Spectroscopic Properties of the Potentiometric Probe Merocyanine‐540 in Solutions and in Liposomes

Abstract

Absorption, fluorescence and resonance Raman spectra of the membrane dye merocyanine‐540 (MC540) were measured. The aggregation of the dye, its binding to lipid membranes and its response to crossmembrane electric potential differences were studied. The dye was found to aggregate even at micromolar concentrations in water, but not in organic solvents. The dimerization constant was evaluated by spectroscopic techniques. The binding constant to liposomes was estimated by a spectroscopic titration method. Resonance Raman spectra of MC540 were measured for the first time. Distinct changes were observed in the vibrational spectrum upon the generation of a valinomycin‐induced K+ diffusion potential (Nernst potential) on liposomes. The ratio of Raman band intensities, which was found to be related to the membrane potential, can be used to evaluate the absolute value of the electric potential.

Location of Pinacyanol in Micellar Solutions of N-Alkyl Trimethylammonium Bromide Surfactants

“…Thus, the presence of micelles increased the ratio monomer/dimer, i.e., reduced the dimerization. With other similar dyes such as merocyanine-540, methylene blue, or methyl orange (10,13,(19)(20)(21)(22)(23)(24)(25)(26), the dimerization is less in nonpolar media (namely, in the presence of micelles) than in polar solvents. On the other hand, the existence of an isosbestic point indicates the formation of a 1 : 1 complex between the dye and the micelles (27).…”

Quantification of lipid bilayer effective microviscosity and fluidity effect induced by propofol

“…As many amphipathic molecules, it has a strong tendency to dimerize in aqueous solutions [26]. The absorption spectrum of the dye in water has a double-banded structure (501 and 533 nm) and the extinction coefficient is concentration dependent, indicating dimerization of the dye [38]. In lipid bilayers, MC540 is located at the membrane interfacial region under dimeric and monomeric forms [36,39].…”

Spectral Imaging of MC540 During Murine and Human Colon Carcinoma Cell Differentiation

“…Excitation ranges were set to 420-480 nm and 545-580 nm based on the light absorbance properties of MC540. In an aqueous environment MC540 absorbs light near 480 nm, and in lipophilic media and membranes at 570 nm (Ehrenberg and Pevzner 1993). However, although the absorbance peak at 570 nm is stronger than at 480 nm, the subcellular distribution pattern of MC540 at both excitation ranges appeared similar.…”

“…It is well established that the fluorescence intensity of fluorophores is affected by the polarity of their microenvironment (Kaschny and Goni 1992;Malik et al 1997) and that their absorbance depends on the ratio between lipophilic and hydrophilic media (Ehrenberg and Pevzner 1993). Spectral measurements revealed maximal light absorbance of MC540 at 480 nm in aqueous environments and at 570 nm in lipophilic media and membranes (Figure 1).…”

“…In some previous studies, MC540 has been used as a probe for measuring changes in the membrane potential of liposomes (Williamson et al 1983;Ehrenberg and Pevzner 1993). These changes depend on two major components of the electric field, the cross membrane potential and the surface potential, and were expressed by a slight alteration in the absorption and fluorescence spectra (Sieber 1987;Singth et al 1991;Kaschny and Goni 1992;Ehrenberg and Pevzner 1993). The first component, also known as the Nernst potential, arises from differences in ion concentrations between the two sides of the membrane, and the second component arises from charged groups at the membrane-water interface.…”