Advances in Physical Organic Chemistry

John Richard received his Ph.D. from Ohio State University, under the direction of Perry Frey. His thesis reported the synthesis of chiral oxygen-18 labelled phosphorothioate analogs of adenine nucleotides, and their use to determine the stereochemical course for enzyme-catalyzed phosphoryl transfer reactions. He worked as a postdoctoral fellow at Brandeis University with Bill Jencks, and developed an azide ion clock to measure the lifetimes of carbocation intermediates of solvolysis reactions. This clock was used to show that the mechanism for nucleophilic substitution reactions at ring-substituted 1 phenylethyl derivatives is controlled by the lifetimes of the carbocation intermediates of the solvolysis reaction. He began his independent career at the Department of Chemistry at the University of Kentucky in 1985 and moved to SUNY Buffalo in 1993.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.

• 1. The Interpretation and MechanisticSignificance of Activation Volumes forOrganometallic Reactions (R. van Eldik, C. Hubbard).2. Mechanisms for Catalysis by Small Molecule Analogs of Metalloprotein Active Sites (L. Berreau).3. Electron Transfer Reactions within Sigma and Pi-bridged Nitrogen-centered Intervalence Radical Ions (S. Nelsen).4. Using Kinetic Isotope Effects to Determine the Structure of the Transition States for Sn2 Reactions (K. Westaway).5. Mechanism for Nucleophilic Aliphatic Substitution at Glycosides (N. Horenstein).6. Effect of Enzyme Enzymatic Eynamics on Catalytic Activity (S. Schwartz).