David F. Zigler

Photochemical methods to assay DNA photocleavage using supercoiled pUC18 DNA and LED or xenon arc lamp excitation

Methods for the study of DNA photocleavage are illustrated using a mixed-metal supramolecular complex [{(bpy)(2)Ru(dpp)}(2)RhCl(2)]Cl(5). The methods use supercoiled pUC18 plasmid as a DNA probe and either filtered light from a xenon arc lamp source or monochromatic light from a newly designed, high-intensity light-emitting diode (LED) array. Detailed methods for performing the photochemical experiments and analysis of the DNA photoproduct are delineated. Detailed methods are also given for building an LED array to be used for DNA photolysis experiments. The Xe arc source has a broad spectral range and high light flux. The LEDs have a high-intensity, nearly monochromatic output. Arrays of LEDs have the advantage of allowing tunable, accurate output to multiple samples for high-throughput photochemistry experiments at relatively low cost.

Analytical methods development for supramolecular design in solar hydrogen production

In the investigation of alternative energy sources, specifically, solar hydrogen production from water, the ability to perform experiments with a consistent and reproducible light source is key to meaningful photochemistry. The design, construction, and evaluation of a series of LED array photolysis systems for high throughput photochemistry have been performed. Three array systems of increasing sophistication are evaluated using calorimetric measurements and potassium tris(oxalato)ferrate(II) chemical actinometry and compared with a traditional 1000 W Xe arc lamp source. The results are analyzed using descriptive statistics and analysis of variance (ANOVA). The third generation array is modular, and controllable in design. Furthermore, the third generation array system is shown to be comparable in both precision and photonic output to a 1000 W Xe arc lamp.

Supramolecular Complexes as Photoinitiated Electron Collectors: Applications in Solar Hydrogen Production

The conversion of light energy into chemical energy is a focus of much research. Solar energy is of sufficient energy to drive water splitting to generate hydrogen and oxygen. The splitting of water involves multi-electron reactions and the breaking and formation of chemical bonds. Light driven water splitting has therefore proven elusive. Supramolecular complexes that contain ruthenium or osmium polyazine units can efficiently absorb visible light and generate charge transfer excited states. While many supramolecular complexes can absorb solar light efficiently, few are able to convert this energy into chemical energy via the conversion of a readily available chemical feedstock into a fuel. One process that is proposed as applicable for light to energy conversion is photoinitiated electron collection. Photoinitiated electron collection is a multi-step process whereby light energy is used to collect reducing equivalents. The collection of reducing equivalents is an essential step in the use of light energy to drive multi-electron reactions such as water splitting. The development of mixed-metal complexes as photoinitiated electron collectors is described, including the factors impacting device function. The use of Rh based electron collectors allows for the reducing equivalents generated by photoinitiated electron collection to be transferred to substrates, such as the reduction of water to produce hydrogen.