Studies on some metal complexes of quinoxaline based unsymmetric ligand: Synthesis, spectral characterization, in vitro biological and molecular modeling studies

Organometallic Platinum(II) Photosensitisers that Demonstrate Ligand-Modulated Triplet-Triplet Annihilation Energy Upconversion Efficiencies

A series of 2-phenylquinoxaline ligands have been synthesised that introduce either CF₃ or OCF₃ electron-withdrawing groups at different positions of the phenyl ring. These ligands were investigated as cyclometalating reagents for platinum(II) to give neutral complexes of the form [Pt(C^N)(acac)] (in which C^N=cyclometalating ligand; acac=acetyl acetonate). X-ray crystallographic studies on three examples showed that the complexes adopt an approximate square planar geometry. All examples revealed strong Pt-Pt linear contacts of 3.2041(6), 3.2199(3) and 3.2586(2) Å. The highly coloured complexes display efficient visible absorption at 400-500 nm (ϵ ≈5000 M^-1  cm^-1 ) and orange red photoluminescent characteristics (λ_em =603-620 nm; Φ_em ≤37 %), which were subtly tuned by the ligand. Triplet emitting character was confirmed by microsecond luminescence lifetimes and the photogeneration of singlet oxygen with quantum efficiencies up to 57 %. Each complex was investigated as a photosensitiser for triplet-triplet annihilation energy upconversion using 9,10-diphenylanthracene as the annihilator species: a range of good upconversion efficiencies (Φ_UC 5.9-14.1 %) were observed and shown to be strongly influenced by the ligand structure in each case.

Polysubstituted Ligand Framework for Color Tuning Phosphorescent Iridium(III) Complexes

A series of ligands have been synthesized based upon a polysubstituted 2-phenylquinoxaline core structure. These ligands introduce different combinations of fluorine and methyl substituents on both the phenyl and quinoxaline constituent rings. The resultant investigation of these species as cyclometalating agents for Ir(III) gave cationic complexes of the form [Ir(C^N)₂(bipy)]PF₆ (where C^N = cyclometalating ligand; bipy = 2,2'-bipyridine). X-ray crystallographic studies were conducted on four complexes and each revealed the expected distorted octahedral geometry based upon a cis-C,C and trans-N,N ligand arrangement at Ir(III). Supporting computational studies predict that each of the complexes share the same general descriptions for the frontier orbitals. TD-DFT calculations suggest MLCT contributions to the lowest energy absorption and a likely MLCT/ILCT/LLCT nature to the emitting state. Experimentally, the complexes display tunable luminescence across the yellow-orange-red part of the visible spectrum (λ_em = 579-655 nm).

Synthesis, characterization, in silico, and in vitro biological screening of coordination compounds with 1,2,4-triazine based biocompatible ligands and selected 3d-metal ions

A bidentate Schiff base ligand, MHMMT, obtained from 1,2,4-triazine derivative and 4-hydroxy-3-methoxy benzaldehyde and its Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) complexes were synthesised in ethanolic media and characterized by various analytical techniques like elemental analyses, magnetic susceptibility measurements, FTIR, UV-VIS, proton NMR, ESR, spectroscopic and thermogravimetric studies. Various geometries like a tetrahedral for Co(II) and Zn(II) complexes, an octahedral for Fe(III) and Ni(II) complexes, and square planar for Cu(II) complex has been assigned. For all metals complexes except Co(II), a 2:1 ligand to metal ratio is observed, while Co(II) complex has a 1:1 ratio. In accordance with the probable activity spectra of substances as obtained from PASS analysis, in vitro α-amylase inhibition studies by starch-iodine method for ligand and complexes except that of Fe(III) and anticancer screening against human breast cancer cell lines MCF-7 using MTT assay for Fe(III) complex were conducted. The tested compounds were found to be good α-amylase inhibitors, characteristically similar to most of the antidiabetic drugs. Among the compounds, Cu(II) complex exhibited the highest α-amylase inhibitory activity. Furthermore, ligand and complexes were also exposed to in vitro antimicrobial activities, drug-likeness, bioactivity score prediction by Molinspiration software. Molecular docking analysis of selected compounds on α-amylase and VEGFR-2 kinase were carried out for confirming the experimental observations.

Heterocyclic Schiff base transition metal complexes in antimicrobial and anticancer chemotherapy

In recent years, the number of people suffering from cancer and multidrug-resistant infections has sharply increased, leaving humanity without any choice but to search for new treatment options and strategies. Although cancer is considered the leading cause of death worldwide, it also paves the way many microbial infections and thus increases this burden manifold. Development of small molecules as anticancer and anti-microbial agents has great potential and a plethora of drugs are already available to combat these diseases. However, the wide occurrence of multidrug resistance in both cancer and microbial infections necessitates the development of new and potential molecules with desired properties that could circumvent the multidrug resistance problem. A successful strategy in anticancer chemotherapy has been the use of metallo-drugs and this strategy has the potential to be used for treating multidrug-resistant infections more efficiently. As a class of molecules, Schiff bases have been the topic of considerable interest, owing to their versatile metal chelating properties, inherent biological activities and flexibility to modify the structure to fine-tune it for a particular biological application. Schiff base-based metallo-drugs are being researched to develop new anticancer and anti-microbial chemotherapies and because both anticancer and anti-microbial targets are different, heterocyclic Schiff bases can be structurally modified to achieve the desired molecule, targeting a particular disease. In this review, we collect the most recent and relevant literature concerning the synthesis of heterocyclic Schiff base metal complexes as anticancer and anti-microbial agents and discuss the potential and future of this class of metallo-drugs as either anticancer or anti-microbial agents.

Synthesis, structural elucidation, antioxidant, CT-DNA binding and molecular docking studies of novel chloroquinoline derivatives: Promising antioxidant and anti-diabetic agents

The synthesized novel chloroquinoline derivatives 1-(2-chloro-4-phenylquinolin-3-yl)ethanone (CPQE), 1-(2,6-dichloro-4-phenylquinolin-3-yl)ethanone (DCPQE), methyl 2,6-dichloro-4-phenylquinoline-3-carboxylate (MDCPQC),methyl 2-chloro-4-methylquinoline-3-carboxylate (MCMQC) were subjected to the elementary analysis like FT-IR, NMR and Mass spectra using GCMS. Also, single crystal X-ray diffraction study was executed for the compound MDCPQC. The crystal packing is stabilized by C-H…π and π-π interactions and also Chlorine-Chlorine short intermolecular contacts generating a three-dimensional supramolecular network. The antioxidant activity reduces high glucose level in the human body and hence the synthesized compounds were subjected for the estimation of antioxidant activity using DPPH method which exhibited good percentage of inhibition in comparison with ascorbic acid, a well-known anti-oxidant. The binding interaction of the chloroquinoline derivatives with calf thymus DNA (CT-DNA) has been explored by fluorescence quenching studies and molecular docking analysis has been employed to confirm the nature of binding. The prediction of pharmacological properties such as drug-likeness, molecular properties like absorption, distribution, metabolism, excretion and toxicity (ADMET) was carried out by computational studies to compare chloroquinoline derivatives with standard drug. Owing to the various potential biological activities of the quinoline compounds, molecular docking studies were also further carried out for the chloroquinoline derivatives, showing that they may act as effective anti-diabetic agents by inhibiting Glycogen Phosphorylase a protein.

Copper complexes bearing 2-aminobenzothiazole derivatives as potential antioxidant: Synthesis, characterization

Novel copper complexes of Schiff base ligands of 2-aminobenzothiazole derivatives were synthesized by the condensation of Knoevenagel condensate of acetoacetanilide (obtained from substituted benzaldehydes and acetoacetanilide) and 2-aminobenzothiazole. They were characterized by elemental analysis, IR, (1)H NMR, UV-Vis., molar conductance, magnetic susceptibility measurements and electrochemical studies. Based on the magnetic moment and electronic spectral data, square planar geometry has been suggested for all the complexes. Antibacterial and antifungal screening of the ligands and their complexes reveal that all the complexes show higher activities than the ligands. The binding behaviour of the complexes with calf thymus DNA has been investigated by electronic absorption spectra, viscosity measurements and cyclic voltammetry. The DNA binding constants reveal that all these complexes interact with DNA through intercalation binding mode. Superoxide dismutase and antioxidant activities of the copper complexes have also been studied. The antioxidant activities of the complexes showed higher activities. Thermal denaturation studies suggested the nature binding affinity of copper complexes with CT-DNA. All complexes exhibit suitable Cu(II)/Cu(I) redox potential to act as antioxidant enzymes mimic. Further, the copper complexes also showed catalase activity. It is hope that copper complexes were capable of decrease ROS levels or reduce oxidative stress in Alzheimer's patients.