Effect of Steric Encumbrance of Tris(3-phenylpyrazolyl)borate on the Structure and Properties of Ternary Copper(II) Complexes Having N,N-Donor Heterocyclic Bases

Abstract

Complexes of formulation [Cu(Tp(Ph))(L)](ClO(4)) (1-4), where Tp(Ph) is anionic tris(3-phenylpyrazolyl)borate and L is N,N-donor heterocyclic base, viz. 2,2'-bipyridine (bpy, 1), 1,10-phenanthroline (phen, 2), dipyridoquinoxaline (dpq, 3), and dipyridophenazine (dppz, 4), are prepared from a reaction of copper(II) acetate.hydrate with KTp(Ph) and L in CH(2)Cl(2) and isolated as perchlorate salts. The complexes are characterized by analytical, structural, and spectral methods. The crystal structures of complexes 1-4 show the presence of discrete cationic complexes having the metal, Tp(Ph), and L in a 1:1:1 ratio and a noncoordinating perchlorate anion. The complexes have a square-pyramidal 4 + 1 coordination geometry in which two nitrogens of L and two nitrogens of the Tp(Ph) ligand occupy the basal plane and one nitrogen of Tp(Ph) binds at the axial site. Complexes 3 and 4 display distortion from the square-pyramidal geometry. The Cu-N distances for the equatorial and axial positions are approximately 2.0 and 2.2 A, respectively. The phenyl groups of Tp(Ph) form a bowl-shaped structure that encloses the [CuL] moiety. The steric encumbrance is greater for the bpy and phen ligands compared to that for dpq and dppz. The one-electron paramagnetic complexes (mu approximately equal to 1.8 mu(B)) exhibit axial EPR spectra in CH(2)Cl(2) glass at 77 K giving g(parallel) and g(perpendicular) values of approximately 2.18 (A(parallel) = 128 G) and approximately 2.07. The data suggest a [d(x(2)-y(2))](1) ground state. The complexes are redox-active and display a quasireversible cyclic voltammetric response for the Cu(II)/Cu(I) couple near 0.0 V versus SCE with an i(pc)/i(pa) ratio of unity in CH(2)Cl(2) or DMF-0.1 M TBAP. The E(1/2) values of the couple vary in the order 4 > 3 > 2 > 1. A profound effect of steric encumbrance caused by the Tp(Ph) ligand is observed in the reactivity of 1-4 with the calf thymus (CT) and supercoiled (SC) DNA. Complexes 2-4 show similar binding to CT DNA. The propensity for the SC DNA cleavage varies as 4 > 3 > 2. The bpy complex does not show any significant binding or cleavage of DNA. Mechanistic investigations using distamycin reveal minor groove binding for 2 and 3 and a major groove binding for 4. The scission reactions that are found to be inhibited by hydroxyl radical scavenger DMSO are likely to proceed through sugar hydrogen abstraction pathways.

(Dipyrido[3,2-a:2′,3′-c]phenazine)(glycinato)copper(II) perchlorate: A novel DNA-intercalator with anti-proliferative activity against thyroid cancer cell lines

“…Selected bond distances and angles are given in Table 2. Cu\N(1) and Cu\N(2) bond distances of N,N dppz are: 2.008(2) Å and 2.015(2) Å respectively while the other bond lengths in the equatorial plane are: Cu\N(5), 2.011(2)Å and Cu\O(2), 1.932(2)Å. Equatorial bond distances as well as the bite angle N(1) \Cu\N (2) and N(5)\Cu\O(2) (81.37(8)°and 84.70(8)°r espectively) are in good agreement with the corresponding ones reported for related compounds [34,36,57,58]. The elongated axial positions are occupied by two oxygen atoms from the carboxylic group and the perchlorate anion [Cu\O(1) 2.251(2)Å, Cu-O(3) 2.741(2)Å].…”

Copper(II) complexes of hydroxyflavone derivatives as potential bioactive molecule to combat antioxidants: synthesis, characterization and pharmacological activities

“…The extent of red shift and hypochromism is commonly found to correlate with the binding strength, but metal complexes that bind nonintercalatively or electrostatically with DNA may result in hyperchromism or hypochromism. [49] Hyperchromic effect and hypochromic effect are the spectral features of DNA concerning its double-helix structure. [50] This spectral change process reflects the corresponding changes of DNA in its conformation and structures after the drug has bound to DNA.…”

Cu(II) Complexes of Isoniazid Schiff Bases: DNA/BSA Binding and Cytotoxicity Studies on A549 Cell Line

“…Cu(II) complexes containing heterocyclic bases have been extensively explored in virtue of their strong interactions with DNA and cytotoxic activity [7][8][9]. They can act as chemical nucleases [10,11] and their cytotoxicity has been proposed to be caused by their ability to bind and cleave DNA that leads to cell cycle arrest and apoptosis or generation of reactive oxygen species (ROS) that in turn leads to cell death [12].…”