Environmental Engineering Reference
In-Depth Information
plant cells. Terrestrial plants can receive high concentrations of rainwater H
2
O
2
(0-199,000 nM: see Table 2 in chapter
“
Photoinduced and Microbial Generation
of Hydrogen Peroxide and Organic Peroxides in Natural Waters
”
), which is a vital
source of exogenous H
2
O
2
and is susceptible to promote photosynthesis in plants
and algae (Komissarov
1994
,
1995
,
2003
; Mostofa et al.
2009
). Experimental
studies demonstrate that H
2
O
2
concentrations (up to 10
−
5
M) in culture media
can stimulate plant growth (Komissarov
1994
,
1995
,
2003
). In addition, H
2
O
2
can
inhibit growth at concentrations as low as 10
−
5
-10
−
4
M under the conditions of a
dialysis culture (Samuilov et al.
2001
). H
2
O
2
can inhibit the photosynthetic elec-
tron transport in cells of cyanobacteria (Samuilov et al.
2001
,
2004
) and can also
destroy the function of the oxygen-evolving complex (OEC) in some chloroplasts
and photosystem II preparations. In such a case it would cause the release of man-
ganese from cyanobacterial cells, which inhibits the OEC activity.
3.5 H
2
O
2
Formation in Water, Lipid and Protein
Environments in the Presence of Chlorophyll
Chlorophyll can produce H
2
O
2
in aqueous solution under acidic and alkaline pH
conditions (pH
=
3.8-12.4) under visible light irradiation (Lobanov et al.
2008
).
The mechanism behind the production of H
2
O
2
from illuminated Chl can be illus-
trated as follows (
3.33
-
3.39
) (Lobanov et al.
2008
; Parmon
1985
; Bruskov
2002
):
At pH < 7
(3.33)
Chl
+
h
υ →
Chl
∗
(3.34)
Chl
∗
+
O
2
→
Chl
+
+
O
2
•−
O
2
•−
+
H
+
→
HO
2
•
K
=
5
×
10
10
MS
−
1
(3.35)
HO
2
•
+
O
2
•−
+
H
+
→
H
2
O
2
+
O
2
K
=
9
×
10
7
MS
−
1
(3.36)
HO
2
•
+
HO
2
•
→
H
2
O
2
K
=
2
×
10
6
MS
−
1
(3.37)
At pH > 7
H
2
O
2
+
Fe
2
+
(
or other metals
) →
HO
•
+
HO
−
+
Fe
3
+
(3.38)
HO
•
+
HO
•
→
H
2
O
2
K
=
6
×
10
9
MS
−
1
(3.39)
The electron donor for the conversion
O
2
→
O
2
•−
(redox potential
φ
°
=
-0.12 V) can be Chl in the singlet or triplet excited state (the S1 and T1),
with
φ
°
=
-1.14 and -1.54 V, respectively (Lobanov et al.
2008
). The occurrence
of reaction (Eq.
3.39
) is confirmed by the addition of 1 M ethanol as a scavenger
of HO
•
into the water suspension of silica gel with immobilized Chl inhibits the
