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C Mertz

Publications and source records attributed to C Mertz.

8 recordsLinked to original sources
PubMed2001

Relativistic effects and two-body currents in (H)((-->)e(')p)n using out-of-plane detection.

Measurements of the (2)H((-->)e,e(')p)n reaction were performed with the out-of-plane magnetic spectrometers (OOPS) at the MIT-Bates Linear Accelerator. The longitudinal-transverse, f(LT) and f(')(LT), and the transverse-transverse, f(TT), interference responses at a missing momentum of 210 MeV/c were simultaneously extracted in the dip region at Q2 = 0.15 (GeV/c)(2). In comparison to models of deuteron electrodisintegration, the data clearly reveal strong effects of relativity and final-state interactions and the importance of two-body meson-exchange currents and isobar configurations. We demonstrate that such effects can be disentangled by extracting these responses using the novel out-of-plane technique.

Journal Article↗
PubMed2001

Search for quadrupole strength in the electroexcitation of the delta+(1232).

High-precision 1H(e,e'p)pi(0) measurements at Q2 = 0.126 (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma*N-->Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole ( I = 3/2) amplitude ratios, R(SM) = (-6.5+/-0.2(stat+sys)+/-2.5(mod))% and R(EM) = (-2.1+/-0.2(stat+sys)+/-2.0(mod))%, are dominated by model error. Previous R(SM) and R(EM) results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.

Journal Article↗
PubMed1999

Evolution of castalagin and vescalagin in ethanol solutions. Identification of new derivatives.

Brandies, cognac, armagnac, whiskeys, and rums are aged in oak barrels to improve their organoleptic properties. During this period, numerous compounds such as ellagitannins are extracted from the wood and can subsequently be transformed into new derivatives by chemical reactions. Model solutions of castalagin and vescalagin have been studied to determine the behavior of polyphenols in ethanol-water. Upon prolonged exposure to 40 and 70% (v/v) ethanol at room temperature, hemiketal derivatives containing ethoxy groups have been characterized by LC/MS and NMR. These compounds further evolve to afford the corresponding ketals. They have also been detected in the extracts of oak wood stored under similar conditions.

Alcoholic Beverages↗
PubMed1990

Bacterial siderophores: structures of pyoverdins Pt, siderophores of Pseudomonas tolaasii NCPPB 2192, and pyoverdins Pf, siderophores of Pseudomonas fluorescens CCM 2798. Identification of an unusual natural amino acid.

Pyoverdins were isolated and characterized respectively from the cultures of Pseudomonas tolaasii NCPPB 2192 (pyoverdins Pt, Pt A, and Pt B) and Pseudomonas fluorescens CCM 2798 (Pyoverdins Pf/1, Pf/2, Pf, Pf/3/1, and Pf/3/2) each grown in iron-deficient conditions. Their structures were established by using FAB-MS, NMR, and CD techniques. These siderophores are chromopeptides, and all but one (pyoverdin Pf/3/3) possess at the N-terminal end of their peptide chain the same chromophore that has been reported in pyoverdin Pa from Pseudomonas aeruginosa ATCC 15692 [Wendenbaum, S., Demange, P., Dell, A., Meyer, J. M., & Abdallah, M. A. (1983) Tetrahedron Lett. 24, 4877-4880] and pseudobactin B 10 from Pseudomonas B10 [Teintze, M., Hossain, M. B., Barnes, C. L., Leong, J., & Van der Helm, D. (1981) Biochemistry 20, 6446-6457] which is derived from 2,3-diamino-6,7-dihydroxyquinoline. In pyoverdins Pt this chromophore is bound to a linear peptide chain D-Ser-L-Lys-L-Ser-D-Ser-L-Thr-D-Ser-L-OHOrn-L-Thr-D-Ser-D-OHOrn (cyclic) which has its C-terminal end blocked by cyclic D-N delta-hydroxyornithine. In pyoverdins Pf, the peptide chain is also linear, SerCTHPMD-Gly-L-Ser-D-threo-OHAsp-L-Ala-Gly-D-Ala-Gly-L-O HOrn(cyclic), and contains an unusual natural amino acid which is the result of the condensation of 1 mol of serine and 1 mol of 2,4-diaminobutyric acid, forming a cyclic amidine. The pyoverdins Pt differ only in substituent bound to the nitrogen on C-3 of the chromophore, which is succinic acid in pyoverdin Pt A, succinamide in pyoverdin Pt, and alpha-ketoglutaric acid bound to the chromophore by its C-5 carbon atom in pyoverdin Pt B. Similarly, pyoverdin Pf/1, pyoverdin Pf/2, pyoverdin Pf (the major compound), and pyoverdin Pf/3/2 are substituted respectively by L-malic acid, succinic acid, L-malic amide, and succinamide. Pyoverdin Pf/3/3 has the same chromophore as azotobactin, the peptidic siderophore of Azotobacter vinelandii. These pyoverdins are very similar to pseudobactin B 10, the siderophore of Pseudomonas B10: they are linear peptides containing three bidentate groups strongly chelating Fe(III) and blocked at their N-terminal end by the catecholic chromophore and at their C-terminal end by cyclic N delta-hydroxyornithine. They differ therefore from other pyoverdins such as those from P. aeruginosa ATCC 15692 which contain a partly cyclic peptide [Briskot, G., Taraz, K., & Budzikiewicz, H. (1989) Liebigs Ann. Chem., 375-384].

Amino Acid Sequence↗