Synthesis of New VO(II), Co(II), Ni(II) and Cu(II) Complexes with Isatin-3-Chloro-4-Floroaniline and 2-Pyridinecarboxylidene-4-Aminoantipyrine and their Antimicrobial Studies

Synthesis, crystal structure, thermal stability and biological study of bis{(2-methoxy-6-[(E)-(propylimino)methyl]phenolato}nickel(II) complex

A Schiff base complex of nickel, bis{(2-methoxy-6-[(E)-(propylimino)methyl]phenolato}nickel(II) was synthesised by condensing bis(2-hydroxy-3-methoxybenzaldehyde) nickel (II) and n-propylamine in methanolic medium. Single crystal X-ray diffraction analysis of the complex revealed it to possess planar geometry with a monoclinic crystal system. The non-isothermal TG/DTA runs on this complex in a high purity (99.99 %) nitrogen environment at atmospheric pressure confirmed the absence of any coordinated water. A sharp endotherm in its DTA shows a melting temperature range of 168-171 °C. It is thermally stable up to 243 °C and decomposes in two steps, yielding NiO and carbon as residue. In addition to the methoxy group (-OCH3), infrared analysis (IR) confirmed the presence of the characteristic azomethine group (-C[bond, double bond]N-) which is also responsible for the biological action. It was further analysed by elemental analyser (C, H, N), 1H and 13C NMR as well as mass spectrometry. It showed considerable antibacterial activity towards Escherichia coli and Staphylococcus aureus when the concentration exceeds 200 μg/ml. The antifungal study shows significant inhibition with the antifungal drug imidazole as a positive control (PC). Small values of MIC, MBC/MIC indicate a lesser quantity of complex is required to inhibit the growth of micro-organisms.

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.

Transition Metal Complexes of 4-Aminoantipyrine Derivatives and Their Antimicrobial Applications

Transition metal complexes of 4-aminoantipyrine derivatives have been gaining great interest due to their rich coordination chemistry and potential applications in the field of pharmaceutical science. The presence of a free amine and a cyclic ketone functionality makes 4-aminoantipyrine an attractive amphoteric substrate for Schiff base formation. Varieties of aldehydes/ketones or amines of versatile steric, electronic and functional nature could be condensed with the 4-aminoantipyrine motif to obtain the ligand systems of multi-denticity and diverse coordination behaviour. The transition metal complexes obtained from these ligand systems exhibit unique structural and functional properties. This review compiles the important transition metal complexes developed from the Schiff base derivatives of 4-aminoantipyrine, and their utility as antibacterial and antifungal agents. Rationale of the strategies involved in the development of highly potential antimicrobial agents is discussed.

Schiff bases and their metal complexes with biologically compatible metal ions; biological importance, recent trends and future hopes

Schiff bases are in the field of medicinal and material chemistry for a long time. There are several advancements from time to time towards facile synthesis and potential applications. As medicines they have been applied as organic molecules as well as their metal complexes. The activities of metal complexes have been found to increase due to increase lipophilicity in comparison to the corresponding free ligand. Besides simple coordination compounds they have been applied as ionic liquid (IL)- supported and IL-tagged species with far enhanced efficiency. Among metal complexes recent advancement deals with photodynamic therapy to treat a number of tumors with fewer side effects. Schiff bases are efficient ligands and their complexes with almost all metal ions are reported. This mini-review article deals with complexes of Schiff bases with biologically compatible metal ions, Co(II), Cu(II), Zn(II), Pd(II), Ag(I), Pt(II) and their potential uses to combat cancerous cells. Strong hopes are associated with photodynamic therapy and IL-tagged and IL-supported Schiff bases and their complexes.

Modification with N-benzylisatin restricts stress-induced aggregation of hen egg white lysozyme: Anti-amyloidogenic property of isatin derivative with possible clinical implications

Hen egg white lysozyme (HEWL) is a structural homolog of human lysozyme and is widely used as a model protein to investigate protein aggregation. The effect of N-benzylisatin on stress-induced aggregation of HEWL has been investigated in the present study. Interaction of the isatin derivative with HEWL induced changes in protein secondary and tertiary structural conformation as evident from different biophysical and spectroscopic studies. In addition, modification with N-benzylisatin was found to increase the conformational stability of HEWL and afford considerable resistance to the protein to stress-induced aggregation as indicated from subsequent experimental studies, including thioflavin T fluorescence, microscopic imaging and dynamic light scattering analysis. Protein modification was analysed and confirmed by MALDI-TOF and ESI-MS studies. The results highlight possible clinical implications of isatin derivative in the treatment of protein misfolding and conformational disorders.

Experimental and molecular topology-based biological implications of Schiff base complexes: a concise review

This review is a gentle introduction toward Schiff bases with special attention to bioinorganic aspects. Depending on the nature of condensation moieties (ketonic or aldehydic) with primary amine, a large number of novel compounds are reported every year with applicability in various material science aspects. Herein, a burgeoning literature overview is presented to provide a salient discussion of the current status of these molecular systems. Schiff bases are designed depending on the particular desirable properties. For instance, to enlighten a biologically relevant molecule, it is always appreciated when a prepared compound shows biological membrane crossing and nucleic acid linking potential. Under such purview, the Schiff base functional group can serve as an enhancer of biomembrane traversing capability. In addition to various other catalytic aspects, the type of disease to be encountered also matters. Nowadays, theoretical chemistry is applied before synthesizing a compound of this sort and fruitful results are first depicted and, if found feasible, a suitable synthetic route is followed to synthesize Schiff base compounds. Molecular charge topology analysis under theoretical expression is analyzed generally to predict the biological relevance of a molecule.

Analysis of DNA protection, interaction and antimicrobial activity of isatin derivatives

Isatin, thiosemicarbazone and their derivatives have been widely used in biological applications such as antimicrobial, antiviral and anticancer therapies. Herein, eight isatin and thiosemicarbazone derivative compounds were re-synthesized and evaluated for DNA binding analysis including DNA protection studies using plasmid DNA (pUC19) and DNA interaction experiments using calf thymus DNA (CT-DNA). All compounds were also utilized in vitro assay to assess the antimicrobial activity of compounds against different pathogenic bacterial strains. All isatin and thiosemicarbazone derivative compounds exhibited DNA protection activity which ranged from 23.5 to 59.5%. Among them, I3-(N-2-MP)-TSC had the greatest DNA protective activity. For DNA binding analysis, all compounds had the same constant concentration (40 μM), which interacts with CT-DNA. It was also observed that DNA interactions gave a high intrinsic binding constant (Kb = 1.72 × 10⁴ M^-1-9.73 × 10⁵ M^-1). Besides, several derivatives of isatin thiosemicarbazone exhibited significant and selective antibacterial activity with low concentration. These compounds primarily affected Gram-positive bacteria, but were not effective against P. vulgaris and E. coli. The Gram-positive methicillin-resistant S. aureus ATCC 43300 (MRSA) was the most influenced strain by these compounds. It was found that methyphenyl group at isatin was essential for its antibacterial activity for MRSA.

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.

Syntheses, spectroscopic characterization, thermal study, molecular modeling, and biological evaluation of novel Schiff's base benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) with Ni(II), and Cu(II) metal complexes

Novel Schiff's base ligand, benzil bis(5-amino-1,3,4-thiadiazole-2-thiol) was synthesized by the condensation of benzil and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio. The structure of ligand was determined on the basis of elemental analyses, IR, (1)H NMR, mass, and molecular modeling studies. Synthesized ligand behaved as tetradentate and coordinated to metal ion through sulfur atoms of thiol ring and nitrogen atoms of imine group. Ni(II), and Cu(II) complexes were synthesized with this nitrogen-sulfur donor (N2S2) ligand. Metal complexes were characterized by elemental analyses, molar conductance, magnetic susceptibility measurements, IR, electronic spectra, EPR, thermal, and molecular modeling studies. All the complexes showed molar conductance corresponding to non-electrolytic nature, expect [Ni(L)](NO3)2 complex, which was 1:2 electrolyte in nature. [Cu(L)(SO4)] complex may possessed square pyramidal geometry, [Ni(L)](NO3)2 complex tetrahedral and rest of the complexes six coordinated octahedral/tetragonal geometry. Newly synthesized ligand and its metal complexes were examined against the opportunistic pathogens. Results suggested that metal complexes were more biological sensitive than free ligand.

Spectral characterization, electrochemical and anticancer studies on some metal(II) complexes containing tridentate quinoxaline Schiff base

Co(II), Ni(II), Cu(II) and Zn(II) complexes of a tridentate ONO donor Schiff base ligand derived from 3-(2-aminoethylamino)quinoxalin-2(1H)-one were synthesized. The ligand and its metal complexes were characterized using elemental analysis, molar conductance, IR, (1)H NMR, mass, magnetic susceptibility, electronic spectra and ESR spectral studies. Electrochemical behavior of the synthesized compounds was studied using cyclic voltammetry. The grain size of the synthesized compounds was determined by powder XRD. The Schiff base and its complexes have been screened for their antimicrobial activities against the bacterial species E. coli, K. pneumoniae, P. aeruginosa and S. aureus; fungal species include, A. niger, and C. albicans by disc diffusion method. The results show that the complexes have higher activity than the free ligand. The interaction of the complexes with calf thymus DNA (CT DNA) has been investigated by electronic absorption method. Furthermore, the DNA cleavage activity of the complexes was studied using agarose gel electrophoresis. In vitro anticancer studies of the ligand and its complexes using MTT assay was also done.