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Project Descriptions:

Potential Energy Surfaces

Solvated Species

CH5+

Porous Crystalline Species

Temperature Effects on Structure

Photodissociation Dynamics

Computational Drug Design

Osteoporosis

Hydrogen Bonding

 

 

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

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 pdf (517 kB)

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). pdf (646 kB)

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). pdf (471 kB)

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). pdf (99 kB)

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). pdf (320 kB)

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). pdf (145 kB)

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). pdf (961 kB)