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Stoichiometry of interaction between soluble (—)‐dopa melanin and enantiomers of ephedrine by NMR spectroscopy
Author(s) -
SalazarBookaman M.M.,
Fowble J.W.,
Patil P.N.
Publication year - 1992
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.530040704
Subject(s) - chemistry , ephedrine , enantiomer , dissociation (chemistry) , stoichiometry , dissociation constant , indole test , autoxidation , stereochemistry , molecule , stereoselectivity , melanin , spectroscopy , nuclear magnetic resonance spectroscopy , organic chemistry , catalysis , biochemistry , neuroscience , biology , physics , receptor , quantum mechanics
Synthetic soluble (—)‐dopa melanin was prepared in deuteriated buffer, pH 8, by autooxidation of the precursor. At 6 m M of the precursor, the incorporation was over 90%. The changes in the line width measurements of N‐CH 3 protons of enantiomers of ephedrine in the soluble melanin were quantified by NMR spectroscopy. The dissociation constants of (—)‐1R,2S‐ephedrine, (+)‐1S,2R‐ephedrine, (—)‐1R,2R‐ψ‐ephedrine, and (+)‐1S,2S‐ψ‐ephedrine were 11.7, 4.20, 3.60, and 4.80 m M , respectively. Since the concentration of (—)‐dopa was known and since the conversion of (—)‐dopa to indole units of melanin was considered as 1:1, the stoichiometry of the interaction between the drug and the indole unit was calculated. Based on the dissociation constants of the enantiomers, it appears that up to four molecules of (—)‐ephedrine can interact with one indole unit of the melanin, while such a ratio for other isomers appear to be 2:1. The preference by indole units of melanin is stereoselective. © 1992 Wiley‐Liss, Inc.