Monomer–eximer dynamics in spread monolayers. I. Lateral diffusion of pyrene dodecanoic acid at the air–water interface

Abstract

In this paper, we present a combined experimental and theoretical study of monomer–eximer dynamics in spread monolayers. The system studied here is a spread monolayer of 12-(1-pyrene) dodecanoic acid (PDA) and oleic acid at the air–water interface of a neutral aqueous solution. The microscopic kinetic behavior of the PDA probe in the monolayer was monitored through the eximer–monomer, steady-state photoexcitation of the pyrene moiety. The steady-state ratio of eximer to monomer intensities, I2/I1, was found to depend linearly on the mole fraction of PDA in oleic acid over the concentration range studied. These data were interpreted theoretically by constructing a reaction-dynamic model to describe the lateral diffusion and subsequent interaction of the pyrene species. Using analytical results from the theory of random walks on lattices with traps, and from data from Monte Carlo simulations, an estimate is obtained for the two-dimensional diffusion coefficient of the pyrene probe in the monolayer; this estimate is 1.7×10−6 cm2/sec.

Two-dimensional diffusion of amphiphiles in phospholipid monolayers at the air-water interface

“…In recent years, monolayers at the air-water interface have received much attention as model membrane systems (Stroeve and Miller, 1975;Teissie et al, 1978;Loughran et al, 1980;Peters and Beck, 1983;Subramanian and Patterson, 1985;Bohorquez and Patterson, 1988;Meller et al, 1989;Caruso et al, 1991;Kim and Yu, 1992;Caruso et al, 1993a). Air-water monolayers of amphiphilic lipids resemble half a biological membrane and thus can serve as an excellent model for biomembranes.…”

“…Several experimental techniques have been applied in studies of lateral diffusion of lipids at air-water monolayers. Values of the lateral diffusion coefficients have been most commonly determined from fluorescence recovery after photobleaching (FRAP) experiments (Teissie et al, 1978;Peters and Beck, 1983;Meller et al, 1989; Kim and Yu, 1992) or from the analysis of the kinetics of pyrene excimer formation (Loughran et al, 1980;Subramanian and Patterson, 1985;Bohorquez and Patterson, 1988). The disadvantages and complications associated with obtaining lateral diffusion coefficients using these techniques have been reported previously (Axelrod, 1977;Peters and Beck, 1983;Caruso et al, 1991).…”

Surface Diffusion in Gaseous Monolayers of an Insoluble Surfactant

“…In this section, we compare the obtained results with the measurements made by other researchers − during studies of insoluble monolayers. A comparative diagram illustrating the results of surface diffusion measurements in various ranges of surface concentration is presented in Figure .…”

“…Diagram illustrating the results of surface diffusion measurements in various ranges of surface concentration, obtained in this and other studies: *refs − , − , **refs , , , , ***refs , .…”

“…The traditional approach for the measurement of the diffusion rate in a liquid volume, which is based on the study of the temporal evolution of initial concentration irregularity, is not suited for surface diffusion measurements since any surfactant concentration heterogeneity at the interface results in the development of solutal Marangoni convection. To avoid this, the surface self-diffusion coefficient is measured in the uniform layer of surfactant molecules part of which is marked with the radiotracer − or fluorescence technique. − Apart from the difficult experimental realization, the method is very sensitive to variations in external conditions, which can initiate convective flows at the interface, resulting in the overestimated surface diffusivity values. It was shown by Agrawal and Neuman , that the reliable control of temperature and humidity gives the surface diffusion coefficient that is 2 orders of magnitude less than in previous studies.…”