Proton transfer, hydrogen bonds molecular clustering

Wolf and co-workers presented a combined experimental and theoretical study employing molecular-dynamics simulations, in which they investigated the proton transfer from a water cluster to bulk water in the same membrane protein bacteriorhodopsin. Their efforts were directed towards the detailed mechanism. They found that the breaking of a hydrogen bond is activating a gate-opening, so that a proton can be released from a water cluster to extracellular water. This is a directed proton transfer and, thus, very different from random proton transfer as observed in liquids (as discussed in Section 2). 

Figure 21-15. Attachment of an excess tt electron to a cyclic hydrogen-bonded cluster facilitates inter-molecular proton transfer (a) formic acid dimer, (b) formamide dimer, and (c) formic acid-formamide (Figure 1 of ref. [51]. Reused with permission. Copyright 2005, American Institute of Physics)...

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