Complex 1 is [Cu(ip)2H2O](ClO4)2
Complex 2 is [Cu(dppz)2H2O](ClO4)2
Based on absorption spectral techniques i have studied binding ability of these complexes with DNA. A reviewer has raised a question as why complex one shows two absorption peak and complex 2 shows one peak.
kindly help me to get the answer.
Dear Dr. Kumar:
Well, thinking in a very simple way, in the dark, if spectrum belong to the study of the interaction of a complex with DNA via UV-Vis, take in account the wavelength at around 270 nm, a very energetic portion of UV-Vis spectra, the observed phenomenon would be a transition type intra-ligand, as one assigned to π-π*.
One of compounds, exhibiting a peak at 269 nm, would be classified as a metallointercalator exhibiting above features, with classical interaction mode correlated to intercalation (see another modes electrostatic interaction, interaction from voids of DNA and intercalation).
Please, consider read the paper:
K. E. Erkkila; D. T. Odom and J. K. Barton, Recognition and Reaction of Metallointercalators with DNA. Chemical Reviews, v.99, n.9, 1999. p. 2777
Please, also, consider read the Chapter:
G. M. Blackburn and M. J. Gait, Nucleic acids in Chemistry and Biology
2nd Ed. New York: Oxford University Press, 1997. p. 528
Another compound, present the same absorption band at 270 nm, only slight shifted to 277 nm, and as reported an additional band occur at 252 nm. If compounds are single phase, crystalline, proper ratio solvent:H2O and pH controlled, a possible phenomenon to be considered is further participation of modes electrostatic interaction and/or interaction from voids of DNA and its correlation with structural distortion of complex. See, this characterization technique is proper to investigate intercalation complex-DNA.
Further inspection of previous publications involving enantiomeric phenomenon and/or binding-modes and/or structural dependence of reactivities can be useful.
Best regards
Marcos Nobre
Thanks for your response Marcos Nobre.
The reviewer did not asked about DNA binding. He asked "The result on the electronic spectra of the complexes has just been literally presented in the text, however, no discussion has been made on the point that why there were two absorption peaks at 252 and 277 nm of complex 1 and one peak at 269 nm for complex 2".
He asked only about the complex and why complex 1 give two peaks and complex 2 give one peak. herewith i have attached the UV spectra of the complexes
Dear Dr. Kumar:
The band centered in 252 nm is sharp and intense being completely resolved in wavelength domain. An additional band ascribed to the structural distortion of complex should be exbibits contrary features.
Yet in the thinking line, in which the simplest answer is the most probable, let’s suppose that you make use aqueous solution with classical relation.
It is possible that your compound exhibits a low solubility in water, verify.
In the above sense, proceed more investigations at about intrinsic optical features of DNA-solution (aqueous) investigating if DNA-solution have an absorption band at 250-265 nm, it is probable. Then, second band intense detected in spectrum centered at around 252 nm would belong to DNA-solution.
Best regards
Marcos Nobre
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