Dhar, S.; Nethaji, M.; Chakravarty, A. R. 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.
Inorganic Chemistry 2005,
44, 8876-8883.
Abstract
Ternary copper(II) complexes [Cu(py2phe)B](ClO4)2 (1-3), where py2phe is the 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)), were prepd. and their DNA-binding and photoinduced DNA-cleavage activities were studied. Complex 1 was structurally characterized by single crystal x-ray crystallog. The mol. structure shows an axially elongated square-pyramidal (4 + 1) coordination geometry in which the phen ligand binds at the basal plane. The tripodal ligand py2phe displays an axial-equatorial binding mode with the amine nitrogen bonded at the axial site. A chem. significant CH-π interaction involving the CH moiety of the Ph group of the tripodal ligand and the arom. ring of phen is obsd. The complexes display good binding propensity to calf thymus DNA giving a relative order of 3 (dppz) > 2 (dpq) > 1 (phen). The DNA binding consts. (Kb) for 1-3, detd. from absorption spectral studies, are 6.2 × 103, 1.0 × 104, and 5.7 × 104 M-1, resp. The complexes show chem. 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 was 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 photoirradn. 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 analog because of the better steric protection of the DNA-bound photosensitizing dppz ligand from the solvent mols. Control expts. reveal the formation of singlet oxygen in the light-induced DNA-cleavage reactions. The obsd. efficient photoinduced DNA-cleavage activity of 2 and 3 is akin to the light switch effect known for the tris-chelates of ruthenium(II). [on SciFinder(R)]