Monday, March 31, 2008

Aaron's Journal Update

J. Phys. Chem. B, 111 (45), 12977 -12984, 2007. 10.1021/jp075840f S1520-6106(07)05840-3 Web Release Date: October 25, 2007
Thermal Degradation in a Trimodal Poly(dimethylsiloxane) Network Studied by 1H Multiple Quantum NMR
Jason R. Giuliani,
Erica L. Gjersing, Sarah C. Chinn, Ticora V. Jones, Thomas S. Wilson, Cynthia T. Alviso, Julie L. Herberg, Mark A. Pearson, and Robert S. Maxwell*
Abstract: Thermal degradation of a filled, cross-linked siloxane material synthesized from poly(dimethylsiloxane) chains of three different average molecular weights and with two different cross-linking species has been studied by 1H multiple quantum (MQ) NMR methods. Multiple domains of polymer chains were detected by MQ NMR exhibiting residual dipolar coupling (<>) values of 200 and 600 Hz, corresponding to chains with high average molecular weight between cross-links and chains with low average molecular weight between cross-links or near the multifunctional cross-linking sites. Characterization of the <> values and changes in <> distributions present in the material were studied as a function of time at 250 C and indicate significant time-dependent degradation. For the domains with low <>, a broadening in the distribution was observed with aging time. For the domain with high <>, increases in both the mean <> and the width in <> were observed with increasing aging time. Isothermal thermal gravimetric analysis reveals a 3% decrease in weight over 20 h of aging at 250 C. Degraded samples also were analyzed by traditional solid-state 1H NMR techniques, and off-gassing products were identified by solid-phase microextraction followed by gas chromatography-mass spectrometry. The results, which will be discussed here, suggest that thermal degradation proceeds by complex competition between oxidative chain scissioning and postcuring cross-linking that both contribute to embrittlement.

J. Phys. Chem. B, 111 (46), 13156 -13166, 2007. 10.1021/jp073968r S1520-6106(07)03968-5 Web Release Date: October 31, 2007
High-Pressure -Al(OH)3 and -AlOOH Phases and Isostructural Hydroxides/Oxyhydroxides: New Structural Insights from High-Resolution 1H and 27Al NMR
Xianyu Xue
* and Masami Kanzaki
Abstract: In order to shed light on the proton distributions and order/disorder in high-pressure -Al(OH)3 and -AlOOH phases, two-dimensional, high-resolution 1H CRAMPS (FSLG)-MAS NMR and 27Al 3QMAS NMR spectra have been obtained. For -Al(OH)3, the 1H CRAMPS-MAS NMR revealed two peaks with an intensity ratio close to 2:1. The 27Al MAS and 3QMAS NMR suggest a single Al site with a well-defined local structure. For -AlOOH, the 1H and 27Al NMR indicate the presence of a single H and Al site each. These results are consistent with crystal structures refined from X-ray diffraction. For comparison, 1H MAS and CRAMPS-MAS NMR spectra were also obtained for several other hydroxides/oxyhydroxides, including In(OH)3 and InOOH that have similar structures to -Al(OH)3 and -AlOOH, respectively. These data not only provide additional insights into the proton distributions in these important crystal structure classes but also together provide a better defined quantitative correlation between 1H chemical shift and hydrogen-bonding O···O distance.

J. Phys. Chem. B, 111 (47), 13353 -13356, 2007. 10.1021/jp077036z S1520-6106(07)07036-8 Web Release Date: November 7, 2007
Solid-State NMR Spectroscopy Reveals That Water Is Nonessential to the Core Structure of -Synuclein Fibrils
Kathryn D. Kloepper,
Kevin L. Hartman, Daniel T. Ladror, and Chad M. Rienstra*
Abstract: Protein aggregation is implicated in the etiology of numerous neurodegenerative diseases. An understanding of aggregation mechanisms is enhanced by atomic-resolution structural information, of which relatively little is currently available. Lewy bodies, the pathological hallmark of Parkinson's disease, contain large quantities of fibrillar -synuclein (AS). Here we present solid-state NMR spectroscopy studies of dried AS fibrils. The spectra have high resolution and sensitivity, and the site-resolved chemical shifts agree very well with those previously observed for hydrated fibrils. The conserved chemical shifts indicate that bulk water is nonessential to the fibril core structure. Moreover, the sample preparation procedure yields major improvements in spectral sensitivity, without compromising spectral resolution. This advance will greatly assist the atomic-resolution structural analysis of AS fibrils

J. Phys. Chem. B, 111 (51), 14362 -14369, 2007. 10.1021/jp075531p S1520-6106(07)05531-9 Web Release Date: December 4, 2007
Crystal Polymorphism of Protein GB1 Examined by Solid-State NMR Spectroscopy and X-ray Diffraction
Heather L. Frericks Schmidt,
Lindsay J. Sperling, Yi Gui Gao, Benjamin J. Wylie, John M. Boettcher, Scott R. Wilson, and Chad M. Rienstra*
Abstract: The study of micro- or nanocrystalline proteins by magic-angle spinning (MAS) solid-state NMR (SSNMR) gives atomic-resolution insight into structure in cases when single crystals cannot be obtained for diffraction studies. Subtle differences in the local chemical environment around the protein, including the characteristics of the cosolvent and the buffer, determine whether a protein will form single crystals. The impact of these small changes in formulation is also evident in the SSNMR spectra; however, the changes lead only to correspondingly subtle changes in the spectra. Here, we demonstrate that several formulations of GB1 microcrystals yield very high quality SSNMR spectra, although only a subset of conditions enable growth of single crystals. We have characterized these polymorphs by X-ray powder diffraction and assigned the SSNMR spectra. Assignments of the 13C and 15N SSNMR chemical shifts confirm that the backbone structure is conserved, indicative of a common protein fold, but side chain chemical shifts are changed on the surface of the protein, in a manner dependent upon crystal packing and electrostatic interactions with salt in the mother liquor. Our results demonstrate the ability of SSNMR to reveal minor structural differences among crystal polymorphs. This ability has potential practical utility for studying the formulation chemistry of industrial and therapeutic proteins, as well as for deriving fundamental insights into the phenomenon of single-crystal growth.

J. Phys. Chem. B, 112 (4), 1189 -1197, 2008. 10.1021/jp077714h S1520-6106(07)07714-0 Web Release Date: January 8, 2008
Quaternary Ammonium Room-Temperature Ionic Liquid Including an Oxygen Atom in Side Chain/Lithium Salt Binary Electrolytes: Ionic Conductivity and 1H, 7Li, and 19F NMR Studies on Diffusion Coefficients and Local Motions
Kikuko Hayamizu,
* Seiji Tsuzuki, Shiro Seki, Yasutaka Ohno, Hajime Miyashiro, and Yo Kobayashi
Abstract:A room-temperature ionic liquid (RTIL) of a quaternary ammonium cation having an ether chain, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)amide (DEME-TFSA), is a candidate for use as an electrolyte of lithium secondary batteries. In this study, the electrochemical ionic conductivity, , of the neat DEME-TFSA and DEME-TFSA-Li doped with five different concentrations of lithium salt (LiTFSA) was measured and correlated with NMR measurements of the diffusion coefficients D and the spin-lattice relaxation times T1 of the individual components DEME (1H), TFSA (19F), and lithium ion (7Li). The ion conduction of charged ions can be activated with less thermal energy than ion diffusion which contains a contribution from paired ions in DEME-TFSA. In the doped DEME-TFSA-Li samples, the and D values decreased with increasing salt concentration, and within the same sample generally DLi < DTFSA < DDEME except for the sample having the lowest salt concentration at low temperatures. Since plots of the temperature dependence of T1 of the 1H and 7Li resonances showed T1 minima, the correlation times c(H) and c(Li) were calculated for reorientational motions of DEME and the lithium jump, respectively. At the same temperature, c(Li) is longer than c(H), suggesting that the molecular motion of DEME occurs more rapidly than the lithium jump. Combining the DLi and c(Li), averaged distances for the lithium jump were estimated.

J. Phys. Chem. B, 112 (4), 1226 -1231, 2008. 10.1021/jp077396m S1520-6106(07)07396-8 Web Release Date: January 9, 2008
Probing the Porosity of Cocrystallized MCM-49/ZSM-35 Zeolites by Hyperpolarized 129Xe NMR
Yong Liu, Weiping Zhang,
* Sujuan Xie, Longya Xu, Xiuwen Han, and Xinhe Bao*
Abstract:One- and two-dimensional 129Xe NMR spectroscopy has been employed to study the porosity of cocrystallized MCM-49/ZSM-35 zeolites under the continuous flow of hyperpolarized xenon gas. It is found by variable-temperature experiments that Xe atoms can be adsorbed in different domains of MCM-49/ZSM-35 cocrystallized zeolites and the mechanically mixed counterparts. The exchange of Xe atoms in different types of pores is very fast at ambient temperatures. Even at very low temperature two-dimensional exchange spectra (EXSY) show that Xe atoms still undergo much faster exchange between MCM-49 and ZSM-35 analogues in the cocrystallized zeolites than in the mechanical mixture. This demonstrates that the MCM-49 and ZSM-35 analogues in cocrystallized zeolites may be stacked much closer than in the physical mixture, and some parts of intergrowth may be formed due to the partially similar basic structure of MCM-49 and ZSM-35.

J. Phys. Chem. B, 112 (4), 1267 -1274, 2008. 10.1021/jp075662q S1520-6106(07)05662-3 Web Release Date: January 5, 2008
NMR Chemical Shifts of the Rhodopsin Chromophore in the Dark State and in Bathorhodopsin: A Hybrid QM/MM Molecular Dynamics Study
Ute F. Röhrig
and Daniel Sebastiani*
Abstract: We investigate nuclear magnetic resonance (NMR) parameters of the rhodopsin chromophore in the dark state of the protein and in the early photointermediate bathorhodopsin via first-principles molecular dynamics simulations and NMR chemical shift calculations in a hybrid quantum/classical (QM/MM) framework. NMR parameters are particularly sensitive to structural properties and to the chemical environment, which allows us to address different questions about the retinal chromophore in situ. Our calculations show that both the 13C and the 1H NMR chemical shifts are rather insensitive to the protonation state of Glu181, an ionizable amino acid side chain located in the vicinity of the isomerizing 11-cis bond. Thus, other techniques should be better suited to establish its protonation state. The calculated chemical shifts for bathorhodopsin further support our previously published theoretical structure, which is in very good agreement with more recent X-ray data.

J. Phys. Chem. B, 112 (11), 3470 -3478, 2008. 10.1021/jp076073n S1520-6106(07)06073-7 Web Release Date: February 26, 2008
31P Chemical Shift Tensors for Canonical and Non-canonical Conformations of Nucleic Acids: A DFT Study and NMR Implications
Jana P ececht lov , Petr Padrta, Markéta L. Munzarov , and Vladimír Sklen
Abstract:31P chemical shift anisotropy (CSA) tensors have been calculated for a set of selected DNA and RNA backbone conformations using density functional theory. The set includes canonical A-RNA, A-DNA, BI-DNA, BII-DNA, ZI-DNA, and ZII-DNA as well as four A-RNA-type, seven non-A-RNA-type, and three non-canonical DNA conformations. Hexahydrated dimethyl phosphate has been employed as a model. The 31P chemical shift tensors obtained are discussed in terms of similarities in the behavior observed for gauche-gauche (gg) and gauche-trans (gt) conformations around the P-O bonds. We show that torsion angles and are major determinants of the isotropic chemical shift iso and of the component of the traceless chemical shift tensor, which is revealed in separate ranges of both iso and for gg- and gt-conformers, respectively. A clear distinction between the two conformation types has not been found for the and components, which is attributed to their different directional properties. The 31P CSA tensors exhibit considerable variations resulting in large spans of ~16 ppm for and ~22 ppm for and . We examine the consequences of the CSA variations for predicting the chemical shift changes upon partial alignment csa and for the values of CSA order parameters extracted from the analysis of 31P NMR relaxation data. The theoretical 31P CSA tensors as well as the experimental 31P CSA tensor of barium diethyl phosphate (BDEP) are used to calculate csa for two eclipsed orientations of the CSA and molecular alignment tensors. Percentage differences between the CSA order parameters obtained using the theoretical 31P CSA tensors and the experimental 31P CSA tensor of BDEP, respectively, are also determined.

J. Phys. Chem. B, 112 (6), 1586 -1593, 2008. 10.1021/jp073428u S1520-6106(07)03428-1 Web Release Date: January 23, 2008
15N and 13C High-Resolution Solid-State NMR Study of the Polymorphism of the L-Enantiomer of N-Benzoylphenylalanine
Sebastian Olejniczak,
Justyna Miku a-Pacholczyk, Colan E. Hughes, and Marek J. Potrzebowski*
Abstract:In this paper, several approaches which allow the investigation of mixtures of polymorphs, employing modern solid-state NMR (SS NMR) spectroscopy are reported. A convenient methodology for characterization of the hydrogen bonding and molecular conformation of a polymorphic sample by means of one-dimensional and two-dimensional, 13C and 15N NMR experiments as well as CSA tensor analysis and theoretical calculations is presented. Two-dimensional heteronuclear SS NMR allowed definition of the polymorphic domain of N-benzoyl-L-phenylalanine (N-Bz-Phe). The graphical method of Herzfeld and Berger was used to measure the 13C and 15N spinning sideband intensities which allowed the calculation of NMR parameters for labeled centers of N-Bz-Phe. The experimental data were compared with computed results obtained by means of the DFT hybrid method with B3PW91 functional and 6-311++G** basis set.

J. Phys. Chem. B, 112 (11), 3470 -3478, 2008. 10.1021/jp076073n S1520-6106(07)06073-7 Web Release Date: February 26, 2008
31P Chemical Shift Tensors for Canonical and Non-canonical Conformations of Nucleic Acids: A DFT Study and NMR Implications
Jana P ececht lov , Petr Padrta, Markéta L. Munzarov , and Vladimír Sklen
Abstract:31P chemical shift anisotropy (CSA) tensors have been calculated for a set of selected DNA and RNA backbone conformations using density functional theory. The set includes canonical A-RNA, A-DNA, BI-DNA, BII-DNA, ZI-DNA, and ZII-DNA as well as four A-RNA-type, seven non-A-RNA-type, and three non-canonical DNA conformations. Hexahydrated dimethyl phosphate has been employed as a model. The 31P chemical shift tensors obtained are discussed in terms of similarities in the behavior observed for gauche-gauche (gg) and gauche-trans (gt) conformations around the P-O bonds. We show that torsion angles and are major determinants of the isotropic chemical shift iso and of the component of the traceless chemical shift tensor, which is revealed in separate ranges of both iso and for gg- and gt-conformers, respectively. A clear distinction between the two conformation types has not been found for the and components, which is attributed to their different directional properties. The 31P CSA tensors exhibit considerable variations resulting in large spans of ~16 ppm for and ~22 ppm for and . We examine the consequences of the CSA variations for predicting the chemical shift changes upon partial alignment csa and for the values of CSA order parameters extracted from the analysis of 31P NMR relaxation data. The theoretical 31P CSA tensors as well as the experimental 31P CSA tensor of barium diethyl phosphate (BDEP) are used to calculate csa for two eclipsed orientations of the CSA and molecular alignment tensors. Percentage differences between the CSA order parameters obtained using the theoretical 31P CSA tensors and the experimental 31P CSA tensor of BDEP, respectively, are also determined.

J. Phys. Chem. C, 111 (45), 17146 -17154, 2007. 10.1021/jp070941z S1932-7447(07)00941-7 Web Release Date: October 18, 2007
Solid-State Characterization of the Nuclear and Electronic Environments in a Boron-Fluoride Co-doped TiO2 Visible-Light Photocatalyst
Enrique A. Reyes-Garcia, Yanping Sun, and Daniel Raftery*
Abstract:We describe the synthesis of a visible light absorbing boron-fluoride co-doped TiO2 photocatalyst by a sol-gel methodology and its structural characterization using magnetic resonance techniques. The formation of photoactive sites was induced by pyrolysis under anaerobic conditions at temperatures of 400 to 500 C, followed by a short exposure to air or oxygen gas and rapid cooling. 11B solid-state nuclear magnetic resonance analysis of B/F-TiO2 shows that the chemical environment of the photochemically active B/F co-doped TiO2 can be described as tetrahedrally coordinated BO4 units ( = -1.4 ppm). 19F NMR indicates that fluorine species form part of the Ti coordination sphere and are of the form TiO5F ( = -152 ppm). Similarly, X-ray photoelectron spectroscopy indicates that fluorine is found at lattice positions forming O-Ti-F fragments. Electron paramagnetic resonance spectroscopy, coupled to spectral simulation of the sample calcined at 485 C, shows that the radicals formed in this material are mainly located on two distinct Ti3+ species. The UV/vis characterization of B/F co-doped TiO2 shows the presence of intraband gap states likely responsible for its absorption of visible light (2.4 eV), while the indirect band gap transition remains unaltered (3.1 eV). The B/F co-doped TiO2 material shows good visible light photocatalytic activity for the photochemical oxidation of methylene blue.

J. Phys. Chem. C, 111 (47), 17564 -17569, 2007. 10.1021/jp074511k S1932-7447(07)04511-6 Web Release Date: November 7, 2007
27Al, 47,49Ti, 31P, and 13C MAS NMR Study of VX, GD, and HD Reactions with Nanosize Al2O3, Conventional Al2O3 and TiO2, and Aluminum and Titanium Metal
Abstract: Reactions of VX, GD, and HD with Al2O3, TiO2 (anatase and rutile), aluminum, and titanium metal powders have been studied by 27Al, 47,49Ti, 31P, and 13C MAS NMR. VX, GD, and HD hydrolyze on both nanosize and conventional Al2O3. A significant droplet size effect on the reaction kinetics is observed. For VX and GD, 27Al and 31P MAS NMR detect the formation of aluminum phosphonate complexes. Similarly, GD hydrolysis on TiO2 yields titanium phosphonate species as detected by 31P MAS NMR. Attempts at obtaining 47,49Ti NMR spectra of these species and those of titanium phosphonate model compounds at 14 T were marginally successful. 47,49Ti NMR spectra were obtainable for anatase and titanium metal; thus, severe second-order quadrupolar linebroadening is suspected for the titanium phosphonate complexes. 47,49Ti NMR spectra obtained for anatase at high magnetic field (17.5 and 21 T) showed anticipated improvement in peak width and resolution. GD reacted with aluminum and titanium powder in the presence of water results in acid-dissolution of the metals and the formation of their respective metal phosphonates

J. Phys. Chem. C, 111 (49), 18279 -18287, 2007. 10.1021/jp077089g S1932-7447(07)07089-6 Web Release Date: November 9, 2007
Study of the Structure of OH Groups on MgO by 1D and 2D 1H MAS NMR Combined with DFT Cluster Calculations
Céline Chizallet,
* Guylène Costentin, Hélène Lauron-Pernot, Michel Che, Christian Bonhomme, Jocelyne Maquet, Françoise Delbecq, and Philippe Sautet
Abstract: Complex 1H MAS NMR spectra of hydroxylated MgO powders have been assigned by combining DFT embedded cluster calculations and experiments using single pulse, Hahn-echo, and 2D NOESY like sequences. Chemical shifts calculations suggest the qualitative classification of protons into three main categories, characterized by different chemical shifts ranges. The highest chemical shifts ( H > -0.7 ppm) are proposed to be characteristic of hydrogen-bond donor OH groups (threefold O3C-H, fourfold O4C-H, and fivefold O5C-H localized on corners, edges, and in valleys respectively). The lowest chemical shifts ( H < -0.7 ppm) are associated to isolated and hydrogen-bond acceptor twofold O2C-H and onefold O1C-H, whereas the central signal at H = -0.7 ppm would correspond to isolated O3C-H and O4C-H on kinks and divacancies. These assignments can be refined by considering dipolar interactions between vicinal protons observed thanks to the NOESY like sequence. It is thus shown that some hydrogen bond donor OH groups are characterized by a lower chemical shift than expected from calculations and also contribute to the central signal. Calculated thermal stabilities and chemical shifts suggest that these protons correspond to O4C-H on monatomic steps. The final assignment is fully consistent with previous experimental results on CD3OH adsorption and quantitative analysis of the evolution of spectra with temperature. This study illustrates the synergism between experiments and theory, by comparison with the results obtained by either one.

J. Phys. Chem. C, 111 (50), 18615 -18623, 2007. 10.1021/jp076410s S1932-7447(07)06410-2 Web Release Date: November 29, 2007 Copyright © 2007 American Chemical Society
Solid-State NMR Studies of the Formation of Monomers and Dimers in Stearic Acid Confined in Titanate Nanotubes
Xiao-Ping Tang,
* Gregory Mogilevsky, Harsha Kulkarni, and Yue Wu
Abstract: This work employs two-dimensional solid-state NMR methods to uncover the structure and molecular arrangement of physically trapped stearic acid (SA) inside a titanate nanotube (TiNT). Thermal annealing the mixture of SA and the water-washed TiNT is shown to induce slow physical trapping of SA into the TiNT. In contrast to that the solid-state bulk exhibits only one carbonyl 13C peak of NMR and consists solely of dimer, the physically trapped SA exhibits two carbonyl 13C peaks with different chemical shifts that are assigned respectively to dimer and monomer both by the 13C homonuclear double-quantum measurement and by the 13C chemical-shift-tensor measurement. The trapped SA monomer and dimer are shown to grow simultaneously during thermal annealing with a constant number ratio between them at ~1:1. The 13C homonuclear double-quantum and the 1H-13C HETCOR spectra indicate that the trapped SA monomer and dimer do not form separated clusters but are neighbors to each other. As such, the trapped SA in the TiNT undertakes a novel molecular arrangement alternating with dimer and monomer. The carbonyl 13C chemical-shift-tensor data and the hydroxyl 1H isotropic-chemical-shift data suggest that the hydrogen bond of the dimer is stronger under nanoconfinement than in the solid bulk SA. The observed novel molecular arrangement for the fatty acid and the correlated variation of the carbonyl 13C and the hydroxyl 1H chemical shift between the different molecular arrangements are of theoretical interest.

J. Phys. Chem. C, 111 (50), 18744 -18750, 2007. 10.1021/jp0759527 S1932-7447(07)05952-3 Web Release Date: November 28, 2007
Kinetic Features of the Platinum Catalyzed Hydrolysis of Sodium Borohydride from 11B NMR Measurements
G. Guella,
* B. Patton, and A. Miotello
Abstract:A full kinetic analysis of the platinum catalyzed hydrolysis of sodium borohydride (NaBH4) in alkaline media has been performed using 11B NMR (nuclear magnetic resonance) spectroscopy with a Pt/C 5 wt % commercial powder as catalyst. By fitting the NMR data by least-square regression techniques, the rate constants of platinum catalyzed borohydride hydrolysis have been evaluated. Within the investigated [borohydride]/[catalyst] molar ratio of 200-1500, the rate law has been found to be of first-order in catalyst and zero order in borohydride. Whereas no reagent-isotope kinetic effect is observed in the NaBD4/H2O reaction system, the hydrolysis of NaBH4 in deuterated water shows a significant solvent-kinetic isotope effect. In both cases, however, 11B NMR analysis indicates that the main reaction product is the tetrahydroxyborate species (D)nH4-nBO4- (n = 1, 2, 3, 4) followed by a minor amount of the partially scrambled BH3D- species while the hydrolysis-intermediates HnB(OD)4-n- (n = 1, 2, 3) species are not detectable during all the reaction time. These results suggest that, differently from the Pd catalyzed/borohydride(borodeuteride) hydrolytic process, the hydrogen/deuterium exchange is slower than hydrolysis and that the rate-determining step of the overall process is the formation of the monohydroxy-borohydride intermediate BH3OH-. The activation energy of the overall process has been also evaluated by 11B NMR rate measurements taken at different temperatures.
J. Phys. Chem. C, 112 (1), 80 -88, 2008. 10.1021/jp7095955 S1932-7447(70)09595-X Web Release Date: December 13, 2007
Solid-State NMR Investigation of the Possible Existence of "Nanoblocks" in the Clear Solution Synthesis of MFI Materials
Colin A. Fyfe,
* Richard J. Darton, Celine Schneider, and Franziska Scheffler
Abstract: The structure of the intermediate species in the clear solution synthesis of the MFI framework (zeolite ZSM 5) has been investigated using the characteristic 13C, 14N, 15N, and 2D spectra of the tetrapropylammonium (TPA) template ions as probes as well as the 29Si spectra of the silicate species present in samples that can be isolated by centrifugation. Comparison with the corresponding spectra of the final products that can be characterized by X-ray diffraction indicates that there is no evidence for the involvement of nanospecies, as has been proposed, and that crystallization is most probably from an amorphous gel. This conclusion is supported by the lack of deuterium rotational echo double-resonance dephasing of the 29Si spectra by deuterated TPA of the earliest intermediate species obtained, while it is clearly observed in the final product. These observations indicate that any TPA ions present in the gel phase are not in intimate contact with the silicon nuclei as they would be if in the local MFI environment. This is supported by the very low amount of TPA found by 14N NMR, which is much less than needed for the proposed nano intermediates and the fact that the TPA present can be removed by simple re-suspension in water and recovery.

J. Phys. Chem. C, 112 (2), 500 -513, 2008. 10.1021/jp074816z S1932-7447(07)04816-9
Solid-State NMR Determination of the Zeolite ZSM-5/ortho-Xylene Host-Guest Crystal Structure
Colin A. Fyfe
* and J. S. Joseph Lee
Abstract: Solid-state NMR spectroscopy has been used to successfully determine the complete three-dimensional structure of the ortho-xylene-ZSM-5 zeolite complex, using complexes of three different specifically deuterated ortho-xylene molecules. The structures determined from these, at two different temperatures, using both cross polarization (CP) and CP drain experiments all agree. The ortho-xylene molecule is located at the channel intersection with one ring carbon-methyl carbon bond oriented along the straight channel while the other ring carbon-methyl carbon bond points toward the zigzag channel.

J. Phys. Chem. C, 112 (3), 860 -866, 2008. 10.1021/jp075130+ S1932-7447(07)05130-8
Probing the Local Environments of Fluorine in Ce-Based Fluorite-Type Oxyfluorides with 19F MAS NMR Spectroscopy

Laetitia Sronek,
Jérôme Lhoste, Manuel Gaudon, Christophe Legein, Jean-Yves Buzaré, Monique Body, Guillaume Crinière, Alain Tressaud, Stanislav Pechev, and Alain Demourgues*
Abstract:Ce-based oxyfluorides Ce1-xCaxO2-x-y/2Fy, with 0.13 x 0.29 and 0.03 y 0.24, adopting the fluorite structure, were prepared by coprecipitation in basic fluorinated medium followed by an annealing under air at T = 600 C. XRD profile and Rietveld analyses allowed the determination of the crystallite sizes as well as the unit cell parameters. In this series, fluorine atoms are in tetrahedral environments of cations. 19F magic angle spinning (MAS) NMR spectroscopy was used to study the local structure and fluoride ion environments. Four distinct 19F resonances were observed and assigned to four different types of environments, FCa4, FCa3Ce, FCa2Ce2, and FCaCe3, whose proportions vary with the calcium content. In these Ce-Ca oxyfluorides, F- anions have a great affinity for Ca2+ cations leading to an increase of the F amount with the Ca content. The absence of FCe4 environment is explained from a steric standpoint: the F-Ce bond lengths in the network are too short to accept fluorine ions in the vicinity of four Ce4+ cations. Finally, the increase of the average Ce-X (X = O, F) bond ionicity with the Ca and F contents was correlated to the evolution of the UV shielding properties of these new compounds, which exhibit outstanding UV absorption and scattering (in the visible range) properties.

J. Phys. Chem. C, 112 (4), 1081 -1089, 2008. 10.1021/jp076679b S1932-7447(07)06679-4 Web Release Date: January 5, 2008
Periodic DFT and High-Resolution Magic-Angle-Spinning (HR-MAS) 1H NMR Investigation of the Active Surfaces of MgCl2-Supported Ziegler-Natta Catalysts. The MgCl2 Matrix
Vincenzo Busico,
* Mauro Causà, Roberta Cipullo, Raffaele Credendino, Francesco Cutillo, Nic Friederichs, Raffaele Lamanna, Annalaura Segre, and Valeria Van Axel Castelli #
Abstract: "Classical" MgCl2-supported Ziegler-Natta catalysts (ZNCs) continue to dominate the industrial production of isotactic polypropylene. There is a growing awareness of the inherent competitive edge of these low-cost systems over single-center (primarily metallocene) catalysts and of the potential for further improvement, particularly if deeper insight into the structure of the catalytic surfaces and the mechanisms of their modification by means of electron donors can be achieved. In the framework of a project ultimately aiming at the implementation of ZNCs with known and controlled surface structures, we are revisiting this whole area by using a combination of advanced computational (periodic DFT) and spectroscopic (high-resolution magic-angle-spinning 1H NMR spectroscopy) tools. In this article, we report on the neat MgCl2 matrix and on model MgCl2/electron-donor adducts. The results indicate that the (104) surface, with five-coordinate Mg cations, is the dominant lateral termination in well-formed large crystals, as well as in highly activated MgCl2 samples prepared by ball-milling. In the latter case, a minor fraction of surface Mg sites with a higher extent of coordinative unsaturation [e.g., four-coordinate Mg cations on (110) edges and/or at crystal corners or other defective locations] also appear to be present. RMe2Si(OMe) (R = octadecyl) binds to both types of Mg sites, albeit with different strengths resulting in different mobilities. The less-electron-donating RMeSi(OMe)2, in contrast, binds to the more unsaturated Mg sites only. The approach described herein is currently being extended to MgCl2/TiCln systems, as well as to their adducts with internal and external donors of different natures, strengths, and steric demands.

J. Phys. Chem. C, 112 (6), 2215 -2221, 2008. 10.1021/jp077254s S1932-7447(07)07254-8 Web Release Date: January 23, 2008
6Li{31P} Rotational-Echo, Double-Resonance Studies of Lithium Ion Site Dynamics in Li3V2(PO4)3
L. S. Cahill,
C. W. Kirby, and G. R. Goward*
Abstract: Low-temperature 6Li{31P} rotational-echo, double-resonance (REDOR) measurements were used to study lithium mobility within each of the three Li sites in monoclinic Li3V2(PO4)3. Each of the Li ions was found to experience a different reduced dipolar coupling with the nearest 31P nucleus. Under fast magic-angle spinning (MAS) conditions (40 kHz), the three crystallographic 31P sites in Li3V2(PO4)3 were resolved. On the basis of the known Li-P internuclear distances, the 31P resonances were assigned by determining the degree of signal attenuation at each phosphorus site. The attenuation of the Li-P dipolar coupling, compared to simulations of the static case, was associated with rattling of the Li ions within the lattice. The relative mobility at each Li site is correlated with structural properties including the shortest Li-O contact within the void and bond valence calculations.

J. Phys. Chem. C, 112 (8), 2997 -3007, 2008. 10.1021/jp077687v S1932-7447(07)07687-X Web Release Date: February 6, 2008
Acidic Properties of SSZ-33 and SSZ-35 Novel Zeolites: a Complex Infrared and MAS NMR Study
Barbara Gil,
Stacey I. Zones, Son-Jong Hwang, Martina Bejblov , and Ji í ejka*
Abstract:Two novel zeolites SSZ-33 and SSZ-35 were investigated with respect to their acidic properties using different probe molecules to characterize the accessibility and acid strength of Lewis and Br nsted acid sites. Ammonia, pyridine, pivalonitrile, and acetonitrile-d3 were used as probe molecules, and the results were correlated with 27Al and 1H magic angle spinning (MAS) NMR. Both SSZ-33 and SSZ-35 zeolites were found to possess bridging Si-OH-Al groups of virtually uniform and high acid strength. For both SSZ-33 and SSZ-35, there is the typical presence of highly disturbed OH groups (IR band around 3500 cm-1), which amounts to almost half of the overall Br nsted acidity. It was found that almost all bridging Si-OH-Al groups in SSZ-33 are located in the 12-MR rings. Both acetonitrile-d3 and pyridine sorptions suggest the presence of two types of Lewis sites in SSZ-35, differing in acid strength and electron-acceptor properties, whereas in the SSZ-33 zeolite only one type is present. The relative strength of these sites is higher than that of the Br nsted type for SSZ-35 and is of comparable strength for SSZ-33. 1H and 27Al MAS NMR measurements during thermal treatment allowed the assignment of NMR peaks to different surface OH species and the establishment of their relation to IR bands. NMR spectroscopy enabled the quantitative analysis of both free and hydrogen-bonded OH groups separately, showing that for both zeolites the amount of disturbed sites is higher than the number of free OH groups.

J. Phys. Chem. C, 112 (8), 3042 -3048, 2008. 10.1021/jp076637n S1932-7447(07)06637-X Web Release Date: February 5, 2008
NMR Study of the Chemisorption and Surface Chemistry of Methylamine on Pd/SiO2
Henrik von Schenck,
Neil Kumar, Christopher A. Klug,* and John H. Sinfelt
Abstract: Results of an investigation of the interaction of methylamine with a Pd/SiO2 catalyst utilizing nuclear magnetic resonance (NMR) spectroscopy are presented. Two sets of experiments were conducted. In one set, a sample of catalyst was initially exposed to 13CH315NH2 at 77 K and then subjected to a lengthy equilibration period at 190 K. A 13C spectrum at 77 K obtained on the sample at this point exhibited a single symmetric line at a frequency very close to the resonance frequency for methylamine in the absence of the catalyst. The line is attributed to methylamine adsorbed without dissociation. In 13C spectra obtained at 77 K on the sample after each of a series of subsequent annealing periods at successively higher temperatures in the range 253-298 K, the line exhibited a gradual broadening on the downfield side. Deconvolution of the spectra resolved the original symmetric line from a very broad downfield line attributed to partially dehydrogenated surface species designated by the formula (CN)Hx. In the second set of experiments, 13CH315NH2 was adsorbed on a sample of catalyst at 298 K. The sample was then annealed at successively higher temperatures in the range 325-450 K. Deconvolution of the 13C spectra obtained at 298 K after the various annealing periods revealed extensive formation of dimethylamine, reaching a maximum after the annealing period at 400 K. Ammonia and methane were first detected in the 15N and 13C spectra, respectively, after the annealing period at 375 K. During the annealing periods at 425 and 450 K, the dimethylamine decomposed almost completely, leaving only methane, ammonia, and residual surface species.

J. Phys. Chem. C, 112 (9), 3164 -3169, 2008. 10.1021/jp710894t S1932-7447(71)00894-X Web Release Date: February 13, 2008
NMR Confirmation for Formation of [B12H12]2- Complexes during Hydrogen Desorption from Metal Borohydrides
Son-Jong Hwang,
* Robert C. Bowman, Jr. Joseph W. Reiter, Job Rijssenbeek, Grigorii L. Soloveichik, Ji-Cheng Zhao, Houria Kabbour, and Channing C. Ahn
Abstract: 11B NMR spectroscopy has been employed to identify the reaction intermediates and products formed in the amorphous phase during the thermal hydrogen desorption of metal tetrahydroborates (borohydrides) LiBH4, Mg(BH4)2, LiSc(BH4)4, and the mixed Ca(AlH4)2-LiBH4 system. The 11B magic angle spinning (MAS) and cross polarization magic angle spinning (CPMAS) spectral features of the amorphous intermediate species closely coincide with those of a model compound, closo-borane K2B12H12 that contains the [B12H12]2- anion. The presence of [B12H12]2- in the partially decomposed borohydrides was further confirmed by high-resolution solution 11B and 1H NMR spectra after dissolution of the intermediate desorption powders in water. The formation of the closo-borane structure is observed as a major intermediate species in all of the metal borohydride systems we have examined.

J. Phys. Chem. C, 112 (13), 5221 -5231, 2008. 10.1021/jp710336h S1932-7447(71)00336-4 Web Release Date: March 8, 2008
Investigations of the Phase Transition and Proton Dynamics in Rubidium Methane Phosphonate Studied by Solid-State NMR
M. Vijayakumar, Jason W. Traer, James F. Britten, and Gillian R. Goward
Abstract:In search of new solid acid proton conductors, we prepared the solid acid rubidium methane phosphonate (RMP). These crystals have a monoclinic structure (P2/c; a = 9.3452, b = 9.3142, and c = 7.5021 Å; = 101.12). The salt incorporates a hydrated lamellar structure. The 1H MAS NMR reveals two different types of acidic protons as well as the water protons in the lamella. The 1H VT MAS NMR of RMP·2H2O single crystal shows a structural phase transition around 320 K, and the high-temperature phase exhibits significant proton dynamics. The proton proximities are established by solid state 1H DQF NMR. The dehydration of RMP crystal leads to structural collapse, and the resultant RMP powder is extremely hygroscopic. The proton environment and dynamics are examined using 1H DQF NMR, which reveals that the dehydrated RMP powder has rigid lattice, in contrast with the hydrated form. Further the 1H VT MAS NMR shows that dehydrated RMP powder has no phase transition, and no significant proton dynamics are observed in the temperature range of 250-350 K. The new hydrated crystal, RMP·2H2O, shows high proton mobility at relatively low temperature (~330 K) and a proton transport mechanism that uniquely relies on crystalline water.

Macromolecules, 40 (24), 8673 -8683, 2007. 10.1021/ma071541c S0024-9297(07)01541-0 Web Release Date: November 1, 2007
Multinuclear Solid-State NMR Characterization, Ion Dissociation, and Dynamic Properties of Lithium-Doped Organic-Inorganic Hybrid Electrolytes Based on Ureasils
Hsien-Ming Kao,
* Tzu-Ti Hung, and George T. K. Fey
Abstract: Solid organic-inorganic hybrid electrolytes based on diureasils doped with LiClO4 have been obtained by the sol-gel process through the reaction of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (H2N-PPG-PEG-PPG-NH2) with 3-isocyanatepropyltriethoxysilane (ICPTES), followed by co-condensation of an epoxy trialkoxysilane, 3-(glycidyloxypropyl)trimethoxylsilane (GLYMO). The structural and dynamic properties of the materials were systematically investigated by a variety of techniques including ac impedance, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), multinuclear (13C, 29Si, 7Li) solid-state NMR, 1H-13C 2D WISE (wide-line separation) NMR, and 7Li pulsed gradient spin-echo (PGSE) NMR measurements. The length of backbone PEG chain, the extent of GLYMO cross-linking, and the salt concentration were varied in order to obtain the materials with high conductivities. A maximum ionic conductivity value of 1.37 × 10-5 S/cm was obtained at 30 C for the hybrid electrolyte with a [O]/[Li] ratio of 32. This ionic conductivity value is 1 order of magnitude higher than that of previously characterized electrolytes based on ureasils without incorporation of GLYMO. The results of 13C cross-polarization magic-angle spinning (CPMAS) NMR with varying contact times and 1H-13C WISE NMR provided a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. Only one distinct 7Li local environment was detected by variable temperature 7Li-{1H} MAS NMR. The temperature dependence of 7Li static line widths and self-diffusion coefficients showed that there is a strong correlation between the dynamic properties of the charge carriers and the bulk ionic conductivity.

Macromolecules, 41 (2), 372 -386, 2008. 10.1021/ma702140g S0024-9297(70)02140-X Web Release Date: December 18, 2007
Epoxy Networks Reinforced with Polyhedral Oligomeric Silsesquioxanes: Structure and Segmental Dynamics as Studied by Solid-State NMR
Jiri Brus,
* Martina Urbanov , and Adam Strachota
Abstract: The epoxy networks based on poly(propylene oxide) chains cross-linked by diglycidyl ether of Bisphenol A and reinforced by polyhedral oligomeric silsesquioxanes (POSS) provide a typical example of polymer nanocomposites with hierarchical architecture. In addition to characterizing the epoxy-POSS composites, this contribution demonstrates valuable applications of solid-state NMR spectroscopy. The size of domains in the nanocomposites was determined by high-speed MAS 1H-
1H spin-diffusion experiments, offering an alternative to the established methods like SAXS, EM, or AFM. While the latter might fail under certain circumstances (low contrast, or small domains), the 1H-1H spin-diffusion measurement yielded the size of unbroken primary domains, making also possible their distinction from "aggregates of primary domains", the size of the latter being measured by EM or SAXS. Depending on the type of the investigated network the size of the POSS aggregates arising in the nanocomposites was determined to be ca. 1-20 nm. Investigations of molecular dynamics (various "domain-selective" relaxation and recoupling solid-state NMR experiments were applied) yielded information making possible the assignment of the contribution of molecular segments to thermomechanical properties like glass transition temperature and storage shear modulus, and to predict the products' ability to absorb mechanical energy. Remarkable motional heterogeneities were found not only in the amorphous phase, where mobile polymer segments of the "free" domains coexist with the immobilized chains of the "constrained" ones, but also in the crystallites of POSS building blocks, where the amplitudes of segmental reorientations occurring in the midkilohertz frequency region remain relatively large: two-site 180 flips dominating to aromatic rings in the POSSPh crystallites are accompanied by the wobbling of the flip axes with an average fluctuation angle ca. 25 . Similarly, cyclopentyl substituents in the POSSCp crystallites undergo to ca. 35 rotational-diffusion motion.

Macromolecules, 41 (2), 387 -389, 2008. 10.1021/ma702089e S0024-9297(70)02089-2 Web Release Date: December 22, 2007
Chain Structure of Substituted Stilbene-Maleic Anhydride Alternating Copolymer Probed by Solid-State NMR
Min Mao, Chul Kim, Sungsool Wi,
* and S. Richard Turner*
Abstract: Double-quantum heteronuclear local field solid-state NMR spectroscopy (2Q-HLF solid-state NMR) has been employed to investigate the chain structure of N,N,N',N'-tetraethyl-4, 4'-diaminostilbene (TDAS) and 13C labeled maleic anhydride (MA) alternating copolymer. The torsional angle of the H-13C-13C-H part of the anhydride ring was found to be 0 , indicating an all cis configuration of the H-13C-13C-H moiety of the anhydride ring. After hydrolysis of the anhydride groups and protonation of the amino groups, the torsional angle of the H-13C-13C-H moiety of the hydrolyzed anhydride groups appears to be 60 , indicating significant rotation of the polymer backbone. Because of the predominately cis configuration of the H-13C-13C-H part of the anhydride ring, the diethylamino phenyl groups are concentrated on the two sides of the backbone plane and the anhydride groups are in the backbone plane.

Organometallics, 26 (27), 6718–6725 10.1021/om7008638
A Polystyrene-Supported Tin Trichloride Catalyst with a C11-Spacer. Catalysis Monitoring Using High-Resolution Magic Angle Spinning NMR
Vanja Pinoie,
Kevin Poelmans, Hans E. Miltner, Ingrid Verbruggen, Monique Biesemans,* Guy Van Assche, Bruno Van Mele, José C. Martins,§ and Rudolph Willem
Abstract: The cross-linked polystyrene grafted organotin [P-H](1−t)[P-(CH2)11-SnCl3]t, in which [P-H] represents the monomeric unit of the nonfunctionalized polymer and t is the functionalization degree, has been synthesized and characterized by 1D and 2D 1H, 13C, and 119Sn high-resolution magic angle spinning (HRMAS) NMR spectroscopy, elemental analysis, and IR spectrometry. Its catalytic activity was assessed in the transesterification model reaction between ethyl acetate and n-octanol. The catalyst displays an average conversion degree of 76% after 2 h and can be recycled at least nine times. The experimental concentration profiles were fitted to a mechanistic model, from which a turnover frequency in the range of 10−2 s−1 was calculated. Residual tin contents on the order of 5 ppm in the reaction products were assessed by inductively coupled plasma/atomic emission spectroscopy (ICP/AES). The combined use of 1H, 13C, and 119Sn HRMAS NMR and modulated DSC enables one to assess the chemical integrity of the catalyst upon recycling. Detailed analysis of 119Sn HRMAS NMR spectra under various chemical conditions mimicking the reaction mixtures allows gaining a better insight into the catalysis mechanism.

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