Repairs on Van de Graaff

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

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Scavenging Reducing Radicals with MV2
1 M Gly 0.5 mM MV2 pH 10.6
? 600 nm
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slow
Suggestions for slow reactions See Scheme on
following slide
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G(MV)
Suggestion for fast component
fast
H2N-CH2-CO2- ?OH ? CO2 ?CH2NH2 OH- ?CH2NH2
MV2 ? MV? CH2NH2
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Fast component dependent on MV2
0
0
50
100
150
Time /?s
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?OH-oxidation ofglycine anions
Scheme from Bonifacic, Stefanic, Hug, Armstrong,
Asmus J. Am. Chem. Soc. 1998, 120, 9930-9940
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Stochastic Simulation of Kinetics Scheme
ks from previous slide
?OHo 40 mM
pH 10.6
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?OH-oxidation of glycine anions
H2N-?CH-CO2-
?CH2-NH2
HN?-CH2-CO2-
5.9 G
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TRESR (Boxcar) H2N-?C(CH3)2
H2N-C(CH3)2CO2- ?OH ?
H2N-?C(CH3)2 CO2 OH-
25 G
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Synthesis of spectrum
H2N-?C(CH3)2 (sharp lines)
?NH-C(CH3)2CO2-
H2N-C(?CH2)(CH3) CO2-
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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

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TRESR - yields methodology SO3?-
Saturating the transition
Conc profile
Turning newly- created spins in the external field
Microwave switch Blocking signals to the detector
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Determination of microwave magnetic field
H1 0.027 G
P -10 dB
P -15 dB
T1 16 ms
T2 7 ms
-O2CCH?CCO2-
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Spin polarization
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Notre Dame Magazine (Matt Cashore)