In the last year, the main focus of research has been on studies of diffusion influenced reactions. One investigation led to a new time dependent version of Berg and Purcell's steady state theory of diffusion influenced ligand binding to receptors randomly distributed on the surface of a cell. The results may be useful, for example, in treating the dynamics of the infection of a cell culture by a virus. Another application of the general theory was to work out the time dependent current to a random ensemble of microdisk electrodes. This is of considerable interest in electroanalytical chemistry. In a second investigation, theory and computer simulations were applied to a model for a chemical reaction whose rate is controlled by an entropy barrier rather than the more common potential barrier. The ideas developed here may be useful in understanding the dynamics of the escape of ligands from the heme pocket on myoglobin and hemoglobin. In a third investigation, attention is given to the general theory of reversible diffusion influenced bimolecular reactions. Considerable progress has been made in formulating a reliable theoretical approach, and this approach is being tested by computer simulations on a simple model.
