Molecular Weight Material Research Articles

Behavior of polyethylene glycol on dialysis and gel filtration.

POLYETHYLENE glycol is now widely used for concentrating protein solutions by dialysis. We have used the material of molecular weight 15,000 (L. Light and Co., Ltd., Colnbrook, England) and have found that it penetrates dialysis sacs to an appreciable extent.

The Effect of Ionizing Radiation on the Synthesis of T1 Phage Protein

The formation of specific antigen, defined as material of large molecular weight, which will combine with T1 antibody, by T1-infected E. coli at various stages of the latent period has been studied. X irradiation of the cells before infection reduces the formation of specific antigen with a two-component inactivation process, some cells being about three times as sensitive as others. X irradiation destroys the ability of free phage to combine with antiserum, but with a very low sensitivity. The ability to produce infectious centers is affected by x rays with a higher sensitivity than for antigen synthesis. The capacity to produce infectious centers is affected by x rays applied before infection, again with a two-component process. At later stages in the multiplication process there appears a less sensitive component which can be identified with mature phage. Irradiation with deuterons and alpha particles of various LET follows the same pattern. The data are consistent with the existence of a single sensitive synthetic site which could be determined by a DNA chain of length 0.97 mu for protein synthesis and 2.5 mu for the formation of infectious centers.

STUDIES ON REACTIONS RELATING TO CARBOHYDRATES AND POLYSACCHARIDES: LX. STABILIZING ACTION OF ETHANOL ON STARCH NITRATES

Fractional dissolution has been applied to nitrated corn starch with the consequent removal of ethanol-soluble fractions. Hot and cold ethanol-soluble fractions have been removed in this way amounting to from 10 to 25% of the crude nitrate. The ethanol-soluble fractions, consisting of low-molecular weight and low nitrogen-content material, are not stabilized by ethanol. The insoluble portion is greatly stabilized as a result of the ethanol treatment.The insoluble residue left after ethanol treatment of crude starch nitrate possesses good explosive properties, a high nitrogen content, and high stability. The stabilization of starch nitrate by ethanol is shown to be the result of a dual action, namely, (a) removal of highly unstable material of low molecular weight and nitrogen content, and (b) the conferring of increased stability by some, as yet unknown, mechanism on the insoluble portion.

Fractionation of Rubber

Abstract Latex rubber which has been purified to the point at which it contains an insignificant amount of nitrogen can be separated by fractional dissolution in a mixture of petroleum and acetone into a series of hydrocarbon fractions of decreasing solubility and increasing molecular magnitude. All these fractions except the highest are soluble in petroleum and in benzene. Crepe rubber, on the other hand, appears invariably to contain a small, most-soluble fraction of oxygenated rubber, and a small similar quite insoluble fraction of material of high molecular weight. Between these extremes the rubber can be divided into fractions of increasing molecular weight, although, up to the present, about 70 per cent of the total rubber has appeared in a single fraction. It may be possible later, by judicious choice of another pair of solvents, to resolve this major fraction into a series of subfractions. Kemp and Peters refer to the effect of polar nonsolvents in reducing the viscosity of rubber solutions and also in assisting to bring gel rubber into solution, phenomena to which the polar molecules conceivably contribute by countering the forces of association between the rubber molecules. The present series of fractionations was conducted throughout in the presence of a polar nonsolvent (acetone), and hence may be considered to approach towards a separation of true rubber molecules as distinct from molecular aggregates. It is found, however, that, whereas the more soluble fractions of acetone-extracted crepe rubber contain small proportions of nitrogen, the least soluble fractions contain substantial proportions. Any effect which the nitrogenous material may have in assisting to link together hydrocarbon molecules to which it is attached, i. e., in contributing to the high-molecular condition of a portion of natural rubber, remains at present uncertain in character. The fractions of rubber, and especially the higher ones, show a strong tendency to become insoluble when they have once been freed from the last traces of solvent. It seems doubtful whether the decreased solubility is due to oxygen as it would require to be effective at exceedingly low concentrations.