Environmental Engineering Reference
In-Depth Information
Fig. 6
Structure of the
Mn
4
CaO
5
cluster. Stereo
view of the Mn
4
CaO
5
cluster
and its ligand environment.
The distances shown are
the average distances
between the two monomers.
Manganese,
purple
; calcium,
yellow
; oxygen,
red
; D1,
green
; CP43,
pink
.
Data
source
Umena et al. (
2011
)
Mn
4
CaO
5
(H
2
O)
4
or Mn
4
CaO
4
(OH)(H
2
O)
4
is formed through five oxygen
atoms that act as oxo bridges linking the five metal atoms, and four water mol-
ecules that are bound to the Mn
4
CaO
5
cluster and can generate O
2
(Fig.
6
) (Umena
et al.
2011
; Yamanaka et al.
2012
). Among the five metal and five oxygen atoms,
three Mn, one Ca and four O form a cubane-like structure in which Ca and Mn
occupy four corners and the O atoms occupy the other four. The fourth manga-
nese (Mn4) is located outside the cubane; it is linked to Mn1 and Mn3 within the
cubane by O5, and to O4 by a di-
μ
-oxo bridge (Umena et al.
2011
). In this way,
every two adjacent Mn atoms are linked by di-
μ
-oxo bridges: Mn1 and Mn2 via
O1 and O3, Mn2 and Mn3 via O
2
and O3, and Mn3 and Mn4 via O4 and O5. The
calcium is linked to all four Mn by oxo bridges: to Mn1 via the di-
μ
-oxo bridge
formed by O1 and O5, to Mn2 via O1 and O2, to Mn3 via O2 and O5, and to Mn4
via the mono-
μ
-oxo bridge formed by O5 (Umena et al.
2011
). It is also shown
that four water molecules (W1 to W4) are associated with the Mn
4
CaO
5
cluster,
of which W1 and W2 are coordinated to Mn4 with respective distances of 2.1 and
2.2 Å, and W3 and W4 are coordinated to Ca with a distance of 2.4 Å. This sug-
gests that some of the four waters may serve as the substrates for water oxidation
(Umena et al.
2011
).
Several studies are conducted to evaluate the functions of the PSI and
PSII (Jordan et al.
2001
; Dashdorj et al.
2004
; Germano et al.
2004
; Diner and
Rappaport
2002
; Li et al.
2006
; Rappaport and Diner
2008
; Müller et al.
2010
;
Nilsson Lill
2011
; Schlodder et al.
2007
,
2011
; Nanba and Satoh
1987
; Dekker
and van Grondelle
2000
; Greenfield and Wasielewski
1996
; Klug et al.
1998
;
Prokhorenko and Holzwarth
2000
; Byrdin et al.
2002
; Yoder et al.
2002
; Holzwarth
et al.
2006
).
