Synthesis, Characterization and in vitro Anticancer Studies of New Co(II), Ni(II), Cu(II) and Zn(II) Complexes of (E)-4-((Quinoline-8-ylimino)methyl)benzene-1,2,3-triol Ligand

Herein, a new tridentate (NNO) Schiff base ligand, (E)-4-[(quinoline-8-ylimino)methyl]benzene-1,2,3- triol derived from the condensation of 8-aminoquinoline with 2,3,4-trihydroxy benzaldehyde is reported. The ligand was complexed with certain metal ions like Co(II) (1), Ni(II) (2), Cu(II) (3), Zn(II) (4) and were characterized by various spectroscopic and analytical techniques such as FT-IR, UV-Vis, 1H NMR, 13C NMR, ESI-Mass, ESR, elemental analysis and magnetic susceptibility. Spectral data revealed octahedral geometry for cobalt(II), nickel(II), copper(II) complexes and tetrahedral geometry for zinc(II) complex. All the metal(II) complexes along with the Schiff base ligand were screened for their anticancer activities. The CT-DNA binding studies revealed high binding propensity for metal complexes with Kb values 1.50 × 104 M-1 for 1; 3.62 × 104 M-1 for 2; 2.53 × 104 M-1 for 3 and 1.8 × 104 M-1 for 4, respectively. Anticancer studies against A549 & MCF-7 demonstrated excellent antiproliferative activity with IC50 values in the range 17.62-48.82 μM. A standard drug cisplatin was employed to compare the activity of metal complexes. The complexes exhibited remarkable antitumour activity due to their high binding ability with DNA. It is interesting to observe that the complexes did not produce any cytotoxicity towards the normal cell lines.

Synthesis, Crystal Structure and Theoretical Investigations of (3-(2-Chlorophenyl)-5-Tosyl-1,3,3a,4,5,9b-Hexahydroisoxazolo[4,3-c]Quinolin-3a-yl)Methanamine

In the title compound (3-(2-chlorophenyl)-5-tosyl-1,3,3a,4,5,9b-hexahydroisoxazolo[4,3-c]quinolin-3a-yl)methanamine (3-CPTHIQM), the Thorpe–Ingold effect causes the S atom's tetrahedral geometry to be deformed, with O-S-O and N-S-C angles diverging from ideal tetrahedral values. The crystal packing features C—H⋯O hydrogen-bond inter¬actions.The supramolecular interactions were confirmed and quantified using Hirshfeld surface analysis. Quantum chemical calculations of sulfonamide are calculated at DFT/B3LYP/6-311++G(d,p) basis set. The NLO properties were calculated at the same level of theory. Furthermore, frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP) surfaces were calculated and analyzed in detail. In a molecular docking study, the investigated sulfonamide compound is evaluated as a new potential cancer inhibitor.

Bis(4-methylpiperidine-1-carbodithioato)-lead(II) and Bis(4-benzylpiperidine-1-carbodithioato)-lead(II) as Precursors for Lead Sulphide Nano Photocatalysts for the Degradation of Rhodamine B

Bis(4-methylpiperidine-1-carbodithioato)-lead(II) and bis(4-benzylpiperidine-1-carbodithioato)-lead(II) were prepared and their molecular structures elucidated using single crystal X-ray crystallography and spectroscopic techniques. The compounds were used as precursors for the preparation of lead sulphide nano photocatalysts for the degradation of rhodamine B. The single crystal structures of the lead(II) dithiocarbamate complexes show mononuclear lead(II) compounds in which each lead(II) ion coordinates two dithiocarbamato anions in a distorted tetrahedral geometry. The compounds were thermolyzed at 180 ℃ in hexadecylamine (HDA), octadecylamine (ODA), and trioctylphosphine oxide (TOPO) to prepare HDA, ODA, and TOPO capped lead sulphide (PbS) nanoparticles. Powder X-ray diffraction (pXRD) patterns of the lead sulphide nanoparticles were indexed to the rock cubic salt crystalline phase of lead sulphide. The lead sulphide nanoparticles were used as photocatalysts for the degradation of rhodamine B with ODA-PbS1 achieving photodegradation efficiency of 45.28% after 360 min. The photostability and reusability studies of the as-prepared PbS nanoparticles were studied in four consecutive cycles, showing that the percentage degradation efficiency decreased slightly by about 0.51–1.93%. The results show that the as-prepared PbS nanoparticles are relatively photostable with a slight loss of photodegradation activities as the reusability cycles progress.

Crystal structure and Hirshfeld surface analysis of bis[(ethoxymethanethioyl)sulfanido](N,N,N′,N′-tetramethylethane-1,2-diamine)mercury(II)

The title four-coordinate mononuclear complex, [Hg(C3H5OS2)2(C6H16N2)] or [Hg(C3H5OS2)2(tmeda)] (tmeda: N,N,N′,N′-tetramethylethane-1,2-diamine), has a distorted tetrahedral geometry. The HgII ion is coordinated to two N atoms of the N,N,N′,N′-tetramethylethylenediamine ligand and two S atoms from two ethylxanthate xanthate ligands. In the crystal, molecules are linked by weak C—H...S hydrogen bonds, forming a two-dimensional supramolecular architecture in the ab plane. The most important contributions for the crystal packing are from H...H (59.3%), S...H (27.4%) and O...H (7.5%) interactions.

Synthesis, Characterization and Antibacterial Activity Study of Cobalt(II), Nickel(II), Copper(II), Palladium(II), Cadmium(II) and Platinum(IV) Complexes with 4-Amino-5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazole-3-thione

New transition metal complexes of cobalt(II), nickel(II), copper(II), palladium(II), cadmium(II), and platinum(IV) with bidentate ligand 4-amino-5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazole-3-thiol were synthesized and characterized by microelemental analyses (CHNS), Fourier-transform infrared (FT-IR), UV-Visible spectra, molar conductance, magnetic susceptibility and thermal analyses (TG-DSC). The ligand was synthesized by ring closure of potassium-2-(3,4,5-trimethoxybenzoyl) hydrazine carbodithioate with an excess amount of hydrazine, and then was acidified using hydrochloric acid. The ligand was used as Lewis bases to prepare metal complexes through the reaction of ratio (1:2) metal:ligand. The ligand was characterized by 1H-NMR and 13C-NMR and the previously described methods to identify the complexes. The results obtained from spectra and elemental analyses indicated the tetrahedral geometry around Cd(II) ion, square-planar for Cu(II) and Pd(II), and octahedral geometry around Co(II), Ni(II), and Pt(IV). All the metal complexes showed significant antibacterial activity in comparison with the free ligand. The antibacterial test of the platinum(IV) complex showed higher activity than other metal complexes against bacteria Staphylococcus aureus (G-positive) and Escherichia coli (G-negative).

Polymeric coordination complex of lithium(I) with aqua and cyanurate ligands

The polymeric title complex, poly[hexa-μ-aqua-diaquatetra-μ-cyanurato-tetralithium] [Li4(C3H2N3O3)4(H2O)7] n , synthesized at room temperature from an aqueous solution of lithium hydroxide and cyanuric chloride, crystallizes in the triclinic space group P\overline{1}. There are two distinct Li+ cations in the asymmetric unit, one of which, Li1, has distorted trigonal–bipyramidal geometry and is coordinated via oxygen to two cyanurate anions occupying equatorial positions, and three water molecules, two in the axial positions and the third in an equatorial position. One of the axial water ligands and the equatorial water ligand are involved in bridging to a crystallographically equivalent Li1 cation. A centre of inversion lies between the two Li1 cations and the Li1...Li1 distance is 3.037 (5) Å. The remaining axial water ligand bridges to the second Li cation, Li2, which is disordered over two crystallographic sites with approximately equal occupancy, and has an Li1...Li2 distance of 3.438 (7) Å. The terminal Li2 cation is coordinated to three water molecules and an oxygen atom from a cyanuric anion and has a distorted tetrahedral geometry. A three-dimensional network of intermolecular hydrogen bonds involving N—H...O, O—H...O and O—H...N interactions serves to hold the structure together, as confirmed by a Hirshfeld surface analysis. The title compound was further characterized using IR and UV–vis spectroscopy and TG–DTA analysis.

Unravelling the Structure of the Tetrahedral Metal-Binding Site in METP3 through an Experimental and Computational Approach

Understanding the structural determinants for metal ion coordination in metalloproteins is a fundamental issue for designing metal binding sites with predetermined geometry and activity. In order to achieve this, we report in this paper the design, synthesis and metal binding properties of METP3, a homodimer made up of a small peptide, which self assembles in the presence of tetrahedrally coordinating metal ions. METP3 was obtained through a redesign approach, starting from the previously developed METP molecule. The undecapeptide sequence of METP, which dimerizes to house a Cys4 tetrahedral binding site, was redesigned in order to accommodate a Cys2His2 site. The binding properties of METP3 were determined toward different metal ions. Successful assembly of METP3 with Co(II), Zn(II) and Cd(II), in the expected 2:1 stoichiometry and tetrahedral geometry was proven by UV-visible spectroscopy. CD measurements on both the free and metal-bound forms revealed that the metal coordination drives the peptide chain to fold into a turned conformation. Finally, NMR data of the Zn(II)-METP3 complex, together with a retrostructural analysis of the Cys-X-X-His motif in metalloproteins, allowed us to define the model structure. All the results establish the suitability of the short METP sequence for accommodating tetrahedral metal binding sites, regardless of the first coordination ligands.

Synthesis and characterization of Ti(IV), Zr(IV) and Al(III) salen-based complexes

New Ti(IV), Zr(IV) and Al(III) salen-based complexes of formulae [(L)TiCl2], 2, [(L)ZrCl2], 3, and [(L){Al(CH2CH(CH3)2)2}2], 4, where L = meso-(R,S)-diphenylethylene-salen, were synthesized in high yields. [(L){Al(CH2CH(CH3)2)2}2] is a bimetallic complex that results from the reaction of H2L with either 1 or 2 equivalent of Al(CH2CH(CH3)2)3. The solid-state molecular structures of compounds 2 and 4·(C7H8) were obtained by single-crystal X-ray diffraction. Crystal data for C44H54Cl2N2O2Ti, (2a): monoclinic, space group C2/c (no. 15), a = 27.384(1) Å, b = 12.1436(8) Å, c = 28.773(2) Å, β = 112.644(2)°, V = 8830.6(9) Å3, Z = 8, μ(MoKα) = 0.350 mm-1, Dcalc = 1.146 g/cm3, 26647 reflections measured (5.204° ≤ 2Θ ≤ 50.7°), 8072 unique (Rint = 0.0967, Rsigma = 0.1241) which were used in all calculations. The final R1 was 0.0640 (I > 2σ(I)) and wR2 was 0.1907 (all data). Crystal data for C62H72Cl2N2O2Ti (2b): monoclinic, space group P21/c (no. 14), a = 19.606(1) Å, b = 12.793(1) Å, c = 23.189(2) Å, β = 105.710(4)°, V = 5599.0(7) Å3, Z = 4, μ(MoKα) = 0.291 mm-1, Dcalc = 1.182 g/cm3, 37593 reflections measured (3.65° ≤ 2Θ ≤ 50.928°), 10304 unique (Rint = 0.0866, Rsigma = 0.1032) which were used in all calculations. The final R1 was 0.0593 (I > 2σ(I)) and wR2 was 0.1501 (all data). Crystal data for C67H97Al2N2O2 (4·(C7H8)): triclinic, space group P-1 (no. 2), a = 10.0619(9) Å, b = 16.612(2) Å, c = 21.308(2) Å, α = 67.193(5)°, β = 78.157(6)°, γ = 77.576(5)°, V = 3176.8(6) Å3, Z = 2, μ(MoKα) = 0.088 mm-1, Dcalc = 1.063 g/cm3, 42107 reflections measured (5.382° ≤ 2Θ ≤ 51.624°), 12111 unique (Rint = 0.0624, Rsigma = 0.0706) which were used in all calculations. The final R1 was 0.0568 (I > 2σ(I)) and wR2 was 0.1611 (all data). The solid-state molecular structure of [(L){Al(CH2CH(CH3)2)2}2] reveals that both metal centres display a slightly distorted tetrahedral geometry bridged by the salen ligand. Both [(L)TiCl2] and [(L)ZrCl2] complexes display octahedral geometry with trans-chlorido ligands.

Stabilization of an elusive tautomer by metal coordination

The solid-state isolation of the different tautomers of a chemical compound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol−1 greater than the most stable 2H form, we show that metal complexation is a successful and reliable way for stabilizing the elusive tautomer. We have prepared two complexes of the neutral ligand with CuBr2 and ZnBr2, namely, aquabromidobis[4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]copper(II) bromide trihydrate, [CuBr(C8H7N7)2(H2O)]Br·3H2O, and dibromido[4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole][4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]zinc(II) monohydrate, [ZnBr2(C8H7N7)2]·H2O. The X-ray analysis shows that, in both cases, the elusive 3H-tautomer is present. The results of the crystallographic analysis of the two complexes reflect the different coordination preferences of CuII and ZnII. The copper(II) complex is homotautomeric as it only contains the elusive 3H-tautomer of the ligand. The complex can be described as octahedral with tetragonal distortion. Two 3H-triazolotriazole ligands are bis-chelated in the equatorial plane, while a water molecule and a bromide ion in elongated axial positions complete the coordination environment. The zinc(II) complex, on the other hand, is heterotautomeric and contains two bromide ions and two monodentate ligand molecules, one in the 2H-tautomeric form and the other in the 3H-tautomeric form, both coordinated to the metal in tetrahedral geometry. The observation of mixed-tautomer complexes is unprecedented for neutral ligands. The analysis of the X-ray molecular structures of the two complexes allows the deduction of possible rules for a rational design of mixed-tautomer complexes.

Synthesis and crystal structure of poly[(3-amino-1,2,4-triazole)(μ3-1H-benzimidazole-5,6-dicarboxylato)cobalt(II)]

The asymmetric unit of the title coordination polymer, [Co(C9H4N2O4)(C2H4N4)] n or [Co(L 1)(L 2)] n , consists of one crystallographically independent Co2+ centre, one L 1 2− ligand and one L 2 ligand (L 1 = 1H-benzimidazole-5,6-dicarboxylic acid, L 2 = 3-amino-1,2,4-triazole). The Co2+ centre is coordinated by two carboxylato-O atoms from two independent L 1 2− ligands and two nitrogen atoms from L 2 and another L 1 ligand. Thus, the metal center adopts a four-coordinate mode, forming a tetrahedral geometry. Interestingly, through the combination of two L 1 2−, two L 2 ligands and two Co2+ ions, a basic repeating unit is constructed, resulting in the formation of a one-dimensional straight chain structure. These chains are further expanded to the final three-dimensional framework via N—H...O hydrogen-bonding interactions.