Valinomycin Crystal Structure Determination by Direct Methods

Abstract

The conformation of an uncomplexed form of the antibiotic valinomycin (C(54)N(6)O(18)H(90)) has been determined by direct methods including a novel technique for strong enantiomorph discrimination via the calculation and systematic analysis of cosine invariants of a special type. The intramolecular hydrogen bonding scheme and the isopropyl group stereochemistry of uncomplexed valinomycin are compatible with interpretations of spectral measurements for the complexed and uncomplexed molecule in solution but are different from any previously proposed structure. The simple conformational change of a hydrogen bond shift, which could be induced by the process of potassium ion complexing, transforms the uncomplexed into the complexed structure.

Raman spectroscopic study of the valinomycin-KSCN complex

“…"free" and intramolecularly H-bonded ester C=O groups (1767 cm-l and 1742 -1, respectively). This interpretation is consistent with the X-ray structure izcribed by Duax et al (1972) (Fig. l(b)).…”

“…The structure of uncomplexed valinomycin crystals (monoclinic, space group P21) grown from warm n-octane has been determined by X-ray diffraction (Duax et al, 1972). Unique to this conformation is the presence of intramolecularly hydrogen-bonded ester C=O groups (Fig.…”

Second febs—ferdinand springer lecture membrane active complexones. chemistry and biological function

“…4) despite recrystallization of the X-ray specimen from isooctane, i.e. from a solution where form A is predominant [7,8]. The structure observed has a pseudo symmetry center.…”

NMR evidence of a valinomycin–proton complex

“…Some of the aliphatic carbon signals 2,4,8,12 are shifted downfield, too. At the same time, most of the methyl signals change their positions.…”

“…[1][2][3][4] The ability of valinomycin to carry ions is primarily due to the formation of a molecular complex. As revealed in particular for the K þ complex by NMR, [5][6][7][8][9][10][11] infrared spectra, 5-9 X-ray diffraction, [12][13][14][15] and other techniques (see reference 16 and references therein), the complex formation requires a change in the conformation of the depsipeptide ring, after which the six peptide units fortify a bracelet-like form of the molecule by intramolecular hydrogen bonds and the six carbonyls of the carboxylic ester groups adopt a hexadentate formation binding the metal cation by a polycentric dipolar bond. The change is more dramatic in polar media, in which valinomycin has a propeller-like conformation 16 due to intermolecular hydrogen bonds with the solvent.…”