repairs on van de graaff. van de graaff & microwave bridge
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Block Diagram of ESR SpectrometerBlock Diagram of ESR Spectrometer
http://www.chm.bris.ac.uk/emr/Phil/Phil_1/p_1.html
Glycine anion controversyGlycine anion controversy
Steady-state Steady-state -radiolysis (1985) showed large yields -radiolysis (1985) showed large yields of COof CO22 at high pH, which suggests large yields of at high pH, which suggests large yields of CHCH22NHNH22 radicals radicals
HH22N-CHN-CH22-CO-CO22 ++ OH OH
COCO22 + + CHCH22NHNH22 + + OHOH
Steady-state electron radiolysis with ESR detection Steady-state electron radiolysis with ESR detection (1971) saw only the capto-dative stabilized NH(1971) saw only the capto-dative stabilized NH22--CH-CH-
COCO22 radical, among the possible C-centered radicals radical, among the possible C-centered radicals
from glycine anionsfrom glycine anions
Scavenging Reducing Radicals with MVScavenging Reducing Radicals with MV2+2+
1 M Gly 0.5 mM MV2+ pH 10.6
Suggestion for “fast” component:
H2N-CH2-CO2 + OH
CO2 + CH2NH2 + OH
CH2NH2 + MV2+ MV + CH2=NH2
Suggestions for “slow” reactions:See Scheme on following slide
Fast component dependent on [MV2+]
= 600 nm
Time /s
G(M
V+)
6
4
2
0
0 50 100 150
fast
slow
OH-oxidation ofOH-oxidation ofglycine anionsglycine anions
Scheme fromBonifacic, Stefanic, Hug, Armstrong, AsmusJ. Am. Chem. Soc. 1998, 120, 9930-9940
Stochastic Simulation of Kinetics SchemeStochastic Simulation of Kinetics Scheme
k’s from previous slide
[OH]o = 40 M
pH 10.6
0 10 20 30 40 50
0
5
10
15
20
25
HN -CH2-CO
2-
H2N- CH-CO
2-
CH2NH
2
[tra
nsi
en
t] (
M)
Time (s)
OH-oxidation of glycine anionsOH-oxidation of glycine anions
0 10 20 30 40 50
-0.5
0.0
0.5
1.0
1.5
ES
R A
mplit
ude
Time (s)
#27avc
0 10 20 30 40 50
0
1
2
3
4
5
6
990930n17av.datGlycine
ES
R A
mplit
ude
Time (s)
D B
H2N-CH-CO2CH2-NH2
Gly-5
B
5.9 G
HN-CH2-CO2
TRESR (Boxcar) HTRESR (Boxcar) H22N-N-C(CHC(CH33))22
25 G
H2N-C(CH3)2CO2 + OH
H2N-C(CH3)2 + CO2 + OH
Synthesis of spectrumSynthesis of spectrum
NH-C(CH3)2CO2-
H2N-C(CH3)2
(sharp lines)
H2N-C(CH2)(CH3) CO2-
Oxidation of Amino Acids - SummaryOxidation of Amino Acids - Summary
TRESR resolved controversy over the fate of the TRESR resolved controversy over the fate of the radicals following the radiolytic oxidation of radicals following the radiolytic oxidation of glycine anionsglycine anions• Showed presence of Showed presence of CHCH22NHNH22
• Showed the “immediate” formation of the C-centered Showed the “immediate” formation of the C-centered radicalsradicals
• Directly detected aminyl radicals in Directly detected aminyl radicals in -methyl alanine-methyl alanine
Advantages of TRESR for these problemsAdvantages of TRESR for these problems• TRESR permitted the detection of short-lived radicalsTRESR permitted the detection of short-lived radicals• Developed methodology of measuring the yield of Developed methodology of measuring the yield of
radicalsradicals
TRESR - yields methodology SOTRESR - yields methodology SO33
Saturating the transition
Turning newly-created spins inthe external field
Microwave switchBlocking signals tothe detector
Concprofile
Determination of microwave magnetic fieldDetermination of microwave magnetic field
O2CCH=CCO2
P = 10 dB
P = 15 dB
T1 = 16 s
T2 = 7 s
H1 = 0.027 G
Spin polarizationSpin polarization
-8 -6 -4 -2 0
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
ES
R s
igna
l
H0 (Gauss)
12 14 16 18 20 22-0.4
-0.2
0.0
0.2
0.4
ES
R s
ign
al
H0 (Gauss)
-10 0 10 20 30 40 50
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
ES
R s
igna
l
Time (s)