Fourier transform infrared and circular dichroism spectroscopic studies ofhydrogen bonding in micacocidin A and micacocidin in dilute CH2Cl2 or CHCl3 solution

FTIR spectra of micacocidin A (I), which is a Zn complex antibiotic, the me tal-free ligand micacocidin (II), its derivatives and their related compoun ds were measured in dilute CH2Cl2 solution in order to elucidate the confor mations of I and II in solution, Curve analysis of the spectra to separate overlapping absorption bands showed that I forms dimers due to two strong i ntermolecular hydrogen bonds between a hydroxy group and the phenolate anio n and II exists in a folded conformation with three rings formed by intramo lecular hydrogen bonds between phenolic, aliphatic and carboxylic OH groups and the N atoms of thiazoline, another thiazoline and thiazolidine, respec tively. The concentration and temperature dependencies of CD spectra of I w ere measured in CHCl3 and CH3OH solutions and CH3CN solution, respectively, in order to confirm the formation of the dimers of I in these solvents. Th e variation of the CD band by addition of ZnCl2 to II was also measured in CH3OH solution, II was shown to be more easily transformed to I by Zn2+ ion in the solution. (C) 2000 Elsevier Science B.V. All rights reserved.