Macromolecular interactions play a crucial role in biological systems. 
Simulation of diffusional association (SDA) is a software for carrying out 
Brownian dynamics simulations that can be used to study the interactions between 
two or more biological macromolecules. webSDA allows users to run Brownian 
dynamics simulations with SDA to study bimolecular association and encounter 
complex formation, to compute association rate constants, and to investigate 
macromolecular crowding using atomically detailed macromolecular structures. 
webSDA facilitates and automates the use of the SDA software, and offers 
user-friendly visualization of results. webSDA currently has three modules: 'SDA 
docking' to generate structures of the diffusional encounter complexes of two 
macromolecules, 'SDA association' to calculate bimolecular diffusional 
association rate constants, and 'SDA multiple molecules' to simulate the 
diffusive motion of hundreds of macromolecules. webSDA is freely available to 
all users and there is no login requirement. webSDA is available at 
http://mcm.h-its.org/webSDA/.