Helen W. Richter

Research Interests

The areas of interest in our research group are applications of chemical kinetics in the study of free radical reaction mechanisms and rates, and the use of spectroscopic methods in the characterization of species in solution. The principal physical methods we use are NMR spectroscopy and UV-vis spectroscopy. X-ray crystallography and mass spectroscopy are used on a collaborative basis. Currently, we are focusing on characterization of organoiodine(III) species in solution, including preparation of new species; reactivity and nature of iron complexes in solution; measurements of magnetic susceptibilities by NMR methods; and the photochemistry of phenyl azides.

Organoiodine(III) species, for example [hydroxy(tosyloxy)iodo]benzene, are widely used in synthetic organic chemistry. We recently characterized the species produced by this compound in aqueous solution using potentiometric titrations, UV-vis spectroscopy, NMR spectroscopy and computer modeling of the results. The protic and dimerization equilibria found help in understanding the chemical reactions of these compounds. We are currently studying species produced in organic solvents, and have found an unexpected complex with pyridine.

Paramagnetic susceptibilities of solution species can be measured via NMR spectroscopy by the Evans-Dickinson method. We found that Fe(II)(2,2'-bipyridine)32+ undergoes an unexpected singlet-triplet spin transition in aqueous solution. Surprisingly, we found that many of the 1H-reference compounds, such as 2-methyl-2-propanol, slip into the hydrophobic environment around the metal ion that is created by the bipyridyl ligands. To circumvent this problem, we used the triflate ion as our reference compound: triflate is especially hydrophilic owing to participation of the fluorine atoms in hydrogen bonding with water, and thus it does not "dissolve" in the bipyridine ligands. Triflate requires 19F-NMR spectroscopy. Iron catalyzed reactions are responsible for much of the tissue damage that occurs in ischemic events, such as myocardial infarction, and also are crucial in the time limitations for heart transplantation. We collaborate with Dr. Daniel Ely of the Department of Biology in studies relating to reperfusion tissue injury and heart transplantation.

Selected Publications

1. "Maintenance of Left Ventricular Function (90 percent) After 24-hour Heart Preservation with Deferoxamine," Ely, D.; Dunphy, G.; Dollwet, H.; Richter, H.; Sellke, F.; and Azodi, M., Free Radicals Biol. Med., 1992, 12, 479-485.
2. "Characterization of Species Present in Aqueous Solutions of [Hydroxy(mesyloxy) iodo] Benzene and [Hydroxy(tosyloxy) iodo ]Benzene," Richter, H.W.; Cherry, B.R.; Zook, T.D.; and Koser, G.F., J. Am. Chem. Soc., 1997, 119, 9614-9623.
3. "Radiation Chemistry: Principles and Applications," in "Photochemistry and Radiation Chemistry, Complementary Methods for the Study of Electron Transfer," H.W. Richter; Nocera, F., and Wishart, J., Eds. ACS Books, Advances in Chemistry Series, 1998, 254, 5-33.
4. "Twenty-Four-Hour Heart Preservation Using Continuous Cold Perfusion and Copper(II) Complexes," Selke, F.W.; Richter, H.W.; Dunphy, G.; Azodi, M.; and Ely, D.L., J. Surgical Res., 1998, 80, 171-176.
5. "The Effects of Mannitol, Albumin and Cardioplegia Enhancers on 24-hour Rat Heart Preservation," Dunphy, G.; Richter, H.W.; Azodi, M.; Weigand, J.; Sadri, F.; Selke, F.W.; and Ely, D.L., American Journal of Physiology: Heart and Circulatory Physiology, 1999, H1591-H1598.