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JPEGThe quantitative determination of reaction or association rate coefficients is a major issue in the field of chemical physics. In a certain number of cases, these rates depend on the time it takes for the reactive species to occupy a specific mutual spatial and orientational configuration that enables subsequent association or reaction step. Such rates are known to be limited by diffusion. Biochemistry offers numerous examples of multi-molecular association (formation of large long-lived complexes) where the mutual diffusion movement of the intervening species is expected to be a key factor controlling the association dynamics.

Moreover, the assumption of viscous hydrodynamics is reasonable for large molecules. The relative simplicity of the association kinetics in homogeneous solutions is lost when one of the reactive species is immobilized near a surface, and deriving the correct association rate in this situation is a challenging issue, even though the volume kon kinetic coefficient is known.

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