Polypeptides. IV. The Molecular Weight, Configuration and Association of Poly-γ-benzyl-L-glutamate in Various Solvents

Abstract

The molecular association of polypeptides in many solvents has heretofore prevented the molecular characterization of these substances. It is shown here that there are two classes of solvents in which poly-7-benzyl-L-glutamates are not associated. In one group (dimethylformamide, cresol, chloroform-fonnamide) the intrinsic viscosities were found to be the same for a given sample and to increase very strongly with molecular weight. In the other group (dichloroacetic acid) the dependence of the intrinsic viscosity on molecular weight was like that typical of randomly coiled polymers. Light scattering studies in chloroform-formamide of very high molecular weight samples showed that their lengths were proportional to their molecular weights and that the length per residue was 1.5 Á. These features demonstrate that the configuration is that of the -helix of Pauling and Corey. Further support for this conclusion was obtained by showing that the intrinsic viscosity-molecular weight relation could be fitted to Simha's equation for ellipsoids by assuming only that the minor axis was 18.2 A. This corresponds to 14.9 A. for the diameter of the solvated helix. The helical configuration appears to be rigid and rod-like up to 300,000 molecular weight but a few observations extending to 800,000 indicate the onset of a very small amount of flexibility. The helix is no longer stable at sufficiently low molecular weights: it is likely that this lower limit depends on the solvent and temperature. The randomly coiled configuration in dichloroacetic acid is due to the unusually strong secondary bonding that this solvent can form with the polypeptide chain. Molecular association occurs in solvents with very low or zero hydrogen bonding potential (purified chloroform, dioxane, benzene). In these cases the viscosity is greatly increased as a result of the association and it is shown that the association is probably of the end-to-end type arising from the formation of intermolecular hydrogen prevent association by solvating the helix-ends.

The Chemical Composition of Wool II. Analysis of the Major Histological Components Produced by Ultrasonic Disintegration

“…The only data that we have found with regard to stability in dichloroacetic acid is that polyglycine yields ninhydrin-positive glycine peptides in 26 hr at 37°C, whereas polyleucine is stable for 50 days (Heyns, Walter, and Grutzmacher 1957). Also the viscosity of a solution ofpoly-y-benzyl-L-glutamate in dichloroacetic acid decreases slowly after 3 days at 25°C (Doty, Bradbury, and Holtzer 1956). These changes are probably due to peptide bond fission.…”

Structural Investigations of Fibers and Films of Poly(p-phenylene benzobisthiazole). Volume 1

“…The average molecular weight is easily determined [112] from the intrinsic viscosity since the polymer does not protonate in solution. The Mark-Howink constants for PBG are given in Table XVII.…”

Understanding the α‐helix to coil transition in polypeptides using network rigidity: Predicting heat and cold denaturation in mixed solvent conditions

“…Second, the inverted transition where a disordered coil at low temperature will self-organize into a helix at high temperature. 11 In mixed solvent conditions, it is at least conceivable that there can exist an experimentally accessible window of temperature in which both effects occur. That is, starting from low temperature and upon heating, the peptide will change conformation characteristics from being a disordered coil to helix, and then to disordered coil at still higher temperature.…”