Dipolar contribution to NMR spin-lattice relaxation of protons

Abstract

Dipole-dipole interactions between protons in a glucopyranose derivative have been studied by means of the nuclear Overhauser effect and by spin-lattice relaxation experiments. The Overhauser enhancement measurements utilize a new pulse technique which permits the saturating field to have any specified spectral density function so that finite frequency bands in the NMR spectrum can be irradiated. By this method, the dipolar interactions between the various pairs of protons are evaluated. In contrast, the dipolar relaxation of a chosen proton by all other protons in the sample has been determined by comparing the inversion-recovery rates after selective and nonselective 180· pulses. The relaxation measurements indicate that the relaxation in this molecule is purely dipolar in origin. The Overhauser enhancement measurements of one proton are used to determine the contribution to its relaxation from two neighboring protons and, from these results, information about the geometry of the pyranose ring is evaluated.4466

13C and 1H NMR investigation of pilocarpine hydrochloride in water solution

“…As for the total 'H NMR data, reported in Table 2, it is apparent that the relaxation mechanism is dominated by the 'H-'H dipole-dipole interactions, as verified by the fact that the ratio, F, between nonselective and single-selective spinlattice relaxation rates (F = R,"""'/R,"') is found at F -1.5 for most protons (10). Lower F values for H2 and H5 are accounted for by dipolar interactions with nitrogens and those for H12a and H12b by imperfect selectivity of the excitation pulse.…”

“…Selective and double-selective 'H NMR spin-lattice relaxation rates were measured with inversion-recovery pulse sequences where the 180" inverting pulse was provided by a DANTE (8) or a double-DANTE pulse train (9). In either case the relaxation rate values were calculated from the initial slope of longitudinal magnetization recovery (10). "c-{'H) nuclear Overhauser effects (nOe) were measured with gated decoupling methods either in the noise-modulated or in the long-pulse mode to provide nonselective or selective presaturation, respectively (1 1).…”

Dynamic behaviour of oxidized glutathione in solution investigated by nuclear magnetic resonance

“…In general, the recovery of proton longitudinal magnetization after a 180" pulse is not a single exponential, due to the sum of different relaxation terms. To account for this, proton spin-lattice relaxations were calculated using the initial slope approximation, considering only the fist part of the recovery curves (25,26). A maximum experimental error of r 6 % was calculated for the relaxation measurements.…”

Nuclear magnetic resonance study of conformation and dynamics in solution of p-(o-propyloxybenzamido)benzoate diethyl(2-hydroxyethyl)methylammonium bromide: a smooth muscle relaxant agent

“…The 7r/2 pulse was, on the contrary, the usual non-selective ~/ 2 pulse given by the proton transmitter. The R, values were measured in the initial slope approximation (2).…”

“…l), which is the first in a series of synthesized drugs which show smooth muscle relaxing activity (1). The combined discussion of (1) 'H and I3C chemical shifts, (2) 'H and l3C spin-lattice relaxation rates, (3) 'H singleselective and double-selective spin-lattice relaxation rates, (4) nuclear Overhauser enhancement experiments, gave us the opportunity of measuring the I3C-'H and 'H-'H dipole-dipole interactions from which motional and structural features could be inferred. Namely, the dipolar interaction gives the function 7,/r6 and measuring 7, from dipolar contributions to 13C spinlattice relaxation rates from directly bonded protons allows the evaluation of interproton distances, provided 'H-'H dipoledipole mechanism-dominates relaxation.…”