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Repairs on Van de Graaff

Repairs on Van de Graaff. Van de Graaff & microwave bridge. Klystron, microwave bridge, & magnet. Block Diagram of ESR Spectrometer. http://www.chm.bris.ac.uk/emr/Phil/Phil_1/p_1.html. Gravity flow system, detector, & magnet. Glycine anion controversy.

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Repairs on Van de Graaff

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  1. Repairs on Van de Graaff

  2. Van de Graaff & microwave bridge

  3. Klystron, microwave bridge, & magnet

  4. Block Diagram of ESR Spectrometer http://www.chm.bris.ac.uk/emr/Phil/Phil_1/p_1.html

  5. Gravity flow system, detector, & magnet

  6. Glycine anion controversy • Steady-state -radiolysis (1985) showed large yields of CO2 at high pH, which suggests large yields of CH2NH2 radicals H2N-CH2-CO2-+OH  CO2 + CH2NH2 +OH- • Steady-state electron radiolysis with ESR detection (1971) saw only the capto-dative stabilized NH2-CH-CO2-radical, among the possible C-centered radicals from glycine anions

  7. Scavenging Reducing Radicals with MV2+ 1 M Gly 0.5 mM MV2+ pH 10.6  = 600 nm 6 slow Suggestions for “slow” reactions: See Scheme on following slide 4 G(MV+) Suggestion for “fast” component: fast H2N-CH2-CO2- + OH  CO2 + CH2NH2 + OH- CH2NH2 +MV2+ MV+ + CH2=NH2 2 Fast component dependent on [MV2+] 0 0 50 100 150 Time /s

  8. OH-oxidation ofglycine anions Scheme from Bonifacic, Stefanic, Hug, Armstrong, Asmus J. Am. Chem. Soc. 1998, 120, 9930-9940

  9. Stochastic Simulation of Kinetics Scheme k’s from previous slide [OH]o = 40 mM pH 10.6

  10. OH-oxidation of glycine anions H2N-CH-CO2- CH2-NH2 HN-CH2-CO2- 5.9 G

  11. TRESR (Boxcar) H2N-C(CH3)2 H2N-C(CH3)2CO2-+OH H2N-C(CH3)2 + CO2 +OH- 25 G

  12. Synthesis of spectrum H2N-C(CH3)2 (sharp lines) NH-C(CH3)2CO2- H2N-C(CH2)(CH3) CO2-

  13. Oxidation of Amino Acids - Summary • TRESR resolved controversy over the fate of the radicals following the radiolytic oxidation of glycine anions • Showed presence of CH2NH2 • Showed the “immediate” formation of the C-centered radicals • Directly detected aminyl radicals in a-methyl alanine • Advantages of TRESR for these problems • TRESR permitted the detection of short-lived radicals • Developed methodology of measuring the yield of radicals

  14. TRESR - yields methodology SO3- Saturating the transition Conc profile Turning newly- created spins in the external field Microwave switch Blocking signals to the detector

  15. Determination of microwave magnetic field H1 = 0.027 G P = -10 dB P = -15 dB T1 = 16ms T2 = 7ms -O2CCH=CCO2-

  16. Spin polarization

  17. Notre Dame Magazine (Matt Cashore)

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