Chemistry section. (Collegiate Division 2002).
Hlatshwayo, M. and J. Bennett. Department of Chemistry, Drury University. EVIDENCE OF A HOMOSERINE ESTER AS A BY-PRODUCT OF PROTEIN CLEAVAGE BY CYANOGEN BROMIDE. Cyanogen bromide is a reagent commonly used in protein sequencing because it specifically cleaves at the C-terminal side of methionine residues. In addition to the generally accepted products of this reaction, recent work suggests that another side reaction may be occurring. This proposed reaction involves the displacement of methyl thiocyanate by the amide carbonyl oxygen from the adjacent N-terminal amino acid. The resulting product would yield an uncleaved protein containing a homoserine ester. In order to prove that this proposed mechanism occurs, a synthetic peptide containing normethionine, rather than methionine, is currently being studied. The expected product from cyanogen bromide treatment of this peptide should occur via the newly proposed mechanism due to ring size constraints. The crude product mix of this reaction will be purified by HP LC and peak-containing fractions will be submitted for mass spectrometric analysis at the University of California, Riverside. Ultimately, after the existence of this undesirable side reaction has been proven, alternative reaction conditions will be developed to limit its occurrence.
Kent, B., C. Nelson, E. Stone, M. Hlatshwayo, and J. Bennett. Department of Chemistry, Drury University. DEVELOPMENT OF A "GREEN" ALDOL CONDENSATION PROJECT FOR ORGANIC CHEMISTRY LABORATORY. The goal of this study was to take current, cutting-edge research and implement it as a laboratory project for sophomore-level organic chemistry students. Biological catalysis is currently being developed to facilitate many classic organic reactions to make them environmentally friendlier than traditional catalysts. A recent communication from the Journal of Organic Chemistry describing an asymmetric, biologically-catalyzed aldol reaction was used as the basis for this study. The experiment involved the use of L-proline, a naturally occurring amino acid, to catalyze the transformation of three equivalents of acetaldehyde into 5-hydroxy-2hexenal, a macrolide antibiotic precursor. The reaction yielded a fairly high enantiomeric excess of the (S)-stereoisomer under the conditions used. A variety of common techniques were per formed to purify and analyze samples, including thin layer chromatography, ultraviolet-visible spectroscopy, infrared spectroscopy, nuclear magnetic resonance, polarimetry, and flash chromatography. The project designed could be performed successfully in two lab periods using all, or a subset, of the aforementioned techniques. Adaptation of this scheme to a more advanced organic course could be achieved by incorporating gas chromatography-mass spectrometry and more extensive nuclear magnetic resonance analyses.
Konneman, H.A. and L.A.Wetmore. Department of Chemistry, William Jewell College. DETECTION OF DNA-ADDUCT FORMATION BY EXPOXY DENTAL MONOMERS USING HPLC. Many dental resin monomers contain epoxide functional groups that can form DNA adducts. We are interested in assessing the ability of the dental resin monomer 3' ,4' -epoxycylohexanemethyl-3, 4-epoxycyclohexane carboxylate (UVR-6105) to form a DNA adduct. Previous studies indicate that extensive DNA damage occurs in L929 mouse fibroblast cells after exposure to UVR-6105. It is thus hypothesized that UVR-6105 forms DNA adducts in these cells. This hypothesis is tested by incubating deoxyribonucleotides and DNA with UVR-6105 then digesting with phosphodiesterase and phosphatase. The resulting nucleosides are analyzed using an adapted HPLC method utilizing solid phase extraction on a C18 cartridge followed by reversed-phase chromatography with an organic/potassium phosphate buffer mobile phase. Eluant peaks are detected by UV absorption at 262 nm.
Pettegrew, B. and J. Gordon. Division of Science and Mathematics, Central Methodist College. THE DETERMINATION OF SULFATE AND NITRATE IN PRECIPITATION BY ION-EXCHANGE HPLC WITH INDIRECT DETECTION. The purpose of this study was to use ion-exchange chromatography to determine the anion species present in precipitation, both rain and snow. The amounts of sulfate and nitrate were of particular interest because they are partially responsible for the acidic character of precipitation. The mobile phase was modified with potassium hydrogen phthalate (KHP) that strongly absorbed at the detection wavelength of 260 nm. Upon elution of the nonabsorbing anion species, the displacement of the KHP caused a decrease in absorbance and a negative detection peak. After concentrating the precipitation samples, several anions including sulfate, nitrate, and chloride were easily detected. The amounts of nitrate and sulfate were determined to be 1.9 ppm and 3.8 ppm, respectively.
Robinson, K. and J. Grant. The Hoffman Department of Chemistry, Drury University, STANDARDS FOR pH MEASUREMENTS OF MOBS IN ISOTONIC SALINE MEDIA OF IONIC STRENGTH. The pH measurements of blood plasma, cerebrospinal fluids, and other clinical media, at an ionic strength I=0.16 mol*[kg.sup.-1] require primary buffer reference standards for the control of pH in the region close to the pH of blood serum. The buffer compound used was 4-[N-morpholino]butanesulfonic acid (MOBS). In order to achieve this objective, the electromotive-force measurements have been performed at temperatures between 5 to 55[degrees]C for (a) the determination of the values of [pK.sub.2] (second dissociation constant of MOBS), (b) the evaluation of pH values for six dilute buffer solutions in which NaCl has been added in amounts sufficient to raise the ionic strengths to 0.16 mol*[kg.sup.-1], (c) confirmation of results of pH by calculation of liquid junction potentials, and (d) recommendation of standard pH values for four useful referenc e standard solutions at ionic strengths near those of blood plasma from 5 to 55[degrees]C. The results will be compared with those of similar systems and application to clinical diagnosis will be discussed.
Sigwing, A.L., E. Ilkowska, and J.F. Gaillard. Department of Civil Engineering. Northwestern University. METAL MICROBE INTERACTIONS: THE OXIDATION OF MANGANESE BY LEPTOTHRIX DISCOPHORA SP-6. The manganese oxidizing activity of Leptothrix discophora is possibly the best characterized example of a biologically mediated oxidation. However, even after a century of study, the mechanisms of Mn(II) oxidation and the biological functions it serves remain enigmatic. The goal of our studies was to understand the molecular mechanism of the redox process occurring in the natural environment. Several analytical (atomic absorption spectrometry) as well as spectroscopic (UV-Vis spectrophotometry, EPR) methods have been applied to study the mechanism of the oxidation process of Mn(II) by an unknown factor produced during the microbial growth. In our experiments we checked the whole cells, unfiltered and filtered media towards ability to oxidize Mn(II). Also various types of buffers and carbon sources have been checked in ord er to avoid the possible subsequent reaction between them and the potential product. It was found that all mentioned above solutions were able to oxidized manganese. It has been also noticed that media with the whole cells are more active than the cell-free supernatant. The detailed concentration dependence as a function of time was performed using flame AA spectrometry. It has been observed that as the concentration of manganese in solution increases (above 200[mu]M) the oxidation ability of the supernatant decreases. It is assumed that the concentration of oxygen in the solution may play a key role in the microbial oxidation of Mn(II). A significant Mn(II) concentration decrease during the reaction may suggest an enzymatic or auto-catalytic type of mechanism.
Wigton, E., K. G. High, B.D. Wing, and M.-T. Tran Drury University AN NMR STUDY OF THE INTERACTIONS OF VARIOUS SUGARS WITH THE DIPEPTIDE CARNOSINE, The interactions of sugars with peptide and protein systems has attracted much interest recently. The understanding of such interactions can say much about the effect of elevated sugar in humans. In our studies, 300 MHz proton, 75 MHz Carbon-13, COSY, and HETCOR NMR techniques were used to study the dipeptide carnosine and sugars such as a-glucose. Various samples of carnosine and glucose or galactose were exposed to thermal conditions (60[degrees]C) in phosphate buffered aqueous media and unbuffered deuterated water. Under the conditions of our study, there is no evidence of reaction between the dipeptide and the sugar even after four days. Also, the dipeptide itself does not hydrolyze. Indeed, the only apparent interaction between carnosine and glucose under the conditions of this study is a shift in the equilibrium between the alpha and beta forms of the sugar.
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|Publication:||Transactions of the Missouri Academy of Science|
|Date:||Jan 1, 2002|
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