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13 C‐ and 1 H‐nmr studies of cis ‐ trans conformers of oligoprolines
Author(s) -
Chao YenYau H.,
Bersohn R.
Publication year - 1978
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1978.360171202
Subject(s) - chemistry , conformational isomerism , dimer , intramolecular force , oligomer , cis–trans isomerism , stereochemistry , nuclear magnetic resonance spectroscopy , aqueous solution , proline , crystallography , molecule , amino acid , polymer chemistry , organic chemistry , biochemistry
Abstract In aqueous solutions, 13 C‐ and 1 H‐nmr studies show that the percentage of trans conformation of proline oligomers + H 2 H Pro‐(Pro) n ‐CO − 2increases substantially from n = 1 (65% trans ) to n = 2 (90% trans ). The relatively low percentage of trans structure for the dimer ( n = 1) very likely is caused by the extra stability acquired by the end‐to‐end intramolecular H‐bonding of the cis dimer. As n increase from 2 to 3 (or 5) in + H 2 N‐Pro‐(Pro) n ‐CO − 2 , the percentage of trans conformation stays more or less constant (∼0.9). A high salt concentration (4 M CaCl 2 ) causes a conformation randomization, so that the short‐chain oligomer ( n = 1, 3, 5) and the long‐chain poly ( L ‐proline) all show about the same frantion of trans conformation (0.7‐0.8).