Conformational analyses of hydrobenzo[c]phenanthridine alkaloids based on 1H relaxation times and nuclear Overhauser effects

1986 ◽  
pp. 175 ◽  
Author(s):  
Makiko Sugiura ◽  
Kinuko Iwasa ◽  
Narao Takao ◽  
Hideaki Fujiwara ◽  
Helmut Beierbeck ◽  
...  
Keyword(s):  
Relaxation Times ◽  
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%.

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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