Spring 2012 Biomedical Seminar Series
Friday, April 13, 2012
Abstract The Metal-Cysteine (M-S-cys) motif is present in many metalloenzymes, and may be quite susceptible to oxidative damage. Lorillee C. Tallorin has previously studied the chemistry of singlet oxygen with Pt-thiolato complexes to elucidate the mechanism by which such oxidations may occur . A mono-thiolate system [Pt(II)(aet)(bpy)]Cl (1) (aet = 1,2-aminoethanethiol, bpy = 2,2Â-bipyridine) was reacted with singlet oxygen (1O2) and products studies involving 195Pt NMR, FTIR, and X-ray crystallography have shown that the initial species is indeed the sulfenato (2) complex followed by a second reaction leading to the sulfinite (3) which suggests an intermolecular oxygen atom transfer mechanism. Kinetic data for the reaction of singlet oxygen with the thiolate, the sulfenate and the sulfinite compounds will be presented and should provide a mechanistically understanding of the reactivity of the metal compound. It is of great importance to understand the oxidative mechanism and reactivity of the platinum thiolato complexes in order to have a better comprehension of the toxicity of anticancer agents like cisplatin.
By revisiting classic hybrid zones we can clarify consequences of long-term hybridization. In 1977, several morphological analyses described first generation (F1) hybrids between two native Californian species (Populus fremontii and P. trichocarpa) and one European exotic (P. nigra) planted as an ornamental. The studies inferred an F1 block between native hybrid tree species (P. fremontii x P. trichocarpa) and exotic hybrid (P. fremontii x P. nigra). To determine how hybridity has changed, eight of the nine hybrid zones, plus one newly discovered population were sampled and genotyped using a 27 single nucleotide variant (SNV) assay (22 biparental nuclear and five chloroplast markers, diagnosing maternal lineage). Genotyping results show a frequency of about 40% of pure species and 52.5% hybrids. Hybrid formation was found in every population and advanced-generation hybrids (F2s and more complex combinations) were seen at five sites, with frequency of 11.9%. In addition, leaf samples from each individual were digitally scanned (5 leaves per tree), and a series of 27 measurements were analyzed with a semi-automated program to determine utility of leaf morphology to identify Populus. The results show a shift in the genotypic composition of hybrid zones toward advanced-generation hybrids, and imply that there are few reproductive barriers among the species. This rampant hybridization suggests the need for long-termed views when assessing impacts of gene flow on natural resources.
Photoluminescence emissions from indium arsenide (InAs) quantum dots (QDs) are studied for their potential use in nano-Âsized optical and electronic devices. Samples consisting of multiple layers of quantum dots are excited using a green (532 nm) 20 mW laser that yields a low intensity photoluminescence. Measurements of the photoluminescence have been taken using a SPEX spectrometer, a SR510 lock-Âin amplifier, and a photomultiplier detector that are controlled by a computer program. The optical response is modeled as a linear combination of several Gaussian distributions. Analysis of the spectra of several QD samples is performed using a Gaussian fitting program. We observe three peaks that we conclude are the s-s transition, the s-s transition modified by electron-phonon interactions, and a p-p transition. Justification for the number and distribution of peaks in the model is discussed.