Metal(ii) schiff base complexes and the insulin-mimetic Studies on the oxovanadium(iv) complexes
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Date
2009
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Abstract
Sixteen symmetrical and four unsymmetrical tetradentate Schiff bases with
the N2O2 chromophore were isolated in pure form and fully characterized by
elemental analyses, melting point, IR and 1H NMR. The appearance of two different
peaks for each of the azomethine protons and phenolic protons confirm the
asymmetry nature of the unsymmetrical Schiff bases. All the Schiff bases were
successfully coordinated to oxovanadium (IV) ion to form the corresponding
complexes. The unsymmetrical Schiff bases were also successfully coordinated to
cobalt(II), nickel(II) and copper(II) ions to form their corresponding complexes. In all
thirty-two metal(II) Schiff bases complexes were isolated. These complexes were
characterized by elemental analyses, melting point, IR, EPR, cyclic voltammetry,
magnetic susceptibility measurements, differential scanning calorimetry and
electronic spectra. The isolation of the unsymmetrical tetradentate Schiff bases and
their complexes as well as some of the symmetrical tetradentate Schiff bases and
their complexes are considered to be novel. The purity and composition of both the
Schiff bases and the metal (II) complexes were established by elemental analyses.
The comparison of the IR spectra of the Schiff-bases and their metal
complexes indicated that the Schiff bases acted as tetradentate ligands. The
observed shifts in the stretching frequencies of (C=N) and (C¯O) are indicative of
the formation of these complexes. Further conclusive evidence of the coordination of
these Schiff-bases with the metal ions was shown by the appearance of new bands
due to (M¯N) and (M¯O) in the metal complexes. Most of the oxovanadium (IV)
complexes exhibit a strong band in the range 959−989 cm−1, which have been
assigned to (V=O) in a monomeric square pyramidal coordination environme oxovanadium (IV) complexes with trimethylene bridge, in which their (V=O)
appeared at 848−860 cm.1, have been assigned polymeric structure with
[V=O∙∙∙•V=O] interactions, which afforded distorted octahedral coordination
geometry.
The electronic spectral and magnetic susceptibility measurements were used
for assigning the stereochemistry of each metal complex. Electronic spectra indicate
a square-planar geometry for all the cobalt(II), nickel(II) and copper(II) complexes.
This was also corroborated by the effective magnetic moment of the complexes.
The electronic spectra of the oxovanadium ( IV) complexes suggest a diversity of
geometries. The electronic spectra indicate a square-pyramidal geometry for the fivecoordinate
species and distorted octahedral geometry for the six-coordinate species.
The room temperature magnetic moments of 1.6.1.8 BM are normal for V(IV) d1
configuration. The solution EPR spectra of the oxovanadium ( IV) are consistent with
square pyramidal geometry. The cyclic voltammetry of the oxovanadium ( IV)
complexes revealed only one quasi-reversible wave for each complex and they all
showed redox couples with peak- to peak separation values ( Ep) ranging from 74
to 83 mV, indicating a single step one electron transfer process.
In vitro glucose uptake was carried out on all the oxovanadium (IV) complexes
using C2C12 cell line. All the complexes tested increased glucose utilization in
C2C12 cells over basal values except two of the complexes whose percentage
glucose uptake was lower than the basal glucose uptake (DMSO). Eighteen of the
complexes significantly increased glucose uptake when compared to the basal
glucose uptake of the solvent vehicle (DMSO). Cytotoxic test carried out on all the
complexes using M at both low and high concentrations. Two of the complexes showed activities
comparable or greater than that of insulin.
Four unsymmetrical and five symmetrical Schiff base complexes of
oxovanadium(IV) have been tested in vivo for their insulin mimetic activities. An
acute oral administration of the four unsymmetrical Schiff base complexes of
oxovanadium (IV) elicited a progressive reduction in plasma glucose over 6 h in STZ
rats. Two of the unsymmetrical Schiff base complexes of oxovanadium( IV) induced
a significant reduction in plasma glucose over a 6 h period. Oral administration of the
five symmetrical complexes also elicited a progressive reduction in plasma glucose
over 6hrs. Two of these complexes induced a significant reduction in plasma glucose
during the 6 hour period.TT assay showed that the complexes were not toxic to the cells.
Description
A thesis in the Department of Chemistry submitted to the Faculty of Science and Agriculture in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy of the University of Zululand, 2009.
Keywords
Metal(ii) schiff base complexes, Insulin-mimetic, Oxovanadium(iv) complexes