et al. (Chem. Mater. 2003, 15, 4476 and 4484). In an ideal LiNi2O4 spinel, only one 7Li NMR signal is expected. DFT (GGA) calculations were carried out and show that the mechanism for the electron spin density transfer from NiO6 octahedra to corner-sharing LiO4 tetrahedra with close to 120 Ni-O-Li configuration is a delocalization one, although the p orbitals on oxygen do not present ideal orientation, leading to a much weaker transfer compared to cases where both Ni and Li are in octahedral coordination with 180 Ni-O-Li configuration. The complex but well-defined experimental NMR signals consistently observed show that the material is far from the ideal spinel structure. However, it could not be correlated to the actual stoichiometry of the compound. It was therefore tentatively assigned to structural defects resulting from incomplete migration of Ni ions from their site to the Li layer in the pristine compound, such as partial occupation of tetrahedral sites.

Wednesday, August 15, 2007

Friday, August 10, 2007

Thrills, Chills, and Spills in Chemistry: An Enrapturing Blog Update

Today we've got a couple real barn-burners to tickle your fancy and light your lantern!

These bad boys are coming to you straight from the mean streets of the Journal of Materials Chemistry and Chemical Physics (read: don't mess with them!).

First up: Nanoparticles Gone Wild!


J. Mater. Chem., 2007, 17, 2695 - 2699, DOI: 10.1039/b702538f

Antibody conjugated magnetic PLGA nanoparticles for diagnosis and treatment of breast cancer

Jaemoon Yang, Choong-Hwan Lee, Joseph Park, Sungbaek Seo, Eun-Kyung Lim, Yong Jin Song, Jin-Suck Suh, Ho-Geun Yoon, Yong-Min Huh and Seungjoo Haam

DOX–magnetic PLGA nanoparticles conjugated with well-tailored antibodies were synthesized for the detection and therapy of breast cancer. Magnetic nanocrystals embedded in polymeric nanoparticles did not inhibit the nanoparticle formulation or drug release kinetics. The multimodal nanoparticles demonstrated remarkable cancer cell affinity and ultrasensitivity via magnetic resonance imaging. Furthermore, the loaded anticancer drugs were released and sustained for three weeks.


And next on the agenda is some quantum computing for our #1 reader, Schroedinger's Cat!


Chemical Physics
Vol: 336, Issue: 1, July 9, 2007

Title: Boolean and fuzzy logic implemented at the molecular level
Author: Gentili, P.L.
Keywords: Mamdani's and Sugeno's methods; Photochromism; Crisp logic; Fuzzy logic; Proximity effect
Abstract (English): In this work, it is shown how to implement both hard and soft computing by means of two structurally related heterocyclic compounds: flindersine (FL) and 6(5H)-phenanthridinone (PH). Since FL and PH have a carbonyl group in their molecular skeletons, they exhibit Proximity Effects in their photophysics. In other words, they have an emission power that can be modulated through external inputs such as temperature (T) and hydrogen-bonding donation (HBD) ability of solvents. This phenomenology can be exploited to implement both crisp and fuzzy logic. Fuzzy Logic Systems (FLSs) wherein the antecedents of the rules are connected through the AND operator, are built by both the Mamdani's and Sugeno's models. Finally, they are adopted as approximators of the proximity effect phenomenon and tested for their prediction capabilities. Moreover, FL as photochromic compound is also a multiply configurable crisp logic molecular element.
Publisher: Elsevier Science


Now for something completely different, grab your calculators and get your matrices ready, kids, because here comes some ab initio to finish up this action-packed update!


Chemical Physics Vol: 333, Issue: 2-3, March 30, 2007
pp. 201-207

Title: Ab initio study of the change from η-5- to η-1-coordination in group 12 dimetallocenes MM'(C5H5)2 with M, M'=Zn, Cd, Hg
Authors: Philpott, M.R.; Kawazoe, Y.
Keywords: Dimetallocene; Dizincocene; Zincous; Zn2^2^+; Cadmous; Cd2^2^+; Mercurous; Hg2^2^+; Quantum electronic structure; Density functional theory (DFT); Electronic structure; Electron localization function (ELF); Partial charge density; Kohn-Sham level; Zn2(η-1-C5H5)2; Zn2(η-5-C5H5)2
Abstract (English): For group 12 dimetallocenes, ab initio plane wave density functional theory (DFT) quantum electronic structure calculations predict that the metal atom can move from center η-5-C5H5 to edge η-1-C5H5 coordination with increase in atomic number. Systems studied include homo- and hetero-dimetallocene systems M2Cp2 and ZnMCp2 (where Cp=C5H5) in staggered and eclipsed initial configurations, and M is a group 12 atom Zn, Cd or Hg. The electronic change that drives the geometrical change is explored in calculations of the total charge density, partial charge densities of Kohn-Sham levels and the electron localization function (ELF). The zinc atoms prefer central η-5-C5H5 coordination, cadmium an off center position and mercury the edge displaced η-1-C5H5 coordination. In this latter configuration the nearest carbon atom shows signs of sp^3-hybridization and the other four carbons adopt a cis-butadiene-like structure. In the hetero-systems we find distinct geometries with each M-Cp unit adopting the coordination of the homo-dimetallocene.


Until next time, kids - drink your V-8 and take your vitamins!

Can. J. Chem. Volume 85, Number 7-8, July/August 2007 (453-559)

EFGShield — A program for parsing and summarizing the results of electric field gradient and nuclear magnetic shielding tensor calculations

Samyuktha Adiga, Dominic Aebi, and David L. Bryce Can. J. Chem./Rev. can. chim. 85(7-8): 496-505 (2007)

Full text (PDF 666 kb)

Abstract: A computer program (EFGShield) is described that simplifies and summarizes the output from electric field gradient (EFG) and nuclear magnetic shielding tensor calculations performed independently using existing quantum chemical software. In addition to summarizing tensor magnitudes according to conventions commonly used by solid-state NMR spectroscopists, the program provides Euler angles relating the orientations of the EFG and shielding tensor principal axis systems (PAS). An atomic coordinate file is generated that also contains dummy atoms representing the orientations of the EFG and shielding tensor PASs in the molecular framework. We demonstrate the functionality of the program using calculations of the chlorine EFG and shielding tensors for strontium chloride dihydrate and calcium chloride dihydrate. Several models of the chloride environment in these compounds are tested, including those where point charges are used to represent the extended three-dimensional lattices within the self-consistent charge field perturbation approach. The results highlight both the shortcomings and successes of traditional localized orbital-based basis sets in the description of the NMR properties of extended systems. We anticipate that EFGShield will be a useful tool for spectroscopists using quantum chemical software to aid in the interpretation of experimental data.

Key words: quantum chemical calculations, computer program, electric field gradient tensor, quadrupolar coupling constant, nuclear magnetic shielding tensor, Euler angles, alkaline earth chloride hydrates.

Thursday, August 09, 2007

J Phys Chem C, Macromolecules and Organometallics

J Phys. Chem. C

-J. Phys. Chem. C, 111 (21), 7605 -7611, 2007. 10.1021/jp070321y S1932-7447(07)00321-4
Pores in Nanostructured TiO2 Films. Size Distribution and Pore Permeability

Dulce Vargas-Florencia, Tomas Edvinsson, Anders Hagfeldt, and Istv n Furó*
Division of Physical Chemistry, Department of Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden

Abstract: Nanoporous films of crystalline anatase with intended application in dye-sensitized photovoltaic cells were investigated by NMR cryoporometry, NMR diffusiometry, electron microscopy, and X-ray diffraction. The nanoparticles from which the films were subsequently sintered were prepared in two ways, one with an acidic and one with a basic aqueous process environment and along different temperature regimes. The average morphology was similar in all films as indicated by the roughly identical <2> values where is the mean curvature of the pore surface and S/V denotes the surface-to-volume ratio. Self-diffusion of water in the pores is strongly reduced with respect to that of bulk and is influenced both by micrometer-scale obstructions to molecular displacement and by pore-size effect in pore interconnectivity. The investigated samples exhibit different transport regimes as concerning those phenomena. In this initial study performed on a limited set of samples, we found no linear correlation between particle and pore sizes. Instead, total porosity is controlled by particle-particle jamming which, together with particle size polydispersity, may also dominate the effects that lead to the observed pore size distributions for the different samples. The rich variation of structural effects and transport properties among the few prepared films call for further studies in order to find an optimal film structure.

-J. Phys. Chem. C, 111 (21), 7720 -7726, 2007. 10.1021/jp068738b S1932-7447(06)08738-3
NMR Study of Proton Sites in Group I Salts of 12-Tungstophosphoric Acid

Steven F. Dec,* George M. Jacobsen, James L. Horan, and Andrew M. Herring

Department of Chemistry and Geochemistry and Department of Chemical Engineering, Colorado School of Mines, Golden, Colorado 8040

Abstract: The Group I salts of 12-tungstophosphoric acid were studied in their limiting hydration state with use of both1H and 31P solid-state nuclear magnetic resonance (NMR). The bulk proton structures of the Li, Na, and Rb salts consist of both lone protons and water molecule protons. The K and Cs salts contain similar proton structures that reside in surface sites. Nonspinning 1H NMR results indicate that all protons in the limiting hydration state in each of the Group I salts are highly mobile at room temperature. 1H spin-lattice relaxation times obtained as a function of temperature indicate that the dominant mechanism responsible for proton relaxation in the Li, Na, and Rb salts is restricted rotation of water molecules while the K and Cs salts have proton spin-lattice relaxation that is dominated by translation of protons through surface sites of the material. Two stable Rb salt phases are crystallized when a stoichiometric amount of RbCl is added to aqueous 12-tungstophosphoric acid at room temperature.

-J. Phys. Chem. C, 111 (26), 9066 -9071, 2007. 10.1021/jp071490l S1932-7447(07)01490-2
Speciation of Silanol Groups in Precipitated Silica Nanoparticles by 1H MAS NMR Spectroscopy

Geoffrey Hartmeyer, Claire Marichal,* Bénédicte Lebeau, Séverinne Rigolet, Philippe Caullet, and Julien Hernandez

Laboratoire de Matériaux à Porosité Contrôlée, ENSCMu, Université de Haute Alsace, UMR 7016, 3 rue Alfred Werner, 68093 Mulhouse Cedex, France, and Centre de Recherches d'Aubervilliers, RHODIA, 52 rue de la Haie Coq, 93308 Aubervilliers, France

Abstract: Speciation of the various proton species present in precipitated silica samples by 1H high-spinning frequency magic-angle spinning (MAS) NMR (25 kHz) is achieved. External standards are used for the calibration of the absolute amount of protons, the relevance of the proton spin counting being checked by comparison with the data deduced from classical thermogravimetric (TG) and 29Si MAS NMR experiments. The method also allows to follow postsynthesis modifications of silica, corresponding for instance to fluorination or deuteration treatments. In particular, a 1H resonance occurring at 1.1 ppm/TMS and corresponding to a constant proton amount whatever the applied treatment is tentatively assigned for the first time to inaccessible isolated silanol groups.

-J. Phys. Chem. C, 111 (28), 10624 -10629, 2007. 10.1021/jp0728757 S1932-7447(07)02875-0
Methane Carbonylation with CO on Sulfated Zirconia: Evidence from Solid-State NMR for the Selective Formation of Acetic Acid

Mikhail V. Luzgin, Vladimir A. Rogov, Nina S. Kotsarenko, Vera P. Shmachkova, and Alexander G. Stepanov*

Boreskov Institute of Catalysis, Prospekt Akademika Lavrentieva 5, Novosibirsk 630090, Russia

Abstract: Using 13C and 1H solid-state NMR it has been shown, that methane can be carbonylated with carbon monoxide to give acetic acid on solid acid catalyst, sulfated zirconia. The carbonylation occurs at 473-573 K with high selectivity and essential conversion. The reaction proceeds both in the absence and in the presence of molecular oxygen. In the presence of oxygen, the catalyst can be used for the carbonylation of further portion of methane without reactivation in air. The mechanism of the reaction is discussed. The reaction observed opens up new possibilities of using sulfated zirconia-based solid catalysts for the synthesis of acetic acid from methane and carbon monoxide.


-Macromolecules, 40 (14), 4736 -4739, 2007. 10.1021/ma0700025 S0024-9297(07)00002-2

Probing Chain Interpenetration in Polymer Glasses by 1H Dipolar Filter Solid-State NMR under Fast Magic Angle Spinning

Xiaoliang Wang, Fangfang Tao, Pingchuan Sun,* Dongshan Zhou, Zhaoqun Wang, Qiang Gu, Jinlei Hu, and Gi Xue*

Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, State Key Laboratory of Co-ordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, and Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry, Nankai University, Tianjin 300071, P. R. China

Introduction. The concept of chain entanglement provides the basis of our current understanding of the flow behavior of polymer melts and solutions.1,2 The interpenetration process is a very important step for polymer chain condensation from the dilute solution to the aggregation state. Such a condensed multiple chain systems possess a structure where polymer chains form an entangled network, which thus establishes the mechanical property of polymers.1-3 Information about interpenetration regions would provide significant insight into intermolecular coupling and the dynamics of local segmental relaxation, which issues remain unclear for glassy polymer physics. However, compared to those in solution and in the rubber state, an intriguing question concerning the characterization of the degree of interpenetration below and around the glass transition temperature (Tg) of a polymer has still not been tackled.4-7 Atomic force microscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, and scattering methods (visible light, X-ray, neutron) are frequently used to investigate chain interpenetration.8-10 One drawback of these methods is that they yield information on length scales of a few to tens of nanometers; thus, they cannot be used to directly identify the individual structure in the interpenetration regions at a molecular level. Nonradiative energy transfer (NET) fluorescence spectroscopy has been used to observe the memory of the chain interpenetration that had existed in the original solution, and many interesting conclusions have been reported.11,12 On the other hand, 13C solid-state NMR and small-angle neutron scattering (SANS) studies have cast doubt on the conclusions regarding the memory of the chain interpenetration for the freeze-dried polymer reported by NET.13-16 Developing new strategies to characterize the chain interpenetration in polymer glasses on a short length scale of 0.5 nm is still a challenge.

-Macromolecules, 40 (14), 4953 -4962, 2007. 10.1021/ma0620924 S0024-9297(06)02092-4

Investigation of Network Heterogeneities in Filled, Trimodal, Highly Functional PDMS Networks by 1H Multiple Quantum NMR

Erica Gjersing, Sarah Chinn, Jason R. Giuliani, Julie Herberg, Robert S. Maxwell,* Eric Eastwood, Dan Bowen, and Tom Stephens

Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, California 94551, Honeywell Federal Manufacturing and Technologies Plant, Kansas City, Missouri, Los Alamos National Laboratory, Los Alamos, New Mexico, and Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, California

Abstract: The segmental order and dynamics of polymer network chains in a filled, trimodal silicone foam network have been studied by static 1H multiple quantum (MQ) NMR methods to gain insight into the structure property relationships. The foam materials were synthesized with two different types of cross-links, with functionalities, , of 4 and near 60. The network chains were composed of distributions of high, low, and medium molecular weight chains. Cross-linking was accomplished by standard acid-catalyzed reactions. MQ NMR methods have detected domains with residual dipolar couplings (<>) of near 4 and 1 krad/s assigned to (a) the shorter polymer chains and chains near the multifunctional ( = 60) cross-linking sites and to (b) the longer polymer chains far from these sites. Three structural variables were systematically varied and the mechanical properties via compression and distributions of residual dipolar couplings measured in order to gain insight into the network structural motifs that contribute significantly to the composite properties. The partitioning and average values of the residual dipolar couplings for the two domains were observed to be dependent on formulation variables and provided increased insight into the network structure of these materials which are unavailable from swelling and spin-echo methods. The results of this study suggest that the domains with high cross-link density contribute significantly to the high strain modulus, while the low cross-link density domains do not. This is in agreement with theories and experimental studies on silicone bimodal networks over the last 20 years. In situ MQ-NMR of swollen samples suggests that the networks deform heterogeneously and nonaffinely. The heterogeneity of the deformation process was observed to depend on the amount of the high functionality cross-linking site PMHS. The NMR experiments shown here provide increased ability to characterize multimodal networks of typical engineering silicone foam materials and to gain significant insight into structure-property relationships.

-Macromolecules, 40 (14), 5001 -5013, 2007. 10.1021/ma062507l S0024-9297(06)02507-1

Solid-State Organization and Morphological Partitioning in Polyoxymethylene-Based Copolymers: A Solid-State NMR and WAXS Study

Cédric Lorthioir,* Françoise Lauprêtre, Karthikeyan Sharavanan, Ronald F. M. Lange, Philippe Desbois, Michel Moreau, and Jean-Pierre Vairon

Laboratoire de Recherche sur les Polymères (CNRS-UMR 7581), 2-8 rue Henri Dunant, 94320 Thiais, France; Laboratoire de Chimie des Polymères (CNRS-UMR 7610), Université Pierre et Marie Curie, Case 185 T44 E1, 4 Place Jussieu, 75252 Paris Cedex 05, France; and BASF Research, GKT/U B1, D-67056 Ludwigshafen, Germany

Abstract: The solid-state organization of copolymers based on methylene oxide (MO) units and tetramethylene oxide (T) units, with T unit contents ranging between 0.9 and 10.0 mol %, is investigated by the combined use of solid-state NMR, WAXS, and DSC experiments. In these semicrystalline copolymers, the T units can be viewed as linear defects inserted along linear poly(oxymethylene) chains. As expected, the insertion of T units induces a significant decrease of both crystallinity and crystallite size: a large part of T units is located in the amorphous domains. However, some T units can also be detected within the crystalline domains and/or the interfacial regions with the amorphous phase. More precisely, the amount of T units at both sides of the noncrystalline/crystalline interfaces seems to be much higher than the T units in the interior of the crystallites. At the lowest T unit content (0.9 mol %), the composition averaged over both interfacial and crystalline phases appears to be identical to the composition of the amorphous phase. When the comonomer content increases, the amount of T units in the interfacial and crystalline zones becomes higher and higher while the partitioning coefficient of the T units in these domains tends to a limiting value of 0.40.

-Macromolecules, 40 (15), 5411 -5419, 2007. 10.1021/ma0707786 S0024-9297(07)00778-4

Quantitative Determination of Phase Content in Multiphase Polymers by Combining Spin-Diffusion and CP-MAS NMR

L. Zhang, Z. Liu, Q. Chen,* and E. W. Hansen*

Physics Department and the State Key Laboratory of Precision Spectroscopy, East China Normal University, 3663 Northern Zhongshan Road, Shanghai 200062, People's Republic of China, and Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, N-0315 Oslo, Norway

Abstract: We present a new approach to determine quantitatively the phase content of multiphase polymers by applying a spin-diffusion pulse sequence (filter) prior to cross-polarization (CP) in a 13C-CPAS experiment. The technique is exemplified for two rather different polymer systems, a high-density polyethylene (HDPE) and four styrene-isoprene diblock copolymers, all of known phase contents. In principle, the technique should be applicable to any multiphase system in which spin-diffusion between different regions/phases exists and where the magnetization of phases can selectively be filtered out

-Macromolecules, 40 (15), 5420 -5423, 2007. 10.1021/ma070790y S0024-9297(07)00790-5

Investigation of Dynamics of Poly(dimethylsilane) in the Mesophase by Solid-State 29Si NMR: Evidence for Rotator Phase

Hironori Kaji* and Fumitaka Horii

Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan

Abstract: The dynamics of poly(dimethylsilane) (PDMS) in the mesophase was investigated by DSC and 29Si solid-state NMR. A solid-solid transition is observed at 166 C based on DSC measurements. Below the transition temperature, typical chemical shift anisotropy (CSA) spectra are obtained by the 29Si solid-state NMR with cross-polarization (CP) preparation for the static PDMS sample. In contrast, the intensities at the isotropic chemical shift are suppressed for the CSA spectra above the transition temperature. The intensity attenuation, termed "magic angle hole", in the CSA spectra is theoretically derived for uniaxially rotating solids. Therefore, it was found that PDMS undergoes a uniaxial rotation motion above the transition temperature. Theoretically, both the direct polarization (DP) experiments without the CP process and ultraslow magic angle spinning (MAS) experiments retrieve standard CSA line shapes. Our DP and ultraslow MAS experiments confirm the theoretical consideration. The retrieved CSA spectra have axially symmetric line shapes, which also confirm the above uniaxial dynamics. On the basis of the solid-state NMR, we clearly show that the solid-solid transition at 166 C is a rigid monoclinic-mobile rotator phase transition.

-Macromolecules, 40 (16), 5776 -5786, 2007. 10.1021/ma070485c S0024-9297(07)00485-8

Various Types of Hydrogen Bonds, Their Temperature Dependence and Water-Polymer Interaction in Hydrated Poly(Acrylic Acid) as Revealed by 1H Solid-State NMR Spectroscopy

Baohui Li, Lu Xu, Qiang Wu, Tiehong Chen, Pingchuan Sun,* Qinghua Jin, Datong Ding, Xiaoliang Wang, Gi Xue,* and An-Chang Shi

Key Laboratory of Functional Polymer Materials, Ministry of Education, College of Chemistry and College of Physics, Nankai University, Tianjin, 300071, P. R. China, Department of Polymer Science and Engineering, The School of Chemistry and Chemical Engineering, State Key Laboratory of Co-ordination Chemistry, Nanjing University, Nanjing 210093, P. R. China, and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada

Abstract: Various types of hydrogen bonds, their temperature dependence and water-polymer interaction in hydrated poly(acrylic acid) (PAA) were systematically investigated using 1H CRAMPS solid-state NMR techniques in the temperature range from 25 to 110 C. The 1H CRAMPS NMR methods are based on a recently developed continuous phase modulation technique for 1H-1H homonuclear dipolar decoupling. The 1H CRAMPS experiments revealed four types of protons in hydrated PAA which are assigned to protons from the mutually hydrogen-bonded COOH groups (1), from the free COOH groups (2), from the COOH groups bounded with water or from water bounded with COOH groups which are undergoing fast chemical exchange mutually (3), and from main chain groups (4), respectively. Furthermore, we proposed double-quantum filtered and dipolar filtered 1H CRAMPS experiments to further assign the protons according to their dipolar coupling strength. In addition, high-resolution spin echo 1H CRAMPS experiments were further employed to accurately determine the chemical shift of these protons. These NMR techniques were also used to elucidate the molecular mobility of the different groups. It was found that dehydration in PAA promotes the formation of hydrogen bonds between COOH groups. Variable-temperature 1H CRAMPS experiments demonstrated that the dissociation of the hydrogen bonds between COOH groups occurs dramatically at lower temperature in hydrated PAA and slowly over a wide range of temperature in dehydrated PAA. It was also found that the dehydration of water bounded with COOH groups in hydrated PAA occurs significantly at high temperature. The NMR results were compared with previous work using DSC and other techniques. Besides undergoing fast chemical exchange, the adsorbed water was also demonstrated in proximity with the free COOH groups and far from the hydrogen bonds between COOH groups by using two-dimensional 1H-1H spin-exchange NMR experiments.

-Macromolecules, 40 (16), 5787 -5790, 2007. 10.1021/ma070793a S0024-9297(07)00793-0

Cross-Link Density of a Dispersed Rubber Measured by 129Xe Chemical Shift
Wallace O. Parker, Jr.,* Angelo Ferrando, Dino Ferri, and Valentino Canepari

Physical Chemistry, Refining & Marketing Division, Eni S.p.A., via Maritano 26, 20097 San Donato Milanese, Italy, and Polymer Research Center "C. Buonerba", Polimeri Europa, via Taliercio 14, 46100 Mantova, Italy

Abstract: 129Xe NMR chemical shifts of adsorbed xenon (natural isotopic abundance) were used to probe the free volume in a cross-linked rubber, polybutadiene (PB), alone and occluded within high impact polystyrene (HIPS). Shift dependency on cross-link density, or Nm (average number of monomer units between chemical cross-links) determined by the classical solvent swelling method, was detailed for high-cis-1,4-PB. A decrease in Nm from 262 to 4 caused the shift to increase 4 ppm. A curve inflection, evident at 218 ppm (and Nm = 30), corresponded to a free volume with an average spherical diameter of 0.49 nm using the empirical (shift-pore size) relation known for zeolites. This diameter is essentially equal to that of the PB chain (0.48 nm) at its Tg (glass transition temperature). Tg plotted against Nm showed the same inflection (at Nm = 25), corroborating a regime with more severe interchain contacts when the free volume diameter is inferior to the chain diameter. The empirical relation between 129Xe shift and Nm observed for pure PB was used to estimate the cross-link density of PB dispersed in HIPS as a function of cure time. Cross-linkage was greatly slowed after 8 h of curing, when Nm estimated by NMR spectroscopy was 10.

Andre's Journal Update: Inorganic Chem. - up to Issue 16 (Aug 06, 2007)

Inorg. Chem., 46 (15), 6069-6077, 2007.
"Solid-State NMR Spectroscopic Study of Coordination Compounds of XeF2 with Metal Cations and the Crystal Structure of [Ba(XeF2)5][AsF6]2"
Michael Gerken, Paul Hazendonk, Adriana Iuga, Jared Nieboer, Melita Tramek, Evgeny Goreshnik, Boris emva, Shaohui Zheng, and Jochen Autschbach

The coordination compounds [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were characterized by solid-state 19F and 129Xe magic-angle spinning NMR spectroscopy. The 19F and 129Xe NMR data of [Mg(XeF2)2][AsF6]2, [Mg(XeF2)4][AsF6]2, and [Ca(XeF2)2.5][AsF6]2 were correlated with the previously determined crystal structures. The isotropic 19F chemical shifts and 1J(129Xe-19F) coupling constants were used to distinguish the terminal and bridging coordination modes of XeF2. Chemical-shift and coupling-constant calculations for [Mg(XeF2)4][AsF6]2 confirmed the assignment of terminal and bridging chemical-shift and coupling-constant ranges. The NMR spectroscopic data of [Ba(XeF2)3][AsF6]2 and [Ba(XeF2)5][AsF6]2 indicate the absence of any terminal XeF2 ligands, which was verified for [Ba(XeF2)5][AsF6]2 by its X-ray crystal structure. The adduct [Ba(XeF2)5][AsF6]2 crystallizes in the space group Fmmm, with a = 11.6604(14) Å, b = 13.658(2) Å, c = 13.7802(17) Å, V = 2194.5(5) Å3 at -73 C, Z = 4, and R = 0.0350 and contains two crystallographically independent bridging XeF2 molecules and one nonligating XeF2 molecule. The AsF6- anions in [Mg(XeF2)4][AsF6]2, [Ca(XeF2)2.5][AsF6]2, [Ba(XeF2)3][AsF6]2, and [Ba(XeF2)5][AsF6]2 were shown to be fluxional with the fluorines-on-arsenic being equivalent on the NMR time scale, emulating perfectly octahedral anion symmetry.

Progress in NMR Spectroscopy, up to Vol. 51 Iss. 2 October 2007

Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 51, Issue: 2, October 18, 2007
pp. 103-137

Title: Chemical shift anisotropy amplification
Authors: Shao, L.; Titman, J.J.
Keywords: Magic angle spinning; Sideband manipulation; Chemical shift anisotropy; CSA amplification; CSA tensor; Orientational order; Molecular dynamics
Abstract: No Abstract
Publisher: Elsevier Science
Language of Publication: English
# Item Identifier: S0079-6565(07)00009-X
Publication Type: Miscellaneous
ISSN: 0079-6565

Progress in Nuclear Magnetic Resonance Spectroscopy
Vol: 51, Issue: 2, October 18, 2007
pp. 139-154

Title: Heterogeneous catalysis in solid acids
Authors: White, J.L.; Truitt, M.J.
Keywords: NMR; Solid state NMR; MAS NMR; Zeolites; Silicoaluminophosphates; Catalysis; Bronsted acid; Solid acids; Mesoporous; In situ NMR; Methanol; MTO; MTG; Hydrocarbon; Mechanism
Abstract: No Abstract
Publisher: Elsevier Science
Language of Publication: English
# Item Identifier: S0079-6565(07)00023-4
Publication Type: Miscellaneous
ISSN: 0079-6565

Solid-State NMR, Vol. 32, August 2007

Solid-State NMR, Vol. 32, August 2007

Using liquid and solid state NMR and photoluminescence to study the synthesis and solubility properties of amine capped silicon nanoparticles

J.R. Giuliani1, a, S.J. Harleya, R.S. Cartera, P.P. Powera and M.P. Augustine
Department of Chemistry, One Shields Avenue, University of California, Davis, CA 95616, USA
Received 12 December 2006. Available online 29 May 2007.


Water soluble silicon nanoparticles were prepared by the reaction of bromine terminated silicon nanoparticles with 3-(dimethylamino)propyl lithium and characterized with liquid and solid state nuclear magnetic resonance (NMR) and photoluminescence (PL) spectroscopies. The surface site dependent 29Si chemical shifts and the nuclear spin relaxation rates from an assortment of 1H–29Si heteronuclear solid state NMR experiments for the amine coated reaction product are consistent with both the 1H and 13C liquid state NMR results and routine transmission electron microscopy, ultra-violet/visible, and Fourier transform infrared measurements. PL was used to demonstrate the pH dependent solubility properties of the amine passivated silicon nanoparticles.

Keywords: Nanoparticles; 29Si nuclear magnetic resonance; Nuclear spin relaxation; Photoluminescence

A computational investigation of 17O quadrupolar coupling parameters and structure in α-quartz phase GeO2

Travis H. Sefzika, Ted M. Clarka and Philip J. Grandinetti
aDepartment of Chemistry, The Ohio State University, 120 W. 18th Avenue, Columbus, OH 43210-1173, USA
Received 12 March 2007; revised 4 June 2007. Available online 10 July 2007.


Ab initio band-structure calculations based on density functional theory have been completed for α-quartz phase GeO2 to obtain electric-field gradients (efg) for oxygen atoms, including those for GeO2 at elevated pressure and temperature. To interpret the resulting efg values and examine correlations between structure and 17O quadrupolar coupling parameters, additional ab initio self-consistent Hartree-Fock molecular orbital calculations were completed. The quadrupolar coupling constant was found to have a strong dependence on Ge–O distance and angleGe–O–Ge, with the quadrupolar asymmetry parameter being primarily dependent on angleGe–O–Ge. Analytical expressions describing these dependencies consistent with earlier investigations of analogous silicate compounds are also reported.

Study of molecular reorientation and quantum rotational tunneling in tetramethylammonium selenate by 1H NMR

K.J. Mallikarjunaiah a, K.C. Paramita b, K.P. Ramesh b and R. Damle a
aDepartment of Physics, Bangalore University, Bangalore 560 056, India
bDepartment of Physics, Indian Institute of Science, Bangalore 560 012, India
Received 27 April 2007. Available online 10 July 2007.


1H NMR spin–lattice relaxation time measurements have been carried out in [(CH3)4N]2SeO4 in the temperature range 389–6.6 K to understand the possible phase transitions, internal motions and quantum rotational tunneling. A broad T1 minimum observed around 280 K is attributed to the simultaneous motions of CH3 and (CH3)4N groups. Magnetization recovery is found to be stretched exponential below 72 K with varying stretched exponent. Low-temperature T1 behavior is interpreted in terms of methyl groups undergoing quantum rotational tunneling.

Keywords: 1H NMR; Internal motions; Magnetization recovery; Spin–lattice relaxation time; Quantum rotational tunneling

Wednesday, August 08, 2007

J Phys. Chem. B Updates

-ADF calculations of 31P chemical shift tensors

Inorg. Chem., ASAP Article 10.1021/ic700514u S0020-1669(70)00514-1 Web Release Date: August 3, 2007
Ethylenebis(triphenylphosphine)platinum as a Probe for Niobium-Mediated Diphosphorus Chemistry
Nicholas A. Piro and Christopher C. Cummins*

Abstract: Ethylenebis(triphenylphosphine)platinum is used as a trap for the P2-containing molecule W(CO)5(P2), which is eliminated at room temperature from a niobium-complexed diphosphaazide ligand. The rate of W(CO)5(P2) elimination is unaffected by the presence of the platinum species. Attempts to generate and trap free P2 with the platinum ethylene complex were hindered by the direct reaction between the platinum starting material and the P2 generator, (Mes*NPP)Nb(N[Np]Ar)3. In this case, reductive cleavage of the P-P bond in the diphosphaazide ligand is induced by platinum coordination, resulting in the formation of a trimetallic system with two bridging, three-coordinate phosphorus atoms.
J Phys. Chem. B

-23Na NMR

J. Phys. Chem. B, 111 (25), 7092 -7097, 2007. 10.1021/jp070533v S1520-6106(07)00533-0 Nonergodic Arrested State in Diluted Clay Suspensions Monitored by Triple-Quantum 23Na Nuclear Magnetic Resonance

T. Gili,* S. Capuani, and B. Maraviglia

CNR-INFM CRS-SOFT, Universit di Roma "La Sapienza",P.zle A. Moro 5, I-00185 Roma, Italy, Dipartimento di Fisica, Universit di Roma "La Sapienza", P.zle A. Moro 5, I-00185 Roma, Italy, Enrico Fermi Center, Compendio Viminale, I-00184 Roma, Italy, and Fondaziona Santa Lucia IRCCS, I-00179 Roma, Italy

Abstract: The aging of water suspension of the synthetic clay Laponite has been studied by liquid-state triple-quantum filter nuclear magnetic resonance techniques, in a range of clay weight concentration (Cw = 0.012-0.028) known as the isotropic phase. Counterions dynamic parameters (rotational correlation time c and quadrupolar coupling constant e2qQ/h) have been extracted from sodium triple-quantum filtered experimental data within the multi-exponential quadrupolar relaxation theory in the fast exchange approximation. By monitoring quadrupolar sodium ions dynamical ( c and e2qQ/h) and static (counterion concentration pb) properties during the aging, we find two different mechanisms of transition toward an arrested state. Our experimental findings match with the description which states, at low concentration, the formation of clusters of Laponite disks trigger the reaching of the arrested state, while at high concentration, single disks are the basic units of the arrested phase. The procedure proposed in this paper, based on multiple quantum filtered NMR data analysis, results to be a useful means to study the routes to arrested states in aqueous colloidal dispersions.

-31P and 27Al spectroscopy

J. Phys. Chem. B, 111 (25), 7105 -7113, 2007. 10.1021/jp0710133 S1520-6106(07)01013-9

Crystallization of AlPO4-5 Aluminophosphate Molecular Sieve Prepared in Fluoride Medium: A Multinuclear Solid-State NMR Study

Jun Xu, Lei Chen, Danlin Zeng, Jun Yang, Minjin Zhang, Chaohui Ye, and Feng Deng*
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, the Chinese Academy of Sciences, Wuhan 430071, People's Republic of China

Abstract: In the present work, multinuclear solid-state NMR techniques, combined with powder X-ray diffraction (PXRD) and infrared (IR) spectroscopy, are employed to monitor the crystallization of AlPO4-5 aluminophosphate prepared in the presence of HF under hydrothermal condition. The crystallization process is characterized by the evolution of intermediate gels, in which the long-rang ordering arrangement is probed by PXRD, revealing the threshold of the crystallization around 120 min. The appearance of 31P signals at ca. -22 and -29 ppm due to the structural P-O-Al unit and 19F signal at -120 ppm due to the structural F-Alpen-O-P unit in the NMR spectra of the series gels indicates that the crystalline framework is starting to form. The onset of the crystallization is also evidenced by the presence of the pentacoordinated Al in the structural F-Alpen-O-P unit which is considered to be associated with the ordered framework. More information about the local ordering of the gels is obtained from two-dimensional 27Al 31P heteronuclear correlation (HETCOR) and 31P/27Al double-resonance experiments. In combination with 1H 31P cross-polarization/magic-angle spinning (CP/MAS) experiments, two microdomains can be identified in the 120 min heated gel. A possible evolution mechanism of the gels consisting of three successive stages is proposed for the crystallization process

-J. Phys. Chem. B, 111 (26), 7529 -7534, 2007. 10.1021/jp070692e S1520-6106(07)00692-X

Structural Changes above the Glass Transition and Crystallization in Aluminophosphate Glasses: An in Situ High-Temperature MAS NMR Study

Leo van Wüllen,* Sebastian Wegner, and Gregory Tricot
Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstrasse 30-36, D-48149 Münster, Germany

Abstract: We present an in situ high-temperature nuclear magnetic resonance study on the structural changes in aluminophosphate glasses occurring in the temperature range between the glass transition temperature Tg and the crystallization temperature Tc, Tg < T < Tc. Decisive changes in the network organization between Tg and Tc in potassium aluminophosphate glasses in the compositional range 50K2O-xAl2O3-(50 - x)P2O5 with 2.5 < x < 20 could be monitored for the first time employing 1D 31P- and 27Al-MAS NMR. Accompanying ex situ NMR experiments (31P-RFDR NMR and 31P-{27Al} CP-HETCOR NMR) on devitrified samples were performed at room temperature to further characterize the phases formed during the crystallization process. The structural role of boron-which is known to inhibit the crystallization process in these aluminophosphate glasses-on short and intermediate length scales was analyzed employing 11B-MQMAS, 11B-{27Al} TRAPDOR and 11B-{31P} REDOR NMR spectroscopy

-J. Phys. Chem. B, 111 (27), 7802 -7811, 2007. 10.1021/jp072504q S1520-6106(07)02504-7

Boltzmann Statistics Rotational-Echo Double-Resonance Analysis

John D. Gehman, Frances Separovic, Kun Lu, and Anil K. Mehta*
School of Chemistry, Bio21 Institute, University of Melbourne, Melbourne, Victoria 3010, Australia, and Department of Chemistry, Emory University, Atlanta, Georgia 30322

Abstract: A new approach to rotational-echo double-resonance (REDOR) data analysis, analogous to Boltzmann maximum entropy statistics, is reported. This Boltzmann statistics REDOR (BS-REDOR) approach is useful for reconstructing an unbiased internuclear distance distribution for multiple internuclear distances from experimentally limited REDOR data sets on isolated spin pairs. The analysis is characterized by exploring reconstructions on model data and applied to both [1-13C,15N]-glycine and a long intramolecular distance in A (16-22) peptide nanotubes. The approach also provides insight into the minimal number of REDOR data points required to allow faithful determination of dipolar couplings in systems with multiple internuclear distances.

-3Q-QCPMG MAS experiments.
J. Phys. Chem. B, 111 (28), 8014 -8019, 2007. 10.1021/jp071539n S1520-6106(07)01539-8

Order and Disorder in Titanosilicate Glass by 17O MAS, off-MAS, and 3Q-QCPMG-MAS Solid-State NMR

Flemming H. Larsen,* Stéphanie Rossano, and Ian Farnan
Department of Food Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark, Université Paris-Est Laboratoire Géomatériaux et Géologie de l'Ingénieur (G2I), EA 4119, 5 bd Descartes, 77454 Marne la Vallée Cedex 2, France, and Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom

Abstract: An 17O-enriched version of the titanosilicate glass, KTS2 (K2O·TiO2·2SiO2), was analyzed by 17O MAS, off-MAS, and 3Q-QCPMG-MAS experiments. Exploiting the variations in EFG and CSA parameters for the 17O sites in KTS2 glass, we detected four types of oxygen by reduction of spinning sideband intensities in the off-MAS experiments. From the 17O off-MAS and 3Q-QCPMG-MAS experiments, the Si-O-Ti and K-O-Ti resonances were characterized by a distribution of isotropic chemical shifts, whereas the Si-O-Si resonance was characterized by very small distributions of both EFG tensor and isotropic chemical shift, which means that the disorder in the glass is closely related to Ti. In addition to the order/disorder issue, the most striking feature about the 17O off-MAS experiments on KTS2 is the lack of signals from Ti-O-Ti, which contradicts linking between corner sharing TiO5 units. Therefore, the structure must consist of linkages between TiO5 units and SiO4 tetrahedra and linkages between SiO4 tetrahedra.

-J. Phys. Chem. B, 111 (30), 8691 -8694, 2007. 10.1021/jp0734979 S1520-6106(07)03497-9

Microscopic Access to Long-Range Diffusion Parameters of the Fast Lithium Ion Conductor Li7BiO6 by Solid State 7Li Stimulated Echo NMR

Martin Wilkening,* Claus Mühle, Martin Jansen, and Paul Heitjans
Institute of Physical Chemistry and Electrochemistry, and Center for Solid State Chemistry and New Materials, Leibniz University Hannover, Callinstr. 3a, 30167 Hannover, Germany, and Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany

Abstract: Li self-diffusion in rhombohedral Li7BiO6, being a promising basic material for cathodes of rechargeable ion batteries, is studied by means of 7Li stimulated echo NMR. Using the pulse sequence introduced by Jeener and Broekaert, a spin-alignment echo is created whose amplitude decay is recorded as a function of mixing time. The so-obtained two-time correlation functions follow stretched exponential behavior and lead to decay rates which can be identified directly with microscopic Li motional correlation rates ( -1). Using a jump distance of about 0.2 nm, this results in a diffusion coefficient (D) of about 0.5 × 10-16 m2 s-1 at 294 K. The activation energy turned out to be 0.53(3) eV which is in very good agreement with recently obtained results by means of dc-conductivity measurements probing long-range diffusion parameters. This shows that stimulated echo NMR, due to its inherent time scale, gives microscopic access to long-range transport. The prefactor 0-1 of the corresponding Arrhenius law lies in the typical range of phonon frequencies, 0-1 = 3 × 1012 s-1.

-J. Phys. Chem. B, 111 (30), 8860 -8867, 2007. 10.1021/jp070782j S1520-6106(07)00782-1

1H NMR and Viscometric Studies on Cationic Gemini Surfactants in Presence of Aromatic Acids and Salts

Kabir-ud-Din,* Waseefa Fatma, Ziya Ahmad Khan, and Aijaz Ahmad Dar
Department of Chemistry, Aligarh Muslim University, Aligarh - 202 002, India, and Department of Chemistry, University of Kashmir, Srinagar - 190 006, Jammu and Kashmir, India

Abstract: In this paper, we are reporting the influence of addition of aromatic acids (anthranilic and benzoic acid) and their sodium salts on the micellar morphological changes in three cationic gemini surfactant solutions, viz. 5 mM tetramethylene-1,4-bis(N-hexadecyl-N,N-dimethylammonium bromide), 10 mM pentamethylene-1,5-bis(N-hexadecyl-N,N-dimethylammonium bromide), and 10 mM hexamethylene-1,6-bis(N,-hexadecyl-N,N-dimethylammonium bromide). The solubilization site of the counterions (obtained from the additives) near the micellar surface are inferred by 1H NMR. The behavior is explained in the light of binding of counterions to the micelle as well as the nature of the functional group attached to the additive.

-J. Phys. Chem. B, 111 (30), 9172 -9178, 2007. 10.1021/jp072755z S1520-6106(07)02755-1

High-Field 1H MAS and 15N CP-MAS NMR Studies of Alanine Tripeptides and Oligomers: Distinction of Antiparallel and Parallel -Sheet Structures and Two Crystallographically Independent Molecules

Yu Suzuki, Michi Okonogi, Kazuo Yamauchi, Hiromichi Kurosu, Masataka Tansho, Tadashi Shimizu, Hazime Saitô, and Tetsuo Asakura*
Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16, Nakacho, Koganei, Tokyo 184-8588, Japan, Graduate School of Humanities and Sciences, Nara Women's University, Kitauoya-Nishimachi, Nara 630-8506, Japan, and National Institute for Material Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan

Abstract: -Strand peptides are known to assemble into either antiparallel (AP) or parallel (P) -sheet forms which are very important motifs for protein folding and fibril formations occurring in silk fibroin or amyloid proteins. Well-resolved 1H NMR signals including NH protons were observed for alanine tripeptides (Ala)3 with the AP and P structures as well as (Ala)n (n = 4-6) by high-field/fast magic-angle spinning NMR. Amide NH and amino NH3+ 1H signals of (Ala)3 with the P structure were well resonated at 7.5 and 8.9 ppm, respectively, whereas they were not resolved for the AP structure. Notably, NH 1H signals of (Ala)3 and (Ala)4 taking the P structure are resonated at higher field than those of the AP structure by 1.0 and 1.1 ppm, respectively. Further, NH 15N signals of (Ala)3 with the AP structure were resonated at lower field by 2 to 5 ppm than those of (Ala)3 with the P structure. These relative 1H and 15N hydrogen bond shifts of the P structure with respect to those of the AP structure are consistent with the relative hydrogen bond lengths of the interstrand N-H···O=C bonds. Distinction between the two crystallographically independent chains present in the AP and P structures was feasible by 15N chemical shifts but not by 1H chemical shifts because of insufficient spectral resolution in the latter. Calculated 1H and 15N shielding constants by density functional theory are generally consistent with the experimental data, although some discrepancies remain depending upon the models used.

Friday, August 03, 2007

Hiyam's Journal Update

J. Am. Chem. Soc., 129 (21), 6670 -6671, 2007.

Solid-State NMR Reveals Structural and Dynamical Properties of a Membrane-Anchored Electron-Carrier Protein, Cytochrome b5
Ulrich H. N. Dürr, Kazutoshi Yamamoto, Sang-Choul Im, Lucy Waskell, and Ayyalusamy Ramamoorthy
Cytochrome b5 (cyt b5) is a membrane-anchored electron-carrier protein containing a heme in its soluble domain. It enhances the enzymatic turnover of selected members of the cytochrome P450 superfamily of catabolic enzymes, localized in the endoplasmic reticulum of liver cells. Remarkably, its -helical membrane-anchoring domain is indispensable for the cyt b5/cyt P450 interaction. Here, we present the first solid-state NMR studies on holo-cyt b5 in a membrane environment, namely, macroscopically oriented DMPC:DHPC bicelles. We have presented approaches to selectively investigate different domains of the protein using spectral editing NMR techniques that utilize the unique motional properties of each domain. Two-dimensional 1H-15N HIMSELF spectra showed PISA-wheel patterns reporting on the structure and dynamics of the membrane anchor of the protein.

J. Am. Chem. Soc., 129 (21), 6682 -6683, 2007.

J-Deconvolution Using Maximum Entropy Reconstruction Applied to 13C-13C Solid-State Cross-Polarization Magic-Angle-Spinning NMR of Proteins
Ingo Scholz, Stefan Jehle, Peter Schmieder, Matthias Hiller, Frank Eisenmenger, Hartmut Oschkinat, and Barth-Jan van Rossum

Scalar couplings between 13C spins can impair both resolution and sensitivity in 13C-labeled preparations. It is demonstrated that deconvolution of magic-angle-spinning NMR data with maximum entropy (MaxEnt) reconstruction allows the removal of splittings due to J-couplings without expenses in sensitivity. A combination of MaxEnt reconstruction in t2 with selective pulses in t1 produces fully J-resolved data in both dimensions. The possibility to obtain J-resolved 13C-13C data without compromising the sensitivity is particularly important for solid-state NMR of "difficult" biological samples, like membrane proteins, where sacrifices in signal-to-noise are fatal. The method is demonstrated using preparations of -spectrin SH3 domain (62 residues) as small test system and of outermembrane protein G as example of a membrane protein with higher molecular weight (281 residues). Both preparations were obtained using [2-13C]-glycerol as the carbon source during the bacterial growth.