Showing papers by "Salah S. Massoud published in 2014"

Efficient hydrolytic cleavage of plasmid DNA by chloro-cobalt(II) complexes based on sterically hindered pyridyl tripod tetraamine ligands: synthesis, crystal structure and DNA cleavage.

Abstract: Four new cobalt(II) complexes [Co(6-MeTPA)Cl]ClO4/PF6 (2/2a), [Co(6-Me2TPA)Cl]ClO4/PF6 (3/3a), [Co(BPQA)Cl]ClO4/PF6 (4/4a) and [Co(BQPA)Cl]ClO4/PF6 (5/5a) as well as [Co(TPA)Cl]ClO4 (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me2TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a–5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH3CN–H2O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H2O)]2+. The pKa values of the coordinated H2O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1–5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis–Menten kinetic conditions, the catalytic rate constants, kcat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the kcat value for complex 4 (6.02 h−1), where [Co(BPQA)(H2O)]2+ is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN3) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the kcat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)]+. The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(II) center.

fac -Cobalt(III)-azido complexes derived from substituted pyridyl-based tridentate amines

Abstract: Four new mononuclear triazido-cobalt(III) complexes [Co(L 1/2/4 )(N3)3] and [Co(L 3 )(N3)3]·CH3CN where L 1 = [(2-pyridyl)-2-ethyl]-(2-pyridylmethyl)-N-methylamine, L 2 = [(2-pyridyl)-2-ethyl]-[6-methyl-(2-pyridylmethyl)]-N-methylamine, L 3 = [(2-pyridyl)-2-ethyl]-[3,5-dimethyl-4-methoxy-(2-pyridylmethyl)]-N-methylamine, and L 4 = [(2-pyridyl)-2-ethyl]-[3,4-dimethoxy-(2-pyridylmethyl)]-N-methylamine, respectively, were synthesized and structurally characterized. The four complexes were characterized by elemental microanalyses, IR and UV–VIS spectroscopy and X-ray single crystal crystallography. The complexes display two strong IR bands over the frequency region 2,020–2,050 cm−1 assigned for the asymmetric stretching frequency, νa(N3) of the coordinated azides indicating facial geometry. The molecular structure determinations of the complexes were in complete agreement with fac-[Co(L)(N3)3] conformation in distorted octahedral Co(III) environment.

Synthesis, structure, thermal, magnetic properties and quantum mechanical calculations of bridged [bis(di(2-methylpyridyl)amine)-(μ2-1,2-bis(4-pyridyl)ethane)-tetraperchlorato-dicopper(II)] dihydrate complex

Abstract: The title compound [Cu2(DPA)2(μ-bpe)(ClO4)4]·2H2O, I where DPA = di(2-methylpyridyl)amine and bpe = 1,2-bis(4-pyridyl)ethane was studied by single crystal X-ray crystallography at different temperatures, spectroscopic methods, differential scanning calorimetry (DSC) and by magnetic susceptibility methods. DSC studies were recorded between 125 K and 647 K and magnetic studies between 2 K and 300 K. The X-ray diffraction studies were carried out at 293, 200, 150 and 100 K. Cooling the crystal from 293 K to 100 K produces a significant change in cell constants but no change in space group. X-ray and DSC studies revealed that significant phase transitions occur at temperatures between 200 K and 100 K that are described herein. The X-ray studies revealed a thermally-induced case of polymorphism whereby the cell volume triples on going from 293 to 100 K. This transition was reversible even though there is a marked hysteresis in the process. The major structural change between 200 K and 100 K is due to the displacement of the central bpe pyridyl rings relative to the plane defining CuN1N2N3 and the bending angle Cu–N1–C3. This transitional phase change was indirectly supported by quantum mechanical calculations which indicated the absence of significant π–π stacking interaction between the central bpe pyridyl rings forming the two parallel dinuclear species. This was attributed to the long 8.28 A distances between the two indicated moieties. Lack of energetic and spatial constraints justified the pyridyl ring displacement along the N–C3 axis. The temperature dependence of the magnetic behavior of I was that of a simple paramagnet down to 2 K. The complex revealed a very weak to non-existent magnetic coupling between the Cu(II) centers (J = −0.34 cm−1).