Spectral characterization and anti-inflammatory activity of Schiff-base complexes derived from leucine and 2-acetylpyridine

Progress of Metal-Based Anticancer Chemotherapeutic Agents in Last two Decades and their Comprehensive Biological (DNA/RNA Binding, Cleavage and Cytotoxicity Activity) Studies

During last two decades, there has been an enormous growth in the discovery of innovative active inorganic anticancer complexes (exerting remarkable cytotoxicity at sub micro-molar levels) derived from myriad ligand scaffolds, mainly acting on cancerous vs healthy cells by either halting or inhibiting their uncontrolled growth. The phenomenal success of cisplatin to treat numerous forms of solid malignancies has placed metal-based drugs to the forefront of treatment strategies against cancers. More than 10,000 platinum anticancer complexes have been developed during the past 40 years, but only five drugs have been approved for usage in humans while ten more complexes are currently undergoing clinical trials. Most of the compounds have failed either at R&D stages or in preclinical trails. This has led to extensive investigations by researchers of medicinal chemistry, including our group to design and prepare tailored 3d-metallo-drugs and organotin(IV) compounds from some naturally occurring bioactive compounds, such as amino-acids, peptides, chromone derivatives and NSAID's etc. that were used either alone or in cocktail combination, capable of specifically targeting DNA, lnc RNAs and proteins. Furthermore, 3d-metal ions such as copper, cobalt and zinc etc. incorporated in these ligand framework are biocompatible and induce a unique multi-modal mechanism of cytotoxic action involving angiogenesis, ROS-induced DNA damage, apoptosis by p53 mitochondrial genes and caspases etc. The results observed a positive correlation between the binding affinity of complexes with DNA (as quantified by intrinsic binding constant values) and their cytotoxic behavior. Complexes with high DNA binding propensity were typically lethal against a diverse panel of malignant cell types compared to normal cells.

Effects on anti-inflammatory, DNA binding and molecular docking properties of 2-chloroquinolin-3-yl-methylene-pyridine/pyrazole derivatives and their palladium(II) complexes

Two new sets of Schiff bases 2-chloroquinolin-3-yl-methylene-pyridin-2-amine (CMPA) and 2-chloroquinolin-3-yl-methylene-pyrazole-5-amine-3-thole (CMPT) and their respective palladium (II) complexes have been synthesised and characterized with the aid of elemental analysis, IR, ¹H &¹³C NMR, UV-Vis., and electrochemical studies. The surface morphology of palladium complexes were examined by Scanning Electron Microscopic image. The binding affinities of complexes with CT-DNA were carried out by absorption spectra and cyclic voltammetric studies. The observed hypochromic (~20%) and bathochromic (~30%) shifts indicates that the complexes bind with Guanine base pair of CT-DNA via intercalation. The increasing cathodic peak potential from +0.968 eV to +1.104 eV in complexes confirm the presence of intercalation. Anti-inflammatory activities of both ligands and complexes have been studied using carrageenan induced hind paw edema in Wistar rats. The change in paw volume revealed that the maximum percentage of inhibition was observed in metal complex at 5th hour with a dose of 200 mg/kg. In order to evaluate the binding affinity of ligand and metal complex, molecular interaction analysis were performed by maestro implemented in Schrodinger.

Differential Immunomodulatory Activities of Schiff Base Complexes Depending on their Metal Conjugation

Immunomodulatory compounds have become crucial with advances in immunotherapy. Using our own immune system cells, we can direct the immune cell function and develop desired response against a certain threat. Immunotherapy applications have been suggested against tumors, autoimmune disorders, and infectious diseases. Vaccination can be considered as one of the best known example of immunotherapy. Infectious agent's signature molecular structures are introduced to the immune cells together with the adjuvants that further activate the immune cells to mount a proper immune response and memory. Immunotherapy and vaccine formulations are in constant need of a library of immunomodulatory reagents that can be applied depending on the target. In order to expand the number of immunomodulatory reagents that can find medicinal applications, our group has been testing unique chemical structures on the immune system cells, especially macrophages. Schiff base complexes are known for their anti-inflammatory and antimicrobial activities. In this study, we used previously characterized Schiff base complexes with different metal conjugations. These molecules had differential immunostimulatory and immunomodulatory potentials on macrophages in vitro depending on the type of the conjugated metal. After light exposure, these complexes changed their characteristics and became powerful anti-inflammatory complexes. Due to their possible antimicrobial potentials, we also tested their activities against gram negative and gram positive bacteria. All of the complexes exerted antimicrobial activities which were not light responsive. Here, we present Schiff base complexes with differential immunostimulatory and immunomodulatory activities that can also efficiently eliminate gram positive and gram negative bacteria. Upon photo activation, they block the production of inflammatory TNFα cytokine. Therefore, together with the light, they can be used to treat bacterial infections associated with damaging inflammation. Graphical Abstract.

Novel Copper Bearing Schiff Bases with Photodynamic Anti-Inflammatory and Anti-Microbial Activities

Schiff bases and their copper complexes have been previously studied for their anti-inflammatory, anti-tumor as well as anti-microbial activities. Schiff bases can be derivatized to gain photoluminiscence capacity. This property of the schiff bases enables the transfer of the electrons upon absorption of the light at a specific wavelength. In this study, we exploited this attribute of novel copper bearing schiff bases and tested their photodynamic biological activities. These compounds exerted photodynamic anti-inflammatory activities on the in vitro activated mammalian macrophages. Compared with salicylic acid control groups, these novel schiff bases had stronger activity which became more prominent with photo-induction. Moreover, they also had anti-microbial activity on gram negative bacteria E.coli and gram positive bacteria S.aureus.This anti-microbial activity was stronger than that of Neomycin on both bacterial strains. Our results suggest their potential use as anti-inflammatory and anti-microbial agents both in the dark as well as after photo-induction.

In Vitro Cytotoxicity Studies on Human Thyroid Gland Undifferentiated Carcinoma Cells Using the Nickel Complex of (Z)-3-Bromo-5-((p-tolylimino)methyl)phenol

Metal complexes for medical applications are the promising area of research and metallo-drugs have been developed and evaluated to enhance the efficiency of drugs and minimize their side effects. This study describes the synthesis of a Schiff base ligand (Z)-3-bromo-5-((p-tolylimino)methyl)phenol from the reaction of 5-bromosalicilaldehyde and p-toluidine, and its subsequent complexation with nickel. Characterization and cell viability studies were performed for both Schiff base ligand and its metal complex with ¹H-NMR, FTIR, TG analysis, and UV-VIS spectrometry. With the aim of proving the Ni complex formation, quantitative analysis was done with flame atomic absorption spectrometry. The recovery result obtained for the formed complex was 103.9%. The cell viability of human thyroid gland undifferentiated carcinoma cells (8305C) treated with the Ni-ligand complex was determined as 12.7 ± 0.17%. It was observed that the nickel complex could be a significant anticancer agent as tested by the MTT assay method. Graphical Abstract .

Sonication-assisted synthesis of a new heterostructured schiff base ligand Silver-Guar gum encapsulated nanocomposite as a visible light photocatalyst

A heterostructured Schiff base ligand (Benzildiethylenetriamine)-Silver-Guar gum encapsulated nanocomposites was intended to prepare by simple sonication assisted reflux method. Appropriate composition of purified guar gum, Schiff base ligand and silver nitrate were used for the synthesis. The synthesised nanocomposites were characterised by photoluminescence spectrum, UV-vis diffuse reflectance spectrophotometer, Fourier transform infra-red spectroscopy, X-ray diffractometer, scanning electron microscopy and transmission electron microscopy. The crystalline peaks of XRD and FTIR reveals that Schiff base ligand and guar gum forms metal-organic matrix. Morphology studies have confirmed the organic framework structure and metallic silver nanoparticles are embedded on the organic framework. The efficiency of nanocomposites depends on adsorption capacity and silver nanoparticles that are encapsulated thereby increasing the visible light absorption through surface plasma resonance. The nanocomposite was proved to be highly selective in hydrogenation reaction which favoured the formation of aniline from nitrobenzene as single product with short reaction time and 90% conversion.

Biological evaluation, molecular docking and DNA interaction studies of coordination compounds gleaned from a pyrazolone incorporated ligand

In this work, we have synthesized a few novel mononuclear complexes of Cu(II), Co(II), Ni(II) and Zn(II) using a pyrazolone-derived Schiff base ligand. They were characterized by spectroscopic and analytical methods. The elemental analyses, UV-Vis, magnetic moment values and molar conductance of the complexes reveal that the complexes adopt an octahedral arrangement around the central metal ions. The interaction of complexes with CT-DNA was studied by absorption spectral titration and viscosity measurements. The observed data show that the complexes bind with CT-DNA via an intercalation mode. Efficient pUC18 DNA cleavage ability of the synthesized compounds was explored by gel electrophoresis. The antimicrobial activity of these compounds against a set of bacterial and fungal strains reveals that the complexes exhibit better activity than the free ligand. Moreover, all the complexes were evaluated against two cancer (HeLa and HepG2) and one normal (NHDF) cell lines. The data were compared with cisplatin. Anti-inflammatory activity has been experimentally validated which proves that theoretical predictions concur with the experimental results. In addition, molecular docking studies have been performed to consider the nature of binding mode and binding affinity of these compounds with DNA (1BNA) and protein (3hb5). These studies reveal that the mode of binding is intercalation and the complexes have higher binding energy scores than the free ligand.

Synthesis, spectral and antimicrobial studies of amino acid derivative Schiff base metal (Co, Mn, Cu, and Cd) complexes

Amino acid derivative Schiff base was synthesized by reaction of leucine with salicyldehyde in basic medium. The Schiff base was used as a ligand which was reacted with Co, Mn, Cu and Cd metals in order to form the stable complexes. The synthesized ligand and metals complexes were characterized by using different spectroscopic tools i.e. FT-IR, Mass spectrometry and NMR. The percentages of different elements present in ligand molecule and complexes was confirmed by Elemental analyzer. All compounds including ligand and complexes were also engaged with different bacterial (Escheria coli, Staphylococcus aureus, Bacillus subbtilis) and fungal strains (Alternaria alternate, Aspergillus flavus and Aspergillus niger) in order to check the inhibitory action of titled compounds. The results showed that the metal complexes have greater antimicrobial activities than ligand.

Synthesis, spectral characterization and DNA binding of Schiff-base metal complexes derived from 2-amino-3-hydroxyprobanoic acid and acetylacetone

Four new metal complexes derived from the reaction of Cu(II), Co(II), Ni(II) and Zn(II) acetates with the Schiff-base ligand (H3L) resulted from the condensation of the amino acid 2-amino-3-hydroxyprobanoic acid (serine) and acetylacetone have been synthesized and characterized by, elemental analyses, ES-MS, IR, UV-Vis., 1H NMR, 13C NMR, ESR, thermal analyses (TGA and DTG) and magnetic measurements. The results showed that the Schiff-base ligand acts as bi-negative tridentate through the azomethine nitrogen, the deprotonated carboxylate oxygen and the enolic carbonyl oxygen. The optical band gaps measurements indicated the semi-conducting nature of these complexes. Molecular docking was used to predict the binding between the Schiff base ligand with the receptor of prostate cancer mutant H874Y. The interactions between the Cu(II) complex and calf thymus DNA (CT-DNA) have been studied by UV spectra. The results confirm that the Cu(II) complex binds to CT-DNA in an intercalative mode.

Synthesis, biological evaluation, and molecular docking studies of 2,6-dinitro-4-(trifluoromethyl)phenoxysalicylaldoxime derivatives as novel antitubulin agents

A series of 2,6-dinitro-4-(trifluoromethyl)phenoxysalicylaldoxime derivatives (1h-20h) have been designed and synthesized, and their biological activities were also evaluated as potential antiproliferation and tubulin polymerization inhibitors. Among all the compounds, 2h showed the most potent activity in vitro, which inhibited the growth of MCF-7, Hep-G2 and A549 cell lines with IC(50) values of 0.70 ± 0.05, 0.68 ± 0.02 and 0.86 ± 0.05 μM, respectively. Compound 2h also exhibited significant tubulin polymerization inhibitory activity (IC(50)=3.06 ± 0.05 μM). The result of flow cytometry (FCM) demonstrated that compound 2h induced cell apoptosis. Docking simulation was performed to insert compound 2h into the crystal structure of tubulin at colchicine binding site to determine the probable binding model. Based on the preliminary results, compound 2h with potent inhibitory activity in tumor growth may be a potential anticancer agent.