Monday, May 10, 2010

MRC - up to May 2010

Magnetic Resonance in Chemistry, ASAP

A comparison of experimental and DFT calculations of 195Pt NMR shielding trends for [PtXnY6-n]2- (X, Y = Cl, Br, F and I) anions
from Magnetic Resonance in Chemistry by Marga R. Burger, J. Kramer, H. Chermette, Klaus R. Koch

A comparison between experimental and calculated gas-phase as well as the conductor-like screening model DFT 195Pt chemical shifts of a series of octahedral [PtX6-nYn]2- complexes for X = Cl, Br, F, I was carried out to assess the accuracy of computed NMR shielding and to gain insight into the dominant [sigma]dia, [sigma]para and [sigma]SO shielding contributions. The discrepancies between the experimental and the DFT-calculated 195Pt chemical shifts vary for these complexes as a function of the coordinated halide ions, the largest being obtained for the fluorido-chlorido and fluorido-bromido complexes, while negligible discrepancies are found for the [PtCl6-nBrn]2- series; the discrepancies are somewhat larger where a significant deviation from the ideal octahedral symmetry such as for the geometric cis/trans or fac/mer isomers of [PtF6-nCln]2- and [PtF6-nBrn]2- may be expected. The discrepancies generally increase in the order [PtCl6-nBrn]2- < [PtBr6-nIn]2- < [PtCl6-nIn]2- < [PtF6-nBrn]2-[ap] [PtF6-nCln]2-, and show a striking correlation with the increase in electronegativity difference [Delta][chi] between the two halide ligands (X- and Y-) bound to Pt(IV) for these anions: 0.09

Digital Object Identifier (DOI)
10.1002/mrc.2607 About DOI


Magnetic Resonance in Chemistry
Volume 48 Issue 4, Pages 270 - 275
Published Online: 22 Feb 2010

Structural characterization of silver dialkylphosphite salts using solid-state 109Ag and 31P NMR spectroscopy, IR spectroscopy and DFT calculations
from Magnetic Resonance in Chemistry by Fu Chen, Roderick E. Wasylishen

High-resolution solid-state 109Ag and 31P NMR spectroscopy was used to investigate a series of silver dialkylphosphite salts, Ag(O)P(OR)2 (R = CH3, C2H5, C4H9 and C8H17), and determine whether they adopt keto, enol or dimer structures in the solid state. The silver chemical shift, CS, tensors and |J(109Ag, 31P)| values for these salts were determined using 109Ag ([Xi] = 4.652%) NMR spectroscopy. The magnitudes of J(109Ag, 31P) range from 1250 ± 10 to 1318 ± 10 Hz and are the largest reported so far. These values indicate that phosphorus is directly bonded to silver for all these salts and thus exclude the enol structure. All 31P NMR spectra exhibit splittings due to indirect spin-spin coupling to 107Ag (I = 1/2, NA = 51.8%) and 109Ag (I = 1/2, NA = 48.2%). The 1J(109Ag, 31P) values measured by both 109Ag and 31P NMR spectroscopy agree within experimental error. Analysis of 31P NMR spectra of stationary samples for these salts allowed the determination of the phosphorus CS tensors. The absence of characteristic P[double bond]O stretching absorption bands near 1250 cm-1 in the IR spectra for these salts exclude the simple keto tautomer. Thus, the combination of solid-state NMR and IR results indicate that these silver dialkylphosphite salts probably have a dimer structure. Values of silver and phosphorus CS tensors as well as 1J(109Ag, 31P) values for a dimer model calculated using the density functional theory (DFT) method are in agreement with the experimental observations.

Digital Object Identifier (DOI)

Magnetic Resonance in Chemistry
Volume 48 Issue 4, Pages 297 - 303
Published Online: 2 Mar 2010

Distribution and mobility of phosphates and sodium ions in cheese by solid-state 31P and double-quantum filtered 23Na NMR spectroscopy
from Magnetic Resonance in Chemistry by Mallory Gobet, Corinne Rondeau-Mouro, Solange Buchin, Jean-Luc Le Quéré, Elisabeth Guichard, Loïc Foucat, Céline Moreau

The feasibility of solid-state magic angle spinning (MAS) 31P nuclear magnetic resonance (NMR) spectroscopy and 23Na NMR spectroscopy to investigate both phosphates and Na+ ions distribution in semi-hard cheeses in a non-destructive way was studied. Two semi-hard cheeses of known composition were made with two different salt contents. 31P Single-pulse excitation and cross-polarization MAS experiments allowed, for the first time, the identification and quantification of soluble and insoluble phosphates in the cheeses. The presence of a relatively 'mobile' fraction of colloidal phosphates was evidenced. The detection by 23Na single-quantum NMR experiments of all the sodium ions in the cheeses was validated. The presence of a fraction of 'bound' sodium ions was evidenced by 23Na double-quantum filtered NMR experiments. We demonstrated that NMR is a suitable tool to investigate both phosphates and Na+ ions distributions in cheeses. The impact of the sodium content on the various phosphorus forms distribution was discussed and results demonstrated that NMR would be an important tool for the cheese industry for the processes controls. Copyright © 2010 John Wiley & Sons, Ltd.

NMR • 23Na • 31P • double-quantum filter • magic angle spinning • solid state • bound sodium ions • phosphate distribution • semi-hard cheese

Digital Object Identifier (DOI)
10.1002/mrc.2576 About DOI

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