Environmental Engineering Reference
In-Depth Information
Carbohydrate C
x
(H
2
O)
y
is formed (Eq.
3.1
), where
x
and
y
are whole num-
bers that differ depending on the specific carbohydrate that is being produced.
The release of O
2
in photosynthesis is the fundamental photoinduced conversion
reaction, which under the present hypothesis is supposed to involve H
2
O
2
either
via disproportionation or upon biological processes (Eq.
3.2
) (Komissarov
2003
;
Buick
2008
; Moffett and Zafiriou
1990
; Liang et al.
2006
).
The release of O
2
from H
2
O
2
instead of H
2
O can be understood from several
mechanistic approaches: (i) Mechanism for oxygen release from H
2
O
2
instead of
H
2
O; (ii) Effective oxidation of H
2
O
2
instead of H
2
O in releasing photosynthetic
O
2
(iii) generation of H
2
O
2
from DOM and POM; (iv) photoinduced generation
of H
2
O
2
from ultrapure H
2
O; (v) Endogenous H
2
O
2
in the photosynthetic cell and
effects of exogenous H
2
O
2
; (vi) H
2
O
2
formation in water, lipid and protein envi-
ronments in the presence of Chlorophyll; and (vii) Occurrence of H
2
O
2
and its
effects on photosynthesis.
3.1 Mechanism for Oxygen Release from H
2
O
2
Instead of H
2
O
Experimental studies show that various cyanobacteria may release O
2
from the
decomposition of H
2
O
2
during photosynthesis (Komissarov
1994
,
1995
,
2003
;
Velthuys and Kok
1978
; Mano et al.
1987
; Renger
1987
; Anan'ev and Klimov
1988
; Bader and Schmid
1988
,
1989
; Schroeder
1989
; Schröder and Åkerlund
1990
; Miyake and Asada
1992
; Bader
1994
). Based on the mechanism given by
Komissarov (
1994
,
1995
,
2003
) and the mechanism of H
2
O
2
photodecomposition
by earlier studies (Christensen et al.
1982
; Bielski et al.
1985
), the release of O
2
from H
2
O
2
can be generalized as follows (Eqs.
3.3
-
3.6
or
3.7
-
3.10
):
(3.3)
H
2
O
2
→
H
+
+
HO
2
−
(3.4)
HO
2
−
+
h
→
HO
2
(3.5)
HO
2
→
H
+
+
O
2
−
(3.6)
O
2
−
+
h
→
O
2
or
H
2
O
2
+
HO
•
→
HO
2
•
+
H
2
O
K
=
3. 0
×
10
7
M
−
1
S
−
1
(3.7)
HO
2
•
+
HO
2
•
→
H
2
O
2
+
O
2
K
=
8. 3
×
10
5
M
−
1
S
−
1
(3.8)
HO
2
•
+
O
2
•−
→
HO
2
−
+
O
2
K
=
9. 7
×
10
7
M
−
1
S
−
1
(3.9)
HO
2
•
↔
O
2
•−
+
H
+
K
=
1. 58
×
10
−
5
M
−
1
S
−
1
(3.10)
