Simplified derivation of angular order and dynamics of rodlike fluorophores in models and membranes. Simultaneous estimation of the order and fluidity parameters for diphenylhexatriene by only coupling steady-state illumination polarization and lifetime of fluorescence

Abstract

We compare numerous values of average degrees of order, (S), and of average correlation times, (phi), as given by many authors for 1-6-diphenyl-1-3-5-hexatriene (DPH) in membrane models. From these comparisons, a relationship arises between (phi),(S), and the absolute temperature, T. This means that each of these variables is a function of both the others: omega [(phi), (S), T] equal 0, and this function defines a surface in a three-dimensional space. Note that omega identical for a large variety of sonicated lipid vesicles. This statement is a new formation of the conclusions of Van Blitterswijk W. J., R. P. Van Hoeven, and B. W. Van Dermeer, 1981, Biochim. Biophys. Acta, 644:323-332, in the light of other recent studies (Kinosita K., Jr., R. Kataoka, Y. Kimura, O. Gotoh, and A. Ikegami, 1981, Biochemistry, 20:4270-4277). It seemed useful to seek an approximate analytical expression for the omega function (supposed unique). Various arguments have led us to define the omega function as the ratio of a diffusive (Arrhenius-type) numerator, v(T), divided by a temperature-independent denominator, sigma((s)) (Kinosita, K., Jr., S. Kawato, and A. Ikegami, 1977, Biophys. J., 20:289-305; Lipari, G., and A. Szabo, 1980, Biophys. J., 30:489-506). However, one could not a priori discard a dependence of the activation energy of v(T) on both the temperature and/or on (S). The analytical form of the proposed approximate omega function and the numerical values of the constants involved are checked for much of the data obtained from DPH/biomembranes systems described in the literature. As a consequence of this new relationship, a simplified procedure is proposed to obtain the order parameter, (S), in unknown systems. In this procedure the starting experimental quantities are only in the steady-state fluorescence anisotropy, (r), the weighted average fluorescence lifetime, tau, and T. In turn, evaluation of a weighted average correlation time, (phi), sometimes becomes simultaneously possible, at least for membranes in their liquid-crystal phase, but with less accuracy than for the determination of (S). Because the method is founded on results arising from transient experiments, it seems difficult to conceive that it could replace these techniques in a generalized manner. However, because fast tests are frequently required in routine studies on biomembranes, the method could still have a broad application provided that some transient-control measurements are performed at the limits of the experimental range studied.