Phone : (787) 764-0000 ext. 2429
E-mail: rarce uprr pr
Ph.D., University of Wisconsin-Madison (1971)
Physical Chemistry: Photochemistry and Photophysics of Purine Bases and Their Derivatives; Heterogeneous Photochemistry of Polycyclic Aromatic Hydrocarbons; Photophysical and Photochemical Properties of Photosynthesizers; EPR; Flash and Laser Photolysis.
There is considerable interest regarding the possible adverse effects on human health by chemical carcinogens encountered in the atmospheric particulate matter. Polycyclic aromatic hydrocarbons and their nitro derivatives are a group of priority pollutants formed during the combustion of organic matter under oxygen deficient conditions or through chemical reactions in the atmosphere. The study of the interactions of these ubiquitous pollutants with light contributes to a better understanding of their behavior in the atmosphere, and helps to establish a more realistic evaluation of their toxicity and risk. Their transformations in the atmosphere is still debated and a possible environmental fate is through their photodecomposition on the atmospheric particulate matter.
In order to understand the phototransformation mechanism of PAHs we (1) examine the interactions of the adsorbed molecules with the different substrates and establish the nature of the participating excited states by absorption and fluorescence techniques, (2) determine relative photodegradation rates, (3) identify intermediate species and triplet states by time resolved diffuse reflectance laser spectroscopy and electron spin resonance and (4) identify the stable products and compare them with those found in the solution photochemistry. A fundamental aim is to study the effect of some chemical and physical properties of the adsorbent such as composition, water content, presence of coadsorbed gases, average pore diameter, and surface coverage on the photophysical and photochemical processes of the adsorbed PAHs.
Photochemical and photophysical studies on the purine nucleosides, nucleotides, dinucleotides, and polynucleotides are relevant for the understanding of the chemical and biological effects of UV radiation on DNA, formation of skin cancers, and premature aging. In our laboratory, we are interested in determining the role of base sequence and conformation on the photochemistry of DNA. This is being studied from the perspective of a comparison of the participating reactive intermediates, photodestruction yields, and products formed on purine dinucleotides and polynucleotides. The effect of low and high intesity UV radiation on the purine bases in aqueous solution is also of interest.
Fluorescence spectroscopy, ESR, GC-MS, HPLC nanosecond Laser transient spectroscopy and UV-visible absorption are used to identify and establish the participating excited states, radical intermediates and stable products resulting from the phototransformation reactions. Our group actively collaborates with researchers at the Humacao University College (Dr. Alegría and Dr. García) in projects dealing with understanding the photochemical and photophysical properties of drugs and photosynthesizers. Our research initiatives have received funding from agencies such as NIH, NSF, DoE and EPA.