Synthesis and spectroscopic characterization of new tetradentate Schiff base and its coordination compounds of NOON donor atoms and their antibacterial and antifungal activity

Manganese(II) and Zinc(II) metal complexes of novel bidentate formamide-based Schiff base ligand: synthesis, structural characterization, antioxidant, antibacterial, and in-silico molecular docking study

A new bidentate Schiff base ligand (C16H16Cl2N4), condensation product of ethylene diamine and 4-chloro N-phenyl formamide, and its metal complexes [M(C16H16Cl2N4)2(OAc)2] (where M = Mn(II) and Zn(II)) were synthesized and characterized using various analytical and spectral techniques, including high-resolution mass spectrometry (HRMS), elemental analysis, ultraviolet-visible (UV-vis), Fourier-transform infrared (FTIR) spectroscopy, AAS, molar conductance, 1H NMR, and powder XRD. All the compounds were non-electrolytes and nanocrystalline. The synthesized compounds were assessed for antioxidant potential by DPPH radical scavenging and FRAP assay, with BHT serving as the positive control. Inhibitory concentration at 50% inhibition (IC50) values were calculated and used for comparative analysis. Furthermore, the prepared compounds were screened for antibacterial activity against two Gram-negative bacteria (Staphylococcus aureus and Bacillus subtilis) and two Gram-positive bacteria (Escherichia coli and Salmonella typhi) using disk-diffusion methods, with amikacin employed as the standard reference. The comparison of inhibition zones revealed that the complexes showed better antibacterial activity than the ligand. To gain insights into the molecular interactions underlying the antibacterial activity, the ligand and complexes were analyzed for their binding affinity with S. aureus tyrosyl-tRNA synthetase (PDB ID: 1JIL) and S. typhi cell membrane protein OmpF complex (PDB ID: 4KR4). These analyses revealed robust interactions, validating the observed antibacterial effects against the tested bacterial strains.

An update on the novel and approved drugs for Alzheimer disease

Introduction

Given the severity of the condition and the increasing number of patients, developing effective therapies for Alzheimer's disease has become a significant necessity. Aggregation of Amyloid-Beta (Aβ) plaques and Tau Protein Tangles in the brain's nerve tissue are two of the most histopathological/pathophysiological symptoms. Another important element involved in the etiology of Alzheimer's disease is the reduction in acetylcholine (ACh) levels in the brain. Currently available medications for Alzheimer's disease treatment, such as cholinesterase inhibitors and an antagonist of the N-methyl-d-aspartate receptor, can temporarily reduce dementia symptoms but not stop or reverse disease development. In addition, several medicinal plants have been shown to diminish the degenerative characteristics associated with Alzheimer's disease, either in its crude form or as isolated chemicals.

Aim

This review summarises the results from previous studies that reflect an array of novel therapies underway in various phases of clinical trials. Many are discontinued due to non-adherence to the designed endpoints or the surfacing of unavoidable side effects. The present piece of article focuses on the approved drugs for the treatment of Alzheimer's disease and their related mode of action as well as the promising therapies for the treatment of the said disease. Special attention has been placed on the researched herbal drugs, with the pipeline of novel therapies underway in various phases of clinical trials.

Result

The current article includes a list of approved pharmaceuticals for treating Alzheimer's disease, prospective therapies for the illness's treatment, and a pipeline of novel therapies in various stages of clinical trials.

Conclusion

The results suggest that the drugs under clinical trials may open new pathways for the effective treatment of patients with Alzheimer's disease while improving their quality of life.

Metal complexes of Tridentate Schiff base: Synthesis, Characterization, Biological Activity and Molecular Docking Studies with COVID-19 Protein Receptor

Mononuclear chelates of Cr(III), Mn(II), Fe(III), Ni(II), Cu(II), Zn(II) and Cd(II) resulted from new tridentate Schiff base ligand, 4-((1-(5-acetyl-2,4-dihydroxyphenyl)ethylidene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one, were synthesized. Metal to ligand ratio was found to be1 : 1, which was revealed via elemental analysis and characterized via various spectroscopic tools. IR has point out that the coordination of the ligand towards the metal ions was carried out via NOO donor atoms. UV-Vis, 1H NMR spectral data, molar conductivity measurements, BET surface area, melting points and theoretically through density function theory were used such as characterizing techniques in supporting further interpretation of the complexes structures. The complexes were octahedral except Cu(II) and Ni(II) complexes were tetrahedral as suggested from the magnetic moment measurement. The complexes were found to have surface area, pore volume and particle radius of 23-176 m2 g-1, 0.02-0.33 cc/g and 8.71-4.32 nm, respectively, as pointed out from BET measurement. Schiff base ligand and metal complexes were tested in vitro to estimate their antimicrobial activity opposed to Gram-negative and Gram-positive bacterial and fungal organisms. MOE 2008 was used headed for screen potential drugs with molecular docking by the protein sites of new coronavirus and the study was constructed to molecular docking without validation through MD simulations.

Synthesis, spectral characterization, DFT calculations, pharmacological studies, CT-DNA binding and molecular docking of potential N, O-multidentate chelating ligand and its VO(II), Zn(II) and ZrO(II) chelates

The pharmacological efficacy of the variety tetradentate ligands encouraged us to design attractive compounds through effective synthetic procedure. The prepared Schiff base ligand 6,6'-((1E,1'E)-((4-chloro-1,2-phenylene)bis(azaneylylidene))bis(methaneylylidene))bis(2-ethoxy phenol (H₂L), which derived from 4-chloro-o-phenylenediamine and 3-ethoxy-salicylaldehyde and its VO(II), Zn(II) and ZrO(II) metal chelates, have been synthesized and characterized with aim of that it may struggle the invasion of drug resistance. The chemical structural of studied compounds were discussed by TGA, elemental analysis, UV-Vis., ¹H NMR, ¹³C NMR, FTIR, mass spectral, PXRD, molar conductance, magnetic susceptibility measurements and density functional theory. The results assigned square pyramid geometries for [VOL] and [ZrOL].2H₂O chelates and an octahedral geometry for [ZnL(H₂O)₂].2H₂O chelate. Powder XRD data showed that the complexes are monoclinic with polycrystalline nature. The results of CT-DNA interaction with the titled chelates showed that the binding between CT-DNA and the metal complexes occurs through intercalation mode. Their CT-DNA binding efficiency estimated in terms of their binding constants (K_b), which gave the order: VOL (6.9 × 10⁵) > ZrOL (6.3 × 10⁵) > ZnL(H₂O)₂ (5.5 × 10⁵). The antimicrobial activities of the synthesized compounds were tested against selected fungal and bacterial strains using well diffusion technique. The obtained chelates showed higher antifungal and antibacterial activities than their corresponding ligand. Furthermore, the M-complexes showed higher potent cytotoxic effect toward HEK-293, human colorectal HepG-2, HCT-116 and MCF-7 adenocarcinoma cell lines compared to the free H₂L ligand. Investigation of antioxidant property represented that all the prepared complexes have better radical scavenging potencies against DPPH radicals than the free H₂L ligand. To study the molecular docking of proposed compounds versus Tyrosine kinases receptor (TKR), we used AutoDock1.5.6rc3® suite. The current compounds (H₂L, VOL, ZrOL and ZnL(H₂O)₂) and STI were found to bind with C-kit of TKR with HBs at ILE789.A, ILE808.A, ASP810.A, GLU640.A and TYR846 amino acid residue and the binding energies were - 8.9, -8.93, -8.83, -1.48 and -10.39 kcal/mol respectively.

Influences of γ-ray irradiation on physico-chemical, structural, X-ray diffraction, thermal and antimicrobial activity of some γ-irradiated N',N'''-((Z)-ethane-1,2-diylidine)bis(2-aminobenzohydrazide) metal complexes

A series of Co(II), Ni(II), Cu(II), Th(IV) and UO₂(II) complexes have been synthesized from reaction of nitrogen based ligand (L) i.e. N',N'''-((Z)-ethane-1,2-diylidine)bis(2-aminobenzohydrazide)(L) with their salts. Investigation of synthesized metal complexes was achieved by using elemental analyses, magnetic moment, molar conductance, FT-IR, UV/Vis. spectroscopy, thermal techniques and 3D molecular modeling. An octahedral geometry has been suggested for all complexes except for Ni(II) complex (2) which adopted tetrahedral geometry. To through a light on the probability of structure changes with γ-irradiation, the effect of gamma irradiation on powder samples of the complexes [Co(L)Cl₂].4H₂O (1); [Ni₂(L)(OAc)₄].5H₂O (2) and [Cu(L)Br₂].5H₂O (3) was investigated after being exposed to high energetic γ-rays at 100 kGy dose (hereafter referred to as (1A,2A,3A, respectively). Spectral, thermal, magnetic susceptibility, molar conductance and powder X-ray diffraction patterns (XRD) were performed before and after irradiation. In addition, the in vitro antimicrobial activity of the complexes against Staphylococcus aureus as Gram-positive strain, Escherichia coli as Gram-negative strain and antifungal Candida albicans was performed for both unirradiated and irradiated samples. The obtained results showed that the irradiated complexes were affected, but not greatly by the applied γ-irradiation dose.

Terpyridine-metal complexes: effects of different substituents on their physico-chemical properties and density functional theory studies

A series of different substituted terpyridine (tpy)-based ligands have been synthesized by Kröhnke method. Their binding behaviour was evaluated by complexing them with Co(II), Fe(II) and Zn(II) ions, which resulted in interesting coordination compounds with formulae, [Zn(tpy)₂]PF₆, [Co(tpy)₂](PF₆)₂, [Fe(tpy)₂](PF₆)₂ and interesting spectroscopic properties. Their absorption and emission behaviours in dilute solutions were investigated in order to explain structure-property associations and demonstrate the impact of different aryl substituents on the terpyridine scaffold as well as the role of the metal on the complexes. Photo-luminescence analysis of the complexes in acetonitrile solution revealed a transition from hypsochromic to bathochromic shift. All the compounds displayed remarkable photo-luminescent properties and various maximum emission peaks owing to the different nature of the functional groups. Furthermore, the anti-microbial potential of ligands and complexes was evaluated with docking analyses carried out to investigate the binding affinity of terpyridine-based ligands along with corresponding proteins (shikimate dehydrogenase and penicillin-binding protein) binding sites. To obtain further insight into molecular orbital distributions and spectroscopic properties, density functional theory calculations were performed for representative complexes. The photophysical activity and interactions between chromophore structure and properties were both investigated experimentally as well as theoretically.

Chromium Coordination Compounds with Antimicrobial Activity: Synthetic Routes, Structural Characteristics, and Antibacterial Activity

A major threat to public health worldwide is that the antimicrobial activity of the established drugs is constantly reduced due to the resistance that bacteria develop throughout the years. Some transition metal complexes show higher antibacterial activity against several bacteria compared to those of clinically used antibiotics. Novel classes of molecules provide new challenges and seem promising to solve the crisis that the overuse of antibiotics has led over the last years. This review discusses the challenges of chromium-based metallodrugs as antimicrobial agents. In particular, the synthetic routes, the structural characteristics, as well as the antimicrobial activity of 32 chromium (III) complexes have been presented.

DFT studies on vibrational and electronic spectra, HOMO-LUMO, MEP, HOMA, NBO and molecular docking analysis of benzyl-3-N-(2,4,5-trimethoxyphenylmethylene)hydrazinecarbodithioate

Benzyl-3-N-(2,4,5-trimethoxyphenylmethylene)hydrazinecarbodithioate (compound 1) is a bidentate and nitrogen-sulfur containing Schiff base, which has been synthesized by the condensation reaction of S-benzylndithiocarbazate and 2,4,5-trimethoxybenzaldehyde. The theoretical calculations of the mentioned compound have been carried out using the more popular density functional theory method, Becke-3-Parameter-Lee-Yang-Parr (B3LYP) in 6-31G+(d,p) basis set. The computational results of the compound were compared with the obtained experimental value. Moreover, the highest occupied molecular orbital, the lowest unoccupied molecular orbital, molecular electrostatic potential, chemical reactivity parameters and natural bond orbital of the optimized structure have been evaluated at the same level of theory. Furthermore, the UV–Vis spectrum of the compound has been carried out for the better understanding of electronic absorption spectra with the help of the time-dependent density functional theory at room temperature. Besides, the molecular docking simulation of the mentioned molecule with target protein was also investigated. In addition, in silico studies were performed to predict absorption, distribution, metabolism, excretion and toxicity profiles of the designed compound. The results indicated that the theoretical data have well correlated with the observed values. The narrow frontier orbital gap indicated that the eventual charge transfer interaction occurs within the studied molecule and showed high chemical reactivity. The global reactivity values showed that the compound is soft molecule, electrophilic species and has strong binding ability with biomolecules. The molecular electrostatic potential structure indicated that the negative and positive potential sites are around electronegative atoms and hydrogen atoms of studied compound, respectively. The natural bond orbital data revealed that the compound contains 97.42% Lewis and 2.58% non-Lewis structure. The intra and inter-molecular charge transfers process occur within the studied compound. The studied compound showed more binding energy (−6.0 kcal/mol) with target protein than hydroxychloroquine (−5.6 kcal/mol). The absorption, distribution, metabolism, excretion and toxicity investigation predicted that the compound has good drug like character.

Synthesis, molecular structure and antioxidant activity of bis [L(μ2-chloro)copper(II)] supported by phenoxy/naphthoxy-imine ligands

A new series of Cu(II) complexes [bis[{(μ₂-chloro)-2-MeO-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-OC₆H₂)}Cu(II)] (Cu1); bis[{(μ₂-chloro)-2-MeS-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-(OC₆H₂)}Cu(II)] (Cu2); bis[{(μ₂-chloro)-2-MeO-Ph-CH₂-(N=CH)-2-(OC₁₀H₆)} Cu(II)] (Cu3); bis[{(μ₂-chloro)-2-MeS-Ph-CH₂-(N=CH)-2-(OC₁₀H₆)}Cu(II)] complex (Cu4); bis[{2-MeS-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-(OC₆H₂)}Cu(II)] (Cu5)] have been synthesized and characterized by elemental analysis, IR, UV-Visible and by X-ray crystallography for Cu1, Cu4 and Cu5. In the solid state, Cu1 features of a chloro-bridged dimer complex with κ² coordination of the monoanionic phenoxy-imine ligand onto the copper center. On the other hand, the molecular structure of Cu4 reveals the naphthoxy-imine ligand with pendant S-group coordinated to the copper atom in tridentate meridional fashion. Treatment of [Cu(OAc)₂·H₂O] with two equiv. of [2-MeS-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-(HOC₆H₂)] led to a monomeric complex Cu5, with the ONS-donor Schiff base acting as a bidentate ligand. The redox behavior was explored by cyclic voltammetry. The reduction/oxidation potential of Cu(II) complexes depends on the structure and conformation of the central atom in the coordination compounds. Antioxidant activities of the complexes, Cu1 - Cu5, were determined by in vitro assays such as 1,1-diphenyl-2-picryl-hydrazyl free radicals (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radicals (ABTS⁺). The dinuclear compounds Cu1-Cu4, from the concentration of 5 μM, presented a good activity in scavenging DPPH radical. In addition, most of the Cu(II) complexes showed ABTS^.+ radical-scavenging activity. The monomeric complex Cu5 at all concentrations tested showed antioxidant inability. The cytotoxicity of the Cu1 and Cu3 was determined in V79 cell line by reduction of 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay.

New series of metal complexes by amphiphilic biopolymeric Schiff bases from modified chitosans: Preparation, characterization and effect of molecular weight on its biological applications

To improve biological activity of chitosans, new Zn(II), Pd(II) and Pt(II) complexes with biopolymeric amphiphilic Schiff bases anchored in different molecular weight chitosans matrices modified with salicylaldehyde and glycidol were prepared. Salicylaldehyde was introduced to generate complexing Schiff base sites in the chitosans matrix while glycidol is intended to increase the water solubility of the resulting biopolymeric complexes. These novel complexes were characterized using various techniques and assayed for antimicrobial and antitumor activity. The effectiveness of modification was evaluated using FTIR spectroscopy, and thermal behavior of the complexes by TG/DTG-DTA. XPRD showed that the crystallinity of the ligand diminished after the metal complexation. Surface morphologies, investigated by SEM, revealed that the complexes are rougher than chitosan matrix, and the presence of metallic ions was confirmed by EDX. Electronic spectra suggested square planar geometry for Pd(II) and Pt(II) complexes. Concerning antimicrobial activity, the novel complexes exhibited higher antibacterial efficiency against Pseudomonas syringae than against the Fusarium graminearum fungi regarding the free ligand. Complexes also exhibited high antitumor effects against the MCF-7 breast cancer cells, with certain selectivity regarding non-tumor cells (Balb/C 3T3 clone A31) depending on concentration and molar mass, indicating that they could potentially be used for antitumor applications.

Sonochemical synthesis, in vitro evaluation and DFT study of novel phenothiazine base Schiff bases and their nano copper complexes as the precursors for new shaped CuO-NPs

The current work reports the ultrasound-assisted synthesis of two nano binuclear copper complexes derived from novel tetradentate (N₂O₂) phenothiazine based Schiff bases. The synthesized compounds were characterized using the physicochemical methods, including ¹H NMR, ¹³C NMR, FE-SEM, Mass, FT-IR, UV-Vis, elemental analysis, magnetic moment and molar conductance measurements. It is found that the geometrical structure of Cu^II₂LⁿCl₄ is distorted tetrahedral around the copper atoms using the results of ¹H NMR, UV-Vis and magnetic moment studies. In addition, CuO nano particles were produced in the nano range (14.3-12.1nm) by the thermal decomposition of the copper complexes CuO NPs were characterized using FT-IR, FE-SEM, XRD, UV-Vis and photoluminescence methods and indicated a close accordance with the standard pattern. Also, the antioxidant studies revealed that the copper complexes exhibit comparable scavenging effects (against O₂ and OH) with the standard antioxidants, such as vitamin C, while, they show more antioxidant activity than ligands. Similarly, the complexes show more antibacterial activity against four gram positive and gram negative bacteria in comparison to their Schiff base ligands. furthermore, The optimized structure, Molecular orbital (M.O.), Mulliken population analysis (MPA), contour of Electrostatic Potential (ESP) and Molecular Electrostatic Potential (MEP) map of the titled compounds were calculated base on DFT calculations that were carried out at the B3LYP levels of theory with a double basis set LANL2DZ for copper, and 6-311+G(d,p) basis set for the other atoms.

Techniques in the synthesis of mononuclear manganese complexes: a review

This article describes an overview of the synthetic techniques and protocols for the preparation of new ligands and respective manganese (Mn) complexes to be tested for biomedical applications. Mn is an essential and biocompatible element, the complexes of which have diverse medicinal applications. The most significant use of Mn complexes is their application against reactive oxygen species in biological systems, and due to this, three Mn-incorporated complexes (AEOL-10150, EUK-134, and M40403) are already under clinical trials. Hence, the interest in synthesizing biologically active Mn complexes is rapidly increasing. Mn complexes are commonly synthesized using either water or ethanol as a reaction medium for their possible usage in biological systems. Using common Mn salts along with suitable organic ligand works well in the presence of little heat to obtain Mn complexes of interest.

Pharmacophore hybrid approach of new modulated bis-diimine Cu(II)/Zn(II) complexes based on 5-chloro Isatin Schiff base derivatives: Synthesis, spectral studies and comparative biological assessment

Novel bioactive 5-chloro isatin based Schiff base ligands, (N,N'E,N,N'Z)-N,N'-(5-chloroindoline-2,3-diylidene)bis(5-nitrobenzo [d]thiazol-2-amine), L(1) and (N,N'E,N,N'Z)-N,N'-(5-chloroindoline-2,3-diylidene)bis(5-nitrothiazol-2-amine), L(2) derived from 2-amino 5-nitrobenzothiazole and 2-amino 5-nitrothiazole and their metal complexes, [Cu(L(1))2]Cl2;1, [Zn(L(1))2(H2O)2]Cl2;2, [Cu(L(2))2]Cl2;3 and [Zn(L(2))2(H2O)2]Cl2;4 have been synthesized. The composition, stoichiometry and geometry of the proposed ligands and their complexes have been envisaged by the results of elemental analyses and spectroscopic data (FT-IR, (1)H NMR and (13)C NMR, Mass and EPR). The molar conductivity values of the metal complexes revealed their ionic nature. The thermal stability of metal complexes was demonstrated by TGA/DTA studies while the crystalline nature of the complexes has been ascertained by XRD. Furthermore, a comparative account of in vitro antibacterial study against different bacterial strains with respect to standard antibiotic and scavenging activity against standard control at different concenterations unfolded pronounced antibacterial and radical scavenging potencies of the metal complexes as compared to free ligands. In addition, in vitro cytotoxicity of ligands and its metal complexes was also screened on MCF7 (Human breast adenocarcinoma), HeLa (Human cervical carcinoma) and HepG2 (Human Hepatocellular carcinoma), cell lines and normal cells (PBMC). The antiproliferative outcomes revealed that metal complexes exhibit superior activity in general as compared to free ligands (L(1) and L(2)) where metal complexes (1 and 2) of 5-chloro isatin linked benzothiazole motif (L(1)) are found to have better prospect of acting as chemotherapeutic agents which can be explained in terms of greater biopotency, planarity and conjugation against all the tested cancer cell lines with IC50<2.80 μM.

Synthesis and spectral studies of metal complexes of a Schiff base derived from (2-amino-5-chlorophenyl)phenyl methanone

Some new complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Fe(III) with the Schiff base 5-chloro-2-(furan-2-yl methylamino)phenyl)phenyl methanone has been synthesized and characterized by elemental analysis, spectroscopic data including FT-IR, (1)H NMR, Electronic, ESI mass, Mössbauer & ESR. It has been found that the Schiff base behaves as a neutral bidentate N, O donor which chelates with the metal ions in 1:2 stoichiometry. Magnetic moment and electrolytic conductance data confirms this. The Schiff base and selected complexes were screened for antimicrobial activity. The complexes and the Schiff base were subjected to antioxidant study. The antitumor activity of Co(II) complex was tested by MTT assay. The result indicates the viability of the complex against tested cell lines.

Spectral Investigation andIn VitroAntibacterial Evaluation of NiIIand CuIIComplexes of Schiff Base Derived from Amoxicillin andα-Formylthiophene (αft)

Two new metal complexes of general formula M(Haαft)2[M =NiIIandCuII] of asymmetrical Schiff base ligand (HL = Haαft) derived from amoxicillin andα-formylthiophene have been prepared and characterized by various physicochemical and spectral techniques. Molar conductance measurement indicates nonelectrolytic nature of the metal complexes. FT-IR spectral study reveals the ligation of metal ions at two different nitrogen [NN] donor sites of Haαft. FT-IR and electronic absorption spectral evidences suggest distorted tetrahedral and square planar geometry forCuIIandNiIIcomplexes, respectively. The structure optimization by molecular mechanics (MM) force field calculation through ArgusLab 4.0.1 version software also supports the concerned geometry of the complexes. The cell dimensions as suggested by XRPD study,a(6.753 Å),b(13.904 Å),c(20.122 Å),α(142.76°),β(106.580°), andγ(72.4343°) forCuIIanda(24.2547 Å),b(6.6371 Å),c(5.5047 Å) (α=β=γ= 90°) forNiIIcomplexes, are in good agreement with their triclinic and orthorhombic crystal systems. Particle size calculation by Scherrer’s formula indicates nanocrystalline nature of the complexes. The antibacterial sensitivity study suggests promising activities of Haαft (Ligand) and M(Haαft)2complexes against four clinical pathogenic bacteria, namely,E. coli,P. vulgaris,P. aeruginosa, andS. aureus, though being less active than the standard drug amikacin.