Gold chemistry elicits visions of alchemists with bubbling flasks in fantastic colors. Sometimes I feel like that except that I take gold and transform it into complexes that might be green, might glow orange under ultraviolet light, or might be dull white. So I might be an anti-alchemist. Gold, besides having an interesting history as the original noble metal, the symbol of wealth and power, is very unique as an element. Its properties, resistance to oxidation, malleability, conductivity, are ultimately related to the arrangement of the electrons in the atom. But gold, being a “heavy metal” is affected also by relativity related to the speed of the electrons around the nucleus. This phenomenon has been used to explain the density of gold, as well as the electronegativity and the color. One of my goals is to learn more about the basic chemistry of gold and its varied and increasingly complex structures.
I have been working with a series of gold phosphine dinuclear compounds of the form, cis and trans bis-diphenylphosphinoethylene gold(I)X:
These compounds exhibit interesting photochemical behavior: they isomerize from cis to trans when they are exposed to light. We want to know how changing the “X” ligand affects the isomerization and if gold-gold interactions in these compounds are involved in this chemical phenomenon. We particularly want to know if we can prove that there are these interactions in solution and if they can be used for self assembly applications.
Some of these gold compounds have phosphine-gold-thiol structures that are similar to the gold arthritis drug, Auranofin. In addition some of the dinuclear gold compounds have shown some anticancer properties. It is not known why gold drugs are effective but ligand substitution is often proposed as a necessary step in the mechanism. Recently it has been suggested that gold complexes bind to the selenium in various selenoenzymes in order to impede the antiradical activity in the cell allowing reactive oxygen species to kill a cell. We are exploring the ligand substitution properties, the photochemical reactivity, and the luminescence of several gold complexes to expand the knowledge of the basic chemistry of this interesting metal. We want to better understand the next generation of heavy metal drugs as well as gain insight into the mechanism of physiological interaction.
We are in southwestern Vermont, an area that has shown high arsenic concentrations in wells in the area. Because of the underlying geology, this is a problem in many parts of New England. In a collaboration with Tim Schroeder, the geologist at Bennington and several students we are setting up a project to examine not only the concentrations of arsenic, but to explore the complex interactions that control the solubilization of arsenite ions including pH and redox conditions. This is a new project and we hope to involve others in the area.
Effect of Climate Change on Coral Reefs: Ocean Acidification and Solubility of Calcium Carbonate
This is a joint biology/chemistry project that applies some very basic chemistry – equilibrium and solubility – to the very real problem of the disintegration of coral reefs all over the world. How much is due to climate or development is difficult to assess. Coral reefs are fundamental to diversity and provide habitats for numerous species of fish and invertebrates. Students traveled to Grand Cayman this winter (2014) to count fish and report them to the worldwide “fish census” at Reef.org. Students also measures pH, conductivity, calcium concentrations and temperature in the ocean as well as tidal pools. We hope to follow up these studies by setting up model systems to tease apart the relevant variables and contribute to the discussions about carbon dioxide concentrations and its effect on the acidification of the ocean and numbers of fish.