Theoretical and Computational Chemistry
Research in my group seeks to understand the interplay between geometric structure of molecules and solids, their electronic structure, and physicochemical properties. We are developing new methods and algorithms for finding global minima on potential energy surfaces of molecules and solids. We design new materials with potential applications as energy storage media, new heterogeneous catalysts, and fundamental elements of semiconductor devices. We study elementary chemical processes driven by excess charge.
1. Electron-Driven Acid-Base Chemistry
Low energy electrons are responsible for a variety of deleterious effects in biological systems. In the course of collaborative studies with the experimental group of Kit Bowen, we demonstrated that the excess electron attachment to complexes of nucleic acid bases (B) with weak acids (HA) might lead to a barrier-free intermolecular proton transfer: B- + HA --> (BH·)A-. More recently we demonstrated that the radical BH· can trigger strand breaks in DNA, with kinetic barriers smaller than 5 kcal/mol. (NH3+HX)- --> (NH4+…X-)-, where X is a halogen, has recently been studied by us in great detail.
Figure 1. Elementary step of intermolecular proton transfer can be triggered by an excess electron.
2. Hierarchical Hydrogen Storage: Hydrogen Clathrates of Ammonia Borane
The concept of hierarchical hydrogen storage is illustrated by clathrates built from ammonia borane (AB) and loaded with molecular hydrogen. These materials would have two levels of hydrogen storage: (i) physisorbed H2 and (ii) hydrogen chemically bound in AB. The advantages of these materials would be: (i) fast kinetics of release of physisorbed hydrogen, and (ii) high hydrogen density. We predicted stability of hydrogen clathrates of ammonia borane at ambient pressure and T=77 K.
Figure 2. Hierarchical hydrogen storage in clathrates of ammonia borane: two levels of hydrogen storage: physisorbed molecular hydrogen (fast rate of release) and hydrogen chemically bound in ammonia borane (slow rate of release).
3. Combinatorial-Computational Methods
Over the last few years we have been developing combinatorial-computational methods. The approach involves three steps: (i) combinatorial generation of a library of molecular “suspects”, (ii) determination of “fitness” of each suspect using electronic structure methods, and (iii) extraction of chemical rules from the properties of members of the library. This approach has been used to find the most stable tautomers and conformers of molecules.
Figure 3. Search for the most stable conformers of a molecule can be performed using a computational method developed in our group. A user specifies which bonds will be rotated and with which increments and a library of initial structures is automatically created.