Steric Protection of a Photosensitizer in a
<i>N,N</i>-Bis[2-(2-pyridyl)ethyl]-2-phenylethylamine-copper(II) Bowl that
Enhances Red Light-Induced DNA Cleavage Activity
Shanta Dhar
Munirathinam Nethaji
Akhil R. Chakravarty
10.1021/ic0505246.s002
https://acs.figshare.com/articles/journal_contribution/Steric_Protection_of_a_Photosensitizer_in_a_i_N_N_i_Bis_2_2_pyridyl_ethyl_2_phenylethylamine_copper_II_Bowl_that_Enhances_Red_Light_Induced_DNA_Cleavage_Activity/3254590
Ternary copper(II) complexes [Cu(py<sub>2</sub>phe)B](ClO<sub>4</sub>)<sub>2</sub> (<b>1</b>−<b>3</b>), where py<sub>2</sub>phe is a tripodal ligand <i>N</i>,<i>N</i>-bis[2-(2-pyridyl)ethyl]-2-phenylethylamine and B is a heterocyclic base (viz., 1,10-phenanthroline (phen, <b>1</b>), dipyrido[3,2-d:2‘,3‘-f]quinoxaline (dpq, <b>2</b>), or dipyrido[3,2-a:2‘,3‘-c]phenazine (dppz, <b>3</b>)), are prepared and their DNA-binding and
photoinduced DNA-cleavage activities are studied. Complex <b>1</b> 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<sub>2</sub>phe 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 <b>3</b> (dppz) > <b>2</b> (dpq) > <b>1 </b>(phen). The
DNA binding constants (<i>K</i><sub>b</sub>) for <b>1</b>−<b>3</b>, determined from absorption spectral studies, are 6.2 × 10<sup>3</sup>, 1.0 × 10<sup>4</sup>, and 5.7
× 10<sup>4</sup> M<sup>-1</sup>, 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 <b>2</b> and <b>3</b> is akin to the “light switch” effect known for the tris-chelates of ruthenium(II).
2005-11-28 00:00:00
complexes show chemical nuclease activity
CH moiety
UV radiation
py 2 phe
Steric Protection
365 nm
694 nm
dpq analogue
hydroxyl radicals
heterocyclic base
phen ligand
tripodal ligand py 2 phe displays
amine nitrogen
Complex 1
complexes display
K b
DNA cleavage
calf thymus DNA
tripodal ligand N
singlet oxygen
phenazine moieties display
DNA binding constants
basal plane
control experiments
dppz ligands
tripodal ligand
photoactive quinoxaline
photoinduced
steric protection
phenyl group
binding propensity
photosensitizing moiety