COLLOIDAL PROPERTIES OF AQUEOUS LOCAL-ANESTHETIC TETRACAINE SOLUTIONS

The present study includes the colloidal solution properties of a loca l anesthetic, tetracaine hydrochloride (C15H24N2O2.HCl). The CMC of C1 5H24N2O2.HCl was determined using a coated wire electrode that is sele ctively sensitive to a local anesthetic cation. The effects of added s alt (NaCl) and temperature on the CMC were studied. A linear relations hip between the logarithm of the CMC and the counterion concentration was confirmed at 25-degrees-C. The CMC in the absence of added NaCl te nds to increase as the temperature rises in the range 15-35-degrees-C. The enthalpy change on micellization was estimated to be -3.7 kJ mol- 1 from the temperature dependence of the CMC. The Krafft phenomenon wa s observed from heating scans obtained by differential scanning calori metry. The transition enthalpy from the hydrated solid to the micellar solution was 29.4 kJ mol-1. Another transition associated with an ent halpy change of 1.7 kJ mol-1 was observed just below the Krafft temper ature. which was assigned to the transition between lyotropic liquid c rystals.