Synthesis, structural characterization and potentiometric studies of divalent metal complexes with an octadentate tetraazamacrocyclic ligand and their DNA cleavage ability
Dy. Kong et Yy. Xie, Synthesis, structural characterization and potentiometric studies of divalent metal complexes with an octadentate tetraazamacrocyclic ligand and their DNA cleavage ability, POLYHEDRON, 19(12), 2000, pp. 1527-1537
Four new metal complexes with an octadentate macrocyclic ligand [L = 1,4,7,
10-tetrakis(2-carbamoylethyl)-1,4,7,10-tetraazacyclododecane] were synthesi
zed and characterized by elemental analyses, IR and MS. These complexes hav
e the general formula: M(L)(NO3)(2). nH(2)O [M = Co (1), Ni (2), n = 2; M =
Cu (3), Zn (4), n = 1]. The structures of complexes 1, 2 and 3 have been d
etermined by X-ray diffraction. [Co(L)(NO3)](NO3). 2H(2)O (1) crystallizes
in the triclinic space group P (1) over bar. The refinement converges with
R = 0.045 and R-w = 0.057 for 3233 reflections with (I > 2.5 sigma(I)). The
Co has an octahedral geometry, and was coordinated with four amine nitroge
n atoms of macrocyclic ligand and two or one acylate oxygen atoms derived f
rom amide pendant groups. Two water molecules crystallize in the lattice ce
ll and two kinds of hydrogen bonds exist between the coordinated acylate gr
oup and the water molecules: N(6)-H(27)... O(11) 2.158, N(8)-H(40)... O(12)
2.158 Angstrom or exist between the uncoordinated acylate group and the ni
trate ion: N(5)-H(21)... O(8) 2.452, N(7)-H(33)... O(5) 2.256 Angstrom. [Ni
(L)(NO3)](NO3). 2H(2)O (2) crystallizes in the monoclinic space group C2/c.
The refinement converges with R = 0.044 and R-w = 0.059 for 2726 reflectio
ns with (I > 3 sigma(I)). The crystal of complex 2 has high symmetry with a
C-2v symmetric operation. The central Ni atom is coordinated to four amine
nitrogen atoms of macrocyclic skeleton and two acylate oxygen atoms of pen
dant amide groups. The polyhedron of the central atom can be described as a
pseudo-octahedron. Two water molecules crystallized in the cell lattice. [
Cu(L)](NO3)(2). H2O (3) crystallizes in the monoclinic space group P2(1)/n.
The refinement converges with R = 0.037 and R-w = 0.048 for 3174 reflectio
ns with (I > 2.5 sigma(I)). Complex 3 has a five-coordinated pyramid. The b
ond lengths of Co-O (av.) 2.088(3), Ni-O 2.089(2) Angstrom are almost equal
, and are shorter than Cu-O 2.137(3) Angstrom. On the other hand, the bond
lengths of Co-N (av.) and Ni-N (av.) are 2.194(3) and 2.153(2) Angstrom, re
spectively. Both of them are longer than Cu-N (av.) 2.0465(3) Angstrom. The
potentiometric experiments in aqueous solution showed that the stability c
onstants of three complexes were in the range of log K-ML = 17.11-15.00. Th
e DNA cleavage results showed that the cobalt complex can effectively cleav
e supercoiled DNA to form nicked or linear DNA by performing single strand
and double strand scissions under aerobic conditions in the presence of hyd
rogen peroxide as co-oxidant. Electron paramagnetic resonance results with
the aid of DMPO as trapping agent demonstrated that the cleavage mechanism
possibly occurred via hydroxy radical attacking. (C) 2000 Elsevier Science
Ltd. All rights reserved.