Chemistry posters abstracts.
The antitumor antibiotic actinomycin D is a DNA binding agent that has been studied extensively for over thirty years. Actinomycin D has been shown to preferentially bind to dGpC steps of duplex DNA, and more recently atypical binding sites such as the T(G) nT motif. These nonclassical binding sites have potential to yield a new class of DNA binding agents that show sequence specificity to the T(G)nT motif of duplex DNA. Here, we describe a unique enthalpic "switch" present in the binding of actinomycin D to the 5'-TGGGT-3' and 5'-TGGT-3' of double stranded DNA. Utilizing isothermal titration calorimetry, the enthalpy of binding was measured and our results show a large enthalpy change (AH) in the binding of actinomycin D to the two sequences that only differ by the presence of one guanine. The enthalpy value switches from a favorable value of-3.8 keal/mol for the 5'-TGGGT-3' to an unfavorable value of + 2 keal/mol for the 5'-TGGGT-3'. These results suggest large enthalpy/entropy compensation present in the thermodynamic binding mechanism. A key component in the binding mechanism is the comparison of association kinetics profiles for the two sequences, which suggests a unique binding mechanism present. This may be responsible for the unusual thermodynamics associated with the binding of actinomycin D to the two sequences that differ only in the presence of one guanine.
ENHANCEMENT OF THE THERMAL STABILITY OF SALMON SPERM DNA BY INTERACTION WITH TRANSITION METAL IONS: A COMPARATIVE STUDY Kathern Wendt and Maureen K. Murphy. Chemistry & Biochemistry Program, Huntingdon College, 1500 East Fairview Avenue, Montgomery, AL 36106-2148.
We have conducted thermal denaturation experiments on modified oligonucleotides and salmon sperm DNA in sodium chloride/sodium citrate solution at pH 7.0 in the presence and absence of 0.10 M aqueous metal ion solutions. In the absence of added metal ions, melting curve data for the modified oligonucleotides and the salmon sperm DNA displayed characteristic sigmoidal behavior and transition temperatures in the range of 38.30-58.90 degrees Celsius. In the presence of added aqueous metal ions, the melting curve data for the modified oligonucleotides and the salmon sperm DNA exhibited significantly higher transition melting temperatures, suggesting enhanced thermal stability in the presence of metal ions. A comparative study of our results with published research on metal ion effects on melting curves of human DNA samples will be presented.
ISOLATING LOW-MOLECULAR-WEIGHT CHROMIUM-BINDING SUBSTANCE FROM HUMAN URINE. John B. Vincent, Keith Bentley, Yuan Chen, and Carolyn J. Cassady, Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487-0336.
Chromium is moved from the body stream to the tissues by the iron transport protein transferrin in an insulin-sensitive fashion. The chromium is transferred in the tissues to the oligopeptide low-molecular-weight chromium-binding substance (LMWCr), also known as chromodulin. LMWCr has been proposed to potentiate insulin signaling. Chromium is ultimately removed from cells and appears in the urine as a low molecular weight species, which has been assumed based on its size to be LMWCr; however, the identity of the chromium-containing species in urine has never been firmly established. The goal of this research is to isolate the chromium-containing biomolecule from urine for the first in sufficient quantity to allow it to be characterized by standard biochemical and spectroscopic methods to establish whether it is LMWCr.
Palladium catalyzed coupling reactions using water-soluble phosphine ligands: DTBPPS and DAPPS and their ability to promote coupling reactions. Mary E. Killian, Sara E. McClendon, William S. Brown, and Kevin H. Shaughnessy. University of Alabama. Tuscaloosa, AL 35487.
The development of water-soluble phosphine ligands for coupling reaction has been an expanding area of research over the past several years. The goal in many of these new reaction conditions has been to improve overall yield, reduce reaction time, and allow for catalyst recyclability. The motivation of this research is to demonstrate the utility of the ligands 3-(di-tert-butylphosphino) propanesulfonate (DTBPPS) and 3-(diadamanlylphosphino) propanesulfonate (DAPPS), which offer an alternative to ammonium based water-soluble ligands previously used (Buchwald's ligands or t-BuAmphos). Replacement of the ammonium group with an anionic sulfate group should provide greater electron donation by the phosphine to the metal center. Previous efforts suggest that increasing the steric demand by addition of bulky groups and increasing the electron donation ability of the phosphine ligand leads to an increase in the reactivity of the phosphine palladium catalyst. This increase in reactivity results in lower catalyst loading and higher turnover frequency of the catalyst, thereby providing a reduction in reaction time. Additionally, an increase in water-solubility of the active catalyst should afford means for the coupling of substrates that previously have proven challenging due to low solubility in traditional organic solvents. Both DTBPPS and DAPPS are being investigated in a number of coupling reactions and will be reported including Heck coupling and palladium-catalyzed enolate coupling with ary1 halides.
STRUCTURE AND STABILITY OF CPG-OLIGONUCLEOTIDES THAT INDUCE TLR9 MEDIATED CELLULAR INVASION. Sonja C. Brooks, Jason S. Hudson, and David E. Graves, Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294.
The focus of this research is to discern the structural and biophysical properties of small DNA oligonucleotides that induce Toll-like 9 receptor (TLR-9) mediated cellular invasion. Cell invasion (metastasis) is a significant problem in the control and treatment of breast cancer. Research in our laboratory has demonstrated enhanced cellular invasion in MDA-231 breast cancer cells by ODN-362, a 25-base (CpG) deoxynucleotide. The mechanism(s) for this induction remain unknown; however, our studies reveal key insights into the structural and sequence requirements for DNA activation of this cellular invasion process. The deoxyoligonucleotides that are effective in eliciting an invasion response have been shown to adopt multiple structural motifs including stem-loops, hairpins or duplex structures. Sequence modifications were designed to discern sequence, structural and stability properties required for initiating TLR-9 mediated cellular invasion. Our results demonstrate that these small deoxyoligonucleotides play a key role as a biological response modifier in this invasion process.
Synthesis and Characterization of New Palladium Complexes Containing Neopentyl Phosphine Ligands. Lensey L. Hill and Kevin. H. Shaughnessy, Department of Chemistry, University of Alabama. Tuscaloosa, AL 35487.
Finding optimal conditions for cross coupling reactions has become an increasingly popular field in current academic and industrial research. The oxidative addition of an ary1 halide to a metal center can prove to be one of the most challenging steps in these catalytic cycles. Steric and electronic effects of bound ligands to the metal center greatly influence the activity of the metal catalyst. The goal for our research was to synthesize new palladium complexes that contain a variety of ligands with tert-butyl and neopentyl groups attatched to a phosphine center. We have found that the cone angle of the ligand affects the complexation to the palladium metal center of several of the new complexes. For example, complexation of di-tert-butylneopentylphosphine with allyl palladium chloride dimer resulted in the allyl palladium chloride phosphine adduct, which shows substantial activity in Hartwig-Buchwald amination. Many of our new compounds have been characterized by NMR spectroscopy and X-ray crystallography.
Isomerization versus Addition reactions of Maleic Acid and its Methyl Ester-A systematic study on the effect of Temperature, Concentration and Reagents/Catalysts Nagarajan Vasumathi, Ashley Casey and Jill Lott, Dept. of Physical and Earth Sciences, Jacksonville State University, Jacksonville, Al 36265.
Maleic acid (cis-2-butene-l,4-dioic acid) is known to undergo isomerization on treatment with Conc. HC1 in aqueous medium under reflux condition or upon treatment with aqueous bromine under UV light to form fumaric acid, the thermodynamically more stable transisomer. The reported reaction mechanism involves a carbocationora free radical intermediate. Alkenes in general are known to undergo addition reactions at lower temperatures and allylic substitution at higher temperatures. There are no literature reports on the possible formation of any addition products. Allylic substitution can be ruled out since there are no allylic hydrogens in maleic acid. In an attempt to identify the formation of any addition product and to better understand the reaction mechanism for the isomerization process, a systematic study is undertaken. The reaction is performed under different conditions by varying the temperature, molar concentration and reagents/catalysts and monitored and analyzed by TLC. Our preliminary studies indicate the addition reaction taking place initially at room temperature followed by rotation, isomerization and elimination at higher temperatures. The results from the reactions of maleic acid with aq.HCl and aq. B[r.sub.2] under different conditions are compared; the products are characterized and the mechanism is discussed. The reactions of the corresponding methyl ester with HC1 in ether and with B[r.sub.2]/ C[Cl.sub.4] will also be explored.
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|Publication:||Journal of the Alabama Academy of Science|
|Article Type:||Author abstract|
|Date:||Apr 1, 2008|
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