Biological activity studies on metal complexes of novel tridentate Schiff base ligand. Spectroscopic and thermal characterization

Medicinal applications of vanadium complexes with Schiff bases

Many transition metal complexes have been explored for their therapeutic properties after the discovery of cisplatin. Schiff bases have an efficient complexation tendency with the transition metals and several medicinal properties have been reported. However, fewer studies have reported the medicinal utility of vanadium and its Schiff base complexes. This paper provides a comprehensive overview of vanadium complexes with Schiff bases along with their mechanistic insight. Vanadium complexes in + 4 and + 5 oxidation states have exhibited well-defined geometry and found to be thermodynamically stable. The studies have reported the G0/G1 phase cell cycle arrest and decreased delta psi m, inducing mitochondrial membrane depolarization in cancer cell lines along with the alterations in the metabolism of the cancer cells upon dosing with the vanadium complexes. Cancer cell invasion and growth are also found to be markedly reduced by peroxo complexes of vanadium. The studies included in the review paper have been taken from leading indexing databases and focus was laid on recent reports in literature. The biological potential of vanadium complexes of Schiff bases opens new horizons for future interdisciplinary studies and investigation focussed on understanding the biochemistry of these complexes, along with designing new complexes which have better bioavailability, solubility and low or non-toxicity.

Physico-Chemical Study of Mn(II), Co(II), Cu(II), Cr(III), and Pd(II) Complexes with Schiff-Base and Aminopyrimidyl Derivatives and Anti-Cancer, Antioxidant, Antimicrobial Applications

A new class of biologically active mineral complexes was synthesized by reacting the following metal salts: MnCl2·4H2O, CoCl2·6H2O, CuCl2·2H2O, CrCl3·6H2O, and PdCl2 respectively with 2-amino-4,6-dimethyl pyrimidine (ADMPY) and Schiff’s base resulting from the condensation reaction between benzaldehyde with p-phenylenediamine and 2-hydroxy-1-naphthaldehyde as ligands have been synthesized and characterized on the basis of their CHN, thermal analysis, XRD, SEM and magnetic measurements along with their FT-IR and UV-vis spectra. The scanning electron microscope SEM measurements and the calculations on the powder XRD data indicate the nano-sized nature of the prepared complexes (average size 32–88 nm). The spectral data confirmed the coordinated ligand (HL) via a nitrogen atom of an azomethine group (-C=N-) and phenolic -OH group and NH2-ADMPY ligand with the metal ions. An octahedral geometry for all complexes has been proposed based on magnetic and electronic spectral data except Pd(II) complex, which has a tetrahedral geometry. Molecular modeling was performed for Cu(II) complex using the density functional method DFT/B3LYP to study the structures and the frontier molecular orbitals (HOMO and LUMO). The antioxidant of the complexes was studied using the 2,2-diphenyl-1-picrylhydrazyl (DPPH)-free radical-scavenging assays. The metal complexes were tested in vitro for anticancer activities against two cancer lines A-549 and MRC-5 cells. Cu(II) and Pd(II) complexes showed the highest cytotoxicity effect, comparable to that of other cis-platinum-based drugs. The complexes showed significant activity against fungi and bacteria.

Design, Synthesis, Spectroscopic Inspection, DFT and Molecular Docking Study of Metal Chelates Incorporating Azo Dye Ligand for Biological Evaluation

A new heterocyclic azo dye ligand (L) was synthesized by the combination of 4-amino antipyrine with 4-aminophenol. The new Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) complexes were synthesized in excellent yields. The metal chelate structures were elucidated using elemental analyses, FT-IR, ¹H-NMR, mass, magnetic moment, diffused reflectance spectral and thermal analysis (TG-DTG), and molar conductivity measurement. According to the FT-IR study, the azo dye ligand exhibited neutral tri-dentate behavior, binding to the metal ions with the azo N, carbonyl O, and protonated phenolic OH. The ¹H-NMR spectral study of the Zn(II) complex supported the coordination of the zo dye ligand without proton displacement of the phenolic OH. Diffused reflectance and magnetic moment studies revealed the octahedral geometry of the complexes, as well as their good electrolytic nature, excepting the Zn(II) and Cd(II) complexes, which were nonelectrolytes, as deduced from the molar conductivity study. The theoretical calculations of optimized HOMO-LUMO energies, geometrical parameters, electronic spectra, natural atomic charges, 3D-plots of MEP, and vibrational wavenumbers were computed and elucidated using LANL2DZ and 6-311G (d, p) basis sets of density functional theory (DFT) with the approach of B3LYP DFT and TD-DFT methods. The ligand and complexes have been assayed for their antimicrobial activity and compared with the standard drugs. Most of the complexes have manifested excellent antimicrobial activity against various microbial strains. A molecular docking investigation was also performed, to acquire more information about the binding mode and energy of the ligand and its metal complexes to the Escherichia coli receptor using molecular docking. Altogether, the newly created ligand and complexes showed positive antibacterial effects and are worth future study.

Pincer Complexes Derived from Tridentate Schiff Bases for Their Use as Antimicrobial Metallopharmaceuticals

Within the current challenges in medicinal chemistry, the development of new and better therapeutic agents effective against infectious diseases produced by bacteria, fungi, viruses, and parasites stands out. With chemotherapy as one of the main strategies against these diseases focusing on the administration of organic and inorganic drugs, the latter is generally based on the synergistic effect produced by the formation of metal complexes with biologically active organic compounds. In this sense, Schiff bases (SBs) represent and ideal ligand scaffold since they have demonstrated a broad spectrum of antitumor, antiviral, antimicrobial, and anti-inflammatory activities, among others. In addition, SBs are synthesized in an easy manner from one-step condensation reactions, being thus suitable for facile structural modifications, having the imine group as a coordination point found in most of their metal complexes, and promoting chelation when other donor atoms are three, four, or five bonds apart. However, despite the wide variety of metal complexes found in the literature using this type of ligands, only a handful of them include on their structures tridentate SBs ligands and their biological evaluation has been explored. Hence, this review summarizes the most important antimicrobial activity results reported this far for pincer-type complexes (main group and d-block) derived from SBs tridentate ligands.

Antitumor Activity and Physicochemical Properties of New Thiosemicarbazide Derivative and Its Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) Complexes

A novel biologically active thiosemicarbazide derivative ligand L (N-[(phenylcarbamothioyl)amino]pyridine-3-carboxamide) and a series of its five metal(II) complexes, namely: [Co(L)Cl₂], [Ni(L)Cl₂(H₂O)], [Cu(L)Cl₂(H₂O)], [Zn(L)Cl₂] and [Cd(L)Cl₂(H₂O)] have been synthesized and thoroughly investigated. The physicochemical characterization of the newly obtained compounds has been performed using appropriate analytical techniques, such as ¹H and ^l3C nuclear magnetic resonance (NMR), inductively coupled plasma (ICP), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR) and magnetic measurements. In order to study the pharmacokinetic profile of the compounds, ADMET analysis was performed. The in vitro studies revealed that the synthesized compounds exhibit potent biological activity against A549 human cancer cell line.

A Treatise on Furan Cored Schiff Base Cu(II), Ni(II) and Co(III) Complexes Accentuating Their Biological Efficacy: Synthesis, Thermal and Spectroscopic Characterization, DNA Interactions, Antioxidant and Antibacterial Activity Studies

Three metal complexes [Cu(FMIMDIP)₂ ] (1), [Ni(FMIMDIP)₂ ] (2) and [Co(FMIMDIP)₃ ] (3) where, FMIMDIP=(((furan-2-yl)methylimino)methyl)-4,6-diiodophenol, were synthesized and characterized by various spectroscopy. The analytical data revealed a square planar geometry for 1 and 2 and an octahedral geometry for 3. The kinetic and thermodynamic parameters of the thermal decomposition steps were calculated from the thermograms. The quantum chemical parameters have been calculated using HOMO-LUMO energies and reveal the stability of the complexes. The DNA interaction of 1-3 towards calf-thymus DNA was investigated by absorption titration, fluorescence spectroscopy and gel electrophoresis. All the complexes bind to DNA via intercalation mode with binding constant (K_b ) values of 4.17×10³  M^-1 to 5.9×10⁴  M^-1 and also effectively cleave pBR322 DNA by oxidative and photolytic techniques. The synergistic action of metal chelates with ascorbic acid induced the generation of free radicals. The antibacterial activity of 1-3 was tested against B. thuringiensis, S. pneumoniae, E. coli, and P. putida. Complex 3 has the best activity among all the complexes.

Enhancement of Schiff base biological efficacy by metal coordination and introduction of metallic compounds as anticovid candidates: a simple overview

In the prevailing apocalyptic times of coronavirus disease (COVID-19), the whole scientific community is busy in designing anticovid drug or vaccine. Under such a fascination, Schiff bases or azomethine compounds are continuously interrogated for antimicrobial properties. These compounds represent interesting molecular scaffolds of huge medicinal and industrial relevance. In order to update the current literature support of such facts this article introduces the synthetic chemistry, mechanism of formation of a Schiff base, followed by biological efficacy and finally a suitable discussion on the mechanism of respective bioactivity. In most of the studies revealing the biological evaluation of azomethine functionalized frameworks, fascinated results have been recorded in case of azomethine-metal complexes as compared with the free ligands. Also, the CH=N or C=N form of organic ligands have indicated marvellous results. Therefore, in connection with the biological relevance and microbicidal implications of such metallic compounds, this works reviews the current update of microorganism fighting efficacy of azomethine metal complexes along with the introduction of some metallodrugs as excellent candidates having COVID-19 defending potentiality.

A trinuclear Zn(ii) Schiff base azido compound: synthesis, structure and exploration of antimicrobial activity

The synthesis, characterization, X-ray crystal structure and antimicrobial activity of a trinuclear zinc(ii) complex have been explored.

4-[(1E)-({[(Benzyl-sulfan-yl)methane-thio-yl]amino}-imino)-meth-yl]benzene-1,3-diol chloro-form hemisolvate: crystal structure, Hirshfeld surface analysis and computational study

The title hydrazine carbodi-thio-ate chloro-form hemisolvate, 2C15H14N2O2S2·CHCl3, comprises two independent hydrazine carbodi-thio-ate mol-ecules, A and B, and a chloro-form mol-ecule; the latter is statistically disordered about its mol-ecular threefold axis. The common features of the organic mol-ecules include an almost planar, central CN2S2 chromophore [r.m.s. deviation = 0.0203 Å (A) and 0.0080 Å (B)], an E configuration about the imine bond and an intra-molecular hydroxyl-O-H⋯N(imine) hydrogen bond. The major conformational difference between the mol-ecules is seen in the relative dispositions of the phenyl rings as indicated by the values of the dihedral angles between the central plane and phenyl ring of 71.21 (6)° (A) and 54.73 (7)° (B). Finally, a difference is seen in the disposition of the outer hydroxyl-H atoms, having opposite relative orientations. In the calculated gas-phase structure, the entire mol-ecule is planar with the exception of the perpendicular phenyl ring. In the mol-ecular packing, the A and B mol-ecules assemble into a two-mol-ecule aggregate via N-H⋯S hydrogen bonds and eight-membered {⋯HNCS}2 synthons. The dimeric assemblies are connected into supra-molecular chains via hydroxyl-O-H⋯O(hydrox-yl) hydrogen bonds and these are linked into a double-chain through hy-droxy-O-H⋯π(phen-yl) inter-actions. The double-chains are connected into a three-dimensional architecture through phenyl-C-H⋯O(hydrox-yl) and phenyl-C-H⋯π(phen-yl) inter-actions. The overall assembly defines columns along the a-axis direction in which reside the chloro-form mol-ecules, which are stabilized by chloro-form-methine-C-H⋯S(thione) and phenyl-C-H⋯Cl contacts. The analysis of the calculated Hirshfeld surfaces, non-covalent inter-action plots and inter-action energies confirm the importance of the above-mentioned inter-actions, but also of cooperative, non-standard inter-actions such as π(benzene)⋯π(hydrogen-bond-mediated-ring) contacts.

A Fluorescent Chemosensor Based on Schiff Base for the Determination of Zn2+, Cd2+and Hg2

Metal complexes were obtained by the reaction of zinc, cadmium and mercury(II) salts with Schiff base HL (N(salicylidene)benzylamine). HL was synthesized by the condensation reaction of benzylamine and 2-hydroxybenzaldehyde. The fluorescence properties of the Schiff base and its metal complexes were studied in ethanol-water solutions. HL was examined for its utility as a fuorescent chemosensor for the determination of Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous samples. The HL chemosensor was found to be sensitive to Zn²⁺, Cd²⁺ and Hg²⁺ than some metal ions and its complexes emitted strong fluorescence at 452 nm for Zn²⁺ at 474 nm for Cd²⁺ and at 491 nm for Hg²⁺, respectively. It was determined that HL forms complexes with a ratio of 2:1 for Zn²⁺ and Hg²⁺ and with a ratio of 1:1 for Cd²⁺ by Job plots. For the detection of Zn²⁺, Cd²⁺ and Hg²⁺ in aqueous samples, pH, solvent type and ligand concentration were optimized for an analytical method based on HL chemosensor. HL gave a wide range of linearity with Zn²⁺, Hg²⁺ and Cd²⁺, the limit of detection was found to be 2.7 × 10^-7 M, 7.5 × 10^-7 M and 6.0 × 10^-7 M, respectively.

Crystal structure of (E)-N-cyclo-hexyl-2-(2-hy-droxy-3-methyl-benzyl-idene)hydrazine-1-carbo-thio-amide

The asymmetric unit of the title compound, C15H21N3OS, comprises of two crystallographically independent mol-ecules (A and B). Each mol-ecule consists of a cyclo-hexane ring and a 2-hy-droxy-3-methyl-benzyl-idene ring bridged by a hydrazinecarbo-thio-amine unit. Both mol-ecules exhibit an E configuration with respect to the azomethine C=N bond. There is an intra-molecular O-H⋯N hydrogen bond in each mol-ecule forming an S(6) ring motif. The cyclo-hexane ring in each mol-ecule has a chair conformation. The benzene ring is inclined to the mean plane of the cyclo-hexane ring by 47.75 (9)° in mol-ecule A and 66.99 (9)° in mol-ecule B. The mean plane of the cyclo-hexane ring is inclined to the mean plane of the thio-urea moiety [N-C(=S)-N] by 55.69 (9) and 58.50 (8)° in mol-ecules A and B, respectively. In the crystal, the A and B mol-ecules are linked by N-H⋯S hydrogen bonds, forming 'dimers'. The A mol-ecules are further linked by a C-H⋯π inter-action, hence linking the A-B units to form ribbons propagating along the b-axis direction. The conformation of a number of related cyclo-hexa-nehydrazinecarbo-thio-amides are compared to that of the title compound.

Schiff base-nickel, palladium, and platinum complexes derived from N-cyclohexyl hydrazine carbothioamide and 3-hydroxy-4-methoxybenzaldehyde: Selective antiproliferative and proapoptotic effects against colorectal carcinoma

The bidentate N-cyclohexyl-2-(3-hydroxy-4-methoxybenzylidene)hydrazine-1-carbothioamide Schiff base ligand (HL) was coordinated to divalent nickel, palladium and platinum ions to form square planar complexes. The nickel and palladium complexes, [NiL₂ ], [PdL₂ ] form square planar complexes with 2:1 ligand to metal ratio. The platinum complex, [PtL(dmso)Cl] formed a square planar complex with 1:1 ligand to metal ratio. Platinum undergoes in situ reaction with DMSO before complexing with the ligand in solution. The cytotoxicity of HL, [NiL₂ ], [PdL₂ ], and [PtL(dmso)Cl] were evaluated against human colon cancer cell line (HCT-116), human cervical cancer (Hela) cell line, melanoma (B16F10) cells, and human normal endothelial cell lines (Eahy926) by MTT assay. The [NiL₂ ] complex displayed selective cytotoxic effect against the HCT 116 cancer cell line with IC₅₀ of 7.9 ± 0.2 μM. However, HL, [PdL₂ ], and [PtL(dmso)Cl] only exhibited moderate cytotoxic activity with IC₅₀ = 75.9 ± 2.4, 100.0 ± 1.8, and 101.0 ± 3.6 μM, respectively. The potent cytotoxicity of [NiL₂ ] was characterized using Hoechst and Rhodamine assays. The nickel complex, [NiL₂ ], caused remarkable nuclear condensation and reduction in mitochondrial membrane potential. In addition, molecular docking studies confirms that [NiL₂ ] possesses significant binding efficiency with Tyrosine kinase. Altogether, the results revealed that [NiL₂ ] exhibits cytotoxicity against the cancer cells via Tyrosine kinase-induced proapoptosis pathway. This study demonstrates that the [NiL₂ ] complex could be a promising therapeutic agent against colorectal carcinoma.

DNA binding, prominent photonuclease activity and antibacterial PDT of cobalt(II) complexes of phenanthroline based photosensitizers

The chemistry of Co(II) complexes showing efficient light induced DNA cleavage activity, binding propensity to calf thymus DNA and antibacterial PDT is summarized in this article. Complexes of formulation [Co(mqt)(B)₂]ClO₄ 1-3 where mqt is 4-methylquinoline-2-thiol and B is N,N-donor heterocyclic base, viz. 1,10-phenanthroline (phen 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq 2) and dipyrido[3,2-a:2',3'-c]phenazine (dppz 3) have been prepared and characterized. The DNA-binding behaviors of these three complexes were explored by absorption spectra, viscosity measurements and thermal denaturation studies. The DNA binding constants for complexes 1, 2 and 3 were determined to be 1.6 × 10³ M^-1, 1.1 × 10⁴ M^-1 and 6.4 × 10⁴ M^-1 respectively. The experimental results suggest that these complexes interact with DNA through groove binding mode. The complexes show significant photocleavage of supercoiled (SC) DNA proceeds via a type-II process forming singlet oxygen as the reactive species. Antimicrobial photodynamic therapy was studied using photodynamic antimicrobial chemotherapy (PACT) assay against E. coli and all complexes exhibited significant reduction in bacterial growth on photoirradiation.

Crystal structure of (E)-2-[3-(tert-but-yl)-2-hy-droxy-benzyl-idene]-N-cyclo-hexyl-hydrazine-1-carbo-thio-amide

In the title compound, C18H27N3OS, the cyclo-hexane ring has a chair conformation. The azomethine C=N double bond has an E configuration. The nearly planar hydrazinecarbo-thio-amide moiety and substituted benzene ring are twisted by 31.13 (5)° relative to each other. The amide moiety and the cyclo-hexane ring are almost perpendicular to each other; a similar conformation was previously observed in reported structures. In the crystal, mol-ecules are linked by N-H⋯S hydrogen bonds, forming inversion dimers with an R 2 2(8) ring motif.

Crystal structure of 2,2′-((((ethane-1,2-diylbis(oxy))bis(2,1-phenylene))bis(azanylylidene))bis(methanylylidene))diphenolato-κ2 N;κ4 O)nickel(II), C28H22N2O4Ni

C28H22N2NiO4, tetragonal, P41212 (no. 92), a = 10.989(4) Å, c = 18.470(2) Å, V = 2230.4(16) Å3, Z = 4, R gt(F) = 0.0571, wR ref(F 2) = 0.1382, T = 293(2) K.

Synthesis and cytotoxic activity of novel steroidal derivatives containing a [1,2,4]triazolo[1,5-a]pyrimidine ring

The synthesis of steroidal derivatives containing [1,2,4]triazolo[1,5- a]pyrimidine derived from progesterone is described. The Claisen condensations of Δ1,4-pregnadien-3,20-dione and 4-chloro-Δ1,4-pregnadien-3,20-dione with dimethyl oxalate afforded 21-methoxalylpregn-1,4-diene-3,20-dione and 4-chloro-21-methoxalylpregn-1,4-diene-3,20-dione, respectively. Furthermore, the reactions of these compounds with 3-amino-1,2,4-triazole yielded the corresponding [1,2,4]triazolo[1,5- a]pyrimidine derivatives. The newly synthesised compounds were evaluated in vitro by means of sulforhodamine B assays for antiproliferative activity against HeLa and MCF-7 cells.