New Zn(II) complexes with N2S2 Schiff base ligands. Experimental and theoretical studies of the role of Zn(II) in disulfide thiolate-exchange

Indole-based NNN donor Schiff base ligand and its complexes: Sonication-assisted synthesis, characterization, DNA binding, anti-cancer evaluation and in-vitro biological assay

A novel indole based NNN donor Schiff base ligand and its Ni(II), Zn(II) and Cd(II) complexes have been synthesized using sonication-assisted method which is a highly efficient eco-friendly mechanism. The synthesized complexes have been characterized using elemental analysis, UV-Vis spectroscopy, mass spectrometry, FT-IR, and NMR and are optimized using DFT approach, which provided their theoretical framework. The stoichiometry between the ligand and the metal ions was also determined using Job's method. The thermogravimetric (TGA/DSC) analyses confirm the stability for all complexes at room temperature followed by thermal decomposition in different steps. DNA binding activities have been assessed by employing UV-visible and fluorescence spectra using the CT-DNA. The estimated intrinsic binding constant (Kb) for NiL, ZnL, and CdL complexes was 6.00 × 105, 5.58 × 105, and 4.7 × 105, respectively. In accordance with the Kb value, the quenching constant (Ksv) values of NiL, ZnL, and CdL are 5.59 × 105 M-1, 4.3 × 105 M-1, and 4.08 × 105 M-1 respectively. The anticancer properties have been assessed using MTT Assay. It has been found that the Ni(II) complex (NiL) is the most potent among the series with IC50 of 169 µg/mL. An in-vitro antioxidant experiment using DPPH was used to evaluate the synthesizedcomplexes' ability to scavenge free radicals. The findings indicated that the complexes exhibited notable antioxidant properties. The antioxidant property ZnL has been found to be the highest with an IC50 of 2.91 µg/mL and it follows the order is ZnL > NiL > CdL > L. Using the egg albumin denaturation technique, the anti-inflammatory property have been assessed, and the amount of protein denaturation inhibition has been computed. NiL has the highest % inhibition among the series studied. Comparatively, the metal complexes have been reported to exhibit higher biological activities than the prepared Schiff base ligand. The reason for the excellent biological properties observed in the metal complexes could be attributed to the incorporation of the electron-withdrawing CH3COO- during complexation. Molecular docking studies have been performed on the 2GYT protein and it has been found that the complexes have excellent binding affinity, with NiL having the lowest binding energy of -6.93 Kcal mol-1. The values suggested that NiL is more effective against HePG2 cancer cells, which is also in accordance with the MTT Assay results.

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O'- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis, Structure and Electrochemical Properties

A number of novel heteroligand Zn(II) complexes (1-8) of the general type (Lⁿ)Zn(NN) containing O,N,O'-, O,N,S-donor redox-active Schiff bases and neutral N,N'-chelating ligands (NN) were synthesized. The target Schiff bases LⁿH₂ were obtained as a result of the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with substituted o-aminophenols or o-aminothiophenol. These ligands with combination with 2,2'-bipyridine, 1,10-phenanthroline, and neocuproine are able to form stable complexes upon coordination with zinc(II) ion. The molecular structures of complexes 4∙H₂O, 6, and 8 in crystal state were determined by means of single-crystal X-ray analysis. In the prepared complexes, the redox-active Schiff bases are in the form of doubly deprotonated dianions and act as chelating tridentate ligands. Complexes 6 and 8 possess a strongly distorted pentacoordinate geometry while 4∙H₂O is hexacoordinate and contains water molecule coordinated to the central zinc atom. The electrochemical properties of zinc(II) complexes were studied by the cyclic voltammetry. For the studied complexes, O,N,O'- or O,N,S-donor Schiff base ligands are predominantly involved in electrochemical transformations in the anodic region, while the N,N'-coordinated neutral nitrogen donor ligands demonstrate the electrochemical activity in the cathode potential range. A feature of complexes 5 and 8 with sterically hindered tert-butyl groups is the possibility of the formation of relatively stable monocation and monoanion forms under electrochemical conditions. The values of the energy gap between the boundary redox orbitals were determined by electrochemical and spectral methods. The parameters obtained in the first case vary from 1.97 to 2.42 eV, while the optical bang gap reaches 2.87 eV.

Polysulfido Chain in Binuclear Zinc(II) Complexes

The synthesis and a detailed reactivity study of a binuclear zinc(II) bis(benzenethiolate) complex, [Zn₂(BPMP)(SPh)₂]⁺ (4), and an unprecedented binuclear zinc(II) pentasulfido complex, [Zn₂(BPMP)(μ₂-S₅)]⁺ (6), are presented. While one-electron oxidation of the coordinated benzenethiolate ligands in 4 by Cp₂Fe⁺ produces diphenyl disulfide and [Zn₂(BPMP)(μ₂-OH)]²⁺ (5), a two-electron redox reaction between coordinated benzenethiolate ligands in 4 and elemental S (S₈) generated diphenyl disulfide and the binuclear zinc(II) pentasulfido complex 6. Complex 6 features a chelating, dianionic, pentasulfido (S₅^2-) chain and can consume up to a maximum of 3 equiv of PPh₃ to generate Ph₃PS and 5, while the reaction of 6 with 1 equiv of diphenylphosphinoethane allowed the isolation of [Zn₂(BPMP)(μ₂-S₄)]⁺ (7). A proteolysis reaction of the coordinated S₅^2- chain in 6 with fluoroboric acid (HBF₄), benzoic acid (PhCOOH), and thioacetic acid (MeCOSH) generates the complexes [Zn₂(BPMP)(MeCN)₂]³⁺ (1), [Zn₂(BPMP)(μ₂-PhCOO)₂]⁺ (8), and [Zn₂(BPMP)(μ₂-SCOMe)₂]⁺ (9), respectively, while the protonated S₅^2- chain liberates S₈ and hydrogen sulfide (H₂S). Finally, the transfer of the coordinated benzenethiolate ligands in 4 and the S₅^2- chain in 6 to selected organic compounds, namely, PhCH₂Br and PhC(O)Cl, for the generation of various organosulfur compounds is demonstrated.

Synthesis and redox reactions of binuclear zinc(ii)–thiolate complexes with elemental sulfur

The synthesis, characterization and reactivity of a series of binuclear zinc(ii) complexes are described featuring the redox reaction of coordinated thiolates with elemental sulfur.

2-[(1E)-[(Z)-2-({[(1Z)-[(E)-2-[(2-Hy-droxy-phen-yl)methyl-idene]hydrazin-1-yl-idene]({[(4-methyl-phen-yl)meth-yl]sulfan-yl})meth-yl]disulfan-yl}({[(4-methyl-phen-yl)meth-yl]sulfan-yl})methyl-idene)hydrazin-1-yl-idene]meth-yl]phenol: crystal structure, Hirshfeld surface analysis and computational study

The complete mol-ecule of the title hydrazine carbodi-thio-ate derivative, C32H30N4O2S4, is generated by a crystallographic twofold axis that bis-ects the di-sulfide bond. The mol-ecule is twisted about this bond with the C-S-S-C torsion angle of 90.70 (8)° indicating an orthogonal relationship between the symmetry-related halves of the mol-ecule. The conformation about the imine bond [1.282 (2) Å] is E and there is limited delocalization of π-electron density over the CN2C residue as there is a twist about the N-N bond [C-N-N-C torsion angle = -166.57 (15)°]. An intra-molecular hydroxyl-O-H⋯N(imine) hydrogen bond closes an S(6) loop. In the crystal, methyl-ene-C-H⋯π(tol-yl) contacts assemble mol-ecules into a supra-molecular layer propagating in the ab plane: the layers stack without directional inter-actions between them. The analysis of the calculated Hirshfeld surfaces confirm the importance of H⋯H contacts, which contribute 46.7% of all contacts followed by H⋯C/C⋯H contacts [25.5%] reflecting, in part, the C-H⋯π(tol-yl) contacts. The calculation of the inter-action energies confirm the importance of the dispersion term and the influence of the stabilizing H⋯H contacts in the inter-layer region.

Synthesis, characterization and bioactivity studies of new dithiocarbazate complexes

Six new dithiocarbazate compounds are synthesized and characterized. HSA interaction and MTT assay are evaluated for all compounds.

Molecular design and synthesis of new dithiocarbazate complexes; crystal structure, bioactivities and nano studies

The syntheses of a new set of metal complexes MoO2L'(CH3OH), VOL'(CH3O)(CH3OH), , , SnL'Cl2 and SnL'I2 with a new ligand (L = (2,2'(disulfanediylbis((ethylthio)methylene)bis(hydrazin-2-yl-1-ylidene)bis(methanylylidene)) diphenol; L' = S-ethyl-3-(2-hydroxyphenyl)methylenedithiocarbazate are described along with characterization by elemental analysis, mass spectrometry, spectroscopic (IR, 1H- and 13C-NMR) and TGA techniques. The crystal structures of compounds were determined by single crystal X-ray diffraction analysis and compared to powder X-ray diffraction (PXRD) patterns of the nano complexes obtained using ultrasonic methods. The PXRD results indicate that the compounds synthesized by ultrasonic methods have high crystallinity. The compounds were evaluated in an in vitro cytotoxicity study with two human cancer cell lines. The results of this study revealed that all complexes exhibit good cytotoxic activity when compared to the clinical drug, cisplatin. Interaction of the samples with human serum albumin (HSA) was investigated using fluorescence spectrophotometric methods and the Stern-Volmer quenching constant (K SV) and free energy changes (ΔG) were calculated at 298 K. The fluorescence quenching method is used to determine the number of binding sites (n) and association constants (K a) at the same temperatures.

The influence of gold(i) on the mechanism of thiolate, disulfide exchange

The mechanism of gold(i)-thiolate, disulfide exchange was investigated by using initial-rate kinetic studies, 2D ((1)H-(1)H) ROESY NMR spectroscopy, and electrochemical/chemical techniques. The rate law for exchange is overall second order, first order in gold(i)-thiolate and disulfide. 2D NMR experiments show evidence of association between gold(i)-thiolate and disulfide. Electrochemical/chemical investigations do not show evidence of free thiolate and are consistent with a mechanism involving formation of a [Au-S, S-S], four-centered metallacycle intermediate during gold(i)-thiolate, disulfide exchange.