Emeritus Professor of Chemistry
Emeritus Vice Provost for Research
Ph.D. California Institute of Technology, 1963
(Physical and Biophysical Chemistry)
Magnetic resonance is one of the most powerful tools for studying molecular structure and dynamics, not only at the conformational level but also at a detailed electronic level. Professor Kwiram's research seeks to expand the repertoire of magnetic resonance methods and to pursue fundamental studies made possible by such methods.
One such area is represented by optically detected magnetic resonance (ODMR). The ODMR method can be used to study the triplet state properties of synthetic DNA oligomers in experiments designed to characterize energy transfer processes, photochemical and photophysical events, and environmental effects on spectroscopic parameters. The availability of defined synthetic DNA fragments provides an unprecedented opportunity to develop a thorough understanding of these much-studied but poorly characterized properties. A related thrust involves the study of small molecules bound to intact DNA and DNA fragments. The enormous sensitivity of ODMR provides unique advantages for this work. This method has also been used to investigate the structure and folding behavior of polypeptides and proteins.
A second area of investigation involves magnetic resonance studies of ground state molecules in the solid state. Various approaches are used including nuclear magnetic resonance (NMR), electron spin resonance (ESR), and nuclear quadrupole resonance (NQR). In some cases NMR and ESR are carried out simultaneously in a method referred to as electron-nuclear double resonance (ENDOR). One variant exploits the magnetic moment of unpaired electrons (introduced selectively) as the abundant "nucleus" in a double resonance experiment designed to detect deuterons and other nuclei with unusually high sensitivity. This approach allows studies to be carried out at very low temperatures where motional problems are minimized so that accurate rigid-lattice properties can be measured. Detailed information on hydrogen bonding and molecular structure for appropriate cases can be obtained this way. The results for bond lengths and angles involving hydrogen are comparable in accuracy to results of neutron diffraction studies.
Recent developments in this laboratory, in collaboration with the Max Planck Institute in Stuttgart, Germany, have resulted in the first demonstration of field cycled electron spin resonance experiments. In this novel approach, the normal ESR signal is initially monitored at high field to establish the base line ESR signal. The external field is then switched to zero in a time of roughly 1 ms. While the sample is in zero-field (zf), magnetic resonance transitions are induced thereby affecting the population distribution. After the external field is switched back on, this disturbance in zf of the level populations is detected as a change in the (high field) ESR base line. This approach combines the advantage of high field to achieve higher sensitivity with zf magnetic resonance which avoids anisotropy broadening. The potential of this new technique is undergoing further investigation.
"EDNMR and ENDOR Study of the beta-gamma Phase Transition in Malonic Acid Crystals," J. Krzystek, A. B. Kwiram, and A. L. Kwiram, J. Phys. Chem. 1995, 99, 402 .
"Field-Cycled Electron Nuclear Double Resonance," J. Krzystek, M. Notter, and A. L. Kwiram, J. Am. Chem. Soc. 1994, 98, 3559.
"ENDOR Studies at 4.2 K of the Radicals in Malonic Acid Single Crystals," R. C. McCalley and A. L. Kwiram, J. Am. Chem. Soc. 1993, 97, 2888.
"Geometry of the Cyclopropane-1, 1-dicarboxylic Acid Molecule at 5 K," J. Krzystek and A. L. Kwiram, J. Am. Chem. Soc. 1991, 113, 9766.
"Experimental Determination of the Methylene Rocking Angle in the Cyclobutane Ring," J. van Zee and A. L. Kwiram, J. Am. Chem. Soc. 1990, 112, 5012.