A detailed listing of research interests and accomplishments, cross-referenced with abstracts from relevant publications, is available on the Research portion of my Group Web Page. A much abbreviated list of current interests follows here:

Variable-spin Systems. Interesting properties are often associated with molecules having two or more frontier molecular orbitals that are similar in energy; e.g., they may exhibit high- or low-spin ground states, unique reactivities, significant sensitivity to condensed-phase effects, etc. Beyond the chemically interesting aspects of specific molecular architectures, the modeling of such systems in general poses unique challenges to electronic structure methodologies. In addition to the development of new theoretical methodologies for the accurate treatment of different aspects of variable-spin systems, we are characterizing key chemical characteristics of carbenes and nitrenes (fundamental organic reactive intermediates and, in the latter case, photoaffinity labelling agents), nitrenium ions (carcinogenic products from aromatic amine catabolysis), arynes (fundamental organic reactive intermediates enjoying a renaissance of interest owing to their intermediacy in certain anticancer therapeutic agents), non-Kekulé molecules (fundamental organic reactive intermediates and possible building blocks for organic ferromagnetic materials), and bimetallic model systems for copper-containing enzymes and the photosynthetic active site.

Solvation and Other Condensed Phase Phenomena. The development of theoretical chemistry methods that are as robust for condensed phases as those already available for the gas phase continues to be at the theoretical frontier. An alternative to approaches involving the explicit inclusion of hundreds to thousands of surrounding atoms/molecules is to treat the embedding medium as a dielectric continuum with additional terms to account for non-electrostatic interactions between explicit and implicit regions. We have pioneered methods for accomplishing this using classical and quantal theories. We have moreover developed the methodology to handle equilibrium and non-equilibrium solvation regimes, the latter being particularly relevant for spectroscopy and reaction dynamics. Concomitant with continuing methods development, particularly with extensions to mixed quantal/classical treatments and to non-homogeneous condensed phase environments, we are also investigating phenomena of fundamental biological, chemical, and environmental interest, e.g. conformational issues in sugars, solvent effects on uni- and bimolecular chemical reactions, partitioning of organic molecules between unlike media, and fate constants of environmental contaminants in aqueous media.

tRNA Structure and Dynamics. One of the key steps in the biological synthesis of proteins is the translation of the genetic code, as carried by messenger ribonucleic acids (mRNAs), into the correct sequence of amino acids that defines a given protein. This translation is accomplished within cellular assemblies of RNAs and proteins called ribosomes. Amino acids are delivered to the ribosome by transfer RNA (tRNA) molecules having "anticodon" regions that are complementary to the 3-base "codon" sequence of the mRNA. Thus, one key aspect of this translation involves ensuring that distinct tRNA molecules always carry their designated amino acid. Using classical simulations with explicit solvent, we are studying the process by which tRNA molecules become "charged" with the proper amino acid and in particular the mechanism by which aminoacyl-tRNA synthetases specifically recognize their substrate tRNA molecules.

Detoxification of Chemical Weapons. Present military doctrine calls for field decontamination of bulk amounts of organophosphorus chemical warfare agents to be accomplished either by hydrolysis in organic/aqueous media, or via bioremediation, either using live bacteria, or immobilized and encapsulated enzymes. Detailed mechanistic understanding of the chemical and biochemical pathways involved is for the most part lacking. We are taking advantage of newly available computational models that (i) accurately represent enzymatic environments and (ii) efficiently include the effects of bulk solvation to perform a systematic study of reagents and reaction conditions in order to clarify critical microscopic details. Particularly with respect to bioremediative systems, computation provides a cost-effective method to explore enzymatic modifications designed to enhance catalytic efficiency, substrate specificity, etc.

Experimental/Theoretical Synergy. Through many collaborations with experimental colleagues, we have contributed to the better understanding of a variety of issues associated with organic and inorganic structure and reactivity. The areas where we continue to have key interests include elucidating the mechanistic and stereochemical course of electrocyclic organic reactions, characterizing processes by which various classes of contaminants are degraded in the environment, and the nature of inter- and intramolecular interactions governing crystal morphology, molecular recognition, etc.

The Electronic Structure of Singlet and Triplet Nitrenium Ions From MCSCF and DFT Calculations

Predicting Regioselectivity in the Reduction of Polynitroaromatics in Aqueous Solution

Substituent Effects on the Structure and Reactivity of Aromatic Nitrenes

On the GAMESSPLUS homepage you can obtain modules that, when added to the free electronic strucure program GAMESS, allow for the inclusion of solvation effects at the ab initio and density functional SCRF levels. Version 4.4 includes analytic derivatives for the solvation terms. The HONDOPLUS homepage provides details on analogous free, stand-alone code having the same functionality.

More information on similar modules available for theGaussian series of programs can be found on the MN-GSM homepage.

OMNISOL is a free (but licensed) program for the rapid (non-quantum-mechanical) estimation of solvation free energies in water or organic solvents. For more information see the OMNISOL homepage.

For a complete comparison of available codes and solvation modules, see http://comp.chem.umn.edu/solvation/comparison.htm.