A nice article in Chemical and Engineering News on solid-state NMR of radioactive materials.
http://pubs.acs.org/isubscribe/journals/cen/88/i21/html/8821sci1.html
Tuesday, May 25, 2010
Thursday, May 20, 2010
J. Phys. Chem. C., vol. 114, Issue 20
1H, 29Si, and 27Al MAS NMR as a Tool to Characterize Volcanic Tuffs and Assess Their Suitability for Industrial Applications
Piero Ciccioli†, Paolo Plescia‡ and Donatella Capitani*§
J. Phys. Chem. C, 2010, 114 (20), pp 9328–9343
DOI: 10.1021/jp103082h
Publication Date (Web): April 29, 2010
Abstract: The type and quality of the information provided by the direct analysis of volcanic tuffs by 1H, 29Si, and 27Al NMR were investigated. At this aim, five tuffs, characterized by different origin, bonding mechanism, and clast composition, were used as test materials. Results consistent with the different nature of the tuff matrix and mineral composition were obtained. While the relative content of Al in the crystal and amorphous phase was determined by 27Al MAS and 3Q MAS NMR, the prevalent glassy or zeolitic nature of the matrix was assessed by 29Si and 1H MAS NMR. Zeolites present at levels as low as 15% w/w were detected by 29Si MAS NMR, and in some tuffs, identification of their framework type was performed together with the determination of the Si/Al ratio and, for the first time, of their configurational entropy. Data obtained were coherent with those provided by X-ray fluorescence (XRF), X-ray powder diffraction (XPRD), thermogravimetric analysis (TGA), differential thermal gravimetry (DTG), cation exchange capacity (CEC) determinations, and scanning electron microscopy, used in both backscattering imaging mode (SEM) and for elemental analysis (SEM-EDS). Results show that, under favorable conditions, solid state NMR techniques can provide a comprehensive view of the chemical and physicochemical behavior of a tuff. A combined use of these techniques is suitable for characterization of tuffs on a routine basis, and can be particularly useful to decide if a material is suitable for industrial applications.
The Comparison in Dehydrogenation Properties and Mechanism between MgCl2(NH3)/LiBH4 and MgCl2(NH3)/NaBH4 Systems
L. Gao†, Y. H. Guo†, Q. Li‡ and X. B. Yu*†
J. Phys. Chem. C, 2010, 114 (20), pp 9534–9540
DOI: 10.1021/jp103012t
Publication Date (Web): May 5, 2010
Abstract: The dehydrogenation properties and mechanism of MgCl2(NH3)/MBH4 (here, M is Li or Na) were investigated by thermogravimetric analysis and mass spectrometry, X-ray diffraction (XRD), solid-state 11B NMR, Fourier transform infrared, and differential scanning calorimetry (DSC). As for the MgCl2(NH3)/LiBH4 system, it was found that a new phase, namely, MgCl2(NH3)·LiBH4, to which the following dehydrogenation relates, is formed after ball milling. Judging from the reaction products, it is confirmed that MgCl2 is inclined to work as an ammonia carrier, and the ligand NH3, transferring from MgCl2, is able to combine with the LiBH4 to release H2 with a trace of ammonia at ca. 240 °C. With the increase of LiBH4 content in the mixture, the emission of ammonia was totally suppressed, and Mg(BH4)2 was produced by the decomposition reaction of MgCl2 with the excessive LiBH4 after the ligand NH3 was exhausted, resulting in an improved dehydrogenation in the whole system. As for the MgCl2(NH3)/NaBH4 system, no new phases are detected by XRD after ball milling. The MgCl2 works as a BH4− acceptor, and the ligand NH3 stays with Mg2+ to combine with the BH4−, which transfers from NaBH4 to Mg2+, resulting in a totally different decomposition route and thermal effects as compared with the MgCl2(NH3)/LiBH4 system. DSC results revealed that the decomposition of MgCl2(NH3)/LiBH4 presented an exothermic reaction with an enthalpy of −3.8 kJ mol−1 H2, while the MgCl2(NH3)/NaBH4 showed two apparent endothermic peaks associated with its two-step dehydrogenation with enthalpies of 8.6 and 2.2 kJ mol−1 H2, respectively. Moreover, the MS profiles of the MgCl2(NH3)/2NaBH4, with excessive BH4−, still released a trace of NH3, indicating that the NaBH4 is not so effective in suppressing the emission of NH3 as LiBH4 did.
Piero Ciccioli†, Paolo Plescia‡ and Donatella Capitani*§
J. Phys. Chem. C, 2010, 114 (20), pp 9328–9343
DOI: 10.1021/jp103082h
Publication Date (Web): April 29, 2010
Abstract: The type and quality of the information provided by the direct analysis of volcanic tuffs by 1H, 29Si, and 27Al NMR were investigated. At this aim, five tuffs, characterized by different origin, bonding mechanism, and clast composition, were used as test materials. Results consistent with the different nature of the tuff matrix and mineral composition were obtained. While the relative content of Al in the crystal and amorphous phase was determined by 27Al MAS and 3Q MAS NMR, the prevalent glassy or zeolitic nature of the matrix was assessed by 29Si and 1H MAS NMR. Zeolites present at levels as low as 15% w/w were detected by 29Si MAS NMR, and in some tuffs, identification of their framework type was performed together with the determination of the Si/Al ratio and, for the first time, of their configurational entropy. Data obtained were coherent with those provided by X-ray fluorescence (XRF), X-ray powder diffraction (XPRD), thermogravimetric analysis (TGA), differential thermal gravimetry (DTG), cation exchange capacity (CEC) determinations, and scanning electron microscopy, used in both backscattering imaging mode (SEM) and for elemental analysis (SEM-EDS). Results show that, under favorable conditions, solid state NMR techniques can provide a comprehensive view of the chemical and physicochemical behavior of a tuff. A combined use of these techniques is suitable for characterization of tuffs on a routine basis, and can be particularly useful to decide if a material is suitable for industrial applications.
The Comparison in Dehydrogenation Properties and Mechanism between MgCl2(NH3)/LiBH4 and MgCl2(NH3)/NaBH4 Systems
L. Gao†, Y. H. Guo†, Q. Li‡ and X. B. Yu*†
J. Phys. Chem. C, 2010, 114 (20), pp 9534–9540
DOI: 10.1021/jp103012t
Publication Date (Web): May 5, 2010
Abstract: The dehydrogenation properties and mechanism of MgCl2(NH3)/MBH4 (here, M is Li or Na) were investigated by thermogravimetric analysis and mass spectrometry, X-ray diffraction (XRD), solid-state 11B NMR, Fourier transform infrared, and differential scanning calorimetry (DSC). As for the MgCl2(NH3)/LiBH4 system, it was found that a new phase, namely, MgCl2(NH3)·LiBH4, to which the following dehydrogenation relates, is formed after ball milling. Judging from the reaction products, it is confirmed that MgCl2 is inclined to work as an ammonia carrier, and the ligand NH3, transferring from MgCl2, is able to combine with the LiBH4 to release H2 with a trace of ammonia at ca. 240 °C. With the increase of LiBH4 content in the mixture, the emission of ammonia was totally suppressed, and Mg(BH4)2 was produced by the decomposition reaction of MgCl2 with the excessive LiBH4 after the ligand NH3 was exhausted, resulting in an improved dehydrogenation in the whole system. As for the MgCl2(NH3)/NaBH4 system, no new phases are detected by XRD after ball milling. The MgCl2 works as a BH4− acceptor, and the ligand NH3 stays with Mg2+ to combine with the BH4−, which transfers from NaBH4 to Mg2+, resulting in a totally different decomposition route and thermal effects as compared with the MgCl2(NH3)/LiBH4 system. DSC results revealed that the decomposition of MgCl2(NH3)/LiBH4 presented an exothermic reaction with an enthalpy of −3.8 kJ mol−1 H2, while the MgCl2(NH3)/NaBH4 showed two apparent endothermic peaks associated with its two-step dehydrogenation with enthalpies of 8.6 and 2.2 kJ mol−1 H2, respectively. Moreover, the MS profiles of the MgCl2(NH3)/2NaBH4, with excessive BH4−, still released a trace of NH3, indicating that the NaBH4 is not so effective in suppressing the emission of NH3 as LiBH4 did.
Wednesday, May 19, 2010
Inorganic Chem
Novel Cis- and Trans-Configured Bis(oxime)platinum(II) Complexes: Synthesis, Characterization, and Cytotoxic Activity
Yulia Yu. Scaffidi-Domianello, Kristof Meelich, Michael A. Jakupec, Vladimir B. Arion, Vadim Yu. Kukushkin, Markus Galanski and Bernhard K. Keppler
Inorg. Chem., Article ASAP
DOI: 10.1021/ic100584b
Publication Date (Web): May 11, 2010
Abstract
Novel cis- and trans-configured bis(oxime)platinum(II) complexes have been synthesized and characterized by elemental analyses, IR, electrospray ionization mass spectrometry, multinuclear (1H, 13C, and 195Pt) NMR spectroscopy, and, in five cases, by X-ray diffraction. Their cytotoxicity was studied in the cisplatin-sensitive CH1 cell line as well as in inherently cisplatin-resistant SW480 cancer cells. Remarkably, every single dihalidobis(oxime)platinum(II) complex (with either a cis or trans configuration) shows a comparable cytotoxic potency in both cell lines, indicating a capacity of overcoming cisplatin resistance. Particularly strong cytotoxicities were observed in the case of trans-[PtCl2(R2C═NOH)2] (R = Me, n-Pr, i-Pr) with IC50 values in the high nanomolar concentration range in both CH1 and SW480 cancer cells. These complexes are as potent as cisplatin in CH1 cells and up to 20 times more potent than cisplatin in SW480 cells. In comparison to transplatin, the novel compounds are up to 90 (CH1) and 120 times (SW480) more cytotoxic. The previously reported observation that the trans geometry yields a more active complex in the case of [PtCl2(Me2C═NOH)2] could be confirmed for at least two structural analogues.
_______________________________________________________________________
Cesium Hydroperoxostannate: First Complete Structural Characterization of a Homoleptic Hydroperoxocomplex
Andrei V. Churakov, Sergey Sladkevich, Ovadia Lev, Tatiana A. Tripol’skaya and Petr V. Prikhodchenko
Inorg. Chem., Article ASAP
DOI: 10.1021/ic100554u
Publication Date (Web): May 11, 2010
Abstract
The crystal structure of cesium hexahydroperoxostannate Cs2Sn(OOH)6 is presented. The compound was characterized by single crystal and by powder X-ray diffraction, FTIR, 119Sn MAS NMR, and TG-DTA. Cs2Sn(OOH)6 crystallizes in the trigonal space group P, a = 7.5575(4), c = 5.1050(6) Å, V = 252.51(4) Å3, Z = 1, R1 = 0.0120 (I > 2σ(I)), wR2 = 0.0293 (all data), and comprises cesium cations and slightly distorted octahedral [Sn(OOH)6]2− anions lying on the threefold axis. The [Sn(OOH)6]2− unit forms 12 interanion hydrogen bonds resulting in anionic chains spread along the c-axis. All six hydroperoxo ligands are crystallographically equivalent; O−O distances are 1.482(2), only slightly longer than the O−O distance in hydrogen peroxide. FTIR and 119Sn MAS NMR reveal the similarity between all alkali hydroperoxostannates.
_________________________________________________________________________
Yulia Yu. Scaffidi-Domianello, Kristof Meelich, Michael A. Jakupec, Vladimir B. Arion, Vadim Yu. Kukushkin, Markus Galanski and Bernhard K. Keppler
Inorg. Chem., Article ASAP
DOI: 10.1021/ic100584b
Publication Date (Web): May 11, 2010
Abstract
Novel cis- and trans-configured bis(oxime)platinum(II) complexes have been synthesized and characterized by elemental analyses, IR, electrospray ionization mass spectrometry, multinuclear (1H, 13C, and 195Pt) NMR spectroscopy, and, in five cases, by X-ray diffraction. Their cytotoxicity was studied in the cisplatin-sensitive CH1 cell line as well as in inherently cisplatin-resistant SW480 cancer cells. Remarkably, every single dihalidobis(oxime)platinum(II) complex (with either a cis or trans configuration) shows a comparable cytotoxic potency in both cell lines, indicating a capacity of overcoming cisplatin resistance. Particularly strong cytotoxicities were observed in the case of trans-[PtCl2(R2C═NOH)2] (R = Me, n-Pr, i-Pr) with IC50 values in the high nanomolar concentration range in both CH1 and SW480 cancer cells. These complexes are as potent as cisplatin in CH1 cells and up to 20 times more potent than cisplatin in SW480 cells. In comparison to transplatin, the novel compounds are up to 90 (CH1) and 120 times (SW480) more cytotoxic. The previously reported observation that the trans geometry yields a more active complex in the case of [PtCl2(Me2C═NOH)2] could be confirmed for at least two structural analogues.
_______________________________________________________________________
Cesium Hydroperoxostannate: First Complete Structural Characterization of a Homoleptic Hydroperoxocomplex
Andrei V. Churakov, Sergey Sladkevich, Ovadia Lev, Tatiana A. Tripol’skaya and Petr V. Prikhodchenko
Inorg. Chem., Article ASAP
DOI: 10.1021/ic100554u
Publication Date (Web): May 11, 2010
Abstract
The crystal structure of cesium hexahydroperoxostannate Cs2Sn(OOH)6 is presented. The compound was characterized by single crystal and by powder X-ray diffraction, FTIR, 119Sn MAS NMR, and TG-DTA. Cs2Sn(OOH)6 crystallizes in the trigonal space group P, a = 7.5575(4), c = 5.1050(6) Å, V = 252.51(4) Å3, Z = 1, R1 = 0.0120 (I > 2σ(I)), wR2 = 0.0293 (all data), and comprises cesium cations and slightly distorted octahedral [Sn(OOH)6]2− anions lying on the threefold axis. The [Sn(OOH)6]2− unit forms 12 interanion hydrogen bonds resulting in anionic chains spread along the c-axis. All six hydroperoxo ligands are crystallographically equivalent; O−O distances are 1.482(2), only slightly longer than the O−O distance in hydrogen peroxide. FTIR and 119Sn MAS NMR reveal the similarity between all alkali hydroperoxostannates.
_________________________________________________________________________
Friday, May 14, 2010
J. Phys. Chem. C., v114, Issue 19
Solution State NMR Techniques Applied to Solid State Samples: Characterization of Benzoic Acid Confined in MCM-41
Thierry Azais*, Geoffrey Hartmeyer†, Sandrine Quignard, Guillaume Laurent and Florence Babonneau
J. Phys. Chem. C, 2010, 114 (19), pp 8884–8891
DOI: 10.1021/jp910622m
Abstract:In this paper we present an NMR methodology to characterize small organic molecules confined in mesoporous materials. In particular, we demonstrate that NMR techniques issued from solution state NMR are well suited to characterize benzoic acid encapsulated in hexagonally ordered mesoporous silica MCM-41 possessing two different averaged pore sizes (30 and 100 Å). As evidenced by differential scanning calorimetry, entrapped benzoic acid molecules are highly mobile at room temperature due to confinement effect and possess a glass phase transition temperature around −55 °C. Thus, the 13C NMR characterization of encapsulated molecules has to be adapted to that particular behavior. In particular, the cross-polarization technique traditionally used in solid state NMR to record 13C magic angle spinning (MAS) spectra is of poor efficiency due to weak 1H−13C dipolar interaction. Nevertheless, the presence of 1H−13C cross-relaxation phenomenon (nuclear Overhauser effect, NOE) allows us to record 13C spectra through power-gated techniques, routinely used in solution state NMR, in order to enhance the 13C signal through NOE. Furthermore, the long T2′(1H) values (up to 22 ms) are compatible with the setup of J-coupling-based experiments such as MAS refocused {1H}−13C INEPT experiments allowing us to characterize the sample through chemical bonds. These results combined with those of MAS 1H NOESY experiments lead us to distinguish unambiguously different benzoic acid populations within the large pore sample. Finally, we show that cooling down the samples at −35 °C diminishes the mobility and allows the reintroduction of the 1H−13C dipolar interaction. Thus, 2D MAS {1H}−13C HETCOR experiments can be performed at low temperature to explore spatial proximities.
Spin Canting of Maghemite Studied by 57Fe NMR and In-Field Mssbauer Spectrometry
T. Jean Daou†, Jean-Marc Greneche‡, Seong-Joo Lee§, Soonchil Lee§, Christophe Lefevre†, Sylvie Bgin-Colin† and Genevive Pourroy*†
J. Phys. Chem. C, 2010, 114 (19), pp 8794–8799
DOI: 10.1021/jp100726c
Abstract: Local probe techniques, 57Fe in-field Mssbauer, and 57Fe NMR spectrometries have been combined to describe the magnetic structure of maghemite nanoparticles of 39 (±5) nm in size and commercial maghemite. Maghemite nanoparticles were obtained from oxidation of magnetite nanoparticles. Commercial maghemite consists of nanostructured rods, and the size of crystalline domain fairly compares to that of nanoparticles. The structure of the two samples is a partially disordered spinel structure. Both local probe techniques agree that Fe magnetic moments of octahedral and tetrahedral sites are canted in both systems. It was concluded that the canting originates not only from surface effects but also from the bulk resulting from the disordered spinel structure and the frustrated cationic topology, giving rise to reversed Fe moments.
Thierry Azais*, Geoffrey Hartmeyer†, Sandrine Quignard, Guillaume Laurent and Florence Babonneau
J. Phys. Chem. C, 2010, 114 (19), pp 8884–8891
DOI: 10.1021/jp910622m
Abstract:In this paper we present an NMR methodology to characterize small organic molecules confined in mesoporous materials. In particular, we demonstrate that NMR techniques issued from solution state NMR are well suited to characterize benzoic acid encapsulated in hexagonally ordered mesoporous silica MCM-41 possessing two different averaged pore sizes (30 and 100 Å). As evidenced by differential scanning calorimetry, entrapped benzoic acid molecules are highly mobile at room temperature due to confinement effect and possess a glass phase transition temperature around −55 °C. Thus, the 13C NMR characterization of encapsulated molecules has to be adapted to that particular behavior. In particular, the cross-polarization technique traditionally used in solid state NMR to record 13C magic angle spinning (MAS) spectra is of poor efficiency due to weak 1H−13C dipolar interaction. Nevertheless, the presence of 1H−13C cross-relaxation phenomenon (nuclear Overhauser effect, NOE) allows us to record 13C spectra through power-gated techniques, routinely used in solution state NMR, in order to enhance the 13C signal through NOE. Furthermore, the long T2′(1H) values (up to 22 ms) are compatible with the setup of J-coupling-based experiments such as MAS refocused {1H}−13C INEPT experiments allowing us to characterize the sample through chemical bonds. These results combined with those of MAS 1H NOESY experiments lead us to distinguish unambiguously different benzoic acid populations within the large pore sample. Finally, we show that cooling down the samples at −35 °C diminishes the mobility and allows the reintroduction of the 1H−13C dipolar interaction. Thus, 2D MAS {1H}−13C HETCOR experiments can be performed at low temperature to explore spatial proximities.
Spin Canting of Maghemite Studied by 57Fe NMR and In-Field Mssbauer Spectrometry
T. Jean Daou†, Jean-Marc Greneche‡, Seong-Joo Lee§, Soonchil Lee§, Christophe Lefevre†, Sylvie Bgin-Colin† and Genevive Pourroy*†
J. Phys. Chem. C, 2010, 114 (19), pp 8794–8799
DOI: 10.1021/jp100726c
Abstract: Local probe techniques, 57Fe in-field Mssbauer, and 57Fe NMR spectrometries have been combined to describe the magnetic structure of maghemite nanoparticles of 39 (±5) nm in size and commercial maghemite. Maghemite nanoparticles were obtained from oxidation of magnetite nanoparticles. Commercial maghemite consists of nanostructured rods, and the size of crystalline domain fairly compares to that of nanoparticles. The structure of the two samples is a partially disordered spinel structure. Both local probe techniques agree that Fe magnetic moments of octahedral and tetrahedral sites are canted in both systems. It was concluded that the canting originates not only from surface effects but also from the bulk resulting from the disordered spinel structure and the frustrated cationic topology, giving rise to reversed Fe moments.
Thursday, May 13, 2010
;o
Natural abundance high field 43Ca solid state NMR in cement science
Igor L. Moudrakovski, Rouhollah Alizadeh and James J. Beaudoin
Phys. Chem. Chem. Phys., 2010 DOI: 10.1039/c000353k
Abstract
This work is a systematic attempt to determine the possibilities and the limitations of the 43Ca high field solid state NMR in the study of cement-based materials. The low natural abundance (0.135%) and small gyromagnetic ratio of 43Ca present a serious challenge even in a high magnetic field. The NMR spectra of a number of cement compounds of known structure and composition are examined. The spectra of several phases important in cement science, e.g., anhydrous beta di-calcium silicate (-C2S) and tri-calcium (C3S) silicate were obtained for the first time and the relation of spectroscopic and structural parameters is discussed. The method was also applied to the hydrated C3S and synthetic calcium silicate hydrates (C–S–H) of different composition in order to understand the state of calcium and transformations in the structure during hydrolysis. The spectra of hydrated C3S reveals a calcium environment similar to that of the C–S–H samples and 11 Å Tobermorite. These observations support the validity of using layered crystalline C–S–H systems as structural models for the C–S–H that forms in the hydration of Portland cement.
Igor L. Moudrakovski, Rouhollah Alizadeh and James J. Beaudoin
Phys. Chem. Chem. Phys., 2010 DOI: 10.1039/c000353k
Abstract
This work is a systematic attempt to determine the possibilities and the limitations of the 43Ca high field solid state NMR in the study of cement-based materials. The low natural abundance (0.135%) and small gyromagnetic ratio of 43Ca present a serious challenge even in a high magnetic field. The NMR spectra of a number of cement compounds of known structure and composition are examined. The spectra of several phases important in cement science, e.g., anhydrous beta di-calcium silicate (-C2S) and tri-calcium (C3S) silicate were obtained for the first time and the relation of spectroscopic and structural parameters is discussed. The method was also applied to the hydrated C3S and synthetic calcium silicate hydrates (C–S–H) of different composition in order to understand the state of calcium and transformations in the structure during hydrolysis. The spectra of hydrated C3S reveals a calcium environment similar to that of the C–S–H samples and 11 Å Tobermorite. These observations support the validity of using layered crystalline C–S–H systems as structural models for the C–S–H that forms in the hydration of Portland cement.
Wednesday, May 12, 2010
Bryan's Journal Update, Part I
I know you've all been on the edge of your seats!
***
This may be useful for the purposes of CASTEP calculations. I think.
Chemical Physics Letters
Volume 484, Issues 4-6, 7 January 2010, Pages 374-379
doi:10.1016/j.cplett.2009.11.041
***
Chemical Physics Letters
Volume 485, Issues 1-3, 18 January 2010, Pages 217-220
doi:10.1016/j.cplett.2009.11.066
***
Chemical Physics Letters
Volume 485, Issues 4-6, 26 January 2010, Pages 275-280
doi:10.1016/j.cplett.2009.12.054
***
Chemical Physics Letters
Volume 485, Issues 4-6, 26 January 2010, Pages 335-342
doi:10.1016/j.cplett.2009.12.044
***
Everyone loves 3H NMR!
Chemical Physics Letters
Volume 486, Issues 1-3, 5 February 2010, Pages 21-26
doi:10.1016/j.cplett.2009.12.087
***
Chemical Physics Letters
Volume 487, Issues 4-6, 5 March 2010, Pages 232-236
doi:10.1016/j.cplett.2010.01.040
***
Chemical Physics Letters
Volume 487, Issues 4-6, 5 March 2010, Pages 285-290
doi:10.1016/j.cplett.2010.01.048
Chemical Physics Letters
Volume 488, Issues 1-3, 12 March 2010, Pages 10-16
doi:10.1016/j.cplett.2010.01.072
Chemical Physics Letters
Volume 488, Issues 4-6, 22 March 2010, Pages 168-172
doi:10.1016/j.cplett.2010.02.015
***
Chemical Physics Letters
Volume 489, Issues 1-3, 1 April 2010, Pages 35-38
doi:10.1016/j.cplett.2010.02.051
***
Chemical Physics Letters
Volume 489, Issues 1-3, 1 April 2010, Pages 107-112
doi:10.1016/j.cplett.2010.02.026
***
Chemical Physics Letters
Volume 489, Issues 4-6, 9 April 2010, Pages 248-253
doi:10.1016/j.cplett.2010.02.078
***
***
This may be useful for the purposes of CASTEP calculations. I think.
Chemical Physics Letters
Volume 484, Issues 4-6, 7 January 2010, Pages 374-379
doi:10.1016/j.cplett.2009.11.041 Influence of plane wave cut-off on structural and electronic properties in Sn-BEA and Ti-BEA zeolite water molecule interaction
Bhakti S. Kulkarnia, Sailaja Krishnamurtyb and Sourav Pala,
Received 12 October 2009;
accepted 21 November 2009.
Available online 26 November 2009.
Abstract
Periodic systems are best described by the pseudo-potential methods. However, the accuracy of its description depends on the cut-off of plane wave basis. This is much more critical in the case of weak interactions, where a clear understanding on the influence of plane wave cut-off on the structural and electronic properties is not readily available in the literature. In the present work, we have taken a metal substituted beta zeolite–H2O complex for understanding this objective. Our studies show that while a lower cut-off of 500 eV is sufficient for the convergence of the structural parameters, description of energy-dependent properties necessitates a high cut-off value.
Chemical Physics Letters
Volume 485, Issues 1-3, 18 January 2010, Pages 217-220
doi:10.1016/j.cplett.2009.11.066
NMR spectroscopy in the milli-Tesla regime: Measurement of 1H chemical-shift differences below the line width
Stephan Appelta, , Stefan Glögglerb, Friedrich W. Häsinga, Ulrich Sielinga, Ali Gordji Nejada and Bernhard Blümichb
Received 16 October 2009;
accepted 29 November 2009.
Available online 1 December 2009.
Abstract
NMR spectroscopy for chemical analysis at high field employs precision measurements of resonance frequencies governed by chemical shift and nuclear spin interactions. At low field and in the absence of hetero-nuclear J-couplings the natural line width limits the chemical shift measurements. We have performed chemical-shift resolved proton NMR spectra in the milli-Tesla regime, and found that in the presence of hetero-nuclear J-coupling, proton chemical-shift differences smaller than the line width can be measured down to nuclear Larmor frequencies of 41 kHz. The measurement of J-couplings and chemical shifts with simple NMR devices operating in the milli-Tesla regime may develop as an attractive tool for chemical analysis.
Chemical Physics Letters
Volume 485, Issues 4-6, 26 January 2010, Pages 275-280
doi:10.1016/j.cplett.2009.12.054 Proton micro-magic-angle-spinning NMR spectroscopy of nanoliter samples
Andreas Brinkmanna, b, , Suresh Kumar Vasaa, Hans Janssena and Arno P.M. Kentgensa, ,
Received 22 October 2009;
accepted 16 December 2009.
Available online 23 December 2009.
Abstract
We present our recent progress in the development of micro-magic-angle-spinning solenoid-based probeheads for the application in high-resolution 1H solid-state NMR of nanoliter sample volumes. The use of fused-silica capillaries as sample holders results in spectra without any 1H background signal. It is possible to obtain 1H spectra of 40–80 nl samples in a few scans. We obtained high-resolution 1H spectra employing different homonuclear decoupling sequences on powdered samples of l-alanine, the tripeptide AGG, and a single crystal of l-tyrosine·HCl. In addition, we recorded high-resolution two-dimensional proton-detected 1H–13C heteronuclear correlation spectra of [U-13C3, 15N]-l-alanine and AGG with natural abundant isotope distribution.
Chemical Physics Letters
Volume 485, Issues 4-6, 26 January 2010, Pages 335-342
doi:10.1016/j.cplett.2009.12.044
NMR polarization transfer by second-order resonant recoupling: RESORT
Ingo Scholza, Beat H. Meiera and Matthias Ernst, a,
Received 13 November 2009;
accepted 15 December 2009.
Available online 22 December 2009.
Abstract
We describe a resonant second-order dipolar recoupling condition for magic-angle spinning (MAS) solid-state NMR where the active spins are irradiated by continuous-wave irradiation and the passive spins by a phase-alternating sequence. The phase-modulation frequency is matched to an integer multiple of the MAS frequency to produce a second-order homonuclear dipolar coupling Hamiltonian that promotes broadband homonuclear zero-quantum polarization transfer on the spin-locked active spins. The recoupling sequence is based on second-order cross terms between two heteronuclear dipolar couplings. Similarities and differences to the proton-assisted recoupling sequence are discussed.
Everyone loves 3H NMR!
Chemical Physics Letters
Volume 486, Issues 1-3, 5 February 2010, Pages 21-26
doi:10.1016/j.cplett.2009.12.087 3H NMR of the tritiated isotopologues of methane in nematic liquid-crystal solvents
Dedicated to the memory of Annalaura Segre (deceased 25 April 2008) and Jaap G. Snijders (deceased 13 August 2004).
E. Elliott Burnella, Cornelis A. de Langeb, , Donatella Capitanic, Giancarlo Angelinic and Ornella Ursinic
Received 18 November 2009;
accepted 29 December 2009.
Available online 4 January 2010.
Abstract
The NMR spectra of the tritiated isotopologues of methane dissolved in several nematic liquid-crystalline solvents are measured. The spectral parameters obtained agree extremely well with those predicted from earlier NMR studies of the deuterated isotopologues, providing excellent confirmation of the theory for vibration–reorientation interaction developed earlier.
Chemical Physics Letters
Volume 487, Issues 4-6, 5 March 2010, Pages 232-236
doi:10.1016/j.cplett.2010.01.040
Solid-state 95Mo NMR of mixed-valence polyoxomolybdates (V, VI) with localized or delocalized d1 electrons
Takahiro Iijimaa, Toshihiro Yamaseb, Masataka Tanshoc, Tadashi Shimizuc and Katsuyuki Nishimuraa, ,
Received 23 October 2009;
accepted 19 January 2010.
Available online 25 January 2010.
Abstract
We report solid-state 95Mo NMR of MoV, MoV,VI and MoVI species in mixed-valence polyoxomolybdates (V, VI) with localized or delocalized d1 electrons. Parameters about chemical shift and quadrupole interactions of 95Mo in diamagnetic crystals of with localized electrons and
with delocalized ones were obtained by simulation of magic-angle-spinning (MAS) 95Mo NMR spectra. The isotropic and anisotropic chemical shifts of sites of MoV in 1 and MoV, VI in 2, respectively, exhibited absolute values quite larger than those of other MoVI sites, which is examined by quantum chemical calculations.
Chemical Physics Letters
Volume 487, Issues 4-6, 5 March 2010, Pages 285-290
doi:10.1016/j.cplett.2010.01.048
Oxygen coordination of aluminum cations in dehydrated AlPW12O40 investigated by solid-state NMR spectroscopy
Arne Bressela, Jörg Freya, Urszula Filekb, Bogdan Sulikowskib, Dieter Freudec and Michael Hungera
Received 4 December 2009;
accepted 20 January 2010.
Available online 25 January 2010.
Abstract
Dehydrated aluminumdodecatungstophosphate (AlPW12O40) was investigated by 27Al MAS NMR spectroscopy in magnetic fields of 9.4 and 17.6 T. Two kinds of octahedrally coordinated (δ27Al = 1–2 ppm, CQ = 2.4–2.5 MHz, and δ27Al = 4–6 ppm, CQ = 6.0–6.5 MHz), two kinds of penta-coordinated (δ27Al = 24–30 ppm, CQ = 7.0–7.3 MHz, and δ27Al = 44 ppm, CQ = 7.5–8.7 MHz), and a small amount of tetrahedrally coordinated aluminum cations (δ27Al = 65 ppm, CQ = 8.2–8.5 MHz) were found. Comparison with 1H MAS NMR spectroscopic studies indicates that the dehydroxylation of aluminum OH groups (δ1H = 4.2 ppm and 5.6 ppm) at temperatures of 473 and 573 K is accompanied by a partially irreversible change of the oxygen coordination of aluminum cations.
***
Volume 488, Issues 1-3, 12 March 2010, Pages 10-16
doi:10.1016/j.cplett.2010.01.072 Broadband magnetization transfer using moderate radio-frequency fields for NMR with very high static fields and spinning speeds
Markus Weingartha, Geoffrey Bodenhausena, b and Piotr Tekelya
Received 4 January 2010;
accepted 29 January 2010.
Available online 4 February 2010.
Abstract
We introduce a new dipolar recoupling scheme, dubbed PARIS-xy (phase-alternated recoupling irradiation scheme using orthogonal radio-frequency phases), to promote efficient broadband magnetization exchange between 13C nuclei using moderate radio-frequency amplitudes at very high magnetic field strengths and spinning speeds. Experimental observations for a wide range of spinning frequencies 30 
νrot 60 kHz and magnetic field strengths (B0 = 9.4, 17.6 and 21.2 T) are backed up by numerical simulations.
A solid-state NMR scheme dubbed PARIS-xy affords efficient low-power recoupling of dipolar interactions between nuclei such as carbon-13 over a wide range of isotropic chemical shifts. The scheme is suitable for very high magnetic fields up to 21.2 T (900 MHz) and spinning speeds up to 60 kHz.
***Chemical Physics Letters
Volume 488, Issues 4-6, 22 March 2010, Pages 168-172
doi:10.1016/j.cplett.2010.02.015
DFT study of possible lattice defects in methane-hydrate and their appearance in 13C NMR spectra
Péter Terleczkya and László Nyulászi
Received 14 December 2009;
accepted 9 February 2010.
Available online 12 February 2010.
Abstract
The effect of the possible cell defects in the methane-hydrate crystal on the chemical shift of the carbon core has been investigated by DFT calculations. The clathrate structure was modeled as a water monolayer, in mono and bicavital clusters. The results show that the radius of the clathrate cell correlates with the chemical shielding of the carbon core. The calculated chemical shifts for the most stable clusters are in good agreement with the observed NMR signals supporting the previous spectral assignment. The occupancy of a neighbouring cell in a bicavital cluster has a small effect on the calculated NMR shift.
Chemical Physics Letters
Volume 489, Issues 1-3, 1 April 2010, Pages 35-38
doi:10.1016/j.cplett.2010.02.051 A theoretical study of the stationary structures of the methane surface with special emphasis on NMR properties
Ibon Alkorta and José Elgueroa
Received 22 January 2010;
accepted 18 February 2010.
Available online 21 February 2010.
Abstract
The seven stationary points of the methane hypersurface were first explored concerning geometries and energies to check previous data. On these geometries, absolute 1H and 13C NMR shieldings as well as 1J(CH) and 2J(HH) coupling constants were calculated. The results show important variations in the NMR parameters depending on the stationary point considered. Relationships have been found between the 1H and 13C shieldings and between these NMR parameters and the relative energy of the different species.
Chemical Physics Letters
Volume 489, Issues 1-3, 1 April 2010, Pages 107-112
doi:10.1016/j.cplett.2010.02.026
1H NMR noise measurements in hyperpolarized liquid samples
Patrick Giraudeaua, 1, Norbert Müllerb, Alexej Jerschowc and Lucio Frydmana
Received 31 August 2009;
accepted 9 February 2010.
Available online 12 February 2010.
Abstract
Noise measurements of nuclear spin systems using a tuned circuit can reveal the signatures of two different phenomena: Thermal circuit noise absorbed by the spin system, and nuclear spin-noise leading to tiny fluctuating magnetization components. Polarization enhancement can increase the observed noise amplitudes due to an enlarged coupling with the reception circuit. In this work we explore the detection of noise in 1H NMR of liquid water samples whose spin alignment is enhanced via ex situ dynamic nuclear polarization. A number of ancillary phenomena related to this kind of experiments are also documented.
Chemical Physics Letters
Volume 489, Issues 4-6, 9 April 2010, Pages 248-253
doi:10.1016/j.cplett.2010.02.078
Characterization of the 19F chemical shielding tensor using cross-correlated spin relaxation measurements and quantum chemical calculations
S. Begam Elavarasia and Kavita Doraib
Received 14 January 2010;
accepted 28 February 2010.
Available online 3 March 2010.
Abstract
The 19F chemical shift anisotropy (CSA) tensor is an indispensable structure estimation tool in the NMR investigations of flourinated biomolecules. This work focuses on the characterization of the 19F CSA tensor in small molecules, through the combined use of quantum chemical methods and liquid-state NMR cross-correlated spin relaxation experiments. The effect of different basis sets and quantum computational methods on the magnitude and orientation of the 19F CSA tensor are discussed. The results from ab initio methods and the liquid-state relaxation experiments match well and are comparable to values of the CSA tensor obtained from previous solid-state studies and from theoretical investigations of similar molecules.
Journal of Solid State Chemistry
Volume 183, Issue 1, January 2010, Pages 120-127
doi:10.1016/j.jssc.2009.10.006
MAS-NMR studies of lithium aluminum silicate (LAS) glasses and glass–ceramics having different Li2O/Al2O3 ratio
A. Ananthanarayanana, G.P. Kothiyala, L. Montagneb and B. Revelb
Keywords: Glass; Glass–ceramics; Silicates; Crystallization; MAS-NMR; XRD
Emergence of phases in lithium aluminum silicate (LAS) glasses of composition (wt%) xLi2O–71.7SiO2–(17.7−x)Al2O3–4.9K2O–3.2B2O3–2.5P2O5 (5.1≤x≤12.6) upon heat treatment were studied. 29Si, 27Al, 31P and 11B MAS-NMR were employed for structural characterization of both LAS glasses and glass–ceramics. In glass samples, Al is found in tetrahedral coordination, while P exists mainly in the form of orthophosphate units. B exists as BO3 and BO4 units. 27Al NMR spectra show no change with crystallization, ruling out the presence of any Al containing phase. Contrary to X-ray diffraction studies carried out, 11B (high field 18.8 T) and 29Si NMR spectra clearly indicate the unexpected crystallization of a borosilicate phase (Li,K)BSi2O6, whose structure is similar to the aluminosilicate virgilite. Also, lithium disilicate (Li2Si2O5), lithium metasilicate (Li2SiO3) and quartz (SiO2) were identified in the 29Si NMR spectra of the glass–ceramics. 31P NMR spectra of the glass–ceramics revealed the presence of Li3PO4 and a mixed phase (Li,K)3PO4 at low alkali concentrations.
______________________________________________________________________________
J. Phys. Chem. A, 2010, 114 (18), pp 5743–5751
DOI: 10.1021/jp100889t
A System for NMR Stark Spectroscopy of Quadrupolar Nuclei
Matthew R. Tarasek and James G. Kempf
Electrostatic influences on NMR parameters are well accepted. Experimental and computational routes have been long pursued to understand and utilize such Stark effects. However, existing approaches are largely indirect informants on electric fields, and/or are complicated by multiple causal factors in spectroscopic change. We present a system to directly measure quadrupolar Stark effects from an applied electric (E) field. Our apparatus and applications are relevant in two contexts. Each uses a radiofrequency (rf) E field at twice the nuclear Larmor frequency (2ω0). The mechanism is a distortion of the E-field gradient tensor that is linear in the amplitude (E0) of the rf E field. The first uses 2ω0 excitation of double-quantum transitions for times similar to T1 (the longitudinal spin relaxation time). This perturbs the steady state distribution of spin population. Nonlinear analysis versus E0 can be used to determine the Stark response rate. The second context uses POWER (perturbations observed with enhanced resolution) NMR. Here, coherent, short-time (T2, the transverse relaxation rate) excitation at 2ω0 is synchronized with an NMR multiple-pulse line-narrowing sequence. Linear analysis of the Stark response is then possible: a quadrupolar multiplet with splitting proportional to E0. The POWER sequence converts the 2ω0 interaction from off-diagonal/nonsecular to the familiar diagonal form (Iz2) of static quadrupole interactions. Meanwhile, background contributions to line width are averaged to zero, providing orders-of-magnitude resolution enhancement for correspondingly high sensitivity to the Stark effect. Using GaAs as a test case with well-defined Stark response, we provide the first demonstration of the 2ω0 effect at high-field (14.1 T) and room temperature. This, along with the simplicity of our apparatus and spectral approach, may facilitate extensions to a wider array of material and molecular systems. The POWER context, which has not previously been tested, is detailed here with new design insights. Several key aspects are demonstrated here, while complete implementation is to be presented at a later time. At present, we (1) account for finite pulse times in pulse sequence design, (2) demonstrate two-channel phase coherence for magnetic (ω0) and electric (2ω0) excitation, and (3) provide line narrowing by a factor of 103. In addition, we find that certain anomalous contributions to the line shape, observed in previous low-field (250 mT) applications, are absent here.
Volume 183, Issue 1, January 2010, Pages 120-127
doi:10.1016/j.jssc.2009.10.006
MAS-NMR studies of lithium aluminum silicate (LAS) glasses and glass–ceramics having different Li2O/Al2O3 ratio
A. Ananthanarayanana, G.P. Kothiyala, L. Montagneb and B. Revelb
Keywords: Glass; Glass–ceramics; Silicates; Crystallization; MAS-NMR; XRD
Emergence of phases in lithium aluminum silicate (LAS) glasses of composition (wt%) xLi2O–71.7SiO2–(17.7−x)Al2O3–4.9K2O–3.2B2O3–2.5P2O5 (5.1≤x≤12.6) upon heat treatment were studied. 29Si, 27Al, 31P and 11B MAS-NMR were employed for structural characterization of both LAS glasses and glass–ceramics. In glass samples, Al is found in tetrahedral coordination, while P exists mainly in the form of orthophosphate units. B exists as BO3 and BO4 units. 27Al NMR spectra show no change with crystallization, ruling out the presence of any Al containing phase. Contrary to X-ray diffraction studies carried out, 11B (high field 18.8 T) and 29Si NMR spectra clearly indicate the unexpected crystallization of a borosilicate phase (Li,K)BSi2O6, whose structure is similar to the aluminosilicate virgilite. Also, lithium disilicate (Li2Si2O5), lithium metasilicate (Li2SiO3) and quartz (SiO2) were identified in the 29Si NMR spectra of the glass–ceramics. 31P NMR spectra of the glass–ceramics revealed the presence of Li3PO4 and a mixed phase (Li,K)3PO4 at low alkali concentrations.
______________________________________________________________________________
J. Phys. Chem. A, 2010, 114 (18), pp 5743–5751
DOI: 10.1021/jp100889t
A System for NMR Stark Spectroscopy of Quadrupolar Nuclei
Matthew R. Tarasek and James G. Kempf
Electrostatic influences on NMR parameters are well accepted. Experimental and computational routes have been long pursued to understand and utilize such Stark effects. However, existing approaches are largely indirect informants on electric fields, and/or are complicated by multiple causal factors in spectroscopic change. We present a system to directly measure quadrupolar Stark effects from an applied electric (E) field. Our apparatus and applications are relevant in two contexts. Each uses a radiofrequency (rf) E field at twice the nuclear Larmor frequency (2ω0). The mechanism is a distortion of the E-field gradient tensor that is linear in the amplitude (E0) of the rf E field. The first uses 2ω0 excitation of double-quantum transitions for times similar to T1 (the longitudinal spin relaxation time). This perturbs the steady state distribution of spin population. Nonlinear analysis versus E0 can be used to determine the Stark response rate. The second context uses POWER (perturbations observed with enhanced resolution) NMR. Here, coherent, short-time (T2, the transverse relaxation rate) excitation at 2ω0 is synchronized with an NMR multiple-pulse line-narrowing sequence. Linear analysis of the Stark response is then possible: a quadrupolar multiplet with splitting proportional to E0. The POWER sequence converts the 2ω0 interaction from off-diagonal/nonsecular to the familiar diagonal form (Iz2) of static quadrupole interactions. Meanwhile, background contributions to line width are averaged to zero, providing orders-of-magnitude resolution enhancement for correspondingly high sensitivity to the Stark effect. Using GaAs as a test case with well-defined Stark response, we provide the first demonstration of the 2ω0 effect at high-field (14.1 T) and room temperature. This, along with the simplicity of our apparatus and spectral approach, may facilitate extensions to a wider array of material and molecular systems. The POWER context, which has not previously been tested, is detailed here with new design insights. Several key aspects are demonstrated here, while complete implementation is to be presented at a later time. At present, we (1) account for finite pulse times in pulse sequence design, (2) demonstrate two-channel phase coherence for magnetic (ω0) and electric (2ω0) excitation, and (3) provide line narrowing by a factor of 103. In addition, we find that certain anomalous contributions to the line shape, observed in previous low-field (250 mT) applications, are absent here.
Synlett
Immobilization of TEMPO Derivatives in Saponite and Use of These Novel Hybrid Materials as Reusable Catalysts
Roben C , Studer A, Hemme WL, Eckert H
SYNLETT Issue: 7 Pages: 1110-1114 Published: APR 2010
Abstract: The letter describes a novel approach for immobilization of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) derivatives by cation-exchange reaction of TEMPO ammonium salts in a commercially available saponite. The organic-inorganic hybrid material is readily prepared and characterized by solid-state H-1 NMR spectroscopy. The hybrid material can be used as recyclable catalyst for oxidation of various alcohols. High catalytic activity for up to 10 runs is obtained. Leaching of the nitroxide salt out of the saponite occurs to a small extent. However, original high activity of the hybrid material can be restored by simply reloading the hybrid material with nitroxide salt by cation exchange.
Roben C , Studer A, Hemme WL, Eckert H
SYNLETT Issue: 7 Pages: 1110-1114 Published: APR 2010
Abstract: The letter describes a novel approach for immobilization of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) derivatives by cation-exchange reaction of TEMPO ammonium salts in a commercially available saponite. The organic-inorganic hybrid material is readily prepared and characterized by solid-state H-1 NMR spectroscopy. The hybrid material can be used as recyclable catalyst for oxidation of various alcohols. High catalytic activity for up to 10 runs is obtained. Leaching of the nitroxide salt out of the saponite occurs to a small extent. However, original high activity of the hybrid material can be restored by simply reloading the hybrid material with nitroxide salt by cation exchange.
Tuesday, May 11, 2010
Journal of Physical Chemistry C, vol. 114, Issue 18
The Role of the Cluster on the Relaxation of Endohedral Fullerene Cage Carbons: A NMR Spin−Lattice Relaxation Study of an Internal Relaxation Reagent
Sabrina Klod, Lin Zhang and Lothar Dunsch*
J. Phys. Chem. C, 2010, 114 (18), pp 8264–8267
DOI: 10.1021/jp101218p
Abstract: The endohedral cluster fullerenes Ih-Sc3N@C80, Ih-Y3N@C80, and Ih-Lu3N@C80 were investigated with respect to the strategy of an internal relaxation reagent by following the cluster size effects and the influence of f-electrons on the carbon relaxation. For endohedral nitride cluster fullerenes of Ih-C80 cage symmetry increased relaxation rates are observed. In general, the enlarged cage size increases the relaxation of the carbons. The encapsulated metal atoms give an additional dipole−dipole interaction to the relaxation rate of the carbon atoms depending on their magnetic character. For different metals the increased nitride cluster size is one reason for the observed stronger dipole−dipole interaction. In contrast, a higher shielding of a metal nucleus by its electron shell leads to a reduced magnetic effect. The negative charge on the cage increases the electron density, thus decreasing T1. In temperature-dependent studies, the diffusion is fast compared to the rotation of the molecule at higher temperatures which is typical for the spherical shape of the fullerene cage. Thus, only a minor deformation of the cage by the endohedral voluminous cluster is found. The shape of the cage is preserved and less influenced by the type and size of the cluster.
Fabrication of Hierarchical Channel Wall in Al-MCM-41 Mesoporous Materials to Enhance Their Adsorptive Capability: Why and How?
Fang Na Gu†‡, Feng Wei†, Jia Yuan Yang†, Ying Wang*‡ and Jian Hua Zhu*†
Key Laboratory of Mesoscopic Chemistry of MOE, College of Chemistry and Chemical Engineering, and Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China
J. Phys. Chem. C, 2010, 114 (18), pp 8431–8439
DOI: 10.1021/jp1009143
Abstract:To overcome the inefficiency of mesoporous materials in the adsorption of small molecules, this article reports the effort how to create hierarchical channel wall in Al-MCM-41 and more important, how to distinguish the contribution of the newly formed micropores in adsorption by the mesoporous materials. Fabrication of hierarchical channel wall is realized through extracting framework aluminum of sample by acid leach to create micropores and defects, providing the fine geometric confinement toward tiny targets. The influence of original Al content of Al-MCM-41 on the controlled dealumination was studied, and X-ray diffraction, N2 adsorption−desorption, 27Al and 29Si MAS NMR, Fourier transform IR techniques were employed to characterize the resulting samples. Besides, volatile nitrosamine N-nitrosopyrrolidine (NPYR) was chosen as a probe to assess the adsorption of the resulting samples. Hierarchical channel wall in Al-MCM-41 significantly increased its ability to trap NPYR, and for the first time the adsorptive contribution of newly formed micropores and defects in the mesoporous silica was distinguished by the instantaneous adsorption under the carrier gas with different flow rate, which is beneficial for developing new functional materials to protect environment.
Structure, Connectivity, and Configurational Entropy of GexSe100−x Glasses: Results from 77Se MAS NMR Spectroscopy
E. L. Gjersing and S. Sen*, B. G. Aitken
J. Phys. Chem. C, 2010, 114 (18), pp 8601–8608
DOI: 10.1021/jp1014143
Abstract:High-resolution 77Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary GexSe100−x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se−Se−Se and Ge−Se−Se linkages as well as Ge−Se−Ge sites where the Se atom is shared by two GeSe4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77Se MAS NMR spectrum of crystalline β-GeSe2. Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of GexSe100−x glasses in this composition range can be described as a randomly interconnected network of GeSe4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.
Sabrina Klod, Lin Zhang and Lothar Dunsch*
J. Phys. Chem. C, 2010, 114 (18), pp 8264–8267
DOI: 10.1021/jp101218p
Abstract: The endohedral cluster fullerenes Ih-Sc3N@C80, Ih-Y3N@C80, and Ih-Lu3N@C80 were investigated with respect to the strategy of an internal relaxation reagent by following the cluster size effects and the influence of f-electrons on the carbon relaxation. For endohedral nitride cluster fullerenes of Ih-C80 cage symmetry increased relaxation rates are observed. In general, the enlarged cage size increases the relaxation of the carbons. The encapsulated metal atoms give an additional dipole−dipole interaction to the relaxation rate of the carbon atoms depending on their magnetic character. For different metals the increased nitride cluster size is one reason for the observed stronger dipole−dipole interaction. In contrast, a higher shielding of a metal nucleus by its electron shell leads to a reduced magnetic effect. The negative charge on the cage increases the electron density, thus decreasing T1. In temperature-dependent studies, the diffusion is fast compared to the rotation of the molecule at higher temperatures which is typical for the spherical shape of the fullerene cage. Thus, only a minor deformation of the cage by the endohedral voluminous cluster is found. The shape of the cage is preserved and less influenced by the type and size of the cluster.
Fabrication of Hierarchical Channel Wall in Al-MCM-41 Mesoporous Materials to Enhance Their Adsorptive Capability: Why and How?
Fang Na Gu†‡, Feng Wei†, Jia Yuan Yang†, Ying Wang*‡ and Jian Hua Zhu*†
Key Laboratory of Mesoscopic Chemistry of MOE, College of Chemistry and Chemical Engineering, and Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China
J. Phys. Chem. C, 2010, 114 (18), pp 8431–8439
DOI: 10.1021/jp1009143
Abstract:To overcome the inefficiency of mesoporous materials in the adsorption of small molecules, this article reports the effort how to create hierarchical channel wall in Al-MCM-41 and more important, how to distinguish the contribution of the newly formed micropores in adsorption by the mesoporous materials. Fabrication of hierarchical channel wall is realized through extracting framework aluminum of sample by acid leach to create micropores and defects, providing the fine geometric confinement toward tiny targets. The influence of original Al content of Al-MCM-41 on the controlled dealumination was studied, and X-ray diffraction, N2 adsorption−desorption, 27Al and 29Si MAS NMR, Fourier transform IR techniques were employed to characterize the resulting samples. Besides, volatile nitrosamine N-nitrosopyrrolidine (NPYR) was chosen as a probe to assess the adsorption of the resulting samples. Hierarchical channel wall in Al-MCM-41 significantly increased its ability to trap NPYR, and for the first time the adsorptive contribution of newly formed micropores and defects in the mesoporous silica was distinguished by the instantaneous adsorption under the carrier gas with different flow rate, which is beneficial for developing new functional materials to protect environment.
Structure, Connectivity, and Configurational Entropy of GexSe100−x Glasses: Results from 77Se MAS NMR Spectroscopy
E. L. Gjersing and S. Sen*, B. G. Aitken
J. Phys. Chem. C, 2010, 114 (18), pp 8601–8608
DOI: 10.1021/jp1014143
Abstract:High-resolution 77Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary GexSe100−x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se−Se−Se and Ge−Se−Se linkages as well as Ge−Se−Ge sites where the Se atom is shared by two GeSe4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77Se MAS NMR spectrum of crystalline β-GeSe2. Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of GexSe100−x glasses in this composition range can be described as a randomly interconnected network of GeSe4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.
Journal of Physical Chemistry B, vol. 114, Issues 18
Molecular Level Characterization of the Inorganic−Bioorganic Interface by Solid State NMR: Alanine on a Silica Surface, a Case Study
Ira Ben Shir†, Shifi Kababya†, Tal Amitay-Rosen‡, Yael S. Balazs† and Asher Schmidt*†
J. Phys. Chem. B, 2010, 114 (18), pp 5989–5996
DOI: 10.1021/jp100114v
Publication Date (Web): April 16, 2010
Abstract: The molecular interface between bioorganics and inorganics plays a key role in diverse scientific and technological research areas including nanoelectronics, biomimetics, biomineralization, and medical applications such as drug delivery systems and implant coatings. However, the physical/chemical basis of recognition of inorganic surfaces by biomolecules remains unclear. The molecular level elucidation of specific interfacial interactions and the structural and dynamical state of the surface bound molecules is of prime scientific importance. In this study, we demonstrate the ability of solid state NMR methods to accomplish these goals. l-[1-13C,15N]Alanine loaded onto SBA-15 mesoporous silica with a high surface area served as a model system. The interacting alanine moiety was identified as the −NH3+ functional group by 15N{1H}SLF NMR. 29Si{15N} and 15N{29Si}REDOR NMR revealed intermolecular interactions between the alanine −NH3+ and three to four surface Si species, predominantly Q3, with similar internuclear N···Si distances of 4.0−4.2 Å. Distinct dynamic states of the adsorbed biomolecules were identified by 15N{13C}REDOR NMR, indicating both bound and free alanine populations, depending on hydration level and temperature. In the bound populations, the −NH3+ group is surface anchored while the free carboxylate end undergoes librations, implying the carboxylate has small or no contributions to surface binding. When surface water clusters grow bigger with increased hydration, the libration amplitude of the carboxyl end amplifies, until onset of dissolution occurs. Our measurements provide the first direct, comprehensive, molecular-level identification of the bioorganic−inorganic interface, showing binding functional groups, geometric constraints, stoichiometry, and dynamics, both for the adsorbed amino acid and the silica surface.
Selective Chemical Shift Assignment of Bacteriochlorophyll a in Uniformly [13C−15N]-Labeled Light-Harvesting 1 Complexes by Solid-State NMR in Ultrahigh Magnetic Field
Anjali Pandit*, Francesco Buda, Adriaan J. van Gammeren†, Swapna Ganapathy and Huub J. M. de Groot
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
J. Phys. Chem. B, 2010, 114 (18), pp 6207–6215
DOI: 10.1021/jp100688u
Abstract: Magic-angle spinning (MAS) 13C−13C correlation NMR spectroscopy was used to resolve the electronic ground state characteristics of the bacteriochlorophyll a (BChl a) cofactors in light-harvesting 1 (LH1) complexes of Rhodopseudomonas acidophila (strain 10050). The BChl a 13C isotropic chemical shifts of the LH1 complexes are compared to the 13C chemical shifts for BChl a dissolved in acetone-d6 and to 13C NMR data that has been obtained for the B800 and B850 BChl molecules in Rps. acidophila peripheral light-harvesting complexes (LH2). Since both complexes contain BChl a cofactors, we can address the chemical shift variability for specific carbon responses between the two types of antennae. The global shift pattern of the LH1 BChl's resembles the shift patterns of the LH2 α- and β-B850 BChl's, while some carbon responses, in particular the C3 and C31, show significant deviations. A comparison with density functional theory (DFT) shift calculations provides insight into the BChl concomitant structural and electronic interactions in the ground state. The differences in the LH1 BChl observed chemical shifts relative to the 13C responses of BChl a in solution cannot be explained by local side chain interactions, such as hydrogen bonding or nonplanarity of the C3 acetyl, but appear to be dominated by protein-induced macrocycle distortion. Such shaping of the macrocycle will contribute significantly to the red shift of the BChl Qy absorbance band in purple bacterial light-harvesting complexes.
Solid-State 137Ba NMR Spectroscopy: An Experimental and Theoretical Investigation of
Hiyam Hamaed†, Eric Ye‡, Konstantin Udachin§ and Robert W. Schurko*†
J. Phys. Chem. B, 2010, 114 (18), pp 6014–6022
DOI: 10.1021/jp102026m
Abstract: Ultrawideline 137Ba SSNMR spectra of several barium-containing systems (barium nitrate, barium carbonate, barium chlorate monohydrate, barium chloride dihydrate, anhydrous barium chloride, and barium hydrogen phosphate) were acquired at two different magnetic field strengths (9.4 and 21.1 T) using frequency-stepped techniques. The recently reported WURST−QCPMG pulse sequence (O’Dell et al. Chem. Phys. Lett. 2008, 464, 97−102) is shown to be very useful for rapidly acquiring high signal-to-noise 137Ba SSNMR spectra. The breadths of the second-order quadrupolar-dominated spectra and experimental times are notably reduced for experiments conducted at 21.1 T. Analytical simulations of the 137Ba SSNMR spectra at both fields yield the quadrupolar parameters, and in select cases the barium chemical shift anisotropies (CSAs). Quadrupolar interactions dominate the 137Ba powder patterns, with quadrupolar coupling constants, CQ(137Ba), ranging from 7.0 to 28.8 MHz. The 137Ba electric field gradient (EFG) parameters extracted from these spectra are correlated to the local environments at the barium sites, via consideration of molecular symmetry and structure, and first principles calculations of 137Ba EFG tensors performed using CASTEP software. The rapidity with which 137Ba SSNMR spectra can be acquired using the WURST pulse sequence and/or at ultrahigh magnetic fields and the sensitivity of the 137Ba EFG tensor parameters to the changes in the barium environment suggest that 137Ba SSNMR has great potential for structural characterization of a variety of barium-containing materials.
Ira Ben Shir†, Shifi Kababya†, Tal Amitay-Rosen‡, Yael S. Balazs† and Asher Schmidt*†
J. Phys. Chem. B, 2010, 114 (18), pp 5989–5996
DOI: 10.1021/jp100114v
Publication Date (Web): April 16, 2010
Abstract: The molecular interface between bioorganics and inorganics plays a key role in diverse scientific and technological research areas including nanoelectronics, biomimetics, biomineralization, and medical applications such as drug delivery systems and implant coatings. However, the physical/chemical basis of recognition of inorganic surfaces by biomolecules remains unclear. The molecular level elucidation of specific interfacial interactions and the structural and dynamical state of the surface bound molecules is of prime scientific importance. In this study, we demonstrate the ability of solid state NMR methods to accomplish these goals. l-[1-13C,15N]Alanine loaded onto SBA-15 mesoporous silica with a high surface area served as a model system. The interacting alanine moiety was identified as the −NH3+ functional group by 15N{1H}SLF NMR. 29Si{15N} and 15N{29Si}REDOR NMR revealed intermolecular interactions between the alanine −NH3+ and three to four surface Si species, predominantly Q3, with similar internuclear N···Si distances of 4.0−4.2 Å. Distinct dynamic states of the adsorbed biomolecules were identified by 15N{13C}REDOR NMR, indicating both bound and free alanine populations, depending on hydration level and temperature. In the bound populations, the −NH3+ group is surface anchored while the free carboxylate end undergoes librations, implying the carboxylate has small or no contributions to surface binding. When surface water clusters grow bigger with increased hydration, the libration amplitude of the carboxyl end amplifies, until onset of dissolution occurs. Our measurements provide the first direct, comprehensive, molecular-level identification of the bioorganic−inorganic interface, showing binding functional groups, geometric constraints, stoichiometry, and dynamics, both for the adsorbed amino acid and the silica surface.
Selective Chemical Shift Assignment of Bacteriochlorophyll a in Uniformly [13C−15N]-Labeled Light-Harvesting 1 Complexes by Solid-State NMR in Ultrahigh Magnetic Field
Anjali Pandit*, Francesco Buda, Adriaan J. van Gammeren†, Swapna Ganapathy and Huub J. M. de Groot
Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
J. Phys. Chem. B, 2010, 114 (18), pp 6207–6215
DOI: 10.1021/jp100688u
Abstract: Magic-angle spinning (MAS) 13C−13C correlation NMR spectroscopy was used to resolve the electronic ground state characteristics of the bacteriochlorophyll a (BChl a) cofactors in light-harvesting 1 (LH1) complexes of Rhodopseudomonas acidophila (strain 10050). The BChl a 13C isotropic chemical shifts of the LH1 complexes are compared to the 13C chemical shifts for BChl a dissolved in acetone-d6 and to 13C NMR data that has been obtained for the B800 and B850 BChl molecules in Rps. acidophila peripheral light-harvesting complexes (LH2). Since both complexes contain BChl a cofactors, we can address the chemical shift variability for specific carbon responses between the two types of antennae. The global shift pattern of the LH1 BChl's resembles the shift patterns of the LH2 α- and β-B850 BChl's, while some carbon responses, in particular the C3 and C31, show significant deviations. A comparison with density functional theory (DFT) shift calculations provides insight into the BChl concomitant structural and electronic interactions in the ground state. The differences in the LH1 BChl observed chemical shifts relative to the 13C responses of BChl a in solution cannot be explained by local side chain interactions, such as hydrogen bonding or nonplanarity of the C3 acetyl, but appear to be dominated by protein-induced macrocycle distortion. Such shaping of the macrocycle will contribute significantly to the red shift of the BChl Qy absorbance band in purple bacterial light-harvesting complexes.
Solid-State 137Ba NMR Spectroscopy: An Experimental and Theoretical Investigation of
Hiyam Hamaed†, Eric Ye‡, Konstantin Udachin§ and Robert W. Schurko*†
J. Phys. Chem. B, 2010, 114 (18), pp 6014–6022
DOI: 10.1021/jp102026m
Abstract: Ultrawideline 137Ba SSNMR spectra of several barium-containing systems (barium nitrate, barium carbonate, barium chlorate monohydrate, barium chloride dihydrate, anhydrous barium chloride, and barium hydrogen phosphate) were acquired at two different magnetic field strengths (9.4 and 21.1 T) using frequency-stepped techniques. The recently reported WURST−QCPMG pulse sequence (O’Dell et al. Chem. Phys. Lett. 2008, 464, 97−102) is shown to be very useful for rapidly acquiring high signal-to-noise 137Ba SSNMR spectra. The breadths of the second-order quadrupolar-dominated spectra and experimental times are notably reduced for experiments conducted at 21.1 T. Analytical simulations of the 137Ba SSNMR spectra at both fields yield the quadrupolar parameters, and in select cases the barium chemical shift anisotropies (CSAs). Quadrupolar interactions dominate the 137Ba powder patterns, with quadrupolar coupling constants, CQ(137Ba), ranging from 7.0 to 28.8 MHz. The 137Ba electric field gradient (EFG) parameters extracted from these spectra are correlated to the local environments at the barium sites, via consideration of molecular symmetry and structure, and first principles calculations of 137Ba EFG tensors performed using CASTEP software. The rapidity with which 137Ba SSNMR spectra can be acquired using the WURST pulse sequence and/or at ultrahigh magnetic fields and the sensitivity of the 137Ba EFG tensor parameters to the changes in the barium environment suggest that 137Ba SSNMR has great potential for structural characterization of a variety of barium-containing materials.
Phys. Chem. Chem. Phys., 2010, vol. 12, Issue 18 and 19
Phys. Chem. Chem. Phys., 2010, 12, 4813 - 4820, DOI: 10.1039/b927449a
Full quadrupolar tensor determination by NMR using a micro-crystal spinning at the magic angle
Suresh Kumar Vasa, Ernst R. H. van Eck, J. W. G. Janssen and Arno P. M. Kentgens
An implementation of rotor-synchronised Magic Angle Spinning (MAS) NMR is presented to determine the quadrupolar coupling tensor values from a single crystal study for half-integer quadrupolar nuclei. Using a microcoil based probehead for studying micro crystals with superior sensitivity, we successfully determine the full quadrupolar tensor of 23Na using a micro crystal of dimensions 210 × 210 × 700 m of NaNO3 as a model system. A two step simulation procedure is used to obtain the orientation of the quadrupolar tensor information from the experimental spectra and is verified by XRD analysis.
Phys. Chem. Chem. Phys., 2010, 12, 5126 - 5139, DOI: 10.1039/b921383j
Understanding the NMR chemical shifts for 6-halopurines: role of structure, solvent and relativistic effects
Stanislav Standara, Kateina Maliáková, Radek Marek, Jaromír Marek, Michal Hocek, Juha Vaara and Michal Straka
A prototypical study of NMR chemical shifts in biologically relevant heteroaromatic compounds containing a heavy halogen atom is presented for two isomers of halogen-substituted purines. Complete sets of 1H-, 13C- and 15N-NMR chemical shifts are determined experimentally in solution. Experimental results are complemented by quantum-chemical calculations that provide understanding of the trends in the chemical shifts for the studied compounds and which show how different physical effects influence the NMR parameters. Chemical shifts for isolated molecules are calculated using density-functional theory methods, the role of solvent effects is studied using polarised continuum models, and relativistic corrections are calculated using the leading-order Breit–Pauli perturbation theory. Calculated values are compared with the experimental data and the effects of structure, solvent and relativity are discussed. Overall, we observe a good agreement of theory and experiment. We find out that relativistic effects cannot be neglected even in the chlorine species when aiming at high precision and a good agreement with the experimental data. Relativity plays a crucial role in the bromine and iodine species. Solvent effects are of smaller importance for 13C shifts but are shown to be substantial for particular 15N shifts. The test of method performance shows that the BLYP and B3LYP functionals provide the most reliable computational results after inclusion of the solvent and relativistic effects while BHandHLYP may—depending on atom in question—slightly improve but mostly deteriorate the data. Ab initio Hartree–Fock suffers from triplet instability in the Breit–Pauli relativistic part while MP2 provides no clear improvement over DFT in the nonrelativistic region. This work represents the first full application of the Breit–Pauli perturbation theory to an organic chemistry problem.
Full quadrupolar tensor determination by NMR using a micro-crystal spinning at the magic angle
Suresh Kumar Vasa, Ernst R. H. van Eck, J. W. G. Janssen and Arno P. M. Kentgens
An implementation of rotor-synchronised Magic Angle Spinning (MAS) NMR is presented to determine the quadrupolar coupling tensor values from a single crystal study for half-integer quadrupolar nuclei. Using a microcoil based probehead for studying micro crystals with superior sensitivity, we successfully determine the full quadrupolar tensor of 23Na using a micro crystal of dimensions 210 × 210 × 700 m of NaNO3 as a model system. A two step simulation procedure is used to obtain the orientation of the quadrupolar tensor information from the experimental spectra and is verified by XRD analysis.
Phys. Chem. Chem. Phys., 2010, 12, 5126 - 5139, DOI: 10.1039/b921383j
Understanding the NMR chemical shifts for 6-halopurines: role of structure, solvent and relativistic effects
Stanislav Standara, Kateina Maliáková, Radek Marek, Jaromír Marek, Michal Hocek, Juha Vaara and Michal Straka
A prototypical study of NMR chemical shifts in biologically relevant heteroaromatic compounds containing a heavy halogen atom is presented for two isomers of halogen-substituted purines. Complete sets of 1H-, 13C- and 15N-NMR chemical shifts are determined experimentally in solution. Experimental results are complemented by quantum-chemical calculations that provide understanding of the trends in the chemical shifts for the studied compounds and which show how different physical effects influence the NMR parameters. Chemical shifts for isolated molecules are calculated using density-functional theory methods, the role of solvent effects is studied using polarised continuum models, and relativistic corrections are calculated using the leading-order Breit–Pauli perturbation theory. Calculated values are compared with the experimental data and the effects of structure, solvent and relativity are discussed. Overall, we observe a good agreement of theory and experiment. We find out that relativistic effects cannot be neglected even in the chlorine species when aiming at high precision and a good agreement with the experimental data. Relativity plays a crucial role in the bromine and iodine species. Solvent effects are of smaller importance for 13C shifts but are shown to be substantial for particular 15N shifts. The test of method performance shows that the BLYP and B3LYP functionals provide the most reliable computational results after inclusion of the solvent and relativistic effects while BHandHLYP may—depending on atom in question—slightly improve but mostly deteriorate the data. Ab initio Hartree–Fock suffers from triplet instability in the Breit–Pauli relativistic part while MP2 provides no clear improvement over DFT in the nonrelativistic region. This work represents the first full application of the Breit–Pauli perturbation theory to an organic chemistry problem.
J. Phys. Chem. C., vol. 114, Issue 17
Solid-State 65Cu and 31P NMR Spectroscopy of Bis(triphenylphosphine) Copper Species
Bryan E. G. Lucier†, Joel A. Tang†, Robert W. Schurko*†, Graham A. Bowmaker‡, Peter C. Healy§ and John V. Hanna*
J. Phys. Chem. C, 2010, 114 (17), pp 7949–7962
DOI: 10.1021/jp907477m
Abstract: Frequency-stepped ultrawideline (UW) 65Cu solid-state NMR (SSNMR) experiments have been performed on a series of nine bis(triphenylphosphine) copper(I) species, with eight of these having an oxyanion-based ligand and one a borohydride ligand. These copper atoms reside in spherically asymmetric environments featuring two covalent Cu−P bonds and coordination from single bidentate ligands. The QCPMG pulse sequence was utilized in NMR experiments on all of the samples, along with the WURST-QCPMG sequence on select samples, to acquire UWNMR spectra of high quality. In all cases, large 65Cu quadrupolar coupling constants (CQ) between 40.8 and 51.7 MHz are observed, and are confirmed by NQR measurements. The immense quadrupolar interactions and their correspondingly large contributions to the central-transition powder patterns make accurate quantification of copper chemical shift anisotropy (CSA) difficult, though CSA effects are observed. 1H−31P CP/MAS NMR spectra reveal one-bond J-couplings, 1J(65/63Cu, 31P), for all complexes, as well as the presence of residual dipolar coupling, which enables determinations of both the sign of CQ and the orientation of the EFG tensor with respect to the Cu−P dipolar vector (both of which are unavailable from standard 65Cu SSNMR experiments). The 65Cu EFG parameters and 1J(65/63Cu, 31P) coupling constants are sensitive to the local geometry and bond lengths about the Cu center. Ab initio calculations are used to confirm experimentally predicted orientations of the Cu EFG tensors, to predict experimental CQ, ηQ, and CS tensor values, and to aid in identifying relationships between the copper NMR parameters and molecular structures. This combination of experimental and theoretical NMR data enables the correlation of symmetry and local structure with copper NMR parameters, further extending the applicability of copper SSNMR spectroscopy to a wide variety of copper-containing systems.
Bryan E. G. Lucier†, Joel A. Tang†, Robert W. Schurko*†, Graham A. Bowmaker‡, Peter C. Healy§ and John V. Hanna*
J. Phys. Chem. C, 2010, 114 (17), pp 7949–7962
DOI: 10.1021/jp907477m
Abstract: Frequency-stepped ultrawideline (UW) 65Cu solid-state NMR (SSNMR) experiments have been performed on a series of nine bis(triphenylphosphine) copper(I) species, with eight of these having an oxyanion-based ligand and one a borohydride ligand. These copper atoms reside in spherically asymmetric environments featuring two covalent Cu−P bonds and coordination from single bidentate ligands. The QCPMG pulse sequence was utilized in NMR experiments on all of the samples, along with the WURST-QCPMG sequence on select samples, to acquire UWNMR spectra of high quality. In all cases, large 65Cu quadrupolar coupling constants (CQ) between 40.8 and 51.7 MHz are observed, and are confirmed by NQR measurements. The immense quadrupolar interactions and their correspondingly large contributions to the central-transition powder patterns make accurate quantification of copper chemical shift anisotropy (CSA) difficult, though CSA effects are observed. 1H−31P CP/MAS NMR spectra reveal one-bond J-couplings, 1J(65/63Cu, 31P), for all complexes, as well as the presence of residual dipolar coupling, which enables determinations of both the sign of CQ and the orientation of the EFG tensor with respect to the Cu−P dipolar vector (both of which are unavailable from standard 65Cu SSNMR experiments). The 65Cu EFG parameters and 1J(65/63Cu, 31P) coupling constants are sensitive to the local geometry and bond lengths about the Cu center. Ab initio calculations are used to confirm experimentally predicted orientations of the Cu EFG tensors, to predict experimental CQ, ηQ, and CS tensor values, and to aid in identifying relationships between the copper NMR parameters and molecular structures. This combination of experimental and theoretical NMR data enables the correlation of symmetry and local structure with copper NMR parameters, further extending the applicability of copper SSNMR spectroscopy to a wide variety of copper-containing systems.
Organometallics, vol. 29, Issue 9
There is no solid-state NMR in this article, but, it is a very handy set of reference data.
NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist
Gregory R. Fulmer*†, Alexander J. M. Miller‡, Nathaniel H. Sherden‡, Hugo E. Gottlieb§, Abraham Nudelman§, Brian M. Stoltz‡, John E. Bercaw‡ and Karen I. Goldberg†
Organometallics, 2010, 29 (9), pp 2176–2179
DOI: 10.1021/om100106e
Abstract: Tables of 1H and 13C NMR chemical shifts have been compiled for common organic compounds often used as reagents or found as products or contaminants in deuterated organic solvents. Building upon the work of Gottlieb, Kotlyar, and Nudelman in the Journal of Organic Chemistry, signals for common impurities are now reported in additional NMR solvents (tetrahydrofuran-d8, toluene-d8, dichloromethane-d2, chlorobenzene-d5, and 2,2,2-trifluoroethanol-d3) which are frequently used in organometallic laboratories. Chemical shifts for other organics which are often used as reagents or internal standards or are found as products in organometallic chemistry are also reported for all the listed solvents.
NMR Chemical Shifts of Trace Impurities: Common Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist
Gregory R. Fulmer*†, Alexander J. M. Miller‡, Nathaniel H. Sherden‡, Hugo E. Gottlieb§, Abraham Nudelman§, Brian M. Stoltz‡, John E. Bercaw‡ and Karen I. Goldberg†
Organometallics, 2010, 29 (9), pp 2176–2179
DOI: 10.1021/om100106e
Abstract: Tables of 1H and 13C NMR chemical shifts have been compiled for common organic compounds often used as reagents or found as products or contaminants in deuterated organic solvents. Building upon the work of Gottlieb, Kotlyar, and Nudelman in the Journal of Organic Chemistry, signals for common impurities are now reported in additional NMR solvents (tetrahydrofuran-d8, toluene-d8, dichloromethane-d2, chlorobenzene-d5, and 2,2,2-trifluoroethanol-d3) which are frequently used in organometallic laboratories. Chemical shifts for other organics which are often used as reagents or internal standards or are found as products in organometallic chemistry are also reported for all the listed solvents.
Energy Fuels, 2010, 24 (4), pp 2536–2544
Structural Features of a Bituminous Coal and Their Changes during Low-Temperature Oxidation and Loss of Volatiles Investigated by Advanced Solid-State NMR Spectroscopy
J.-D. Mao, A. Schimmelmann, M. Mastalerz, P. G. Hatcher and Y. Li
Abstract
Quantitative and advanced 13C solid-state NMR techniques were employed to investigate (i) the chemical structure of a high volatile bituminous coal, as well as (ii) chemical structural changes of this coal after evacuation of adsorbed gases, (iii) during oxidative air exposure at room temperature, and (iv) after oxidative heating in air at 75 °C. The solid-state NMR techniques employed in this study included quantitative direct polarization/magic angle spinning (DP/MAS) at a high spinning speed of 14 kHz, cross polarization/total sideband suppression (CP/TOSS), dipolar dephasing, CH, CH2, and CHn selection, 13C chemical shift anisotropy (CSA) filtering, two-dimensional (2D) 1H−13C heteronuclear correlation NMR (HETCOR), and 2D HETCOR with 1H spin diffusion. With spectral editing techniques, we identified methyl CCH3, rigid and mobile methylene CCH2C, methine CCH, quaternary Cq, aromatic CH, aromatic carbons bonded to alkyls, small-sized condensed aromatic moieties, and aromatic C−O groups. With direct polarization combined with spectral-editing techniques, we quantified 11 different types of functional groups. 1H−13C 2D HETCOR NMR experiments indicated spatial proximity of aromatic and alkyl moieties in cross-linked structures. The proton spin diffusion experiments indicated that the magnetization was not equilibrated at a 1H spin diffusion time of 5 ms. Therefore, the heterogeneity in spatial distribution of different functional groups should be above 2 nm. Recoupled C−H long-range dipolar dephasing showed that the fraction of large charcoal-like clusters of polycondensed aromatic rings was relatively small. The exposure of this coal to atmospheric oxygen at room temperature for 6 months did not result in obvious chemical structural changes of the coal, whereas heating at 75 °C in air for 10 days led to oxidation of coal and generated some COO groups. Evacuation removed most volatiles and caused a significant reduction in aliphatic signals in its DP/MAS spectrum. DP/MAS, but not CP/MAS, allowed us to detect the changes during low-temperature oxidation and loss of volatiles. These results demonstrate the applicability of advanced solid-state NMR techniques in chemical characterization of coal.
J.-D. Mao, A. Schimmelmann, M. Mastalerz, P. G. Hatcher and Y. Li
Abstract
Quantitative and advanced 13C solid-state NMR techniques were employed to investigate (i) the chemical structure of a high volatile bituminous coal, as well as (ii) chemical structural changes of this coal after evacuation of adsorbed gases, (iii) during oxidative air exposure at room temperature, and (iv) after oxidative heating in air at 75 °C. The solid-state NMR techniques employed in this study included quantitative direct polarization/magic angle spinning (DP/MAS) at a high spinning speed of 14 kHz, cross polarization/total sideband suppression (CP/TOSS), dipolar dephasing, CH, CH2, and CHn selection, 13C chemical shift anisotropy (CSA) filtering, two-dimensional (2D) 1H−13C heteronuclear correlation NMR (HETCOR), and 2D HETCOR with 1H spin diffusion. With spectral editing techniques, we identified methyl CCH3, rigid and mobile methylene CCH2C, methine CCH, quaternary Cq, aromatic CH, aromatic carbons bonded to alkyls, small-sized condensed aromatic moieties, and aromatic C−O groups. With direct polarization combined with spectral-editing techniques, we quantified 11 different types of functional groups. 1H−13C 2D HETCOR NMR experiments indicated spatial proximity of aromatic and alkyl moieties in cross-linked structures. The proton spin diffusion experiments indicated that the magnetization was not equilibrated at a 1H spin diffusion time of 5 ms. Therefore, the heterogeneity in spatial distribution of different functional groups should be above 2 nm. Recoupled C−H long-range dipolar dephasing showed that the fraction of large charcoal-like clusters of polycondensed aromatic rings was relatively small. The exposure of this coal to atmospheric oxygen at room temperature for 6 months did not result in obvious chemical structural changes of the coal, whereas heating at 75 °C in air for 10 days led to oxidation of coal and generated some COO groups. Evacuation removed most volatiles and caused a significant reduction in aliphatic signals in its DP/MAS spectrum. DP/MAS, but not CP/MAS, allowed us to detect the changes during low-temperature oxidation and loss of volatiles. These results demonstrate the applicability of advanced solid-state NMR techniques in chemical characterization of coal.
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