The effects of the hyaluronic acid complex on the distribution of ions

Abstract

The distribution of NaCl in solutions of the hyaluronic acid complex was examined. At low pH values and at ionic strengths approaching the physiological, anomalous distributions were observed which could be characterized as following "binding" of Cl- ions. The theory of the distributions of univalent ions around an amphoteric polyelectrolyte was briefly treated, and it was shown that distribution experiments cannot provide sufficient information to permit the derivation of parameters of the polyelectrolyte other than its net equivalence. On the basis of this theory, the use of the concept of "ion-binding" is discussed and criticized. NaCl-distribution experiments were qualitatively interpreted as indicating that hyaluronic acid complex exhibits zwitterion characteristics at values below about pH 6.1. Brief studies of the distributions of KC1 and potassium thiocyanate in solutions of the complex did not show any differences from the distributions of NaCL The distribution of CaCl2 in solutions of the complex was briefly examined. With the observation of the concurrence of Ca in washed preparations of the complex, this showed that Ca++ ion was tightly associated with it, and that it can be expected that hyaluronic acid would be expected to be physiologically associated with Ca++ ion. The complex should not introduce any error into determinations of "sodium space". The direct titration of the complex with solutions of cetylpyridinium chloride consistently gave estimates of the equivalence of the complex at 3.2 meq/g, which is surprisingly high. The distribution of raffinose in solutions of the complex was approximately consistent with the steric requirements of a thread model for the complex. The domain of the random coil of the acid is thus confirmed as being permeable to solutes. The error in determinations of "raffinose space" due to this effect should not exceed 2%.