STRUCTURE CONTROL OF SYNTHETIC BILAYER-MEMBRANES FROM SINGLE-CHAIN AMPHIPHILES CONTAINING THE SCHIFF-BASE SEGMENT .2. PH AND TEMPERATURE DEPENDENCE OF THE AGGREGATIONAL BEHAVIORS

The aggregational behaviors in aqueous solutions of the single-chain a mmonium amphiphiles with a rigid Schiff base segment, the diphenylazom ethine chromophore, have been investigated by electronic absorption sp ectroscopy under various chemical(pH) and physical (temperature) envir onments. pH dependence is not observed for amphiphiles with the sum of tail and spacer not larger than C-14. As for bilayer-forming amphiphi les, different pH-dependent spectral features take place at temperatur es below and above the phase transition temperature (T-c) of the corre sponding bilayer membranes at neutral environment, Basic environment f avors the planar conformation of the chromophores in the whole tempera ture range investigated, and its influence diminishes with increasing alkyl chain length, On the opposite site of pH, i.e., under the strong ly acidic condition with a pH of 1.2, a new absorption band attributed to the protonated species appears below room temperature, while it do es not show itself at temperature above T-c. Temperature dependence of the absorption spectra under the strongly acidic condition (pH < 3) r eveals that a deprotonation on the amphiphiles takes place at a temper ature below T-c. In basic solution (pH > 10.6), planar conformation in creases with raising temperature, so leading to the appearance of a st rong 330-nm absorption, Under intermediate pHs (3 < pH < 10.6) the bil ayer aggregational behaviors are relatively stable, The observed spect ral changes with pH were fully reversible. (C) 1996 Academic Press, In c.