Protolytic photodissociation of hydroxyaromatic compounds in micelles and lipid bilayer membranes of vesicles

Abstract

Protolytic photodissociation of some hydroxyaromatic compounds, ArOH (1-and 2-naphthol, chlorosubstituted naphthols), was studied in micellar solutions and phospholipid vesicles by fluorescence spectra and kinetics. Experimental results give evidence of two localization sites of naphthols in the microphase of these systems. In lipid bilayer membranes of vesicles there are two comparable fractions of ArOH molecules, one of which undergoes photodissociation but the other does not dissociate. In micelles, a minor fraction (few percent) of ArOH molecules, which are located probably in the core of the micelle, do not take part in excited-state proton-transfer reaction. These phenomena refllect heterogeneous structure and dynamic properties of lipid bilayer membranes and micelles.

Hydrogen‐Bonded Large Molecular Aggregates of Charged Amphiphiles and Unusual Rheology: Photochemistry and Photophysics of Hydroxyaromatic Dopants

“…The rise time of the fluorescence of the anion of naphthol, almost in all cases, coincides with the lifetime of the faster component of the excited naphthol molecules [77]. The fluorescence kinetic curves for 2-naphthol and the anion of 1-naphthol are shown in Figures 31.22 and 31.23.…”

“…On excitation into the lowest singlet excited state, the pK a values drop by several units (2-naphthol: pK a à $ 2.78; 1-naphthol: pK a à $ 0.40) [74,75], i.e. they undergo deprotonation in the excited state (DES) [76,77]. As a result, the emission from the neutral forms of 1-and 2-naphthols at 360 and 357 nm, respectively, exhibits a very much lower intensity than that of the anion forms near 450 or 420 nm respectively.…”

“…The authors found that 1-naphthol distributes between two different sites of different excited state reactivity in liposome, and the relative population at the two different sites changes with any perturbation Figure 31.23 Fluorescence decay curve (0.125 ns channel -1 ) of the anion of 1-naphthol in DTAB micelles. Adapted with permission from [77]. Copyright 1991 American Chemical Society [77].…”

“…Adapted with permission from [77]. Copyright 1991 American Chemical Society [77]. Copyright 1991 American Chemical Society in membrane fluidity.…”

Observation of the phase transition in phospholipid liposomes taking advantage of the particular optical properties of octa-α-butyloxy-H2phthalocyanines

“…In the literature several methods have been reported to monitor the phase transition of membranes by using calorimetric methods [13,14], fluorescence sensors, which show differences in fluorescence spectra [14][15][16] or in fluorescence lifetime [17], electron transfer reactions [18] and by using magnetic field sensitive probes [19]. The most widely used method for determining the phase transition temperature is microcalorimetry [12].…”