Abstract
Three ternary copper(II) complexes of formulation [CuL
n
B](ClO
4) having anionic NSO-donor Schiff base and NN-donor heterocyclic ligand are prepared and structurally characterized. The 1,10-phenanthroline complex binds DNA in the minor groove and displays oxidative photo-induced DNA cleavage on red light irradiation.
New ternary copper(II) complexes [CuL
n
B](ClO
4) (
1–
3), where HL
n
is the NSO donor Schiff base derived from the condensation of 2-mercaptoethylamine hydrochloride with salicylaldehyde (HL
1) or 2-hydroxy-3-methoxybenzaldehyde (HL
2) and B is NN-donor heterocyclic base like 2,2′-bipyridine (bpy,
1), 1,10-phenanthroline (phen,
2) or 2,9-dimethyl-1,10-phenanthroline (dmp,
3), are prepared, structurally characterized by X-ray crystallography and their DNA cleavage activity studied. The complexes show distorted square-pyramidal (4
+
1) CuN
3OS coordination geometry in which the NSO-donor Schiff base is bonded at the basal plane and the NN-donor heterocyclic base displays axial-equatorial mode of bonding [Cu–S distance: ∼2.4
Å]. The one-electron paramagnetic (
μ
eff
=
∼1.9
μ
B) complexes display axial EPR spectra in DMF glass at 77
K giving g
∥
=
∼2.2 (A
∥
=
162
G) and g
⊥
=
∼2.0, indicating
{
d
x
2
-
y
2
}
1
ground state. The complexes exhibit visible spectral d–d band in MeCN near 650
nm and two charge transfer bands near 400
nm. Complexes
1 and
2 display quasireversible cyclic voltammetric response in DMF–Tris buffer (1:4 v/v, pH 7.2) for the Cu(II)/Cu(I) couple at ca. −0.1
V vs. SCE. Complex
3 exhibits an irreversible reduction process forming [Cu
I(dmp)
2]
+. Binding of
1–
3 to calf thymus DNA shows the relative order:
2 (phen)
⩾
3 (dmp)
>
1 (bpy). Complex
2 efficiently cleaves supercoiled pUC19 DNA in the presence of mercaptopropionic acid (MPA) forming hydroxyl radical or on irradiation with light of 312, 532 and 632.8
nm wavelength in a type-II process. Complexes
1 and
3 are cleavage inactive.
