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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
journal contribution
posted on 2005-11-28, 00:00 authored by Shanta Dhar, Munirathinam Nethaji, Akhil R. ChakravartyTernary copper(II) complexes [Cu(py2phe)B](ClO4)2 (1−3), where py2phe 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 py2phe displays an axial−equatorial
binding mode with the amine nitrogen bonded at the axial site. A chemically significant CH−π 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 (Kb) for 1−3, determined from absorption spectral studies, are 6.2 × 103, 1.0 × 104, and 5.7
× 104 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).
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complexes show chemical nuclease activityCH moietyUV radiationpy 2 pheSteric Protection365 nm694 nmdpq analoguehydroxyl radicalsheterocyclic basephen ligandtripodal ligand py 2 phe displaysamine nitrogenComplex 1complexes displayK bDNA cleavagecalf thymus DNAtripodal ligand Nsinglet oxygenphenazine moieties displayDNA binding constantsbasal planecontrol experimentsdppz ligandstripodal ligandphotoactive quinoxalinephotoinducedsteric protectionphenyl groupbinding propensityphotosensitizing moiety
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