(94b) Investigating the Methanol Oxidation Mechanism by Mg+2 and Sr+2-Containing Methanol Dehydrogenase Enzyme

   Global revolution
in technologies demands for power sources with high energy density, low cost
and portability. One of the promising alternatives to current power sources
being studied these days are the Proton Exchange Membrane (PEM) fuel cells [1].
They use expensive anode catalysts like platinum which easily get poisoned by carbon
monoxide, a byproduct of oxidation reactions that take place in fuel cells [1].
A solution to these problems is using biofuel cells which use enzymatic
catalysts in place of expensive catalysts and are more eco friendly in nature
[2]. Methanol
dehydrogenase (MDH)is one such enzyme used as an anodic catalyst
for a methanol-fed biofuel cell producing enough power for small electronic
device applications [3]. Understanding the oxidation mechanism at the active
site is necessary to study the power output limitations associated with this
MDH fuel cell. The active site of MDH contains a Ca⁺²
ion which acts as a Lewis acid during the oxidation mechanism [4].

Previously, it was observed that the
energy barrier for the oxidation of methanol was influenced by the atomic size
of the metal ion in the active site of MDH [5]. Thus we expect that there might
be a change in the barrier if Mg⁺² andSr⁺² are
placed instead of Ca⁺² as they are the same periodic group elements.
Quantum
mechanical (Density Functional Theory) simulations are performed to obtain
geometry, energy and electronic configurations of small portions of the active
site and the activation energies for the various methanol oxidation steps have
been calculated. The geometries and free energy barriers
obtained from the rate-limiting steps with these cations are compared with the previous
results [5]. This comparison could help us in determining whether these
ion-modified MDH would be more/less active for the oxidation of methanol.

References:

1. Cleghorn S. J. C., Ren X.,
Springer T. E., Wilson M. S., Zawodzinski C., Zawodzinski T. A., and Gottesfeld
S., "Pem Fuel Cells for Transportation and Stationary Power Generation
Applications". Int. J. Hydrogen Energy, 22, 1997.

2. Palmore G. T. R. and Whitesides
G. M., "Microbial and Enzymatic Biofuel Cells", Enzymatic   Conversion
of Biomass for Fuels Production, J.O.B. M.E. Himmel, and R.P. Overend, Washington,
DC., 1994.

3. Zhang X. C., Ranta A., and Halme
A, "Effect of Different Catalytic Oxidants on the Performance of a Biocatalytic
Methanol Fuel Cell", in Proceedings 204th Meeting of The
Electrochemical Society, 2003.

4.  C. Anthony, ?Methanol
Dehydrogenase, a PQQ-Containing Quinoprotein Dehydrogenase?, Kluwer
Academic/ Plenum Publishers, New York, 2000.

5. Idupulapati, N.B., Mainardi, D.S., ?Coordination
and binding of ions in Ca2+- and Ba2+-containing methanol dehydrogenase and
interactions with methanol?, Journal of Molecular Structure: THEOCHEM,
901 (1-3), 2009.