Combination of silk fibroin with acid and with base

Abstract

A study was made of the dependence on pH of the amounts of hydrochloric acid and of potassium hydroxide that are taken up by silk fibroin at 0° C. The effect of added potassium chloride on this dependence was also investigated, and was shown to be the binding of an increased quantity of acid or base at a given pH.The maximum acid-combining capacity of silk fibroin is 0.13 milliequivalent per gram; the maximum base-binding capacity is greater than 0.90 milliequivalent per gram. The presence of 0.13 to 0.17 milliequivalent of free carboxyl groups in silk fibroin is estimated from the titration curve. The great amount of base bound can be accounted for only if the phenolic hydroxyl groups of tyrosine take part in the equilibria with base. Further evidence that these groups bind base is provided by the greatly decreased amount of base bound by methylated fibroin. CONTENTS Page

Relative affinities of the anions of strong acids for wool protein

“…Obviously, the comparison should be made between solutions which are as far as possible from the isoionic point in order to minimize the effects of the convergence. The data do not extend to very acid solutions, but at the extreme of the range represented the differences in the pH coordinates of the curves approach values only slightly smaller than the differences between curves for the same acids in figure 1,13 Since the theory of stoichiometric anion combination was originally formulated to account for the large effects of the presence of salt on the hydrochloric acid combination curves of wool, the application of this theory to the much smaller salt effects described by Cannan for egg albumin [6] seemed at first uncalled for. The experiments just described, however, suggest that the difference between the titration curves of dissolved and undissolved proteins in the absence of salt [36] cannot be due to the failure of anions to combine with the dissolved protein.…”