Solution conformation of valinomycin-potassium ion complex.

The complete conformation of the valinomycin-potassium ion complex in methanol is presented. Extension from the reported secondary structure requires arguments and data relating to ester orientation, direction of coiling, side-chain orientation, and conformational stability. Conformation of the valinomycin-potassium ion complex provides a clear-cut example in which elucidation of conformation is sufficient to gain an understanding of molecular function which, in this case, is selective ion transport by a carrier mechanism.

Secondary structure of the cyclic moiety of the peptide hormone oxytocin and its deamino analog.

The secondary structure of the cyclic moiety of oxytocin and deamino-oxytocin has been determined by nuclear magnetic resonance spectroscopy (220 MHz). Oxytocin, in a dimethylsulfoxide-methanol mixture, contains a beta-turn involving the sequence -L-tyrosyl-L-isoleucyl-L-glutaminyl-L-asparaginyl-. Deamino-oxytocin, in addition to the beta-turn, contains a hydrogen bond involving the amide hydrogen of the tyrosine residue and the peptide carbonyl group of the asparagine residue, resulting in an antiparallel beta-type conformation for the ring component.

Differential scatter of left and right circularly polarized light by optically active particulate systems.

Because of the many heterogeneous systems which are of interest to the chemist and biochemist, the problems of distortions in circular dichroism patterns have been investigated. Specifically in this communication it is shown with a relatively well-characterized particular system (a suspension of alpha-helical poly-L-glutamic acid) that there is a measurable differential scatter of left and right circularly polarized light by suspensions of the optically active particles. This is a specific example of Perrin's assertion in 1942 (Perrin, F.

Approximation of rotational strengths from molar rotation data and generation of rotatory dispersion curves for d-camphor-10-sulfonate.

Starting with the expression for optical rotatory dispersion in the absorption region that was arrived at by Condon, two series were considered for the purpose of achieving the experimentally observed, steeper wavelength dependence in the absorption region while retaining the established 1/lambda(2) law in regions removed from absorption. The first two terms of one series in which the second term exhibits a 1/lambda(6) wavelength dependence were found to calculate satisfactorily the optical rotatory dispersion curve of d-camphor-10-sulfonate from 400 mmu to 190 mmu when only three bands were considered. Evaluated at the extrema, the two-term expression can be approximated by a simple equation which allows calculation of the rotational strength of a nonoverlapping band by using only the wavelength and molar rotation of the extrema and the index of refraction of the solution.