The Zhu group is interested in asking and addressing fundamental questions in organic chemistry. During the process of using scientific methods to solve these problems, new observations are made which by not letting go often lead to the development of new tools that benefit other areas of science. The specific subdisciplines that we focus our research in are the interconnected areas of physical organic chemistry, supramolecular chemistry, and chemical biology. Our group has contributed to the understanding of molecular photophysics of organic molecules and mechanisms of copper-catalyzed reactions. Based on these fundamental works, new fluorescence imaging labels and methods, as well as new catalytic processes, have been created. Several current research topics are briefly described in the following sections.
Organic reactions and mechanisms
Our interest in the mechanistic aspects of copper-mediated coupling reactions arose when we discovered that copper(II) acetate and chelating azide possess unique reactivities in copper(II)-mediated azide-alkyne “click” cycloaddition reactions. The coordination between a chelating azide, such as 2-picolylazide, to copper(II) not only elevates the electrophilicity of the azido group, but increases the longevity of the copper catalyst by preventing aggregation. Copper(II) acetate provides a dinuclear scaffold that efficiently mediates both the inducting oxidative homocoupling of alkynes and the azide-alkyne cycloaddition. Based on the mechanistic understanding of this initial work, we have developed several methods to prepare triazole variants that have been applied by an increasing number of researchers.
Organic fluorescent dyes in microscopy
Our group has studied organic fluorophores that have zinc(II)-sensitive fluorescence properties. These compounds can be used as fluorescent labels for imaging zinc(II) in living cells using various fluorescence-based microscopic methods. We have developed a fluorescent heteroditopic ligand platform, whose fluorescence responds to the presence of zinc(II) over a large concentration range, a distinctive feature of zinc(II) from other biologically interesting (and also physiologically important) small molecules and ions. We have integrated 1,2,3-triazole in new ligands for metal ions. Some of these ligands upon incorporating a fluorophore become zinc(II)-sensitive indicators. We are expanding this project to include fluorescent molecules that can be used in imaging other intracellular metabolic and signalling molecules. Students in this project will master a plethora of skills in chemistry and biology including synthesis, photophysical characterization of light-emitting compounds, coordination chemistry, cell culture, and fluorescence microscopy.
Multiple emission organic fluorophores
We are interested in organic fluorophores that efficiently emit from multiple excited states. We study how the environmental factors, such as solvent polarity, viscosity, hydrogen bonding, etc., alter the energies and hence distribution of species of a fluorophore in both ground and excited states, and how that change of distribution affects both the composite color (mixing of frequency) and brightness (fluorescence quantum yield) of a fluorophore. By creating polymer matrices that cleverly model environment factors, the dye-doped polymers can be applied in the production of energy efficient light emitting materials with tunable composite colors.
In some instances, we follow up compulsively on interesting (and unexpected) observations from an onging project. For example, we studied the effect of boronic acid binding on the electrochemical oxidation of catechol derivatives; and we reported the characterizations and syntheses of a few new metal coordination ligands. By doing so, new knowledge has been produced, which may or may not yield immediate or future benefits to other areas of science or humanity in general. Still, it is gratifying to know that we have understood this world a little better.