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Douglas Poland
Theoretical Chemistry Johns Hopkins University Phone: 410.516.7441 PhD - Cornell University My research centers around the application of statistical mechanics to problems in chemistry and biology. When I first came to Hopkins my interests were mainly in the statistical mechanics of helix-coil transitions in proteins and nucleic acids. Over the years I expanded my interests to include studies of phase transitions in lattice models and the thermodynamics of chemical reactions in nonideal, nonequilibrium systems. Lately most of my work has centered around the calculation of distribution functions for chemical and biochemical systems. For example, if one knows the heat capacity of a system as a function of temperature (say, expressed as a Taylor series in the temperature), then one can show that this experimental data can be turned into a set of moments of the energy distribution. Thus given the heat capacity through the second power in the temperature, this turns out to be enough information to calculate four moments of the energy distribution. Using the maximum-entropy method, one can then use the moments to calculate an approximate energy distribution (the more moments one has, the more accurate the distribution). When one applies this method to the heat capacity of proteins, one finds that many proteins show a bimodal (two peak) energy distribution, indicating that the thermal unwinding of these molecules involves two distinct populations of species (native and unfolded). This same approach can be applied to the binding of ligands to biopolymers. In that case the appropriate titration curve yields binding moments which in turn can be used to calculate the distribution of species bound to the macromolecule. In this manner the complete binding polynomial (for hundreds of binding sites) can be calculated explicitly. |
