The research was supported by National Institutes of Health grant ES-05202. This paper is the Environmental Sciences and Resources Program publication No. 265.
Adsorption, Membranes (Biology), Gel electrophoresis, Zeta potential
Dipalmitoylphosphatidylcholine (DPPC) vesicles acquire negative surface charge on adsorption of negatively charged pentachlorophenolate (PCP-), and lipophilic ions tetraphenylborate (TPhB-), and dipicrylamine (DPA-). We have obtained (a) zeta-potential isotherms from the measurements of electrophoretic mobility of DPPC vesicles as a function of concentration of the adsorbing ions at different temperatures (25–42 degrees C), and (b) studied the effect of PCP- on gel-to-fluid phase transition by measuring the temperature dependence of zeta-potential at different PCP- concentrations. The zeta-potential isotherms of PCP- at 25, 32, and 34 degrees C correspond to adsorption to membrane in its gel phase. At 42 degrees C the zeta-potential isotherm corresponds to membrane in its fluid phase. These isotherms are well described by a Langmuir-Stern-Grahame adsorption model proposed by McLaughlin and Harary (1977. Biochemistry. 15:1941–1948). The zeta-potential isotherm at 37 degrees C does not follow the single-phase adsorption model. We have also observed anomalous adsorption isotherms for lipophilic ions TPhB- and DPA- at temperatures as low as 25 degrees C. These isotherms demonstrate a gel-to-fluid phase transition driven by ion adsorption to DPPC membrane during which the membrane changes from weakly to a strongly adsorbing state. The anomalous isotherm of PCP- and the temperature dependence of zeta-potential can be described by a two-phase model based on the combination of (a) Langmuir-Stern-Grahame model for each phase, (b) the coexistence of gel and fluid domains, and (c) depression of gel-to-fluid phase transition temperature by PCP-. Within the anomalous region the magnitude of zeta-potential rapidly increases concentration of adsorbing species, which was characterized in terms of a Esin-Markov coefficient. This effect can be exploited in membrane-based devices. Comments are also made on the possible effect of PCP, as an uncoupler, in energy transducing membranes.
Smejtek, Pavel, and Shanru Wang. "Domains and anomalous adsorption isotherms of dipalmitoylphosphatidylcholine membranes and lipophilic ions: pentachlorophenolate, tetraphenylborate, and dipicrylamine." Biophysical journal 59.5 (1991): 1064-1073.