Chemistry

ABSTRACTS

Dr. Herbet Burhenn, UTC, "Science or Pseudoscience?

A regular topic of discussion in the philosophy of science over the past century is the distinction between science and pseudo-science. Candidates for the latter designation have typically been such endeavors as astrology, parapsychology, and Freudian psychoanalysis. Figuring out how to differentiate these fields from legitimate science is trickier than it might first appear and forces us to think carefully about how to answer the question "What is science?"

Dr. Susanna Weaver, Emory University, Prebiotic Astrochemistry in the "THz-Gap"

Fundamental biological molecules such as amino acids and sugars have been discovered in meteorites, but none of these species have yet been definitively detected in the interstellar medium (ISM). While both the number of detected interstellar molecules and their chemical complexity continue to increase, understanding of the processes leading to their formation is lacking. Our recent chemical modeling work suggests that organic radicals formed during the photolysis of interstellar ices provide the building blocks for the larger organic molecules found in star-forming regions. In order to investigate these interstellar prebiotic chemical pathways, we are developing new terahertz (THz) spectrometers to study the unstable, reactive molecules that are key reaction intermediates. We are also conducting deep, broadband observational spectral line surveys in the millimeter, submillimeter, and THz ranges to further examine the effects of physical environment on the chemical complexity in interstellar clouds. In this talk, I will present results from our modeling, laboratory, and observational studies that focus on the THz spectral signatures of prebiotic molecules in the ISM.

Dr. Markus Germann, Georgia State University, "Structural and Dynamic Effects of the DNA Sequence Context: Consequences for Detection and Repair of Lesions"

Nucleic acids play a central role in many biological processes, including information storage, gene expression and even catalysis. Their diverse roles have made them targets of interest to diagnose and treat an array of human disorders such as infections, degenerative diseases and cancer. In this talk I will show our research on the effects of the sequence environment on the local structure and dynamics of DNA that contains damaged bases. Examples will be shown where either changes in structure or dynamics will determine the “repairability” of a given lesion. NMR will also be used to investigate how a minor groove specific drug binds and bends a DNA structure and pinpoint the dynamic events that the bound drug experiences. Further, I will highlight a number of modern NMR applications to address widely different problems in chemistry and biology.

Dr. David Sherrill, Georgia Tech, "Pi-Stacking Interactions between Base Pairs in DNA and RNA"

Base stacking is just as critical as H-bonding in stabilizing the double-helix structure of DNA and RNA. High-level quantum computations have been used to elucidate the fundamental nature of these pi-stacking interactions. Using the world's fastest energy component analysis code, we have computed the electrostatic, London dispersion, polarization, and repulsion contributions to base stacking between all possible DNA and RNA base pairs as a function of the helix parameters Rise, Twist, and Slide [J. Am. Chem. Soc. 135, 1306 (2013)]. We find that the B-DNA helix is optimally arranged to maximize pi-stacking forces, while A-form RNA is less optimal in this respect. Polarization effects are significant but not large. Surprisingly, electrostatic interactions are quite attractive for all values of Twist at the value of Rise appropriate for DNA and RNA. This seems incompatible with the alignment of dipoles at low Twist angles when one base pair is stacked above an identical base pair. A careful analysis of this situation reveals the source of the counterintuitive attraction. Implications of this effect for biomolecular modeling using popular force fields (e.g., CHARMM, AMBER) will be discussed.

Dr. David Giles, UTC, "It’s What’s on the Outside that Counts: Bacterial Lipid Strategies for Adapting to Their Environment"

Some bacteria have the molecular machinery to scavenge lipid molecules from their environment, a strategy long thought to provide extra carbon sources for energy and thus enhanced survival. The Gram-negative pathogen Vibrio cholerae, the causative agent of the acute intestinal infection cholera, poses significant health concerns because of its persistence in aquatic environments prior to human ingestion. The studies described herein have uncovered several unique characteristics with regard to V. cholerae's lipid uptake and utilization capabilities. V. cholerae possesses additional lipid handling proteins, conferring the potential to draw from a wider range of exogenous lipids. We observed atypical strategies used by V. cholerae to remodel its membrane, including uptake and assimilation of a wide range of exogenous fatty acids as well as the capacity to enzymatically liberate and utilize fatty acids from exogenous lysophospholipids. The evident resourcefulness of V. cholerae may provide as-yet-determined survival advantages based upon its host and aquatic environments.