Deuterium-substitution effects on relaxation times and interligand nuclear Overhauser effects for assignment of ligand resonances and isomer identification in cobalt(III) complexes

1985 ◽  
Vol 24 (8) ◽  
pp. 1269-1271 ◽  
Author(s):  
Carlyle B. Storm ◽  
A. H. Turner ◽  
N. S. Rowan
Keyword(s):  
Relaxation Times ◽  
Substitution Effects ◽  
Deuterium Substitution ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Relaxation Processes in the N-Methyl Group of 1,2,2,6,6-Pentamethylpiperidine

1990 ◽  
Vol 43 (2) ◽  
pp. 447 ◽  
Author(s):  
ID Rae ◽  
ML Woolcock
Keyword(s):  
Relaxation Times ◽  
Spin Rotation ◽  
Relaxation Processes ◽  
Methyl Group ◽  
Methyl Methyl ◽  
Overhauser Effect ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Relaxation times (T1) and methyl-methyl nuclear Overhauser effects were measured for 1H, 13C and 2H nuclei in 1,2,2,6,6-pentamethylpiperidine and its N-CHD2 analogue which was synthesized by LiAlD4 reduction of the N-CHO compound. The relaxation pathways for hydrogens of the N-CH3 group were estimated to be as follows: spin-rotation 0.046 s-1, dipole-dipole within N-methyl 0.069 s-1, and dipole-dipole with the hydrogens of the C- methyls 0.027 s-1. The 1H{1H) Overhauser effect at the N-CH3 was 7.6%.

1H–1H internuclear distance measurements in carbohydrates: proton transient nuclear Overhauser enhancement and spin-lattice relaxation in (13C)- and (2H)-substituted compounds

1990 ◽  
Vol 68 (12) ◽  
pp. 2171-2182 ◽  
Author(s):  
Paul C. Kline ◽  
Anthony S. Serianni ◽  
Shaw-Guang Huang ◽  
Michael Hayes ◽  
Robert Barker
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Lattice Relaxation ◽  
Substitution Effects ◽  
Distance Measurements ◽  
Spin Lattice ◽  
Nuclear Overhauser Enhancement ◽  
Nuclear Overhauser

Proton transient nuclear Overhauser enhancement (TnOe) and spin-lattice relaxation times (T1) have been used to evaluate the conformations of several monosaccharides and disaccharides containing (13C) and (2H) substitution. Absolute 1H–1H internuclear distances were determined by TnOe and DESERT (deuterium substitution effects on relaxation times) experiments on conformationally rigid methyl β-D-galactopyranoside and α- and β-D-xyloses, respectively. The DESERT method was extended to examine O-glycoside conformation in two blood-group disaccharides that were prepared enzymically with (13C) and (or) (2H) substitution. Preferred disaccharide conformations deduced from these distance measurements are compared to those determined from 13C–13C and 13C–1H spin coupling constants, theoretical calculations, and crystallographic studies. Keywords: TnOe, DESERT, carbohydrate conformation.

scholarly journals Studies of the conformation of bilirubin and its dimethyl ester in dimethyl sulphoxide solutions by nuclear magnetic resonance

1982 ◽  
Vol 201 (3) ◽  
pp. 605-613 ◽  
Author(s):  
D Kaplan ◽  
G Navon
Keyword(s):  
Hydrogen Bonding ◽  
Chemical Shifts ◽  
Dimethyl Ester ◽  
Relaxation Times ◽  
Dimethyl Sulphoxide ◽  
13C Relaxation Times ◽  
Solvent Molecules ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
13C Relaxation

The conformation of bilirubin and its dimethyl ester in dimethyl sulphoxide (DMSO) was investigated by n.m.r. spectroscopy. The chemical shifts of the pyrrole NH and Lactam protons of bilirubin and its dimethyl ester in DMSO indicate a strong interaction with the solvent. Inter-proton distances were calculated from nuclear Overhauser effects (NOE), selective and non-selective relaxation times (T1) and rotational correlation times taken from 13C relaxation times. The interproton distances indicate that the conformation of the skeleton of bilirubin and its dimethyl ester in DMSO is similar to that of bilirubin and mesobilirubin in the crystalline state and in chloroform solutions, except for a possible slight twist of the pyrrolenone rings about the methine bonds, which may be a consequence of solvation of the NH groups by DMSO. Unlike in chloroform solutions, no direct hydrogen-bonding occurs between the carboxylic acid and the lactam groups of bilirubin in DMSO, as shown by the absence of an NOE between these groups. The fast exchange of the pyrrole NH protons with 2H shows that no hydrogen-bonding occurs between these protons and the propionic residues, in line with their solvation by DMSO. From the above results, and from the slowness of the internal motion of the propionic residues of bilirubin and its dimethyl ester, it is concluded that these residues are tied to the skeleton via bound solvent molecules.

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