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Biological Systems

Biological systems pose a major challenge to Theoretical Chemistry in terms of their mesoscpopic size and complexity. Our effort in understanding the electrostatics and reactivity of biopolymers is currently directed into solvation and redox properties of redox biopolymers and the thermodynamics of biological electron transfer in photosynthesis.

Redox thermodynamics of metalloproteins.

Recent extensive Molecular Dynamics simulations of metalloproteins have revealed a very broad distribution of electrostatic fluctuations produced by hydrating water, far exceeding the previous estimates and results typically obtained on synthetic molecules. The study was featured on the cover of the Journal of Physical Chemistry B (image). The new statistics of electrostatic fluctuations is responsible for a gigantic reorganization energy of electron transport in biological energy chains. The finding will have significant implementations for the energetics of photosynthesis and other biological energy transformations. The protein fluctuations were found to lose ergodicity on the typical time-scale of the process suggesting that regulation in biology might be achieved by optimizing the time-scales instead of Gibbs energies as is currently widely accepted.



Charge transfer in DNA.

The goal of research on charge transfer in DNA fragments is to understand the experimentally observed relatively low values of the distance decay parameter of charge transfer rates. The current estimates of the decay parameter arising from the distance dependence of the solvent reorganization energy lead to overall too fast decay of the rate constant with the donor-acceptor distance when the Marcus-Hush model for the activation barrier is used. In contrast, the dependence of the activation barrier on the reorganization energy is much weaker in the Q-model (see J. Chem. Phys. 2000, 113, pp. 5413-5424). The Q-model was used to fit experimental energy gap laws for hole injection into DNA hairpins (Figure) studied by Lewis and co-workers (see J. Phys. Chem. B 2003, 107, pp. 14509-14520).