THERMODYNAMIC STUDY OF AQUEOUS MICELLAR SOLUTIONS OF BIOLOGICALLY-ACTIVE BISQUATERNARY AMMONIUM CHLORIDES

Thermodynamic properties of aqueous solution of bisquaternary ammonium salts, which are derivatives of N,N-bisdimethyl-1,2-ethanediamine (bi s-C-n-BEC), of general formula H2(CH3)(2)N+CH2CH2N+(CH3)(2)CH2COOCn-H- 2n+1/2Cl(-) (bis-C-n-BEC, where the subscript n stands for the number of carbon atoms of the alkyl chain bound to the carboxyl group) are he re reported and compared with those of the corresponding monomers, Dil ution enthalpies have been measured by means of a flow type microcalor imeter at 313 K, and densities have been measured by means of a vibrat ing tube densimeter at 298 K. Apparent and partial molar quantities ha ve been obtained from the experimental data and expressed as a functio n of molalities, assuming the infinite dilution as standard state. The changes in enthalpy and in volume upon micellization have been evalua ted by assuming the pseudo-phase transition model, From the calculated enthalpy changes at 313 K and that previously reported at 298 K, the changes in heat capacity for micellization has been evaluated. The dat a suggest the hypothesis that the alkyl chain in the dimers are alread y partially associated in solution, Moreover, the trends of the cmc as a function of the chain length for monomers and dimers suggest that t he association of the chains probably leaves out the first three methy lene groups of the alkyl chains bound to the carboxylic groups. The pa cking parameter, P, gives 0.37 for bis-C-10-BEC, and the formation of rod-like micelles is therefore suggested. (C) 1996 Academic Press, Inc .