Professor Hynes's research area is theoretical chemistry and, in particular, its application to reaction and relaxation problems in chemistry. His work focuses on the theory of chemical reactions in solution,at interfaces, and in biomolecules, as well as such related phenomena such as solvationdynamics, vibrational energy transfer and molecular reorientation. The methodologies employed in the group include quantum chemistry, statistical mechanics, dynamics simulations and analytic theory, and mixtures of these.
While most chemical reactions occur in solution, little has been understood at the molecular level concerning the influence of the solvent on reaction rates. Hynes and his students have constructed theories of this influence for various reaction classes, and in recent years have focused on acid-base proton transfer reactions, e.g. AH + B ---> A- + HB+, one of the most important in chemistry and biochemistry. Emphasis is on a quite nontraditional picture for these reactions, in which the quantum mechanical character of the proton's motion is critical and in which the reaction coordinate and the reaction barrier are largely associated with the surrounding polar solvent molecules. Related issues also apply in photochemical proton transfers. Extension of these ideas to biological reactions such as enzymes is underway. Further, the role of proton transfers for the formation of a peptide bond (for protein synthesis) in vivo is under study.
Another area of reaction dynamics under study is conical intersections (CIs) in photochemical reactions in solution, which serve as very important 'funnels' for the rapid and efficient passage of the molecule from the excited electronic state to the ground state. It has already been found that a surrounding polar solvent can strongly influence such CIs and drastically influence the ultrafast dynamics of the electronic deactivation, and applications to both small molecules and photoactive biomolecules are underway.
The intramolecular and intermolecular flow of vibrational energy in molecules is central to chemical reactions and mode-selective laser chemistry. Reactions of particular interest that are under study are proton transfers and hydrogen bond breaking induced by infrared radiation. In related work, the ultrafast dynamics of water as probed by femtosecond infrared techniques has been examined, and a key part of the dynamics is the making and breaking of a hydrogen bond between water molecules. Current work is focused on related issues for the dynamics of water molecules in the first solvation shell of ions in water, including reorientational dynamics, where we have found that the mechanism is quite different than the traditional ‘rotational diffusion’ view.
Heterogeneous reactions on ice and other aerosol surfaces are critical in many atmospheric contexts, perhaps most notably for stratospheric ozone depletion, e.g. the Antarctic Ozone Hole. We have studied the molecular level mechanisms of a number of these reactions, finding the water molecules of the surface are actually active participants in the reactions, due to previously unsuspected proton relay mechanisms. Current efforts are focused on heterogeneous reactions on e.g. sulfate aerosols, which are the key aerosols in the mid-latitude stratosphere and elsewhere. Acid dissociation of sulfuric and nitric acids on aqueous aerosol surfaces is also intimately related to the above issues. While these are strong acids in solution, we find that they can become quite weak at a water surface. Related work is underway in an astrobiological topic: heterogeneous reactions on ice surfaces in the Interstellar Medium, such as the synthesis of amino acids.
In addition to the biochemically related reactions mentioned above, we are also currently attempting to understand the molecular mechanism of the intercalation of anti-cancer drugs into DNA.
(Prof. Hynes is also affiliated with the Department of Chemistry, Ecole Normale Supérieure, Paris).
P. M. Kiefer and J.T. Hynes, « Proton Transfer Reactions in a Polar Environment », in Vol. 1 , Hydrogen Transfer Reactions, J. T. Hynes and H.-H. Limbach, eds, R.Schowen, general editor. (Wiley-VCH, Weinheim, 2007). P. 307.
I. Burghardt and J. T. Hynes, “Excited-State Charge Transfer at Conical Intersections: Effect of an Environment, J. Phys. Chem. A, 110, 11411 (2006)
D. Laage and J.T. Hynes, “A Molecular Jump Mechanism of Water Reorientation”, Science, 311, 832 (2006).
D.Laage and J. T. Hynes, “Reorientational Dynamics of Water Molecules in Anionic Hydration Shells’, Proc. Natl. Acad. Sci., 104, 11167 (2007)
R.Bianco, S.Wang and J.T. Hynes, “ Theoretical Study of the First Acid Dissociation of H2SO4 at a Model Aqueous Surface”, J. Phys. Chem. B, 109, 21313 (2005).
R. Bianco and J.T. Hynes, “ Heterogeneous Reactions Important in Atmospheric Ozone Depletion; A Theoretical Perspective “, Accts. Chem. Res., 39, 150 (2006).
M. Roca, V. Moliner, I.Tunon, and J.T. Hynes, “Coupling Between Protein and Reaction Dynamics in Enzymatic Processes. Application of Grote-Hynes Theory to Catechol O-Methyltransferase”, J. Am. Chem. Soc., 128, 6186 (2006).
S.Pal, J.T. Hynes and B.Bagchi, “Multiple Timescales in Solvation Dynamics of DNA in Aqueous Solution: Role of Water, Counterions, and Cross-Correlations », J. Phys. Chem . B , 110, 26396 (2006).