An NMR self-diffusion study of the interaction between sodium hyaluronate and tetradecyltrimethylammonium bromide

Abstract

A decrease of the NMR self-diffusion coefficient of sodium hyaluronate (NaHy) upon increasing tetradecyltrimethylammonium bromide (TTAB) concentration in 202 mM NaCl (just enough to attain single phase conditions irrespective of the TTAB concentration) is interpreted in terms of the formation of NaHy-TTAB complexes containing several NaHy chains. The complexes are judged to be induced by multiple-site electrostatic condensation ofTTAB micelles onto the Hy chains. Thus, the TTAB micelles may act as bridging points between, and within, the NaHy chains. For a 1% wt NaHy solution, at 202 mM NaCl, the fraction of adsorbed TTAB has a maximum at 10 mM TTAB where an estimated 54% of all the added TTAB is bound. At 70 mM TTAB, the fraction of bound TTAB has decreased to 42%. The decrease of the binding constant with increasing TTAB concentration is attributed to a more efficient electrostatic screening ; i.e., the ionic strength (due to uncondensed species) increases. The observed NaHy-TTAB complexes are likely to be precursors of the precipitated phase formed at lower salt concentrations.