SummaryA series of ybenzyl-L-glutamate-L-leucine copolymers were prepared and cast films of the copolymers were subjected to dynamic mechanical and stress-strain tests. Dynamic mechanical testing revealed that the copolymers had a molecular relaxation at about 5OoC and that the magnitude of this relaxation was directly proportional to the molar concentration of glu(0Bz) in the copolymer. The magnitude of the 5OoC relaxation was also dependent upon orientation. The stress-strain behavior of the copolymers was examined before and after PECF treatment. Prior treatment with PECF caused in increase in the tensile strength to failure and a decrease in the elongation at failure. Increasing concentrations of leu caused the tensile strength to failure to increase. Efforts to degrade the films by refluxing 6 N HC1 and enzymic attack were unsuccessful and suggested that these copolymers could find use as biomedical materials.
Quasi-elastic laser light scattering studies have shown that large multimolecular aggregates are formed on mixing dilute aqueous solutions of poly(L-lysine) and chondroitin 6-sulfate. For the two components in equimolar residue proportions at a total concentration of 0.178 mg/mL, the aggregates have hydrodynamic radii of 1200 A. Circular dichroism spectroscopy indicates that the polypeptide conformation changes from a coil to the alpha-helix on cooling the solution. This change can be reversed by increasing the temperature; the midpoint for the transition is 47 degrees C. Throughout these changes the size of the aggregates remains approximately constant, and thus the conformational transition detected by circular dichroism occurs within the aggregates, which otherwise remain intact. In addition, changes in ratio of the two components, pH, and ionic strength, affect the size of the aggregates.
SynopsisCircular dichroism (CD) spectroscopy has been used to investigate the effects of changes in salt concentration and pH on the interactions between basic polypeptides and connective tissue glycosaminoglycans in dilute aqueous solution. The polypeptides undergo conformation-directing interactions in the presence of glycosaminoglycans, which are subject to transitions as the ionic strength and pH are varied. For poly(L-lysine), the conformational change due to interaction breaks down as the ionic strength (monovalent ions) is increased. Based on the ionic strength a t which disruption occurs, the glykosaminoglycans can be placed in order of increasing strength of interaction: chondroitin 6-sulfate, hyaluronic acid, chondroitin 4-sulfate, heparin, and dermatan sulfate. Prior to the conformational transition, scattering effects are observed, indicating the development of larger aggregates. Each glycosaminoglycan induces a-helicity for poly(L-arginine), which does not break down as the ionic strength is increased, indicating a stronger interaction for this polypeptide. The pHinduced transitions are in the pH range 2.5-3.8 and are probably related to deionization of carboxyl groups. For poly(L-lysine) the conformational effect is disrupted at low pH. For poly(L-arginine), the transitions are not complete, but appear to correspond to an increase in scattering.
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