Nita A. Lewis

ASSOCIATE PROFESSOR, INORGANIC CHEMISTRY

Ph.D., University of Guelph, 1977
NRC Postdoctral Fellow, Stanford University, 1977-79
Von Humbolt Fellow, University of Frankfurt, 1986-87

Email: n.lewis@miami.edu

Brief description of research

Selected Publications


Brief description of research

Preparation and Study of Molecular Wires
One of the most exciting topics in modern chemistry is the possibility of creating nano-devices such as molecular computers. Already there are molecules which can operate as transistors, resistors, diodes, motors and molecular switches which may be activated by temperature, pressure or electro-magnetic radiation. Tying these devices together will require some sort of molecular wires. Many groups worldwide are working on this problem. It is necessary to prepare some sort of polymer and this usually results in making large numbers of molecules having different lengths controlled by a binomial distribution (Bell curve). Our approach allows the preparation of long wires of uniform length and in addition allows us to make wires which are bent to any desired angle. This project requires students to be skilled in both organic and inorganic synthesis. Other students are studying the properties of these wires using electronic and infrared spectroscopy, nmr and mass spectrometry techniques and electrochemistry. Several of our molecules are candidates for collaborative studies with Professor Leblanc's group in Langmuir-Blodgett techniques and scanning tunneling microscopy experiments. 

Electron Transfer by Tunneling Methods
Electron transfer reactions are fundamentally important to most areas of industrial endeavors as well as to all living organisms. During the past decade, a substantial effort has been put forth to attempt to understand the complexities of this process in redox proteins where the metal center is usually buried deep within the molecule. The theoretical analysis of real proteins is a formidable task although tremendous progress has been made and new tools have been developed specifically for the quantum electronic analysis of the inhomogeneous, three-dimensional aperiodic nature of the protein structures. These tools rely heavily on the lessons learned from an analysis of the electron transfer reactions in small model compounds. Originally, it was thought that the factors that controlled the rate of electron transfer were the driving force, reorganization energy and the distance between the reacting centers. It is now generally believed that the nature of the intervening residues and their orientation relative to the donor and acceptor groups are also important both for small molecules and for proteins. In addition, it has been found that conformational change may be a controlling factor for biological electron transfer. Our approach to examining this problem was to construct simple model systems which allow us to probe in a systematic way one variable at a time affecting the electronic pathway. For example, molecules of the type shown below where R=R'=CH3, R=CH3, R'=C6H5, and R=R'=C6H5 were constructed to determine whether phenyl rings could participate in through-space electron transfer processes. We found that the two halves of the molecules chose to orient themselves with parallel phenyl/phenyl and phenyl/pyridyl rings by changing the dihedral angle of the bridging group at the expense of maximizing the space they could occupy which would require a dihedral angle of 90o. This argues for a strong inductive effect on the electronic pathway rather than a true through-space "hopping" mechanism. We are currently constructing other models which are designed to separate inductive and through-space components of the electronic pathways in an effort to address these questions. 

Phenotyping Normal and Diseased Populations for P450 Isozymes
We are employing traditional probe drugs such as caffeine and dextromethorphan to determine the expression of some P450 enzymes in normal and diseased populations. Our efforts are concentrated on the comparatively little studied Hispanic and Caribbean populations as well as on the frequency of negative drug interactions occurring as a result of the lack of or over-expression of particular P450 isozymes in certain disease states. We have also begun to investigate a new harmless probe for a completely different P450 isozyme.


Selected Publications

Philip D. Acott, Ghazala Ali and Nita A. Lewis, The Cr(II) Reduction of Pentane-2,4-dionatobis(ethylenediamine)cobalt(III). An Apparent Failure of the Product Criterion for Assigning Inner-sphere Mechansims, Inorg. Chim. Acta, 99, 169-176 (1985).

Nita A. Lewis and Ananda M. Ray, Reduction of Sulfinato- and Sulfenato-Cysteine Derivatives of Cobalt(III), Inorg Chem., 24, 340-346 (1985).

Ghazala Ali and Nita A. Lewis, "Evidence for a Two-electron Transfer using Cr(II) as a Reductant", Inorg. Chim. Acta, 128, L19 (1987).

Nita A. Lewis and Robert J. Balahura, "An Autocatalytic Redox Reaction Involving Cr(II) Attack at a b-diketone Carbon Atom", Inorg. Chim. Acta, 130, 151 (1987).

Nita A. Lewis and Ananda M. Ray, "Solvent Effects on Redox Reactions. 2. The Cr(II) Reduction of Tris(pentane-2,4-dionato)cobalt(III) in Acetone/Water Mixtures", Inorg.Chim. Acta, 132, 49 (1987).

Nita A. Lewis and Yaw S. Obeng, "Ionic Strength Dependence of Intervalence Transition Bands in Electron Tunnelling Processes", J. Am. Chem. Soc., 110, 2306 (1988).

Nita A. Lewis, Christian Friesen, Peter S. White and Robert J. Balahura, "Use of Extended Huckel Molecular Orbital Calculations in Determining the Position of Attack in Inner-Sphere Electron-Transfer Reactions: X-ray Crystal Structure of (1,3-Diphenyl-propane-1,3-dionato)bis(ethylenediamine)cobalt(III)", Inorg. Chem., 27, 1662-1666, (1988).

Nita A. Lewis, Daniel V. Taveras and William L. Purcell, "Effects of Anions on Redox Reactions. 2. The Chromium(II) Reduction of [Co(sep)]3+ in the Presence of Halide Ions", Inorg. Chem., 28, 133 (1989).

Nita A. Lewis, Yaw S. Obeng, Daniel V. Taveras and Rudi van Eldik, "Pressure Tuning Spectroscopic Study of Electron Tunnelling Processes in Solution", J. Am. Chem. Soc., 111, 925 (1989).

Nita A. Lewis and Yaw S. Obeng, "Oxidant-dependent Non- adiabatic Intervalence Transitions", J. Am. Chem. Soc., 111, 7624 (1989).

Nita A. Lewis, Yaw S. Obeng and William L. Purcell, "Medium Effects in Weakly Coupled Electron Transfer Processes. Calculation of Inner-sphere Reorganizational Energies at Zero Ionic Strength", Inorg. Chem., 28, 3796 (1989).

Ghazala Ali and Nita A. Lewis, "The Cr(II) Reduction of [Co(bipy)3]3+. Observation of a Dimeric Cr(III) Product", Inorg. Chim. Acta, 167, 5-13, 1990.

Nita A. Lewis and Daniel V. Taveras, "High Pressure Studies of Long Range Electron Transfer Processes in Solution", Advances in Chemistry, 197-210, 1990. (INVITED PAPER)

Nita A. Lewis, Richard R. McNeer and Daniel V. Taveras, "The Use of Pressure-tuning Spectroscopy to Distinguish between One and Two Electron Transfer Processes", Inorganica Chimica Acta, 225, 89-93 (1994). (INVITED PAPER).

Nita A. Lewis and Wei Pan, "The Influence of Side-chains on Electronic Coupling between Metal Centers in Simple Model Systems", Inorganic Chemistry, 1995, 34, 2244.

Nita A. Lewis, "High Pressure Studies on Intervalence Transition Bands of Mixed-valence Complexes", Trends in Inorganic Chemistry, 4, 107-119, 1996 (INVITED REVIEW).

Nita A. Lewis and Dipankar Datta, On the Structure of CH3OOCCH2CH2Co(DH)2.H2O [DH = Dimethylclyoximate Mono Anion], submitted to Organometallics.

Gouram K. Patra, Nita A. Lewis and Dipankar Datta, Use of barbituric acid as a "padlock" to generate an azamacrocyclic complex of Ni(II) containing fused aromatic rings, submitted to Inorganic Chemistry.

Nita A. Lewis and Richard R. McNeer, "Calculation of Minimum Enclosing Ellipsoidal Volumes in Binuclear Metal Complexes", Models in Chemistry, back for revision.