122
Due to the involvement of valence (outer) orbitals, the energy of these orbitals is
quite high and the complex is reactive and labile. An octahedral complex with low
energy involvement is also possible by the use of inner d-orbitals. In this case, the
unpaired electrons in d-orbitals are forced to pair up, then spin of unpaired ions will
reduce and becomes low spin complex. In this case also, the hybridisation is d
2
sp
3
,
hence the structure of the complex is octahedral.
With an exception of α-hydroxycarboxylate type of chelation in rhizoferrin (1)
(Fig. 8.4), isolated from Rhizopus microsporus var. rhizopodiformis, which is composed of citric acid and diaminobutane (Drechsel et al. 1991), siderophores reported
from the fungus are all hydroxamate type of chelation.
Structurally, the fungal hydroxamate siderophores are classified into three families, namely, coprogens, fusarinines and ferrichromes.
M. S. A. Shukkoor and S. I. Khalivulla
Due to the involvement of valence (outer) orbitals, the energy of these orbitals is
quite high and the complex is reactive and labile. An octahedral complex with low
energy involvement is also possible by the use of inner d-orbitals. In this case, the
unpaired electrons in d-orbitals are forced to pair up, then spin of unpaired ions will
reduce and becomes low spin complex. In this case also, the hybridisation is d
2
sp
3
,
hence the structure of the complex is octahedral.
With an exception of α-hydroxycarboxylate type of chelation in rhizoferrin (1)
(Fig. 8.4), isolated from Rhizopus microsporus var. rhizopodiformis, which is composed of citric acid and diaminobutane (Drechsel et al. 1991), siderophores reported
from the fungus are all hydroxamate type of chelation.
Structurally, the fungal hydroxamate siderophores are classified into three families, namely, coprogens, fusarinines and ferrichromes.
M. S. A. Shukkoor and S. I. Khalivulla