Diffusion Controlled Reactions in Two-Dimensional Space. The Pyrene Excimer Example

Abstract

Diffusion-controlled reactions in two dimensional or quasi two dimensional space are important in both, surface, and membrane reaction kinetics. A model reaction that have been extensively used to study the dynamics and structural properties of membranes is that of the formation of the excimer of pyrene. We present experimental evidence that in multilamelar liposomes of dimyristoylphosphatidylcholine, at temperatures above phase transition, and for probe:phospholipid ratio of 1:100, or lower, the fluorescence decay of both, pyrene, and 3-palmitoyl-2-(l-pyrenodecanoyl)-L-α-phosphatidylcholine follows a kinetic law specific of 2D diffusion-controlled reactions. The parameters obtained for the diffusion coefficient, 1.6 × 10−⁷ cm² s-¹ for the free pyrene and 1.0 × 10-⁷ cm² s-¹ for the pyrene-labeled phospholipid, and the activation energy for diffusion, are in perfect accordance with the figures that came out from independent techniques.