The Calculation of Correlation Time (τ) forT1Spin–Lattice andT2Spin–Spin Relaxation Times in Agar Solutions

13C spin-lattice and spin–spin relaxation times and nuclear Overhauser enhancements have been used to examine the molecular dynamics of the α- (1) and β- (2) anomeric forms of poly(acrylamide-co-allyl 2-acetamido-2-deoxy-D-glucopyranoside) glycopolymers. The timescale of motions and the spatial restriction of these motions were determined by using various forms of the "model-free" approach. It is shown that the motions of the C—H vectors of the polymer backbone may be described by a scaled Lorentzian spectral density function, giving rise to an effective correlation time for overall tumbling. The temperature dependence of this correlation time suggests that the overall motion is dependent on viscosity. The overall motion of the polymer molecules is shown to be anisotropic in nature by including the spin–spin relaxation data in the analysis. The N-acetyl methyl and sugar hydroxymethyl (C6) groups exhibit internal motions. The activation energies associated with these internal motions are derived. The difference in relaxation rates between the α and β anomeric forms, though small, suggests that the motions of the sugar ring may be different for the two systems. This conclusion is supported by potential energy contour map calculations, which indicate that the β anomer (2) has almost twice the conformational flexibility of the α anomer (1).

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Theory of spin relaxation in the limit of slow motion. Nuclear and electron spin relaxation in paramagnetic transition-metal complexes

Australian Journal of Chemistry ◽

10.1071/ch9761869 ◽

1976 ◽

Vol 29 (9) ◽

pp. 1869 ◽

Cited By ~ 16

Author(s):

DT Pegg ◽

DM Doddrell

Keyword(s):

Spin Relaxation ◽

Electron Spin ◽

Correlation Time ◽

Initial Density ◽

Relaxation Times ◽

Proton Spin ◽

Time Limit ◽

Zero Field ◽

Zero Field Splitting ◽

Electron Spin Relaxation

A theory of spin relaxation is developed which can be applied to cases where the Redfield limit (T2 � tt) does not hold. A simplification over the conventional approach is achieved by working entirely in a reference frame in which the initial density matrix is diagonal. This allows the general relaxation equations to be written in a simple analytic form without the need for perturbation theory. In the short correlation time limit this general form reduces to the usual Redfield equations for the relaxation times. In the long correlation time limit a corresponding result can be obtained, but is dependent on the assumed ensemble distribution. Electron spin relaxation by modulation of the quadratic zero-field splitting for S = 3/2 is treated explicitly. The theory is used to analyse proton spin relaxation in some halogenobis(N,N-diethyl-dithiocarbamato)iron(111) complexes.

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The solution conformation of prostacyclin as determined by high field proton magnetic resonance techniques

Canadian Journal of Chemistry ◽

10.1139/v80-154 ◽

1980 ◽

Vol 58 (10) ◽

pp. 974-983 ◽

Cited By ~ 9

Author(s):

George Kotovych ◽

Gerdy H. M. Aarts ◽

Tom T. Nakashima ◽

Glen Bigam

Keyword(s):

Magnetic Resonance ◽

Correlation Time ◽

Proton Magnetic Resonance ◽

Double Resonance ◽

Relaxation Times ◽

Segmental Motion ◽

Solution Conformation ◽

Nmr Spectrum ◽

H Nmr ◽

The Difference

The proton magnetic resonance (1H nmr) spectrum at 400 MHz of prostacyclin at pH 10.4 in glycine buffer has been completely analyzed utilizing homonuclear double resonance, inversion recovery, and difference nOe experiments. The spectral analysis shows that the two protons at C-4 are non-equivalent even though they are removed from the asymmetric centres at C-8 and C-9 by five bonds. The difference nOe measurements verify the configuration at C-5.Proton longitudinal relaxation times (T1) were measured at 400 and 200 MHz. From the T1 frequency dependence, effective rotational correlation times ranging from 2.3 × 10−10 to 3.0 × 10−10 s were calculated for H-5, H-9, H-11, and H-15. This indicates that the portion of the molecule encompassed by these protons has a longer correlation time than is observed for the C-2 and the C-17 to C-19 protons, for which the average correlation time is 1.2 × 10−10 s. Hence the aliphatic side chains have more segmental motion.

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