Effect of alkyl chain length on translocation of rhodamine B n-alkyl esters across lipid membranes

Voltage-dependent translocation of a series of cationic rhodamine B derivatives, differing in n-alkyl chain length (ethyl, butyl, octyl, dodecyl, octadecyl), from one lipid monolayer to another was studied by measuring electrical current relaxation after a voltage jump on a planar bilayer phosphatidylcholine (PC) membrane. The rate of the translocation decreased in the following series of lipids: Diphytanyl-PC > Dioleyl-PC > Diphytanoyl-PC > Dierucoyl-PC. For all the lipids studied, the rate increased with lengthening of the hydrocarbon chain of the rhodamine derivatives, with the increase being most pronounced for the compounds having a short alkyl chain.

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