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Project
Descriptions: Temperature
Effects on Structure |
Solvated Species
Deborah Crittenden, Keiran Thompson, James Erickson,
Peng Xu We have
developed new computational protocols and implemented quantum diffusion Monte
Carlo methods to study and predict the structure and properties of relatively
large molecules and clusters, particularly loosely bound solvated species. We have a
particular interest in biologically active amino acids that exist as
zwitterions at biological pH. We have used our computational protocols to
investigate the lowest energy structures for a range of amino acids and
phosphonic and phosphinic species. We have also used QDMC methods on
interpolated potential energy surfaces to investigate the vibrationally
averaged, or ground state structure of species such as: the water dimer, as a prototype ethanediol:water complexes, which provide a model for polyhdroxylated
carbohydrate species, glycine:water
complexes, the smallest amino acid, which will provide benchmark calculations
for understanding the interactions of amino acids with water glycy
radical:water complexes, a model for radical peptide reactions (with Prof Leo
Radom, Sydney) GABA:water complexes, a larger amino acid that is the major
neuroinhibitory species in mammalian central nervous systems. |
GABA Glycyl
radical
|
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We will
complete these investigations and definitively predict the structures of
these species. We also plan to use the glycine:(H2O)8 PES to investigate and
quantify the effects of holding solvent water molecules rigid, an approximation
used in almost all solvation models and the approximation most in question in
the solvation of charged or zwitterionic species like the amino acids glycine
and GABA. Another
important aspect of this project is understanding how the local protein
environment affects the structure of an amino acid such as GABA or glutamic
acid. We will model the local environment in the metabatropic glutamate
receptor, GluR2, using a distributed multipole analysis. The environment
within the receptor will be modelled as an anisotropic electric field which
will preferentially stabilize some conformers over others. Our potulate is
that this local electric field selects the biologically active conformer of
the amino acid. The field effects on structure will be modelled using a power
series expansion in the electric field and the dipole moment surface of the
amino acid, a model that we have shown works well for hydrogen bonded
systems. The field changes as the conformation of the receptor changes and
this will also be modelled. Selected Publications: M. J. T.
Jordan, D. L. Crittenden and K. C. Thompson, “Quantum Effects in Loosely
Bound Complexes”, in Advances in Quantum Diffusion Monte Carlo, J. B.
Anderson, S. R. Rothstein Eds.; American Chemical Society: Washington D. C.; 2007
D. L.
Crittenden, R. J. Kumar, J. Hanrahan, M. Chebib and M. J. T. Jordan "The
Stabilisation of Zwitterions in Solution: Phosphonic and Phosphinic Acid GABA
analogues", J. Phys. Chem. A, 109, 8398-8409 (2005). D. L.
Crittenden, M. Chebib and M. J. T. Jordan “The Stabilisation of Zwitterions
in Solution: GABA Analogues” J. Phys. Chem. A, 109, 4195-4201 (2005).
D. L.
Crittenden, K. C.Thompson and M. J. T. Jordan “On the Extent of
Intramolecular Hydrogen Bonding in Gas-Phase and Hydrated 1,2-Ethanediol” J.
Phys. Chem. A 109, 2971-2977 (2005). D. L.
Crittenden, K. C. Thompson, M. Chebib and M. J. T. Jordan “Efficiency
Considerations in the Construction of Interpolated Potential Energy Surfaces
for the Calculation of Quantum Observables by Diffusion Monte Carlo” J. Chem.
Phys. 121, 9844-9854 (2004). D. L.
Crittenden, M. Chebib and M. J. T. Jordan “The Stabilisation of Zwitterions
in Solution: g-Aminobutyric Acid (GABA)” J. Phys.
Chem. A 108, 203-211 (2004). M. J. T. Jordan and K. C.
Thompson “The Response of a Molecule to an External Electric Field:
Predicting Structural and Spectroscopic Change”, Chem. Phys. Lett. 370, 14-20
(2003). |