Advances in Physical Organic Chemistry

Richard is interested in understanding the mechanism for the reactions of small molecules in water, and for their catalysis by enzymes. His early independent studies focused on developing methods to determine rate and equilibrium constants for reactions of simple carbanions and carbocations intermediates of organic reactions in water. This led to a broad characterization of substituent effects on the stability of these intermediates, and a rationale for the observation that many polar electron-withdrawing substituents cause a decrease in both the stability and reactivity of resonance stabilized carbocations. Richard transitioned to studies on the mechanism for small molecule catalysis in models for enzyme-catalyzed reactions. These included proton transfer, hydride transfer, aldol condensation reactions, and phosphate diester hydrolysis. Most recently he has focused on determining the mechanism for the stabilization of reactive carbocation and carbanion enzymatic reaction intermediates through interactions with active-site protein side chains. An important outcome of this work is the determination that the most proficient enzyme catalysts of metabolic reactions utilize substrate binding interactions as glue in the construction of protein-substrate cages that provide a tremendous stabilization of carbanion and carbocation reaction intermediates. These results provide a simple rational for the existence of enzyme catalysts that follow Koshland's induced-flt mechanism.