New dimeric Schiff base quinoline complexes: Synthesis, spectral characterization, electrochemistry and cytotoxicity

Reactions of cobalt(ii) chloride and cobalt(ii) acetate with hemisalen-type ligands: ligand transformation, oxidation of cobalt and complex formation. Preliminary study on the cytotoxicity of Co(ii) and Co(iii) hemisalen complexes

Several molecular cobalt(ii) complexes, one Co(ii) coordination polymer and one ionic cobalt(iii) complex with imine hemisalen ligands were synthesized. The hemisalen ligands were synthesized from o-vanillin (oVP) and diverse aminopyridines (compounds HL1-HL4) or aminophenol (compound HL5). It was observed that cobalt(ii) chloride in dry acetonitrile catalyzes a transformation of HL1 and HL3 instead of complex formation. The conversion of these imines proceeded via self-cyclization to N-2''-pyridyl-2,6-dioxo-9-aza-[c,g]di-2'-methoxybenzo nonan or its methyl derivative as the major product. The remaining reactions were performed using imines HL1-HL5 and cobalt(ii) acetate Co(Ac)₂ in methanol or DMSO/acetonitrile resulting in forming a series of cobalt complexes. The following series of compounds was obtained: two similar tetrahedral molecular Co(ii) complexes [Co(L1)₂] and [Co(L3)₂], one trinuclear, mixed-ligand Co₃(Ac)₂(L4)₂(oVP)₂, one coordination polymer {Co(L2)₂}_∞ and finally one octahedral anionic Co(iii) complex [HNEt₃][Co(L5)₃]. The latter complex formed in a cobalt(ii) acetate reaction with a hemisalen HL5 derived from oVP and 2-aminophenol. The molecular structures of all compounds were confirmed by X-ray diffraction, and the cytotoxicity of Co(ii) and Co(iii) complexes towards cancer cell lines HCT116, HL-60 and normal cell line MRC-5 was studied.

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.

Synthesis, comparative in vitro antibacterial, antioxidant and UV fluorescence studies of bis indole Schiff bases and molecular docking with ct-DNA and SARS-CoV-2 Mpro

In this study, synthesis of 15 novel bis indole-based Schiff bases (SBs) 4a-4o was conducted by condensation of 2-(1-aminobenzyl)benzimidazole with symmetrical bis-isatins linked via five alkyl chains (n = 2-6). These were subjected to ADME (absorption, distribution, metabolism and excretion), physiochemical properties, molecular docking, in vitro antibacterial and antioxidant studies. The in silico studies indicated lower toxicity with metabolic stability for nearly all the derivatives proving reliability as drug candidates. The comparative antibacterial study against Staphylococcus aureus and Escherichia coli, also showed a superior inhibition than reference drug and their mono counterparts. The increase in linker alkyl chain length and variation of substituents in indole, further predicted increased inhibition, with maximum value for compound 4o at 50 μg/ml. The in vitro calf thymus DNA (ct-DNA) binding ability of compounds 4c, 4f, 4i, 4l, 4 m, 4n, and 4o was evaluated via ultraviolet-visible and fluorescence spectroscopy techniques. A hyperchromic effect was observed with no apparent wavelength shift which predicted for the groove binding mode. A moderate binding constant for 4o, in fluorescence results, confirms groove binding. The molecular docking of 4o with ct-DNA (PDBID:1BNA) and SARS-CoV-2 M^pro (3CL protease, PDBID:6LU7) prove its efficacy as potential DNA binder and antiviral agent.

Cytotoxicity, anti-microbial studies of M(II)-dithiocarbamate complexes, and molecular docking study against SARS COV2 RNA-dependent RNA polymerase

Ten transition metal dithiocarbamate (DTC)complexes of the type [M(κ 2-Et2DT)2] (1-5), and [M(κ 2-PyDT)2] (6-10) (where M = Co, Ni, Cu, Pd, and Pt; Et2DT = diethyl dithiocarbamate; PyDT = pyrrolidine dithiocarbamate) were synthesized and characterized by different methods. The dithiocarbamate acted as bidentate chelating ligands to afford a tetrahedral complexes with Co(II) ion and square planner with other transition metal ions. The dithiocarbamate complexes showed good activity against the pathogen bacteria species. The results showed the Pt-dithiocarbamate complexes are more active against all the tested bacteria than the Pd-dithiocarbamate complex. The dithiocarbamate complexes displayed the maximum inhibition zone against E. coli bacteria, whereas the lowest activity of the dithiocarbamate against Salmonella typhimurium bacteria. The cytotoxicity of the Pd(II) and Pt(II) complexes was screened against the MCF-7 breast cancer cell line and the complexes showed moderate activity compared with the cis-platin. The results indicated that the MCF7 cells treated with 500 μg\ml of ligands and Pd(II) and Pt(II) complexes after 24 hr exposure showed intercellular space and dead cells. Finally, molecular docking studies were carried out to examine the binding mode of the synthesized compounds against the proposed target; SARS COV2 RNA-dependent RNA polymerase.

Quinoline Functionalized Schiff Base Silver (I) Complexes: Interactions with Biomolecules and In Vitro Cytotoxicity, Antioxidant and Antimicrobial Activities

A series of fifteen silver (I) quinoline complexes Q1-Q15 have been synthesized and studied for their biological activities. Q1-Q15 were synthesized from the reactions of quinolinyl Schiff base derivatives L1-L5 (obtained by condensing 2-quinolinecarboxaldehyde with various aniline derivatives) with AgNO₃, AgClO₄ and AgCF₃SO₃. Q1-Q15 were characterized by various spectroscopic techniques and the structures of [Ag(L1)₂]NO₃Q1, [Ag(L1)₂]ClO₄Q6, [Ag(L2)₂]ClO₄Q7, [Ag(L2)₂]CF₃SO₃Q12 and [Ag(L4)₂]CF₃SO₃Q14 were unequivocally determined by single crystal X-ray diffraction analysis. In vitro antimicrobial tests against Gram-positive and Gram-negative bacteria revealed the influence of structure and anion on the complexes' moderate to excellent antibacterial activity. In vitro antioxidant activities of the complexes showed their good radical scavenging activity in ferric reducing antioxidant power (FRAP). Complexes with the fluorine substituent or the thiophene or benzothiazole moieties are more potent with IC₅₀ between 0.95 and 2.22 mg/mL than the standard used, ascorbic acid (2.68 mg/mL). The compounds showed a strong binding affinity with calf thymus-DNA via an intercalation mode and protein through a static quenching mechanism. Cytotoxicity activity was examined against three carcinoma cell lines (HELA, MDA-MB231, and SHSY5Y). [Ag(L2)₂]ClO₄Q7 with a benzothiazole moiety and [Ag(L4)₂]ClO₄Q9 with a methyl substituent had excellent cytotoxicity against HELA cells.

DNA Binding and DNA Cleavage Activities of Newly Synthesized CoII and CuII Complexes of a β-Cyclodextrin Based Azo-Functionalized Schiff Base

Two water soluble complexes with CoII and CuII ions were synthesized using a novel β-cyclodextrin based azo-functionalized Schiff base as a ligand. The Schiff base and its metal complexes were characterized by different physico-chemical and spectroscopic methods. From the analyses of the experimental data, distorted octahedral geometry has been assigned for both the metal complexes. The binding interactions between the metal complexes and DNA were investigated by means of a thermal denaturation study and viscosity measurements as well as by electronic absorption and fluorescence spectroscopy. The DNA cleavage efficacy of the metal complexes was also studied by agarose gel electrophoresis using pBR DNA. These studies revealed that both the metal complexes followed an intercalative mode of binding to calf thymus (CT)-DNA and also effectively cleaved the supercoiled pBR DNA. The CoII complex, however, more efficiently cleaved CT-DNA than the CuII complex as much as the experimental results are concerned.