Molecular proton wire

Molecular protonic devices acting as proton wires, rectifiers, charge separation components, etc., represent highly significant goals in the development of information handling systems based on ionic species. They deserve active synthetic and physico-chemical studies. 

Frank,R.A.,Titman, C. M.,Pratap,J.V.,Luisi, B.F., and Perham, R.N. (2004) A molecular switch and proton wire synchronize the active sites in thiamine enzymes. Science306, 872-876. 

In order to understand the factors controlling plumbing and pumping, it is very important to explore the detailed molecular properties of proton wires in membrane proteins. In particular, it is essential to determine the subtle interplay between structural, equilibrium, and non-equilibrium properties in the molecular mechanism of proton transport in complex hydrogen-bonded networks. 

Another important class of proteins that contain water channels are the aquaporins, which regulate the flow of water in and out of cells. They will let water through but not salts or other dissolved substances, and as such, they act as molecular water filters. Water transport occurs via a chain of nine hydrogen-bonded molecules (Fig. 6.13). But if this chain were to permit rapid transmembrane proton motion, that would disturb the delicate charge balance across the membrane. So aquaporin must somehow disrupt the potential proton wire that threads through it. The mechanism has been much debated, but it now seems that the inhibition of proton transport is dominated by electrostatic repulsion by positively charged groups in a narrow constriction in the middle of the pore [72]. 

The energetic stabilization of a proton in a membrane provided by a proton wire raises a question about the likelihood of the spontaneous formation of such wires. This issue was addressed in separate calculations in which the free energy of a chain of water molecules spanning the bilayer was estimated at approximately 25 kcal/mol [14]. In unconstrained molecular dynamics simulations it was further found that transmembrane water chains are very transient, with lifetimes of only a few picoseconds. These lifetimes are much shorter that the time required for the water reorientation in the chain needed to transfer another pro-... 

In the same way, the host of a host-guest complex can fimction as, or as part of, a sensor. Sensors are devices that announce the presence of analytes via reversible, real-time signals discernible by one of the human senses. Molecular recognition complexes utilized toward this end fimction as reusable indicators. One school of thought holds that a sensor is a macroscopic device with wires and the like a pH meter is one such embodiment. We prefer the view that molecules themselves can be sensing devices as well. A solution of a colorimetric pH indicator fulfills all the requirements of a sensor the solution announces the presence of protons via a reversible, real-time signal discernible by one of the human senses (sight). 

Protonic molecular wires containing metal complexes 01MI52. 

M. Akeson and D.W. Deamer. Proton conductance by the Gramicidin water wire — model for proton conductance in the Fi Fq ATPases. Biochim. Biophys. Acta, 60 (1990) 101-109. M.S.P. Sansom, I.D. Kerr, and H.S. Son. The influenza A virus M2 ion channel A molecular modeling and simulation study. Virology, 233 (1997) 163-173. 

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