Edward Chikwana
Present Work and Research

My research interests are in chemical systems that generate chaotic dynamics. Studies done in various nonlinear systems maintained far from equilibrium have demonstrated a universal sequence of instabilities that are system-independent. The Belousov-Zhabotinskii (BZ) oscillator has been the most well-studied nonlinear chemical system. So far our studies on reactions of oxyhalogens with small organosulfur compounds have generated nonlinear behavior that rivals the BZ. I am not only interested in temporal chaos, but also in spatiotemporal chaos in which structure and form can be derived from erstwhile homogenous environments. When maintained far from equilibrium, these systems generate chemical oscillations, symmetry-breaking bifurcations, and traveling waves. Several studies have also been done on systems that suppress convection. In my project we introduce a possible new mechanism for pattern-formation that involves both convection and advection. Most realistic problems that need to be studied as in ocean layering dynamics, weather patterns and crystal growth do involve convection as the major driving force for self-organization. This self-organization behavior involves the characterization of the symmetry-breaking bifurcations based on the chemistry of the driving reaction. Other parameters that we use to understand these remarkable systems include viscosity of the medium, ambient temperature, vessel geometry, and gravity. Most of the studies, however, will involve the study of the coupling between thermogravitational and thermocapillary effects.  My work is mostly focused on the oxyhalogen oxidation of thiourea and its derivatives and trying to explain the patterns that are formed from the self-organization of the traveling chemical waves generated in these reactions.

I have also been involved in kinetics of selected organosulfur compounds in the presence of physiological oxidants such as oxyhalogens and peroxide.  The beauty of working with oxyhalogens as oxidants is that their chemistry has been thoroughly studied and and they also produce HOCl, HOBr and HOI as their most reactive species. These reactive oxygen species are also produced in the human body from the myeloperoxidase and eosinophil-catalyzed peroxidation of halide ions and as such we hope to be able to extrapolate our findings to the physiological system. I have worked on the oxidation of thiocarbamides that have been implicated in goitrogenic activities and have also worked with thiols, such as cysteamine, that have been implicated in DNA repair mechanisms and as antioxidants.  I am also involved in comparative studies on  the effects of substitution on the reactivities of thiourea and its methyl substituted derivatives.  Substituted thioureas are known to have varying toxicities in the physiological environment and some of them are known carcinogens, goitrogens and teratogens.

Publications:

  • Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Amidinothiourea by Acidified Iodate, Journal of  Physical Chemistry A;  2004; 108(6); 1024-1032.

  • Antioxidant Chemistry: Oxidation of L-Cysteine and Its Metabolites by Chlorite and Chlorine Dioxide, Journal of Physical Chemistry A.;  2004; 108(26); 5576-5587.

  • Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Guanylthiourea by Acidified Bromate, Journal of Physical Chemistry A; 2004; 108(52); 11591-11599.

  • S-oxygenation of Thiocarbamides: Oxidation of Phenylthiourea by Chlorite in Slightly Acidic Media, Journal of Physical Chemistry A; 2005; 109(6); 1081-1093.

  • Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of the Oxidation of Cysteamine by Acidified Iodate and Iodine, Canadian Journal of Chemistry; 2006; 84(1); 49 -57.

  • Comprehensive Kinetics and Mechanistic Studies of the Oxidation of Thiourea and its Metabolites by Oxychlorine Species, 2006; In Press.