Bernard Ancian

Description of natural abundance deuterium 2D-NMR experiments in weakly ordered liquid-crystalline solvents using a tailored cartesian spin-operator formalism

We report an appropriate cartesian spin-operator formalism which retains all physical insights and provides a pictorial representation for I=1 spin nuclei subjected to both a chemical shift and a small quadrupolar moment such as deuterons in liquid crystals with low order-parameters. Using a tree-like pictorial representation, this approach allows a straightforward description of natural abundance deuterium autocorrelation 2D-NMR experiments in weakly ordered solvents. As illustrative examples we study the 2D Q-COSY and Q-resolved NMR sequences which have been recently developed to facilitate the analysis of overcrowded proton-decoupled deuterium spectra in natural abundance of enantiomers oriented in liquid-crystalline solutions of poly-γ-benzyl-L-glutamate (PBLG). These 2D-NMR experiments allow the correlation between the two components of each quadrupolar doublet in the deuterium spectra to be obtained, and their assignment on the basis of chemical shifts. Several improvements of the basic sequences are proposed and discussed. Applications of these sequences in natural abundance deuterium NMR spectroscopy using a 9.4 T magnetic field and standard NMR equipment are examined.

Salicylate isomer-specific effect on the micellization of dodecyltrimethylammonium chloride: large effects from small changes.

Specific effects of the sodium salts of m- and p-hydroxybenzoates (m-HB and p-HB) on the aggregation process of dodecyltrimethylammonium chloride have been investigated by isothermal titration calorimetry, electrical conductivity, and (1)H NMR and compared with already reported data for the sodium salt of o-hydroxybenzoate (o-HB). For p-HB, it has been found that the aggregate is only formed by spherical micelles at all p-HB concentrations. On the other side, the situation is more complex for o-HB, where two distinct states of aggregation can be involved, depending on the concentration of o-HB. At high salt concentration, rodlike micelles are formed, whereas at lower concentration spherical aggregates are predominant. The transition from the cylinder to the sphere increases the mobility of the surfactant because the core of the rodlike micelles is more closely packed due to the expulsion of water from the interior of the aggregate. m-HB exhibits an intermediate behavior between these two extreme situations. The effect of the position of hydrophilic substituents on the aromatic ring on the insertion of the hydroxybenzoate anion in the micellar aggregate has been discussed.

2H nuclear magnetic relaxation study of the rotation of adamantane in n‐alkanes

Deuteron spin–lattice relaxation time has been measured for adamantane‐d1 in several n‐alkane solutions at variable temperature. It is found that solvent viscosity plays only a minor role in adamantane reorientation. This latter involves an activated Arrhenius process with a solvent‐independent activation energy (1.3 kcal/mole in the 183–423 °K temperature range). It follows that adamantane rotation is mainly governed by microscopic collisional motions rather than by collective hydrodynamic effects and can be pictured by the concept of transient solvent cavities in which the solvent molecule reorients.

NMR and CD studies of sulfur chirality center in Pd(II) complexes with S-benzyl-cysteine and glycyl-S-benzyl-L-cysteine

Abstract 1 H NMR and CD spectra have shown the creation of chirality centers on thioether sulfur atoms when bound to metal ions in Pd(II) complexes with S-benzyl-L-cysteine and glycyl-S-benzyl-L-cysteine. Two diastereomers are formed with R or S configuration on the sulfur. The 1 H NMR and CD spectra as well as the molecular model considerations were used to suggest the absolution configuration of the respective diastereomers in the series of Pd(II) complexes with S-methyl, S-ethyl and S-benzyl-L-cysteine derivatives. The S-substituent was also found to have a critical influence on the absolute configuration of sulfur atom in the studied complexes.

14N nuclear magnetic relaxation study of acetonitrile in carbon tetrachloride: An unexpected behavior at low concentration

An unexpected behavior at low concentration of the molecules liquid autonitrile in CCl4 is studied.(AIP)

Molecular interactions and reorientational motion of neat acetone in the liquid state. 17O NMR chemical shifts and linewidths at variable temperature

Abstract The structure and dynamics of neat liquid acetone have been studied in the 181–325 K temperature range by 17 O NMR. The chemical shift data are consistent with a monomer—dimer equilibrium; the standard enthalpy and entropy of association for the acetone dimer are −1.1 kcal/mol and −8.5 cal mol −1 K −1 , respectively. From the linewidth measurement, it seems that the dimer is only a short-lived electrostatic-collided complex which does not reorient as a whole: rotational motion of the oblate spheroid acetone is found to fit the hydrodynamic equation under “slip” boundary conditions.

Total Assignment of 1H and 13C NMR Chemical Shifts of a Natural Anthocyanidin, Apigeninidin, Using Two-Dimensional COLOC and HMBC Techniques

The 1H and 13C NMR spectra of apigeninidin chloride were assigned utilizing the two‐dimensional δC, δH correlation and COLOC and HBMC techniques. The full 13C NMR data are reported for the first time. A good correlation was found between 13C chemical shifts and carbon charge obtained by AM1 calculation.

Molecular reorientation of CCl4 and CS2 in alkanes: a 13C and 33S NMR relaxation study

Abstract Reorientational and angular momentum correlation times τ c and τ J for CCl 4 and CS 2 in alkanes have been derived from 13 C spin-spin relaxation times of CCl 4 and 33 S linewidths of CS 2 . In contrast with neat liquids, molecular reorientation does not obey J -diffusion, but tends towards M -diffusion in large solvents.

14N nuclear magnetic resonance study of the rotation of acetonitrile in n‐alkanes

14N linewidths have been measured for acetonitrile in several n‐alkane solutions at variable temperatures. Unlike previously reported results on adamantane in the same solvents, the correlation time for reorientation of the major axis of acetonitrile is linearly related to the solvent viscosity function η/T. The slope, i.e., Kivelson’s κ parameter, decreases as the size of the solvent increases. Moreover, unlike the activation for the reorientation of spherical adamantane which remains constant as the size of the solvent increases, that of acetonitrile increases.

Natural abundance 17O NMR as a tool for intermolecular interaction studies: acetone self-association

Abstract The nuclear magnetic resonance 17 O chemical shift and Iinewidth of acetone have been measured in several alkanes of various viscosities Chemical shift variation with concentration allows the determination of an acetone self-association equilibrium constant ( K c ≈ 0.09 xxx mole −1 ) Linewidth-vanation analysis cannot ascertain that the dimer reorients as a whole.