D. Mustafi, W. Boisvert, M. W. Makinen
May 1, 1993
Citations
0
Influential Citations
8
Citations
Journal
Journal of the American Chemical Society
Abstract
Formic, propenoic, and pentadienoic acid derivatives of the nitroxyl spin-label 2,2,5,5-tetramethyl-1-oxypyrroline and their corresponding ethyl ester and aldehyde analogues have been synthesized and characterized by chemical methods. Because the π-bonding orbitals of the olefinic side chains are conjugated to the vinyl group of the oxypyrrolinyl ring, these spin-labeled derivatives are excellent spectrophotometic probes, exhibiting high molecular absorption extinction in the near ultraviolet. The molecular structures and conformations of these spin-labeled derivatives have been determined by electron nuclear double resonance (ENDOR) spectroscopy and molecular modeling. Conformational analysis based on torsion angle search calculations, constrained by ENDOR-determined electron-proton separations, showed that the polyene chain has an all planar, trans conformation. In the aldehydes the conformation of the C=O group with respect to the alkene chain is found to be s-trans, while in the acids and esters the -OH and -OC 2 H 5 groups were found to be s-trans, placing the C=O group in an s-cis conformation. The different conformations of the carbonyl group in these compounds are explained on the basis of resonance energy and dipolar interactions of the polyene side chain and the carbonyl or carboxyl group