Diffusion-influenced reactions involving a reactant with two active sites

We consider the kinetics of diffusion-influenced reactions which involve a reactant species that can be modeled as a sphere with two reactive patches located on its surface at an arbitrary angular distance. An approximate analytic expression for the rate coefficient is derived based on the Wilemski-Fixman-Weiss decoupling approximation and a multivariable Pade approximation. The accuracy of the rate expression is evaluated against computer simulations as well as an exact analytic expression available for a special case. The present theory provides accurate estimates for the magnitude of diffusive interference effects between the two reactive patches. We also present an efficient Brownian dynamics method for calculating the time-dependent rate coefficient, which is applicable when the reactants involve multiple active sites.