ABA-C₁₅:  A New Dye for Probing Solvent Relaxation in Phospholipid Bilayers

Abstract

We synthesized and studied N-palmitoyl-3-aminobenzanthrone (ABA-C15), which we proved to be an advantageous new fluorescent phospholipid membrane label. While the absorption of ABA-C15 in protic solvents shows negative solvatochromism, its fluorescence emission is substantially red-shifted when the polarity of the solvent is increased. ABA-C 15 is excitable by lasers emitting in the range between 390 and 490 nm; it exhibits reasonable quantum yields in protic solvents and binds with high affinity to small unilamellar phospholipid vesicles. Absorption, steady state fluorescence, and solvent relaxation data indicate that the aminobenzanthrone chromophore is located in the headgroup region of phospholipid bilayers in the liquid crystalline state of small unilamellar vesicles. The solvent relaxation kinetics probed by ABA-C 15 in the liquid crystalline state is characterized by three solvent relaxation times in the order of 0.05, 0.2, and 1.5 ns, respectively. We observed that the relative contribution of the 0.05 ns component and the overall Stokes shift became larger with increasing difference between the experimental temperature and the main phase transition temperature; this suggests that the chromophore becomes more accessible by water molecules. In the gel phase, a component faster than 30 ps significantly contributes to the solvent relaxation kinetics. However, the solvent relaxation on the nanosecond time scale appears to be slower than in the liquid crystalline phase. The shape and time evolution of the time-resolved emission spectra suggest that two distinct microenvironments of the dye might be responsible for the atypical solvent relaxation characteristics in the gel phase.

Laurdan and Di-4-ANEPPDHQ probe different properties of the membrane

“…It has been shown that the spectral half width, i.e. the FWHM value passes through a maximum during the solvation process [32][33][34], which is in line with a nonuniform distribution of solvent response times [34,35].…”

3-Aminobenzanthrone, a human metabolite of the carcinogenic environmental pollutant 3-nitrobenzanthrone, induces biotransformation enzymes in rat kidney and lung

“…3-ABA was also the main metabolite of 3-NBA formed in human fetal bronchial cells and rat lung alveolar type II cells [7]. In addition, 3-ABA was found suitable for dyeing microporous polyethylene films, which are widely used for practical purposes such as separation of liquid mixtures, in particular, as separation membranes in chemical batteries [8], or to fluorescently label phospholipid membranes in the form of its N-palmitoyl derivative [9]. This suggests its industrial and/or laboratory utilization, leading to a putative exposure of people.…”

Probing relaxation dynamics of a cationic lipid based non-viral carrier: a time-resolved fluorescence study

“…One or two faster decay components, (s 1 , s 2 ), associated with the time-resolved uorescence decay monitored at the blue edge of the steady state uorescence spectrum becomes a rise component at the emission peak maximum (Table 1.) and at the red edge of the steady state uorescence spectrum. This is typical of solvation dynamics 11,[13][14][15] which is manifested by a time-dependent Stokes shi of the uorescence spectrum to the red (Fig. 4a-c).…”

“…Solvation dynamics is a powerful technique to probe relaxation dynamics of water molecules (hydration dynamics) associated with biomolecular surfaces and interfaces [11][12][13][14][15] where relaxation of the local environment of an optically excited uorophore is monitored by measurements of time-dependent uorescence Stokes shi (TDFSS). In the present work we have chosen a novel uorophore, 6-acetyl-(2-((4-hydroxycyclohexyl)(methyl)amino)naphthalene) 16 (ACYMAN, Scheme 1) to investigate hydration dynamics in the lipid-water interfaces of different DODAB/MO mixed vesicles, because, ACYMAN was found to be more suitable in probing water dynamics in micelle-water and protein-surfactant interfaces 14 compared to common solvation probes coumarin-500 (C500) and 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM).…”