Equilibrium and structural studies of copper(II) complexes with a tridentate ligand containing amide, pyrazyl and pyridyl nitrogen donors: Effect of anions coligands on crystal structures of copper(II) complexes

An investigation of the pH dependence of copper-substituted anthrax lethal factor and its mechanistic implications

Anthrax lethal factor (LF) is a zinc-dependent endopeptidase involved in the cleavage of proteins critical to the maintenance of host signaling pathways during anthrax infections. Although zinc is typically regarded as the native metal ion in vivo, LF is highly tolerant to metal substitution, with its replacement by copper yielding an enzyme (CuLF) 4.5-fold more active than the native zinc protein (at pH 7). The current study demonstrates that by careful choice of the buffer, ionic strength, pH and substrate, the activity ratio of CuLF and native LF can be increased to >40-fold. Using a fluorogenic LF substrate, such optimized assay conditions can be exploited to detect LF concentrations as low as 2 pM. In contrast to the zinc form, CuLF was found to be inhibited by bromide and iodide ions, to be resistant to metal loss under acidic conditions, and to display a sharp pH dependence with significantly shifted alkaline limb towards more acidic conditions. The alkaline limb in the enzyme's pH profile is suggested to originate from changes in the protonation state of the metal-bound water molecule which serves as the nucleophile in the catalytic mechanism. Based on these observations and studies on other zinc proteases, a minimal mechanism for LF is proposed.

Metal ion binding by pyridylethyl-containing polymers: experimental and theoretical study

Binding of Cu(2+), Ni(2+) and Ag(+) ions to polyallylamine (PAA), polyethylenimine (PEI), poly(N-2-(2-pyridyl)ethylallylamine) (PEPAA), poly(N-2-(2-pyridyl)ethylethylenimine) (PEPEI), and N-2-(2-pyridyl)ethylchitosan (PEC) has been investigated using batch sorption experiments, spectrophotometric titration, ESR, and XPS to elucidate how the structure of polymer precursors affects the ion binding efficiency of their pyridylethylated derivatives. It has been shown that pyridylethylation increases the sorption capacities of PAA and PEI cross-linked with epichlorohydrin toward Ag(+) and Ni(2+) ions, but does not improve or decrease that toward Cu(2+) ions. PEC was the most efficient material for Ag(+) ion sorption with the sorption capacity of 1.21 mmol g(-1). The highest sorption capacity for Ni(2+) (0.62 mmol g(-1)) was found for PEPEI. According to density functional theory (DFT) calculations, lower Cu(2+) binding efficiency to PEPEI results from the "looser" structure of this complex in comparison with unmodified PEI. DFT calculations have also suggested that the Cu(2+) ion is four-coordinated in the complexes with PEPAA and PAA and five-coordinated in all other complexes, which have the structures of distorted square pyramids with Cu-N bond lengths varying significantly depending on the ligand nature. The results of the theoretical investigations of the Cu(2+) complex structures were supported by the ESR data, which revealed the decrease of A‖ and the increase of g‖ values with increasing deviation from the square planar geometry of complexes in the ligands in the order PEI < PEPEI < PEPAA.

New 15-membered tetraaza (N4) macrocyclic ligand and its transition metal complexes: spectral, magnetic, thermal and anticancer activity

Novel tetraamidemacrocyclic 15-membered ligand [L] i.e. naphthyl-dibenzo[1,5,9,12]tetraazacyclopentadecine-6,10,11,15-tetraoneand its transition metal complexes with Fe(II), Co(II), Ni(II), Cu(II), Ru(III) and Pd(II) have been synthesized and characterized by elemental analysis, spectral, thermal as well as magnetic and molar conductivity measurements. On the basis of analytical, spectral (IR, MS, UV-Vis, (1)H NMR and EPR) and thermal studies distorted octahedral or square planar geometry has been proposed for the complexes. The antitumor activity of the synthesized ligand and some complexes against human breast cancer cell lines (MCF-7) and human hepatocarcinoma cell lines (HepG2) has been studied. The complexes (IC50=2.27-2.7, 8.33-31.1μg/mL, respectively) showed potent antitumor activity, towards the former cell lines comparable with their ligand (IC50=13, 26μg/mL, respectively). The results show that the activity of the ligand towards breast cancer cell line becomes more pronounced and significant when coordinated to the metal ion.

Transition metal complexes of a new 15-membered [N5] penta-azamacrocyclic ligand with their spectral and anticancer studies

Novel penta-azamacrocyclic 15-membered [N5] ligand [L] i.e. 1,5,8,12-tetetraaza-3,4: 9,10-dibenzo-6-ethyl-7-methyl-1,12-(2,6-pyrido)cyclopentadecan-5,7 diene-2,11-dione and its transition metal complexes with Co(II), Ni(II), Cu(II), Ru(III) and Pd(II) have been synthesized and structurally characterized by elemental analysis, spectral, thermal as well as magnetic and molar conductivity measurements. On basis of IR, MS, UV-Vis 1H NMR and EPR spectral studies an octahedral geometry has been proposed for all complexes except Co(II), Cu(II) nitrate complexes and Pd(II) chloride complex that adopt tetrahedral, square pyramidal and square planar geometries, respectively. The antitumor activity of the synthesized ligand and some complexes against human breast cancer cell lines (MCF-7) and human hepatocarcinoma cell lines (HepG2) has been studied. The complexes (IC50=2.04-9.7, 2.5-3.7 μg/mL) showed potent antitumor activity comparable with their ligand (IC50=11.7, 3.45 μg/mL) against the above mentioned cell lines, respectively. The results evidently show that the activity of the ligand becomes more pronounced and significant when coordinated to the metal ion.

Crystal structure of poly[[(acetato-κO){μ3-N-[(pyridin-4-yl)meth-yl]pyrazine-2-carboxamidato-κ(4) N:N (1),N (2):N (4)]copper(II)] dihydrate]: a metal-organic framework (MOF)

The title compound, [Cu(C11H9N4O)(CH3CO2)]·2H2O (CuL), is a hydrated copper acetate complex of the ligand N-[(pyridin-4-yl)meth-yl]pyrazine-2-carboxamide (HL). Complex CuL has a metal-organic framework (MOF) structure with a 10 (3) network topology. The ligand coordinates in a bidentate and a bis-monodentate manner, bridging three equivalent Cu(II) atoms via the pyridine N atom and the second pyrazine N atom. The Cu(II) atom has a fivefold coordination sphere, CuN4O, being coordinated to three N atoms of the ligand and the acetate O atom in the equatorial plane and to the second pyrazine atom in the apical position. This gives rise to a fairly regular square-pyramidal geometry. In the crystal, the water mol-ecules are linked to each other and to the three-dimensional framework via O-H⋯O hydrogen bonds. There are also a number of C-H⋯O hydrogen bonds present within the framework.

Crystal structures of N-(pyridin-2-ylmeth-yl)pyrazine-2-carboxamide (monoclinic polymorph) and N-(pyridin-4-ylmeth-yl)pyrazine-2-carboxamide

The title compounds, C11H10N4O (HL1) and C11H10N4O (HL2), are pyridine 2-ylmethyl and 4-ylmethyl derivatives, respectively, of pyrazine-2-carboxamide. HL1 was measured at 153 K and crystallized in the monoclinic space group P21/c with Z = 4. There has been a report of the same structure measured at room temperature but assumed to crystallize in the triclinic space group P-1 with Z = 4 [Sasan et al. (2008 ▶). Monatsh. Chem. 139, 773-780]. In HL1, the pyridine ring is inclined to the pyrazine ring by 61.34 (6)°, while in HL2 this dihedral angle is 84.33 (12)°. In both mol-ecules, there is a short N-H⋯N inter-action involving the pyrazine carboxamide unit. In the crystal of HL1, mol-ecules are linked by N-H⋯N hydrogen bonds, forming inversion dimers with an R 2 (2)(10) ring motif. The dimers are linked via bifurcated-acceptor C-H⋯O hydrogen bonds, forming sheets lying parallel to (102). The sheets are linked via C-H⋯N hydrogen bonds, forming a three-dimensional structure. In the crystal of HL2, mol-ecules are linked by N-H⋯N and C-H⋯N hydrogen bonds to form chains propagating along [010]. The chains are linked via C-H⋯O hydrogen bonds, forming sheets lying parallel to (100). Within the sheets there are π-π inter-actions involving neighbouring pyrazine rings [inter-centroid distance = 3.711 (15) Å]. Adjacent sheets are linked via parallel slipped π-π inter-actions involving inversion-related pyridine rings [inter-centroid distance = 3.6395 (17) Å], forming a three-dimensional structure.