Elucidation of Reaction Mechanism with the Unified Reaction Valley Approach: Part III Homogeneous Catalysis and Beyond

Southern Methodist University, Dallas TX

Investigators

Abstract

With this award, the Chemical Structure, Dynamics and Mechanism (CSDM-B) and Computational and Data-Enabled Science and Engineering (CDS&E) programs are supporting Professors Elfi Kraka and Dieter Cremer at Southern Methodist University to derive a general design principle for the next generation of chemical catalysts combining features of homogenous and enzyme catalysis. The unified reaction valley approach (URVA) of Cremer and Kraka aims to serve as a quantum chemical tool to study the mechanism of catalyzed reactions at a greater level of than is currently easily achieved. URVA acts like a "high-resolution-camera" attached to the reaction complex, being able to reveal the interplay between vibrations and the electronic structure changes of the reaction complex. It records all events when the reaction complex follows the energy valley on the reaction side up to the energy pass point and then down through the exit valley to the products. Important and less important events are differentiated by analyzing direction and curvature of the reaction path rather than features of the reaction complex itself. Basic differences between and catalyzed and non-catalyzed reactions can be determined in this way, but also the limitations of man-made catalysts are apparent. Enzymes are the well-tuned catalysts developed in response to stringent survival pressures. Given the remarkable catalytic power seen in many enzymes, the major focus will be on the extension and application of the URVA methodology to enzyme catalysis to determine its major advantages. The mechanism of transition metal, non-transition metal or metal-free- and (artificial) enzyme-catalyzed reactions will be systematically analyzed and compared. A strategy for de novo catalyst design is to be developed, which, by including aspects of both chemo- and bio-catalysis, can serve as an incubator for enhanced interdisciplinary efforts to generate target-specific catalysts. The data of all reactions investigated (including reaction movies) will be collected in the CATCO reaction library, which will increase to more than 500 reactions. This library will be available to the chemical community for research, teaching, and student training. During the past two years, URVA has proven to be a unique tool for the mechanistic study of more than 150 homogenous catalysis reactions. In addition to following the chemical processes of bond breaking and forming, URVA uses a substantially improved algorithm for following the reaction valley far out into the van der Waals region to monitor pre- and post-chemical processes in a high level of detail. The direction and curvature of the reaction valley are analyzed in terms of internal coordinate or curvilinear coordinate components and then directly related to electronic structure changes. Other essential tools of URVA are the local vibrational mode analysis, the charge transfer and charge polarization analysis as well as the presentation of the chemical reaction in terms of reaction phases. Method development will include the design and programming of i) URVA methodologies for an implicit or explicit inclusion of solvent effects, ii) 2-component relativistic methods for the investigation of "relativistic" systems, and iii) new QM/MM methodologies for the description of chemical reactions in an enzymatic environment.