Determination Of Cross-relaxation Rates Research Articles

H NOESY NMR on Adsorbed Molecules

First 1H NOESY NMR investigations on adsorbed molecules are presented. Experiments have been carried out on allyl alcohol adsorbed on NaX zeolite with a loading of approximately four molecules per supercage. By application of magic angle spinning (MAS) on the sealed samples, all five magnetically inequivalent protons could be resolved spectroscopically. 1H MAS NMR spectra in the temperature range from 260 to 420 K are reported. Cross peak and diagonal peak intensities of 2D NOESY spectra at room temperature for different mixing times have been measured. Subsequently the matrix of cross relaxation rates has been obtained by a single least mean square deviation fit to all 2D peak intensities. Errors in the determination of cross relaxation rates are discussed. Selected cross relaxation rates could be interpreted by isotropic reorientation of the allyl group with a correlation time τc = (6.1 ± 0.4) × 10-9 s at a temperature of 300 K.

Heteronuclear Overhauser effect measurements in surfactant systems. IV. Direct and remote correlations within alkyl chains

This paper deals with the complete interpretation of the heteronuclear Overhauser effect spectroscopy (HOESY) two dimensional nuclear magnetic resonance (NMR) experiment. This experiment aims at the determination of cross relaxation rates (having their origin in dipolar interactions) between two different nuclear species, here proton and carbon-13. Extra correlation peaks observed in the 2D map of the system under investigation (micellized sodium octanoate) are shown to arise from remote dipolar interactions and not from strong (J) coupling effects. Several experiments have been performed at different mixing times (during which the nuclear Overhauser effect builds up), allowing the observation of the whole carbon-13 magnetization evolution. Their analysis yields cross-relaxation rates, refined with respect to those derived from initial behavior. However, this requires inclusion of the effect of spin diffusion, within the proton spin system, in the data treatment. A novel approach is proposed which models the multiexponential character by means of effective proton relaxation parameters. All the results of this study are consistent with data obtained by other methods [nuclear Overhauser effect (NOE) factor determinations and frequency dependent longitudinal 13C relaxation times).

Determination of cross relaxation rates by 3D NOE-NOE spectroscopy

A method for quantitative determination of cross-relaxation rates of macromolecules in solution is developed. The method is based on the analysis of the intensities of cross peaks in 3D NOE-NOE spectra. The linear combination of the intensities of 3D peaks (spin-diffusion peaks, back-transfer peaks) results in an expression directly proportional to the cross-relaxation rate. The proposed approach allows to determine interproton distances in macromolecules more accurately.