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Theory and application of fully anisotropic overall molecular tumbling, with restricted group internal rotation: 13 C NMR relaxation studies of sodium taurocholate and ginsenoside‐Re
Author(s) -
Wang Dehua,
Xu Xiaolong,
Deng Nianyong,
Pen Lianqang,
Zhang Wenbin,
Stark Ruth E.
Publication year - 1995
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260330505
Subject(s) - chemistry , methyl group , anisotropy , internal rotation , relaxation (psychology) , rotation (mathematics) , ginsenoside , molecular dynamics , rotational diffusion , isotropy , stereochemistry , nuclear magnetic resonance , computational chemistry , group (periodic table) , molecule , crystallography , organic chemistry , geometry , physics , quantum mechanics , mechanical engineering , psychology , social psychology , mathematics , engineering , medicine , alternative medicine , pathology , ginseng
A theory is presented for fully anisotropic overall molecular tumbling with restricted group internal rotation. This formalism is used with 13 C NMR relaxation data and results from molecular mechanics to compute the rotational diffusion rates and methyl group internal rotation rates for sodium taurocholate and ginsenoside‐Re in organic solvents. Although existing theories for steroid derivatives describe methyl internal rotation in terms of free isotropic motion, methyl rotation in ginsenoside‐Re is found to be both sluggish and spatially restricted. The energetic barrier to methyl internal rotation increases significantly with the bulkiness of flexible side‐chains in a series of steroid natural products.