Monday, September 6, 2010
7.5.1 inroduced the hydrogen bond network observed in water and some of its consequences (boiling points, hydrophobic effect). Another interesting effect of the hydrogen bond network is proton hopping also termed the "Grotthuss mechanism".
The structure of the hydrogen bond network allows a charged proton to 'hop' across multiple water molecules. This is a way in which the charges can be quickly distributed throughout the water volume and is related to the conductivity of water.
This effect must also be prevented within water channel transport. As cells utilise proton transport as a way of generating energy, this proton hopping would act to discharge the potential energy from localising the protons. Thus water channel proteins eliminate proton hopping by disrupting the hydrogen bond network of water as it moves through the channel. They can achieve this in a few ways. For example by moving single water molecules across one at a time or by twisting the orientation of the water molecule to dislocate the linear hydrogen bond.
The wikipedia file on Grotthuss mechanism has a quick video on proton hopping.
Posted by Heather at 10:55 PM