SURFACE-ADSORPTION AND VOLUME BEHAVIOR OF LOCAL-ANESTHETICS

The surface tension and densities of the aqueous solutions of six hydr ochloride salts of local anesthetics in clinical use, tetracaine (TC.H Cl), procaine (PC.HCl), dibucaine (DC.HCl), bupivacaine (BC.HCl), mepi vacaine (MC.HCl), ana lidocaine (LC.HCl), were measured as a function of the molality at 298.15 K under atmospheric pressure. It was observe d that the surface tension vs molality and density vs molality curves of DC.HCl; and TC.HCl have distinct break points at concentrations cor responding to the critical micelle concentration (cmc) and the surface tension vs molality curves of DC.HCl, TC.HCl, and BC-HCl have other b reak points at lower concentrations than the cmc. The surface densitie s of anesthetics were evaluated numerically by applying the thermodyna mic equations to the surface tension data. They decreased in the order of DC.HCl, TC.HCl, BC.HCl, MC.HCl, LC.HCl, and PC.HCl in accordance w ith anesthetic potency. Further, the adsorbed films of DC.HCl, TC.HCl, and BC.HCl were turned out to occur phase transition from a gaseous s tate to an expanded state by examining the surface pressure vs area pe r adsorbed molecule curves. On the other hand, by analyzing the densit y data, volume properties of anesthetics in aqueous solution were eval uated and the volume parameters of micelle formation of DC.HCI and TC. HCI were also determined. The surface adsorption and volume behavior o f these anesthetics were revealed on the basis of the thermodynamic qu antities.