Structure and Membrane Permeability of Charged Molecules: Membrane Experiments with Tetraphenylborate Analogs

Abstract

AbstractCharge‐pulse experiments were performed on membranes made of dioleoyl phosphatidylcholine/n‐decane in the presence of 4 structural analogs of tetraphenylborate (TPB, triphenylcyanoborate (TPCB), tetrakis (4‐fluorophenyl)borate (TFPB), tetrakis (4‐chlorophenyl)borate (TCPB), and tetrakis (3‐trifluoromethylphenyl)borate (TTFPB)). The analysis of the experimental results using a previously proposed model allowed the calculation of the partition coefficient, β, and of the translocation rate constant, ki, of the lipophilic ions. The adsorption of the different TPB‐analogs to the membranes was similar, whereas their structure had a dramatic influence on the translocation rate constants and they increased by almost six orders of magnitude from TPCB to TTFPB. The free energy of the ions in the membranes as calculated from the translocation rate constants, decreased from TPCB to TTFPB by about 31 kJ/mol (7.4 kcal/mol). The change of the free energy in the membrane was used for the estimation of an effective radius of the TPB‐analogs with respect to the van der Waals radius of TPB.