R.S. Sancheti et al. / Polyhedron 31 (2012) 12–18
17
in the visible region of electronic spectrum due to the presence of d
5. Conclusion
electrons (d8). However, we could not locate a d–d absorption for
the complex when studied in DMF as a solvent, although we iden-
tified one in the solid state (at 15900 cmꢁ1). The absorption due to
the d–d transition in the solid complex is weak. Therefore, it is sug-
An asymmetric tetradentate ligand H2L and four metal com-
plexes with approximate trigonal bipyramidal geometry have been
prepared. All the compounds are effective in promoting cleavage of
gested that due to the solvent effect (DMF,
e = 37), the complex
plasmid DNA at a minimum concentration of 5 lM by an oxidative
vibrations are suppressed or alternatively the complex may exist
in a centrosymmetric octahedral form for which d–d transitions
are forbidden on parity grounds [54,55]. The zinc complex exhibits
only one ligand based transition at 288 (2100). The spectra of the
iron and copper complexes have nearly the same transitions in
both solid and solution states.
mechanism. A binding investigation with CT-DNA confirmed that
the ligand and metal complexes bind to the DNA. There is a close
correlation between the Kb and the DNA cleavage pattern of the li-
gand and the complexes.
Acknowledgements
The frozen glass electron paramagnetic resonance spectrum of
[Cu(HL)Cl] in DMF at liquid nitrogen temperature is shown in
Fig. 2, while the EPR parameters and IR assignments are summa-
rized in Table 2. The EPR spectrum of the copper complex shows
four well resolved copper hyperfine lines, characteristic of a mono-
nuclear copper(II) complex, and it exhibits three distinct features
at 2.25, 2.05 and 2.01, corresponding to a distorted tbp/sp structure
with 165 G as the ACu component (shown in Fig. 2).
The authors acknowledge the RFSMS Fellowship from the
University Grant Commission, India and are thankful to Dr. K.K.
Sharma and Prof. K. J. Patil, School of Chemical Sciences, North
Maharashtra University, India and Dr. E. Suresh, Central Marine Re-
search Institute, Bhavnagar, India for the valuable discussions.
Appendix A. Supplementary data
4.3. DNA cleavage
CCDC 785617 contains the supplementary crystallographic data
for structure [Cu(HL)Cl] (1). These data can be obtained free of
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
The DNA cleavage activity of the ligand, H2L and its Cu(II) (1),
Ni(II) (2) and Zn(II) (3) complexes has been studied using super-
coiled plasmid pBR322 DNA in Tris–boric acid–EDTA (TBE) buffer
in the absence of any external additives under dark conditions.
The Fe(III) complex (complex 4) was found to be very unstable in
solution and hence was not studied. It was observed that all the
compounds, including the ligand, convert supercoiled plasmid
(SC) DNA into nicked circular (NC) DNA and the linear form
(Figs. 3A and 3B) very efficiently, even at very low concentrations
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