Exposed salt bridge

Both the charged species are initially solvated by water, and to form the salt bridge both ions must be desolvated. This comes at some enthalpic cost, but the freeing of water molecules leads to a concomitant, favorable increase in entropy. The strength of the ion pair will depend on the stability of the salt bridge vs. that of the individual solvated ions. If the salt bridge is buried in a relatively hydrophobic active site, it is less solvated and will be more favored than the same interaction in a solvent-exposed active site. 

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