J. Am. Chem. Soc., ASAP Article 10.1021/ja073170l S0002-7863(07)03170-8 Web Release Date: October 6, 2007 Copyright © 2007 American Chemical Society
Internuclear 31P-51V Distance Measurements in Polyoxoanionic Solids Using Rotational Echo Adiabatic Passage Double Resonance NMR Spectroscopy
Wenlin Huang, Alexander J. Vega,* Terry Gullion, and Tatyana Polenova*
We report the first results establishing rotational echo adiabatic passage double resonance (REAPDOR) experiments for distance measurements between a spin-1/2 (31P) and spin-7/2 (51V) pair in a series of vanadium-substituted polyoxoanionic solids from the Keggin and Wells-Dawson families. We have quantitatively measured 31P-51V distances in monovanadium substituted K4PVW11O40, 1-K7P2VW17O62, and 4-K7P2VW17O62. Numerical simulations of the experimental data yield very good agreement with the averaged P-W/P-V distances determined from the X-ray diffraction measurements in the same or related compounds. REAPDOR is therefore a very sensitive P-V distance probe anticipated to be especially useful in the absence of long-range order. Our results suggest that REAPDOR spectroscopy could be broadly applicable for interatomic distance measurements in other spin-7/2-spin-1/2 nuclear pairs.
J. Am. Chem. Soc., ASAP Article 10.1021/ja074428a S0002-7863(07)04428-9 Web Release Date: October 9, 2007 Copyright © 2007 American Chemical Society
17O and 29Si NMR Parameters of MgSiO3 Phases from High-Resolution Solid-State NMR Spectroscopy and First-Principles Calculations
Sharon E. Ashbrook,* Andrew J. Berry, Daniel J. Frost, Alan Gregorovic, Chris J. Pickard, Jennifer E.
The 29Si and 17O NMR parameters of six polymorphs of MgSiO3 were determined through a combination of high-resolution solid-state NMR and first-principles gauge including projector augmented wave (GIPAW) formalism calculations using periodic boundary conditions. MgSiO3 is an important component of the Earth's mantle that undergoes structural changes as a function of pressure and temperature. For the lower pressure polymorphs (ortho-, clino-, and protoenstatite), all oxygen species in the 17O high-resolution triple-quantum magic angle spinning (MAS) NMR spectra were resolved and assigned. These assignments differ from those tentatively suggested in previous work on the basis of empirical experimental correlations. The higher pressure polymorphs of MgSiO3 (majorite, akimotoite, and perovskite) are stabilized at pressures corresponding to the Earth's transition zone and lower mantle, with perovskite being the major constituent at depths >660 km. We present the first 17O NMR data for these materials and confirm previous 29Si work in the literature. The use of high-resolution multiple-quantum MAS (MQMAS) and satellite-transition MAS (STMAS) experiments allows us to resolve distinct oxygen species, and full assignments are suggested. The six polymorphs exhibit a wide variety of structure types, providing an ideal opportunity to consider the variation of NMR parameters (both shielding and quadrupolar) with local structure, including changes in coordination number, local geometry (bond distances and angles), and bonding. For example, we find that, although there is a general correlation of increasing 17O chemical shift with increasing Si-O bond length, the shift observed also depends upon the exact coordination environment.
J. Am. Chem. Soc., ASAP Article 10.1021/ja075272h S0002-7863(07)05272-9 Web Release Date: October 9, 2007 Copyright © 2007 American Chemical Society
Conformational Preferences of Chondroitin Sulfate Oligomers Using Partially Oriented NMR Spectroscopy of 13C-Labeled Acetyl Groups
Fei Yu, Jeremy J. Wolff, I. Jonathan Amster, and James H. Prestegard*
A new method is presented for the retrieval of information on the conformation of glycosaminoglycan oligomers in solution. The method relies on the replacement of acetyl groups in isolated native oligomers with 13C labeled acetyl groups and the extraction of orientational constraints from residual dipolar couplings (RDCs) and chemical shift anisotropy (CSA) offsets observed in NMR spectra of partially oriented samples. A novel method for assignment of resonances based on the correlation of resonance intensities with isotope ratios determined from mass spectrometric analysis is also presented. The combined methods are used in conjunction with more traditional NMR structural data to determine the solution structure of a pentasaccharide, GalNAc6S(1-4)GlcA(1-3)GalNAc4S(1-4)GlcA(1-3)GalNAc4S-ol, derived by enzymatic hydrolysis of chondroitin sulfate. The geometry derived is compared to that for similar molecules that have been reported in the literature, and prospects for use of the new types of data in the study of protein-bound oligosaccharides are discussed.
J. Am. Chem. Soc., ASAP Article 10.1021/ja075768z S0002-7863(07)05768-X Web Release Date: October 10, 2007 Copyright © 2007 American Chemical Society
Hyperpolarized 89Y Offers the Potential of Direct Imaging of Metal Ions in Biological Systems by Magnetic Resonance
Matthew E. Merritt, Crystal Harrison, Zoltan Kovacs, Preeti Kshirsagar, Craig R. Malloy, and A. Dean Sherry*
Hyperpolarization of 89YCl3 and three 89Y-complexes was achieved by dynamic nuclear polarization of aqueous samples. The long T1s of 89Y make its application as an NMR imaging probe extremely promising. In addition, the wide chemical shift range for various chelates of 89Y means that agents sensitive to their biological/chemical milieu could serve as exquisite sensors of important biological events.