SINGLET OXYGEN OXIDATION

1
Free Radicals   They form in the
sunlight, they float in the smog.   They are
present in food and increase when you
jog.   They form in the liver from all kinds of
drugs, from solvents from nasty things used to
kill bugs-   They will damage your heart, even
make you grow old, and they will mutate your
genome is what were told.   Their causes,
reactions, and guessed repercussions are turning
up often in journal discussions.   The least
stable radicals varnish so quick, that publishing
on them is no minor trick.   But those with a
half-life that lets them react with biocomponents
will also attract spectroscopists, spin
trappers, and all of the rest--   Wholl show you
the things at which others just guess.
Unknown  

2
SINGLET OXYGEN OXIDATION
3
Molecular Orbital of Singlet Oxygen
Molecular
Atomic
Atomic
s

p

p

p
p
2Pz
2Py
2Px
2Px
2Py
2Pz
s
E
s

2S
2S
s
s

1S
1S
s
4
1O2 and 3O2 with Linoleic Acid
1.6
nm
1.2
1
O
2
Absorbance at 233
0.8
0.4
3
O
2
0
200
400
600
800
1,000
Reaction Time in Minutes
5
MECHANISMS OF PHOTOSENSITIZED OXIDATION
6
Photosensitizers
1.

Dye Methylene Blue, Rose Bengal, Eosin, Crystal
Violet,
and Acridine Orange.

2.
Pigment Chlorophyll, Hematoporphyrines,
Riboflavin
7
Photosensitizer Properties

• Absorption of the light in the 380 900 nm range
• Exhibition of fluorescence and phosphorescence
• reflecting two separate electronically excited
  states
• the Singlet state and the Triplet state
• 3. The singlet state is produced first by the
  light
• absorbed, but it has a short lifetime, decaying
  by fluorescence to the ground state and by
  electronic intersystem crossing to the Triplet
  state.

8
Photosensitizer Properties

• The triplet state decays to the ground state at a
  slower rate that varies depending on the
  sensitizer.
• 5.The most effective photosensitizers have a
  high quantum yield of a long-lived triplet state.

9
Excitation and Deactivation of Photosensitizer
1
Excited state
Sen
8

k 1- 20
10
/sec
ISC
3
Sen

8
n
k 2
10
/sec
h

3

O
4
k 10 - 10
/sec
2
9

k 1 - 3
10
/sec
Singlet oxygen formation
Sen
Ground state
10
Riboflavin
11
Chlorophyll
H
C
H
H
C
R
2
C
H
C
H
H
C
2
3
3
N
N
M
g
H
H
N
N
C
H
H
C
3
3
O
C
O
C
H
2
3
C
H
2

C
O
2
C
H
C
H
C
H
C
H
3
3
3
3
12
Excitation and Deactivation of Chlorophyll for
Singlet Oxygen Formation
1Sen
K1- 20?108/sec
ISC
Fluorescence K 2?108/sec
3Sen
Energy
hv
3O2
Phosphorescence
K1- 3?109/sec
K10-104/sec
1Sen (Chlorophyll)
Singlet Oxygen
Ground State
13
Formation of Triplet Riboflavin
O
H
O
H
O
H
O
H
O
H
O
H
O
H
O
H
N
N
O
N
N
O
ISC
h
v
1RF
N
H
N
H
N
N
O
O
1
3
R
F
R
F
14
Singlet Oxygen Trapping
O
O
H3C
CH3
CH3
H3C
1O2
..
2
2
H2O
2
2
N
N
H3C
CH3
H3C
CH3
O
H

TAN
TMPD
15
ESR of 2,2,6,6- Tetramethyl- 4 -Piperidone-N-Oxyl
3370 G 3390 G
3410 G
16
Excited Triplet Sensitizer Reactions
n
h
ISC
Sen
1
3
Sen
Sen
Type II
Type I

3

RH

O
K
.
.
2
1


3
R

Sen H

O
1

2
O
K
2
2

3
RH

O
2
.
.
ROOH

-

O

Sen
ROOH
2
17
Singlet Oxygen Formation Mechanisms
3

Xanthine
Xanthine Oxidase
3
O
-
Cu
Ascorbate
O

2
O
2

2

H

2H

2H
Superoxide Dismutase
HOO

3
H
O

O
2
2
2
Spontaneious Dismutation
Riboflavin
H2O2
1
3

O
O
2
2
Spontaneious Dismutation

2H
-
Reduced Riboflavin

3
O
O

2
2
18
Production of 1O2 by Photochemical, Chemical,
and Biological Systems
(11)
R
C
O


R
C
O
H
PRODUCTS
PRODUCTS
.
_
-
O
H

O
H

-
O
H
H
O

2
H
O
.
2
2
-
O
H

-
e
Y

2H
.
.
.
.
19
(No Transcript)
20
Singlet Oxygen Oxidation
1,4- Cycloaddition

H
O
O
ENE Reaction

O
O

Allyl

Hydroperoxide
O
CH
O
2
1,2 Cycloaddition

O
O
CH
2
Dioxetane
21
Reactions of Singlet Oxygen with Double Bonds
R
R
'
R
R'
O
O
H
O
H
O
I
II
22
Conjugated and Nonconjugated Hydroperoxides
via the 6-Centered Transition State
O
O
H

n
h
/sensitizer/O
R
2
R
'
isomerization
23
Reversion Flavor in Soybean Oil
Reversion FlavorThe development of a
characterisitc beany and grassy flavor in
soybean oil prior to the development of rancidity
C
H
C
H
C
H
C
H
C
H
3
2
2
O
24
2-Pentenylfuran from Linolenic Acid by Singlet
Oxygen
O
(
C
H
)
C
H
C
H
C
H
C
H
C
H
C
H
C
O
H
C
H
C
H
C
H
C
H
C
H
2
6
3
2
2
2
2
1
O
2
O
(
C
H
)
C
H
C
H
C
H
C
H
C
H
C
H
C
O
H
C
H
C
H
C
H
C
H
C
H
2
6
3
2
2
2
O
O
H
O
(
C
H
)
C
H
C
H
C
H
C
H
C
H
C
H
C
O
H
C
H
C
H
C
H
C
H
C
H
2
6
3
2
2
2
O
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
O
1
O
2
25
.
C
C
H
C
H
C
H
C
H
C
H
C
H
C
H
H
C
H
3
2
2
2
O
O
O
H
.
C
C
H
C
H
C
H
C
H
C
H
H
C
H
C
H
C
H
3
2
2
2
.
O
O
C
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
2
2
O
O
C
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
3
2
2
O
O
H
H
-

H
O
2
C
H
C
H
C
H
C
H
C
H
3
2
2
O