Repairs on Van de GraaffRepairs on Van de Graaff

Van de Graaff & microwave bridgeVan de Graaff & microwave bridge

Klystron, microwave bridge, & magnetKlystron, microwave bridge, & magnet

Block Diagram of ESR SpectrometerBlock Diagram of ESR Spectrometer

http://www.chm.bris.ac.uk/emr/Phil/Phil_1/p_1.html

Gravity flow system, detector, & magnetGravity flow system, detector, & magnet

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)

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