Environmental Engineering Reference
In-Depth Information
monolayers and colloidal dispersions used as models for the in vivo systems (Katz
et al.
1991
). Red shifts generally occur when electron releases follow the easiest
way in the functional groups bound to the component system (see also chapters
Waters
”
and
“
Fluorescent Dissolved Organic Matter in Natural Waters
”
) (Mostofa
et al.
2009
; Senesi
1990
). Chl
b
found in chlorophytes and prochlorophytes can
absorb sunlight at around 470 nm (highest peak) and 650 nm (small peak) (Satoh
et al.
2001
). The Chl
c
isolated from
Peridinium gatunense
showed two peaks at
448-449 and 634-635 nm (Yacobi et al.
1996
).
All pigments can bind to their specific proteins to form pigment-protein com-
plexes (Cogdell et al.
1996
; Pearlstein
1996
). Complexation can provide the easi-
est way of electron release, as depicted in other chapters (see
“
Photosynthesis in
Metal ions in Natural Waters
”). The Chl
b
content of the light-harvesting complex
(LHC) of PSII in higher plants is highly preserved, approximately between 45 and
50 % or in the approximate ratio of 3:1 of Chl
a
to Chl
b
(Anderson
1986
; von
Elbe and Schwartz
1996
). Conversely, the contents of Chl
b
in cyanobacteria are
variable and relatively low (1.4-10.6 % or more) (Bianchi et al.
2002
; Satoh et al.
2001
). Experimental and other observation have shown that Chl
a
molecules can
bind to LHC of PSII at Chl
b
binding sites (Thornber and Highkin
1974
; Terao
and Katoh
1989
; Murray and Kohorn
1991
; Paulsen et al.
1993
; Polle et al.
2000
).
Correspondingly, Chl
b
is vital for the stability of LHC of PSII in the thylakoid
membrane (Murray and Kohorn
1991
; Bellemare et al.
1982
). The core antenna
complexes of chlorophytes have Chl
a
and do not bind Chl
b
, despite its presence
(Satoh et al.
2001
; Anderson et al.
1978
).
2.1 Properties and Functions of Chlorophyll
Chlorophyll (Chl)
a
has a methyl group at the C-3 carbon (molecular formula
C
55
H
72
MgN
4
O
5
), while Chl
b
has the same chemical structure as Chl
a
but
with a -CH
3
group replaced by a -CHO one, providing the molecular formula
C
55
H
70
MgN
4
O
6
(Fig.
1
) (Clarke et al.
1976
). The correct gross structure of Chl
has been suggested at first by Fischer (Fischer and Wenderoth
1940
) and verified
in a synthesis by Woodward (Woodward et al.
1960
; Woodward
1961
). The rela-
tive configuration of the methyl and propionic ester groups on the D ring in the
structure was shown to be
trans
by Ficken and his colleagues (Ficken et al.
1956
).
The stereochemistry and absolute configuration of the phytyl group is 2′-
trans
-
7′
R
,11′
R
, as discovered in 1959 (Burrell et al.
1959
; Crabbe et al.
1959
). The
relative configuration at C
10
is such that the methoxycarbonyl group is
trans
to
the propionic ester side chain on C
7
(Closs et al.
1963
; Wolf et al.
1967
). In addi-
tion to their structural differences, Chl
a
is observed to be thermally less stable
than Chl
b
(Buckle and Edwards
1970
; Lajollo et al.
1971
; Schwartz and von Elbe
1983
; Canjura et al.
1991
; Schwartz and Lorenzo
1991
).