Steric Protection of a Photosensitizer in a N,N-Bis[2-(2-pyridyl)ethyl]-2-phenylethylamine-copper(II) Bowl that Enhances Red Light-Induced DNA Cleavage Activity

Dhar, Shanta and Nethaji, Munirathinam and Chakravarty, Akhil R (2005) Steric Protection of a Photosensitizer in a N,N-Bis[2-(2-pyridyl)ethyl]-2-phenylethylamine-copper(II) Bowl that Enhances Red Light-Induced DNA Cleavage Activity. In: Inorganic chemistry, 44 (24). pp. 8876-8883.

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Abstract

Ternary copper(II) complexes $[Cu(py_2phe)B](ClO_4)_2$ (1-3), where $py_2phe$ is a tripodal ligand N,N-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine and B is a heterocyclic base (viz., 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2), or dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3)), are prepared and their DNA-binding and photoinduced DNA-cleavage activities are studied. Complex 1 has been structurally characterized by single crystal X-ray crystallography. The molecular structure shows an axially elongated square-pyramidal (4 + 1) coordination geometry in which the phen ligand binds at the basal plane. The tripodal ligand $py_2phe$ displays an axial-equatorial binding mode with the amine nitrogen bonded at the axial site. A chemically significant CH-\pi interaction involving the CH moiety of the phenyl group of the tripodal ligand and the aromatic ring of phen is observed. The complexes display good binding propensity to calf thymus DNA giving a relative order of 3 (dppz) > 2 (dpq) > 1 (phen). The DNA binding constants $(K_b)$ for 1-3, determined from absorption spectral studies, are $6.2 \times 10^3$, $1.0 \times 10^4 and \hspace {2mm} 5.7 \times 10^4 M^{-1}$, respectively. The complexes show chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent forming hydroxyl radicals as the cleavage active species. The photoinduced DNA-cleavage activity of the complexes has been studied using UV radiation of 365 nm and red light of 632.8 and 694 nm. The phen complex in absence of any photosensitizing moiety does not show any DNA cleavage upon photoirradiation. The dpq and dppz ligands with their photoactive quinoxaline and phenazine moieties display significant photoinduced DNA-cleavage activity. The dppz complex is more active than its dpq analogue because of the better steric protection of the DNA-bound photosensitizing dppz ligand from the solvent molecules. Control experiments reveal the formation of singlet oxygen in the light-induced DNA-cleavage reactions. The observed efficient photoinduced DNA-cleavage activity of 2 and 3 is akin to the "light switch" effect known for the tris-chelates of ruthenium(II).

Item Type:	Journal Article
Publication:	Inorganic chemistry
Publisher:	American Chemical Society
Additional Information:	The Copyright belongs to American Chemical Society.
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	29 Mar 2006
Last Modified:	19 Sep 2010 04:24
URI:	http://eprints.iisc.ac.in/id/eprint/5858

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