Office: CHB 312 Phone: (405) 325-3820 Email: rwtaylor@ou.edu	Richard W. Taylor Professor A.B. (Temple University) 1968 Ph.D. (Wayne State University) 1973 Postdoctoral Fellow (Purdue University) 1973-1976
Division: Analytical chemistry Research Interests Metal ion complexation chemistry; membrane transport processes of polyether ionophores; selective chelating agents for heavy metal ions.

Research Description

Our research is focused on several areas involving various aspects of coordination chemistry: (i) transport of cations across membranes, (ii) metal ion sensors, and (iii) complexation chemistry of macrocyclic ligands.

Membrane Transport by Polyether Ionophores. Naturally occurring carboxylic acid polyether antibiotics, such as A23187, monensin, and ionomycin, transport divalent cations across artificial or biological membranes with varying degrees of selectively. These compounds, called ionophores, are used as biological tools to manipulate transmembrane ion gradients, as carriers in metal ion separations, and in the fabrication of ion selective electrodes. We employ spectroscopic (UV-Vis, circular dichroism, fluorescence, NMR), potentiometric, and structural (X-ray) techniques to study the equilibria and kinetics of the individual steps (complexation, transmembrane diffusion, dissociation) that comprise the overall membrane transport cycle, and the structures of the associated complexes. The goals of this research are to obtain a better understanding of the mechanism(s) of cation transport mediated by carboxylic acid ionophores, to elucidate the physicochemical properties which underlie the cation transport selectivity, and to design ionophores with improved transport selectivity and efficiency.

Selective Chelating Agents. Synthetic macrocyclic multidentate ligands form stable complexes with a wide variety of metal ions. The ligand structures may be changed in a systematic manner to alter the absolute and relative values of the complexation constants. The complexation selectivity can be influenced by varying ligand properties such as (i) cavity size, (ii) number and type (O,N,S) of donor atoms, and (iii) backbone substituents (benzo, n-alkyl). Macrocyclic ligands, derivatized by the addition of hydrophobic substituents, act as metal ion extractants or ionophores, while introduction of a chromophore into the backbone allows the development of metal ion sensors. Our research program involves synthesis of new macrocyclic ligands, determination of their metal binding properties, and evaluation of their spectroscopic, membrane transport, and extraction properties.

Selected Publications

"The Ionophore Nigericin Transports Pb²⁺ With High Activity and Selectivity: A comparison to Monensin and Ionomycin" Hamadinia, S. A.; Tan, B.; Erdahl, W. L.; Chapman, C. J.; Taylor, R. W.; Pfeiffer, D. R., Biochemistry 2004, 43, 15956-15965.

"Surfactant-Based Technologies Applicable to Remediation of Mercury Pollution in the Subsurface" Rouse, J. D.; Bjornen, K. K.; Taylor, R. W.; Schiau, B.-J., Environmental Practice 2004, 6, 157-164 .

"Ligand-Modified Colloid Enhanced Ultrafiltration.  Use of Nitrilotriacetic Acid Derivatives for the Selective Removal of Lead From Aqueous Solution" Roach, J. D.; Christian, S. D.; Tucker, E. E; Taylor, R. W.; Scamehorn, J. F. Sep. Sci. Technol. 2003, 38, 1925-1947.

"Monensin Mediates a Rapid and Selective Transport of Pb²⁺: Possible Application of Monensin for the Treatment of Pb²⁺ Intoxication" Hamadinia, S. A.; Shimelis, O. G.; Tan, B.; Erdahl, W. L.; Chapman, C. J.; Renkes, G. D.; Taylor, R. W.; Pfeiffer, D. R.  J. Biol. Chem. 2002, 277, 38113-38120.

"Transport Properties of the Calcium Ionophore ETH-129" Wang, E.; Erdahl, W. L.; Hamidinia, S. A.; Chapman, C. J.; Taylor, R. W.; Pfeiffer, D. R.  Biophys. J. 2001, 81, 3275-3284.

"Ionomycin, a Carboxylic Acid Ionophore, Transports Pb²⁺ with High Selectivity" Erdahl, W. L.; Chapman, C. J.; Taylor, R. W.; Pfeiffer, D. R. J. Biol. Chem., 2000, 275, 7071-7079.

"Mechanism and Specificity of Lanthanide Series Cation Transport by Ionophores A23187, 4-BrA23187 and Ionomycin" Wang, E.; Taylor, R. W.; Pfeiffer, D. R. Biophys. J. 1998, 75, 1244-1254.

"Evidence Against formation of Dimers by A23187: Photo-Induced Degradation of Ionophore A23187" Thomas, T. P.; Wang, E.; Pfeiffer, D. R.; Taylor; R. W. Arch. Biochem. Biophys. 1997, 342, 351-361.

"Acid-Catalyzed Dissociation of Copper(II) and Lead(II) Complexes of Macrocyclic Diazapolyoxa-N,N'-diacetic Acids" Laing, J. L.; Taylor, R. W.; Chang, C. A. J. Chem. Soc., Dalton Trans. 1997, 1195-1200.

"Ionophore 4-BrA23187 Transports Zn²⁺ and Mn²⁺ with High Selectivity Over Ca²⁺" Erdahl, W. E.; Chapman, C. J.; Wang, E.; Taylor, R. W.; Pfeiffer, D. R. Biochemistry 1996, 35, 13817-13825.

"Ca²⁺ Transport Properties of Ionophores A23187, Ionomycin, and 4-BrA23187 in a Well Defined Model System" Erdahl, W. E.; Chapman, C. J.; Taylor, R. W.; Pfeiffer, D. R. Biophys. J. 1994, 66, 1678-1693.