Partitioning behavior of indocarbocyanine probes between coexisting gel and fluid phases in model membranes

Abstract

Gel-fluid partition coefficients, K p, were measured for a series of indocarbocyanine dyes in multilamellar lipid vesicles. The dyes examined had alkyl chain lengths from 12 to 22 carbons. Fluorescence quenching by a spin-labeled phosphatidylcholine-enriched fluid phase created a large difference in quantum yield for indocarbocyanine fluorescence between fluid and gel phases, enabling reliable K p determinations. The values range from K p = 8 for the 12-carbon chain, favoring a fluid phase over a Ca 2phosphatidylserine rigid phase, to K p = 0.02 for the 20-carbon chain dye, favoring a distearoylphosphatidylcholine-rich gel phase over the fluid phase.