Synthesis and spectral characterization of 14- and 16-membered tetraazamacrocyclic Schiff base ligands and their transition metal complexes and a comparative study of interaction of calf thymus DNA with copper(II) complexes

Antibacterial Activity and Mechanism of Oxidized Bacterial Nanocellulose with Different Carboxyl Content

Oxidized bacterial nanocellulose (OBC) is reported to prevent microbial growth, but its antibacterial characteristics and mechanism are still unclear. Here, the antibacterial mechanism of OBC is explored by detecting and assessing the interaction of OBC with different carboxyl content on Staphylococcus aureus and Escherichia coli. The results show that OBC has strong antibacterial activity and antibiofilm activity against S. aureus and E. coli, which is positively correlated with the carboxyl content of OBC. After OBC treatment, the bacteria adhesion is inhibited and the cell membrane is destroyed leading to increased permeability. Further investigation reveals that the concentration of cyclic diguanosine monophosphate (c-di-GMP) that induced biofilm formation is significantly decreased to 1.81 pmol mg^-1 after OBC treatment. In addition, OBC inactivates mature biofilms, with inactivation rates up to 79.3%. This study suggests that OBC has excellent antibacterial and antiadhesion properties, which can increase the cell membrane permeability and inhibit c-di-GMP formation. In addition, OBC also has a strong inactivation effect on mature biofilm, which can be used as an effective antibiofilm agent.

Synthesis and characterization of violurate - based Mn(II) and Cu(II) complexes nano-crystallites as DNA-binders and therapeutics agents against SARS-CoV-2 virus

Synthesis and structural characterization of nano crystallites of bis-violurate-based manganese(II) and copper(II) chelates is the subject of the present study. Analytical data and mass spectra as well as thermal analysis determined the molecular formulas of the present metal chelates. Spectroscopic and magnetic measurements assigned the structural formula of the present violurate metal complexes. The spectroscopic and magnetic investigations along with structural analysis results indicated the square planar geometry of both the Mn(II) and Cu(II) complexes. The structural analysis of the synthesized metal complexes was achieved by processing the PXRD data using specialized software Expo 2014. Spectrophotometeric and viscosity measurements showed that violuric acid and its Mn(II) and Cu(II) complexes successfully bind to DNA with intrinsic binding constants K_b from 38.2 × 10⁵ to 26.4 × 10⁶ M⁻¹. The antiviral activity study displayed that the inhibitory concentrations (IC₅₀) of SARS-CoV-2 by violuric acid and its Mn(II) and Cu(II) complexes are 84.01, 39.58 and 44.86 μM respectively. Molecular docking calculations were performed on the SARS-CoV-2 virus protein and the computed binding energy values are −0.8, −3.860 −5.187 and −4.790, kcal/mol for the native ligand, violuric acid and its Mn(II) and Cu(II) complexes respectively. Insights into the relationship between structures of the current compounds and their degree of reactivity are discussed.

Injectable, Intrinsically Antibacterial Conductive Hydrogels with Self-Healing and pH Stimulus Responsiveness for Epidermal Sensors and Wound Healing

Torealize intelligent and personalized medicine, it is a huge challenge to develop a hydrogel dressing that can be used as a sensor to monitor human health in real-time while promoting wound healing. Herein, an injectable, self-healing, and conductive chitosan-based (CPT) hydrogel with pH responsiveness and intrinsic antibacterial properties was fabricated via a Schiff base linkage and a hydrogen bond. Due to the introduction of Schiff base bonds, the injectable CPT hydrogel exhibits various excellent properties, such as pH responsiveness to sol-gel transition, self-healing properties, and broad-spectrum antibacterial properties even without additional antibacterial agents. In vitro experiments verify the excellent biocompatibility of the as-prepared hydrogel. An in vivo experiment in a mouse full-thickness skin-wound model was performed to confirm the outstanding effect on wound healing. Meanwhile, as epidermal sensors, the conductive hydrogel that perceives various human activities in real-time could provide the real-time analysis of the patient's healthcare information. Based on these excellent properties, the CPT hydrogel, as a biological dressing with a sensing function, lays a solid foundation for the further realization of personalized medicine.

Exploiting the biological efficacy of benzimidazole based Schiff base complexes with l-Histidine as a co-ligand: Combined molecular docking, DNA interaction, antimicrobial and cytotoxic studies

Four new metal complexes were synthesized and screened for their cytotoxic activity after sufficient assertion from the preliminary DNA binding studies. The metal complexes could bind to CT-DNA through intercalation binding mode. This has also been confirmed by the molecular docking studies. The DNA cleavage efficiencies of these complexes with pBR322 DNA were investigated by gel electrophoresis. The complexes were found to promote the cleavage of pBR322 DNA from the supercoiled form I to the open circular form II in the presence of an oxidizing agent (H₂O₂). The in vitro chemosensitivity of the studied complexes exhibits significant cytotoxic effects, compared to those reported for cisplatin. These findings represent a prompting to search for the probable interaction of these complexes with other cellular elements of fundamental consequence in cell proliferation. The in vitro anticancer activities indicate that the Cu(II) complex is active against the selected human tumor cell lines, and the order of in vitro anticancer activities is consistent with the DNA-binding affinities. Towards noncancerous cell line, Cu(II) complex exhibits very low toxicity. On the other hand all the complexes have been found to exhibit cytotoxic effects against cancerous cell lines with potency more than that of the widely used drug cisplatin and hence they have the potential to act as promising anticancer agents. Captivatingly, they are non-toxic to normal cell lymphocytes revealing that they are selective in killing only the cancer cells.

Screening the DNA interaction ability and antimicrobial activity of a few novel bioactive complexes tethering N-((2-aminophenyl)(phenyl)methylene)-4-nitroaniline

Few novel transition metal complexes having N-((2-aminophenyl)(phenyl)methylene)-4-nitroaniline were synthesized and characterized by elemental analyses, IR, (1)H and (13)C NMR, electronic, EPR and mass spectra, conductivity and magnetic susceptibility measurements. All the metal complexes adopted square planar geometrical arrangements. The DNA-binding properties of the metal(II) complexes have been investigated by electronic absorption, fluorescence, CD spectra, cyclic voltammetry, differential pulse voltammogram and viscosity measurements. The results obtained indicate that these complexes bind to DNA via an intercalation binding mode. DNA cleavage activities indicate that the metal complexes exhibit greater activity than the ligand. The antimicrobial screening reveals that all the metal complexes exhibit better activity than the free ligand.

Spectroscopic and antibacterial studies of new octaazamacrocyclic complexes derived from carbohydrazide and isatin

A novel series of the macrocyclic complexes of the type: [M(C18H14N10O2)X2], where M = Co(II), Ni(II), Cu(II) and Zn(II); X = Cl(-), NO3(-) and CH3COO(-), has been synthesized by template condensation of carbohydrazide and isatin in methanolic medium. The complexes were characterized by various physico-chemical techniques, such as elemental analyses, molar conductance measurements, magnetic measurements, and electronic, NMR, IR and EPR spectral studies. The low value of molar conductance indicates them to be non-electrolytes. Based on various studies, a distorted octahedral geometry was proposed for all the metal complexes. Metal complexes were tested for their in vitro antibacterial activities against some pathogenic bacterial strains and compared with standard antibiotic, Ciprofloxacin. Some of the tested complexes was found effective against Gram-positive bacterial strains.

Synthesis, spectroscopic characterization and antimicrobial activity of binuclear metal complexes of a new asymmetrical Schiff base ligand: DNA binding affinity of copper(II) complexes

The 1:1 condensation of o-acetoacetylphenol and 1,2-diaminopropane under condition of high dilution gives the mono-condensed Schiff base, (E)-3-(1-aminopropan-2-ylimino)-1-(2-hydroxyphenyl)butan-1-one. The mono-condensed Schiff base has been used for further condensation with isatin to obtain the new asymmetrical dicompartmental Schiff base ligand, (E)-3-(2-((E)-4-(2-hydroxyphenyl)-4-oxobutan-2-ylideneamino) propylimino)indolin-2-one (H3L) with a N2O3 donor set. Reactions of the ligand with metal salts give a series of new binuclear complexes. The ligand and its metal complexes were characterized by elemental analyses, IR, (1)H and (13)C NMR, electronic, ESR and mass spectra, conductivity and magnetic susceptibility measurements as well as thermal analyses. The analytical and spectroscopic tools showed that the complexes can be formulated as: [(HL)(VO)2(SO4)(H2O)]·4H2O, [(HL)Fe2Cl4(H2O)3]·EtOH, [(HL)Fe2(ox)Cl2(H2O)3]·2H2O, [(L)M2(OAc)(H2O)m]·nH2O; M=Co, Ni or Cu, m=4, 0 and n=2, 3, [(HL)Cu2Cl]Cl·6H2O and [(L)(UO2)2(OAc)(H2O)3]·6H2O. The metal complexes exhibited octahedral geometrical arrangements except copper complexes that exhibited tetrahedral geometries and uranyl complex in which the metal ion is octa-coordinated. The Schiff base and its metal complexes were evaluated for antimicrobial activity against Gram positive bacteria (Staphylococcus aureus), Gram negative bacteria (Escherichia coli) and fungi (Candida albicans and Aspergillus flavus). The ligand and some of its complexes were found to be biologically active. The DNA-binding properties of the copper complexes (6 and 7) have been investigated by electronic absorption, fluorescence and viscosity measurements. The results obtained indicate that these complexes bind to DNA via an intercalation binding mode with an intrinsic binding constant, Kb of 1.34×10(4) and 2.5×10(4) M(-1), respectively.

Spectroscopic, electrochemical, and alkylation reactions: tert-butyl N-(2-mercaptoethyl)carbamate copper(II) and nickel(II) complexes as structural mimics for the active site of thiolate-alkylating enzymes

Two new dithiolate copper(II) and nickel(II) complexes with the ligand tert-butyl N-(2-mercaptoethyl)-carbamate (Boc-SH) were prepared. Their structures were established to be [(Boc-S)2M], where M=Cu (1) and Ni (2) by using elemental analysis, thermal analysis, molar conductivity, FT-IR, Raman, UV/VIS, and ESR as well as EI-mass spectroscopic methods. The X-ray structure of the ligand Boc-SH was also determined. Spectral data showed that the carbamate ligand act as anioinic bidentate through one immine nitrogen and one thiolate sulfur donor atoms. The spectral techniques suggest that both complexes appear to have square planar geometries. The very low electrical conductance of the two complexes supports their neutral nature. The redox behaviors of the obtained complexes were also investigated by cyclic voltammetry. The monomeric nature of both complexes was assessed from their magnetic susceptibility values. The thermoanalytical data evidence that complex (2) is stable up to 165°C and undergo complete decomposition, resulting in NiO as a residual product. The TEM image of the obtained oxide residue showed its nanosize cluster, suggesting that complex (2) may be used as a precursor for the formation of nanooxide. The methylation reactions of the two dithiolate complexes (1) and (2) with methyl iodide appear to occur intramolecularly at the metal(II)-bound dithiolates, forming the metal(II)-bound dithioether complexes [M(Boc-SCH3)2]I2 with clean second-order constants of 7.95×10(-2) and 10.59×10(-2) M(-1) s(-1), respectively.

DNA damage induction and antiproliferative activity of vanadium(V) oxido monoperoxido complex containing two bidentate heteroligands

Several peroxidovanadium(V) complexes have been shown as a potent anticancer agents. The aim of this study was to investigate the interaction of monoperoxidovanadium(V) complex Pr(4)N[VO(O(2))(ox)(phen)], (Vphen), [phen=1,10-phenantroline, ox=oxalate(2-) and Pr(4)N=tetra(n-propyl)ammonium(1+)] with DNA. UV-Vis spectrophotometry and the alkaline single-cell gel electrophoresis (SCGE, the comet assay) were used to examine the possibility of the vanadium(V) complex to induce changes in DNA. The interaction of Vphen with calf thymus DNA resulted in absorption hyperchromicity in DNA spectrum and shift of the absorption band of DNA to longer wavelengths for the [complex]/[DNA] concentration ratio equals to 4 and after 60 min of incubation. The rise in DNA absorption (by 34%) and bathochromic shift (Δλ(max)=6 nm) are indicative of the interaction between DNA and the complex molecules. DNA strand breaks in cellular DNA were investigated using the comet assay. The human lymphocytes were exposed to various concentrations of Vphen for 30 min. The results revealed that Vphen contributed to the DNA damage expressed as DNA strand breaks in concentration dependent manner. The used concentrations of Vphen (ranging from 0.1 to 100 μmol/L) caused higher DNA damage in lymphocytes compared to untreated cells (from 1.2 times for 0.1 μmol/L to 1.8 times for 100 μmol/L). Vphen was screened for its potential antitumor activity towards murine leukemia cell line L1210. Vphen exhibited significant antiproliferative activity depending on its concentration and time of exposure. The IC(50) values were 0.247 μg/mL (0.45 μmol/L) for 24h, 0.671 μg/mL (1.21 μmol/L) for 48 h and 0.627 μg/mL (1.13 μmol/L) for 72 h.

Synthesis, spectroscopic characterization and crystal structure of novel NNNN-donor μ-bis(bidentate) tetraaza acyclic Schiff base ligands

Novel NNNN-donor μ-bis(bidentate) tetraaza acyclic Schiff base ligands with different substituents (CF(3), N(CH(3))(2) or OH groups) were synthesized by the condensation reaction of triethylenetetramine with 4-substituted benzaldehydes. Triethylenetetramine tris(4-trifluoromethylbenzylidene) (TTFMB), triethylenetetramine tris(4-dimethylaminobenzylidene) (TTDMB) and triethylenetetramine tris(2,4-dihydroxybenzylidene) (TTDHB) were formed as N(4) donor ligands. The formation of a five-membered imidazolidine ring from the ethylenediamine backbone as a spacer-cumbridging unit gives rise to a new type of imidazolidine ligand. The structure of the TTFMB and TTDMB were determined by single crystal X-ray crystallography. The synthesized ligands have been characterized on the basis of the results of cyclic voltammetry (CV) and spectroscopic studies viz. FT-IR spectroscopy (FT-IR), mass spectroscopy (MS) and UV-Vis spectroscopy (UV-Vis).

Synthesis, characterization and thermal studies of binary and/or mixed ligand complexes of Cd(II), Cu(II), Ni(II) and Co(III) based on 2-(Hydroxybenzylidene) thiosemicarbazone: DNA binding affinity of binary Cu(II) complex

A new series of metal complexes of Cd(II), Cu(II), Ni(II) and Co(III) with Schiff base ligand, H(2)L, 2-(Hydroxybenzylidene) thiosemicarbazone were synthesized. The mixed ligand complexes were prepared by using glycine (Gly), 2-aminopyridine (2-Ampy) and 1,10-phenanthroline (Phen) as secondary ligands. The structure of these complexes was identified and confirmed by elemental analysis, molar conductivity, UV-Vis, FT-IR and (1)H NMR spectroscopy and magnetic moment measurements as well as TG-DSC technique. The discussions of the prepared complexes indicate that the ligand behaves as a monoanionic tridentate ligand through ONS donor sites. Thermal studies suggested a mechanism for the degradation of the metal complexes as a function of temperature supporting the chelation modes and showed the possibility of obtaining new complexes pyrolytically in the solid state which cannot be synthesized from the solution. The absorption studies support that the binary Cu(II) complex exhibits a significant binding affinity to HS-DNA through intercalative mode.

Synthesis, characterization, X-ray crystallography, acetyl cholinesterase inhibition and antioxidant activities of some novel ketone derivatives of gallic hydrazide-derived Schiff bases

Alzheimer's disease (AD) is the most common form of dementia among older people and the pathogenesis of this disease is associated with oxidative stress. Acetylcholinesterase inhibitors with antioxidant activities are considered potential treatments for AD. Some novel ketone derivatives of gallic hydrazide-derived Schiff bases were synthesized and examined for their antioxidant activities and in vitro and in silico acetyl cholinesterase inhibition. The compounds were characterized using spectroscopy and X-ray crystallography. The ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays revealed that all the compounds have strong antioxidant activities. N-(1-(5-bromo-2-hydroxyphenyl)-ethylidene)-3,4,5-trihydroxybenzohydrazide (2) was the most potent inhibitor of human acetyl cholinesterase, giving an inhibition rate of 77% at 100 μM. Molecular docking simulation of the ligand-enzyme complex suggested that the ligand may be positioned in the enzyme's active-site gorge, interacting with residues in the peripheral anionic subsite (PAS) and acyl binding pocket (ABP). The current work warrants further preclinical studies to assess the potential for these novel compounds for the treatment of AD.

Synthesis, characterization, acetylcholinesterase inhibition, molecular modeling and antioxidant activities of some novel Schiff bases derived from 1-(2-ketoiminoethyl)piperazines

Some novel Schiff bases derived from 1-(2-ketoiminoethyl)piperazines were synthesized and characterized by mass spectroscopy, FTIR, UV-Visible, 1H and 13C-NMR. The compounds were tested for inhibitory activities on human acetylcholinesterase (hAChE), antioxidant activities, acute oral toxicity and further studied by molecular modeling techniques. The study identified the compound (DHP) to have the highest activity among the series in hAChE inhibition and DPPH assay while the compound LP revealed the highest activity in the FRAP assay. The hAChE inhibitory activity of DHP is comparable with that of propidium, a known AChE inhibitor. This high activity of DHP was checked by molecular modeling which showed that DHP could not be considered as a bivalent ligand due to its incapability to occupy the esteratic site (ES) region of the 3D crystal structure of hAChE. The antioxidant study unveiled varying results in 1,1-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. This indicates mechanistic variations of the compounds in the two assays. The potential therapeutic applications and safety of these compounds were suggested for use as human acetylcholinesterase inhibitors and antioxidants.

Synthesis and thermal studies of tetraaza macrocylic ligand and its transition metal complexes. DNA binding affinity of copper complex

A Tetraaza Macrocylic Ligand (H2L) and its complexes, [Cd(H2L)(OH2)2](NO3)(2)·1/2OH2 (I), [Co(H2L)(OH2)](NO3)(2)·1/2OH2 (II), [Cu(H2L)(NO3)2]·3/2OH2 (III) and [Ni(H2L)(NO3)(OH2)]NO3·OH2 (IV), have been synthesized and characterized on the basis of elemental analysis, molar conductivity, 1H NMR, UV-vis, FT-IR and mass spectroscopy. All results confirm that the prepared compounds have 1:1 metal-to-ligand stoichiometry, octahedral configuration and the ligand behaves as a neutral tetradendate towards the metal ions. [CdL(OH2)2] (V), [CoL(OH2)2] (VI), [CuL(OH2)2] (VII) and [Ni(H2L)(NO3)2] (VIII) were synthesized pyrolytically in solid state from corresponding compounds (I-IV). Analytical results of complexes (V-VIII) show that the ligand behaves either as a neutral tetradendate or dianionic tetradentate ligand towards the metal ions. The binding of H2L and its copper complex (III) to DNA has been investigated by ultraviolet absorption spectroscopy. The experiments indicate that H2L and its copper complex (III) can bind to DNA through an intercalative mode. The H2L and its copper complex (III) exhibited anti-tumor activity against Ehrlich Acites Carcinoma (E.A.C) at the concentration of 100 μg/ml.

Spectroscopic studies and antibacterial activities of some new 16-membered octaazamacrocyclic complexes derived from thiocarbohydrazide and pentane-2,4-dione

A series of macrocyclic complexes of the type [M(C12H20N8S2)X2]; where M=Co(II), Ni(II), Cu(II), Zn(II); X=Cl-, NO3-, CH3COO- has been synthesized by template condensation of thiocarbohydrazide and pentane-2,4-dione in the presence of divalent metal salts in methanolic medium. The complexes have been characterized with the help of elemental analyses, conductance measurements, magnetic measurements, electronic, NMR, IR, EPR and MS spectral studies. The low value of molar conductance indicates them to be non-electrolytes. On the basis of various studies a distorted octahedral geometry may be proposed for all of these complexes. These metal complexes were also tested for their in vitro antibacterial activities against some Gram-positive bacterial strains, i.e., Bacillus subtilis, Bacillus stearothermophilus and two Gram-negative bacterial strains, i.e., Escherichia coli, Pseudomonas putida. The results obtained were compared with standard antibiotics, Chloramphenicol and Streptomycin and found that some of the synthesized complexes show good antibacterial activities as compared to the standard antibiotics.

Macrocyclic metal complexes derived from 2,6-diaminopyridine and isatin with their antibacterial and spectroscopic studies

Condensation reaction of 2,6-diaminopyridine with isatin in the presence of divalent metal ions results in the formation of the macrocyclic complexes of the type [M(C(26)H(16)N(8))X(2)], where M=Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and X=Cl(-), NO(3)(-), CH(3)COO(-). The complexes have been characterized with the aid of elemental analyses, conductance measurements, electronic, NMR, infrared and EPR spectral studies. The lower values of molar conductance indicate them to be non-electrolytes. On the basis of these studies, a six coordinate distorted octahedral geometry in which four nitrogen atoms are suitably placed for coordination towards metal ion, has been proposed for all the complexes. The complexes were tested for their in vitro antibacterial activity. Some of the complexes showed good antibacterial activities against some selected bacterial strains.

New 14-membered octaazamacrocyclic complexes of divalent transition metal ions with their antimicrobial and spectral studies

A novel series of macrocyclic complexes of the type [M(C(18)H(14)N(10)S(2))X(2)]; where M=Co(II), Ni(II), Cu(II), Zn(II) and Cd(II); X=Cl(-), NO(3)(-), CH(3)COO(-) has been synthesized by [2+2] condensation of thiocarbohydrazide and isatin in the presence of divalent metal salts in methanolic medium. The complexes have been characterized with the help of elemental analyses, conductance measurements, magnetic measurements, electronic, NMR and infrared spectral studies. The low value of molar conductance indicates them to be non-electrolytes. On the basis of various studies a distorted octahedral geometry may be proposed for all of these complexes. These metal complexes were also tested for their in vitro antimicrobial activities against some Gram-positive bacteria viz. Staphylococcus aureus, Bacillus subtilis, and some Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa and some fungal strains Aspergillus niger, Aspergillus flavus (molds), Candida albicans, Saccharomyces cerevisiae (yeasts). The results obtained were compared with standard antibiotic: Ciprofloxacin and the standard antifungal drug: Amphotericin-B.