Phospholipid Vesicles as Organized Media in Spectroluminescence Analysis

Abstract

The membrane properties of pure dimyristoyl phosphatidylcholine (DMPC), dimyristoyl phosphatidylserine (DMPS), and dimyristoyl phosphatidylglycerol (DMPG) vesicles were compared using the fluorescence of the probe pyrene in an assessment of the potential utility of phospholipids as organized media in spectroluminescence analysis. The partition coefficients, excimer stability constants, vibronic band ratios, triethylamine quenching constants, and fluorescence lifetime distribution widths of pyrene were used as measures of the solute capacity, solute aggregation promotion, polarity, sequestering efficiency, and heterogeneity of the three media. The results indicate that the head group hydrophobicity and membrane fluidity required to reduce the incidence of excimer formation and to promote solute sequestering in the most hydrophobic part of the aggregate precludes efficient sequestering from cosolubilized quenchers. This implies that significant improvements in dynamic range would be expected in spectroluminescence analyses utilizing DMPG, but improvements of detection limits would be moderate compared to those observed in bile salts, cyclodextrins, or surfactant aggregates.