Environmental Engineering Reference
In-Depth Information
Fig. 1
Molecular structure
of chlorophyll
a
and
chlorophyll
b
with some
medication.
Data source
Clarke et al. (
1976
)
5
5
H
R
2
, and meso-Chl
b
with two ethyl groups at R
1
and R
2
(Fig.
1
) (Clarke et al.
1976
). Moreover, Chl
c
composed of a 17-acrylic side-chain has been isolated
from two Moroccan oil shales of Cretaceous age (Verne-Mismer et al.
1988
).
Petroporphyrins, showing both a free C-7 position and a C-13 to C-17 substitu-
tion pattern typical of Chl
c
fossils, have been isolated from two Cretaceous
Moroccan oil shales and may arise from a still unknown Chl, 7-formylchloro-
phyll
c
for Chl
c
3
(Verne-Mismer et al.
1990
). Chl
c
3
, isolated from a microalga,
has tentatively been identified as 7-demethyl-7-methoxycarbonyl chlorophyll
(Fookes and Jeffrey
1989
). Chl
c
2
, isolated from the coccolithophorid
Emiliania
huxleyi
(Prymnesiophyceae), is present in approximately equal proportions as
Chl
c
3
. It has absorption maxima at 447, 579 and 628 nm, whilst no Chl
c
1
has
been detected (Jeffrey and Wright
1987
). Cells of the new prokaryote have an
absorption maximum in the red region (714-718 nm) due to Chl
d
absorption, but
they do not show any characteristic absorption peak of Chl
a
at around 680 nm
(Miyashita et al.
1997
). Chl
f
is [2-formyl]-chlorophyll
a
(C
55
H
70
O
6
N
4
Mg), and
its in vitro absorption (706 nm) and fluorescence (722 nm) maxima are red-shifted
compared to all other Chls from oxygenic phototrophs (Chen et al.
2010
).
Uncoupled Chls in PSII of cyanobacteria or phytoplankton and red algae
can absorb at shorter wavelength, e.g. 670 nm (close to their site energy),
whilst electronically coupled chlorins (the central cofactors) or Chl dimers can
absorb between 676 and 684 nm (Zhang et al.
2009
; Telfer et al.
1990
; Durrant
et al.
1995
; Renger and Marcus
2002
). Formation of Chl dimers and their light-
induced excitations are extensively discussed in the photosynthesis chapter
“
Photosynthesis in Nature: A New Look
”. Upon 440-nm excitation of Chl
a
bound
to
Synechocystis
cells, a typical PSII fluorescence at 685 nm has been observed
both at room temperature and at 77 K (Satoh et al.
2001
). Two additional fluo-
rescence components have been detected at 695 and 722 nm, whilst no fluores-
cence peak for Chl
b
has been observed in these cyanobacteria (Satoh et al.
2001
).
Red shifts are commonly observed in in vitro Chl
a
systems, including thin films,
