Metal complexes of pyrimidine derived ligands – Syntheses, characterization and X-ray crystal structures of Ni(II), Co(III) and Fe(III) complexes of Schiff base ligands derived from S-methyl/S-benzyl dithiocarbazate and 2-S-methylmercapto-6-methylpyrimidine-4-carbaldehyde

Molecular modeling of [VO(L1-4)(R)] complexes (R = bipyridine, phenanthroline): DFT study of antioxidant activity, DNA binding and evaluation of electron-donating and -withdrawing substituent groups

A DFT (density functional theory) study was conducted with eight oxovanadium complexes (C1 - C8) of general formula [VO(L1-4)(R)] (R = bipyridine, phenanthroline; L1-4 = group of ligands derived from dithiocarbamate). The obtained geometries showed a good correlation with the experimental structures. Molecular orbital analysis revealed that the contribution of the L-ligand in the SOMO (single-occupied molecular orbital) of the complexes correlated with the experimental antioxidant activity (IC50), while the contribution of the R-ligand to the LUMO (lowest unoccupied molecular orbital) of the complexes correlated with the experimental complex-DNA interaction (Kb). It has been identified that the presence of an electron-donating substituent group (such as -NH2) in the C5 - C6 structures should enhance these complexes' antioxidant and DNA interaction activities.

In vitro and In silico anticancer activities of Mn(ii), Co(ii), and Ni(ii) complexes: synthesis, characterization, crystal structures, and DFT studies

Complexes 1, 2 and 3 showed significant activity against K562, MCF-7, and DL cancer cell lines. Complexes 1–3 showed higher growth inhibition than metal salts or ligands in tumour cell growth and colony formation. Complex 1 exhibited higher anticancer activity than cisplatin.

Antiproliferative activity and electrochemical oxygen evolution by Ni(II) complexes of N'-(aroyl)-hydrazine carbodithioates

The electrochemical water splitting by transition metal complexes is emerging very rapidly. The nickel complexes also play a very vital role in various biological activities. Here, three new ligands {H₂mbhce = N'-(4-methyl-benzoyl), H₂pchce = N'-(pyridine-carbonyl) and H₂hbhce = N'-(2-hydroxy-benzoyl) hydrazine carbodithioic acid ethyl ester} and their corresponding Ni(II) complexes [Ni(Hmbhce)₂(py)₂] (1), [Ni(pchce)(o-phen)₂]·CH₃OH·H₂O (2) and [Ni(hbhce)(o-phen)₂]·1.75CHCl₃·H₂O (3) have been synthesized and fully characterized by various physicochemical and X-ray crystallography techniques. The photoluminescence study and thermal degradations were also examined. The treatment of K562 cells with the increasing concentrations of the nickel salts, ligands, and complexes 1, 2, and 3 showed dose-dependent cytotoxicity. The cytotoxic activity of ligands reveals that ligand H₂mbhce is more potent in inhibiting the growth of tumor cells in comparison to other ligands H₂pbhce and H₂hbhce. Cytotoxicity assay results indicate that all complexes have remarkable cytotoxic potential in comparison to either nickel salts or the free ligands. Among these complexes, complex 1 has significantly better anti-tumor activity as compared to complexes 2 and 3. The electrochemical study of complexes 1, 2, and 3 for water oxidation reveals that all the complexes possess admirable electrocatalytic activity towards oxygen evolution reaction (OER) and have lower overpotential (328, 338, and 370 mV, respectively) than many previously reported complexes and RuO₂ (390 mV). Among complexes 1, 2, and 3, complex-2 shows a better water oxidation response. Consequently, these complexes have great potential to be utilized in fuel cells. The more reliable electrochemical parameter TOF is also calculated for all three complexes.

Antimicrobial and antitumor activity of S-methyl dithiocarbazate Schiff base zinc(II) complexes

Schiff bases (SB) obtained from S-methyl dithiocarbazate and aromatic aldehydes: salicylaldehyde (H₂L¹), o-vanillin (H₂L²), pyridoxal (H₂L³) and 2,6-diformyl-4-methylphenol (H₃L⁴), and their corresponding Zn(II)-complexes (1-4), are synthesized. All compounds are characterized by elemental analyses, infrared, UV-Vis, nuclear magnetic resonance spectroscopy and mass spectrometry. The structures of H₂L² and [Zn₂(L¹)₂(H₂O)(DMF)] (1a) (DMF = dimethylformamide) are solved by single crystal X-ray diffraction. The SB coordinates the metal center through the O_phenolate, N_imine and S_thiolate atoms. The radical scavenging activity is tested using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, with all ligand precursors showing IC₅₀ values ~40 μM. Cytotoxicity studies with several tumor cell lines (PC-3, MCF-7 and Caco-2) as well as a non-tumoral cell line (NHDF) are reported. Interestingly, 1 has relevant and selective antiproliferative effect against Caco-2 cells (IC₅₀ = 9.1 μM). Their antimicrobial activity is evaluated in five bacterial strains (Klebsiella pneumoniae, Acinetobacter baumannii, Listeria monocytogenes, Pseudomonas aeruginosa and Staphylococcus aureus) and two yeast strains (Candida albicans and Candida tropicalis) with some compounds showing bacteriostatic and fungicidal activity. The minimal inhibitory concentration (MIC₉₀) of H_nL against Mycobacterium tuberculosis is also reported, with H₂L² and H₃L⁴ showing very high activity (MIC₉₀ < 0.6 μg/mL). The ability of the compounds to bind bovine serum albumin (BSA) and DNA is evaluated for H₃L⁴ and [Zn₂(L⁴)(CH₃COO)] (4), both showing high binding constants to BSA (ca. 10⁶ M^-1) and ability to bind DNA. Overall, the reported compounds show relevant antitumor and antimicrobial properties, our data indicating they may be promising compounds in several fields of medicinal chemistry.

Crystal structure of benzyl N'-[(1E,4E)-1,5-bis-(4-meth-oxy-phen-yl)penta-1,4-dien-3-yl-idene]hydrazine-1-carbodi-thio-ate

In the title hydrazinecarbodi-thio-ate derivative, C27H26N2O2S2, the asymmetric unit is comprised of four mol-ecules (Z = 8 and Z' = 4). The 4-meth-oxy-phenyl rings are slightly twisted away from their attached olefinic double bonds [torsion angles = 5.9 (4)-19.6 (4)°]. The azomethine double bond has an s-trans configuration relative to one of the C=C bonds and an s-cis configuration relative to the other [C=C-C= N = 147.4 (6)-175.7 (2) and 15.3 (3)-37.4 (7)°, respectively]. The torsion angles between the azomethine C=N double bond and hydrazine-1-carbodi-thio-ate moiety indicate only small deviations from planarity, with torsion angles ranging from 0.9 (3) to 6.9 (3)° and from 174.9 (3) to 179.7 (2)°, respectively. The benzyl ring and the methyl-enesulfanyl moiety are almost perpendicular to each other, as indicated by their torsion angles [range 93.7 (3)-114.6 (2)°]. In the crystal, mol-ecules are linked by C-H⋯O, N-H⋯S and C-H⋯π(ring) hydrogen-bonding inter-actions into a three-dimensional network. Structural details of related benzyl hydrazine-1-carbodi-thio-ate are surveyed and compared with those of the title compound.

Steering the azido-tetrazole equilibrium of 4-azidopyrimidines via substituent variation - implications for drug design and azide-alkyne cycloadditions

This paper focuses on an interesting constitutional isomerism called azido-tetrazole equilibrium which is observed in azido-substituted N-heterocycles. We present a systematic investigation of substituent effects on the isomer ratio within a 2-substituted 4-azidopyrimidine model scaffold. NMR- and IR-spectroscopy as well as X-ray crystallography were employed for thorough analysis and characterization of synthesized derivatives. On the basis of this data, we demonstrate the possibility to steer this valence tautomerism towards the isomer of choice by means of substituent variation. We show that the tetrazole form can act as an efficient disguise for the corresponding azido group masking its well known reactivity in azide-alkyne cycloadditions (ACCs). In copper(I)-catalyzed AAC reactions, substituent-stabilized tetrazoles displayed a highly decreased or even abolished reactivity whereas azides and compounds in the equilibrium were directly converted. By use of an acid sensitive derivative, we provide, to our knowledge, the first experimental basis for a possible exploitation of this dynamic isomerism as a pH-dependent azide-protecting motif for selective SPAAC conjugations in aqueous media. Finally, we demonstrate the applicability and efficiency of stabilized tetrazolo[1,5-c]pyrimidines for Fragment-Based Drug Design (FBDD) in the field of quorum sensing inhibitors.

Spectral characterization, molecular modeling and antimicrobial studies on hydrazone metal complexes of 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)dione and S-methyl dithiocarbazate

Metal complexes of copper(II), nickel(II), cobalt(II), oxovanadium(IV), chromium(III) and cadmium(II) with a new bridged ONS dibasic tridentate hydrazone (H2L) derived from 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione with S-methyl dithiocarbazate have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibility measurements, spectral (infrared, electronic, mass, 1H NMR and ESR) studies as well as thermal gravimetric analysis (TGA). The synthesized complexes have dimeric structures with the general formula [ML(NO3)m(H2O)x]2·nH2O·zMeOH, L=dianion of the hydrazone, m=0-1, x=0-2, n=0-4 and z=0-1. The metal complexes exhibited square planar, tetrahedral and octahedral geometrical arrangements, the molar conductivity data indicates that all complexes are neutral. The Coats-Redfern equation was used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition stages of some complexes. Structural parameters of the ligand and its metal complexes have been theoretically computed on the basis of semiempirical PM3 level and the results were correlated with their experimental data. Antibacterial activities of the free ligand and its metal complexes were screened against various organisms.

Synthesis, spectral, electrochemical and X-ray single crystal studies on Ni(II) and Co(II) complexes derived from 1-benzoyl-3-(4-methylpyridin-2-yl) thiourea

1-Benzoyl-3-(4-methylpyridin-2-yl) thiourea ligand was coordinated with Ni(II) and Co(II) perchlorate salts to isolate complexes. All the prepared compounds are deliberately investigated by all possible spectral tools. A comparative study for IR spectra reveals the neutral bidentate coordinating nature of the ligand towards the two metal ions. The UV/Vis spectra of the complexes display d-d transition bands proposed an octahedral geometry for the complexes. MS analysis data are concerned especially with the base peak which is corresponding to C28H25N6O2S2 M ion. The fragmentation patterns are relatively matched with each others. Electrochemical studies were carried out using platinum wire and Ag/AgNO3 as counter and reference electrodes, respectively. The data reflect the irreversible nature of the electrode couple and showed two successive one electron transfer process. X-ray single crystal studies are used to verifying the octahedral geometry proposed as well as calculating crystal parameters beside the structural refinements.

Fluorescence Properties and Electrochemical Behavior of Some Schiff Bases Derived from N-Aminopyrimidine

A series of Schiff bases (L 1 , L 2 and L 3) were prepared by refluxing aromatic aldehydes with N-Aminopyrimidine derivatives in methanol and ethanol. The structures of synthesized compounds were characterized by FTIR, (1)H NMR, (13)C NMR and microanalysis. The electrochemical behaviors of the Schiff base ligands were also discussed. Moreover, the evaluation of absorption and emission properties of the structures were carried out in five different solvents. The products show visible absorption maxima in the range of 304-576 nm, and emission maxima from 636 to 736 nm in all solvents tested.

Shuttling of nickel oxidation states in N4S2 coordination geometry versus donor strength of tridentate N2S donor ligands

Seven bis-Ni(II) complexes of a N(2)S donor set ligand have been synthesized and examined for their ability to stabilize Ni(0), Ni(I), Ni(II) and Ni(III) oxidation states. Compounds 1-5 consist of modifications of the pyridine ring of the tridentate Schiff base ligand, 2-pyridyl-N-(2'-methylthiophenyl)methyleneimine ((X)L1), where X = 6-H, 6-Me, 6-p-ClPh, 6-Br, 5-Br; compound 6 is the reduced amine form (L2); compound 7 is the amide analog (L3). The compounds are perchlorate salts except for 7, which is neutral. Complexes 1 and 3-7 have been structurally characterized. Their coordination geometry is distorted octahedral. In the case of 6, the tridentate ligand coordinates in a facial manner, whereas the remaining complexes display meridional coordination. Due to substitution of the pyridine ring of (X)L1, the Ni-N(py) distances for 1~5 < 3 < 4 increase and UV-vis λ(max) values corresponding to the (3)A(2g)(F)→(3)T(2g)(F) transition show an increasing trend 1~5 < 2 < 3 < 4. Cyclic voltammetry of 1-5 reveals two quasi-reversible reduction waves that correspond to Ni(II)→Ni(I) and Ni(I)→Ni(0) reduction. The E(1/2) for the Ni(II)/Ni(I) couple decreases as 1 > 2 > 3 > 4. Replacement of the central imine N donor in 1 by amine 6 or amide 7 N donors reveals that complex 6 in CH(3)CN exhibits an irreversible reductive response at E(pc) = -1.28 V, E(pa) = +0.25 V vs saturated calomel electrode (SCE). In contrast, complex 7 shows a reversible oxidation wave at E(1/2) = +0.84 V (ΔE(p) = 60 mV) that corresponds to Ni(II)→Ni(III). The electrochemically generated Ni(III) species, [(L3)(2)Ni(III)](+) is stable, showing a new UV-vis band at 470 nm. EPR measurements have also been carried out.

Pyridazine-based Schiff base ligands with N4OxS2 (x=2, 4) donor set atoms: synthesis, characterization, spectral studies and 13C chemical shifts computed by the GIAO-DFT and CSGT-DFT methodologies

Six pyridazine-based Schiff base ligands, H(2)L(n) (n=1-5) and H(4)L, with N(4)O(2)S(2) and N(4)O(4)S(2) donor set atoms, respectively, were prepared by condensation reaction of 3,6-bis-((2-aminoethyl)thio)pyridazine with various salicyladehyde derivatives in ethanol and under solvent-free polyphosphate ester catalyzed conditions. The acid-base properties of H(2)L(2) and H(2)L(3) in DMSO/water (1:1) solution have been studied by spectrophotometric method at 25 degrees C. Optimized geometries of all compounds were also obtained at the B3LYP level of theory. Additionally, the (13)C chemical shielding of gas phase H(2)L(1) and H(2)L(2) were studied by the gauge independent atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods at the level of density functional theory (DFT). The 6-311++G* basis set was utilized for all of the atoms.