The stereochemistry and dynamics of natural products and biopolymers from proton relaxation spectroscopy: Spin-label delineation of inner and outer protons of gramicidin S including hydrogen bonds

Since each conformational moiety of a natural product, polymer, or biopolymer has specific exposed and shielded protons, the parameter is proposed as a criterion for distinguishing conformational moieties; S1p is defined as the enhancement of spin-lattice relaxation rates, R1, per mole of added paramagnetic free radical. The specific effect of Tempo on all protons, NH, Hα, and side chain, of gramicidin S is reported here; the data semiquantitatively reflect proton-nitroxide distances and are consistent with random approach of these two solutes in Me2SO-d6 under the concentration used. Extension to other peptides, floppy peptides, and organic natural products, as well as accurate correlations with theory, is now underway. © 1982, American Chemical Society. All rights reserved.