PYRENE FLUORESCENCE LIFETIME AS A PROBE FOR OXYGEN PENETRATION OF MICELLES

INTRODUCTION When bound to proteins and membranes, fluorescence probes can provide valuable information about the environment of the binding site (Edelman & McClure, 1968; Brand & Gohlke, 1972). Recently much interest has been shown in aromatic hydrocarbons as fluorescence probes. Because they are non-polar molecules, they should not interact as strongly with charged groups as the amino-napthalene sulfonate probes do. Aromatic hydrocarbons exhibit environment dependent fluorescence lifetime and polarization (e.g. Hautala et a!., 1973; Shinitsky et al., 1971; Gratzel & Thomas, 1973). These properties can be used to characterize the probe environment in biological systems. Additionally, the well-known quenching behavior of aromatic hydrocarbons has been exploited to obtain information about the permeability of membrane-like systems (Gratzel & Thomas, 1973 ; Infelta et al., 1974; Wallace & Thomas, 1973; Pownall & Smith, 1974; Chen et al., 1974) and the accessibility of protein environments (Vaughan & Weber, 1970; Lakowicz & Weber, 1973). Synthetic micelles have been particularly useful in characterizing the fluorescence and quenching behavior of aromatic hydrocarbons in various environments (e.g. Hautala et al., 1973; Infelta et al., 1974; Pownall & Smith, 1974; Patterson & Vieil, 1974; Chen et al., 1974 Soutar et al., 1974; Cheng et al., 1974). Although oxygen quenching of aromatic hydrocarbon fluorescence has been studied in proteins (Vaughan & Weber, 1970; Lakowicz & Weber, 1973), the question of oxygen permeability in micelles has not been resolved. Previous work in this group suggests that oxygen is soluble in the micelle interior and that oxygen solubility is one of the factors which determines the lifetime of solubilized probes (Hautula et al., 1973). However, Dorrance & Hunter (1972) failed to obtain any increase in fluorescence quantum yield of pyrene upon deoxegenation of aqueous hexadecyltrimethylammonium bromide (HDTBr) solutions containing this hydrocarbon. They suggest that the lack of fluorescence quenching results because a barrier exists to oxygen penetration of micelles containing pyrene molecules. Wallace and Thomas (1973) report rate constants for oxygen quenching of pyrene solubilized in HDTBr and in sodium dodecyl sulfate (SDS) which are slower than the quenching rate constant in water. The effect of oxygen upon the fluorescence lifetime of a probe solubilized in micelles presented in this paper provides further evidence that micelles are penetrated by oxygen. We have studied the pyrene: HDTBr, HDTCl (hexadecyltrimethyl ammonium chloride) and SDS systems in oxygen, air and nitrogen saturated, as well as degassed solutions.