Spectral properties of two betaine-type cyanine dyes in surfactant micelles and in the presence of phospholipids

Abstract

The interaction of two betaine-type cyanine dyes: 3,3 ′-disulfopropyl-4,5,4 ′,5 ′-dibenzo-9-ethyl-thiacarbocyanine ( I) and 3,3 ′-disulfobutyl-5,5 ′-diphenyl-9-ethyl-oxacarbocyanine ( II) with ionic surfactants [sodium dodecyl sulphate (SDS), cetyltrimethylammonium chloride (CTAC), dimethyl-hexadecyl-ammonio-propanesulphonate (HPS)] and with dispersions of naturally occurring phospholipids [phosphatidylethanoloamine (PE), phosphatidylserine (PS) and lyso-phosphatidylcholine (LPC)] has been studied by electronic absorption and fluorescence measurements. It was found that micelles of CTAC, SDS, HPS, LPC and bilayers of PS bind the dyes mainly as monomer species. The binding results in strong fluorescence enhancement. In all cases the absorption and fluorescence maxima of the monomers shift to lower frequencies as their local effective polarity decreases. In the presence of PE, PS with Ca 2+ and CTAC below critical micelle concentration (cmc) cyanine II forms highly fluorescent J-aggregates, which was demonstrated by the appearance of a new intense J-absorption band at lower frequencies than the monomer band and strong fluorescence with very small Stokes shift. In cases when both, monomer and J-aggregate are present in the system, dual fluorescence was observed. It seems that both dyes may serve as a valuable molecular probes for detection of micelles and changes of biomembrane structure.