Aminothiazole-Linked Metal Chelates: Synthesis, Density Functional Theory, and Antimicrobial Studies with Antioxidant Correlations

Synthesis, characterization, DNA binding interactions, DFT calculations, and Covid-19 molecular docking of novel bioactive copper(I) complexes developed via unexpected reduction of azo-hydrazo ligands

In this work, we focused on the 3rd goal of the sustainable development plan: achieving good health and supporting well-being. Two redox-active hydrazo ligands namely, phenylcarbonohydrazonoyldicyanide (PCHD) and pyridin-4-ylcarbonohydrazonoyl-dicyanide (PyCHD), and their copper(I) complexes have been synthesized and characterized. The analytical data indicates the formation of copper(I) complexes despite starting with copper(II) perchlorate salt. The 1H-NMR and UV-visible spectral studies in DMSO revealed that PyCHD mainly exists in its azo-form, while PCHD exists in azo ↔ hydrazo equilibrium form, and confirmed the copper(I) oxidation state. XPS, spectral and electrochemistry data indicated the existence of copper(I) valence of both complexes. Cyclic voltammetry of PCHD and its copper(I) complex supported the reduction power of the ligand. The antimicrobial activity, cytotoxicity against the mammalian breast carcinoma cell line (MCF7), and DNA interaction of the compounds are investigated. All compounds showed high antimicrobial, and cytotoxic activities, relative to the standard drugs. Upon studying the wheat DNA binding, PCHD and PyCHD were found to bind through external contacts, while both [Cu(PCHD)2]ClO4.H2O and [Cu(PyCHD)2]ClO4.H2O were intercalated binding. In-silico molecular docking simulations against Estrogen Receptor Alpha Ligand Binding Domain (ID: 6CBZ) were performed on all produced compounds and confirmed the invitro experimentally best anticancer activity of [Cu(PyCHD)2]ClO4.H2O. The molecular docking tests against SARS-CoV-2 main protease (ID: 6 WTT) showed promising activity in the order of total binding energy values: [Cu(PCHD)2]ClO4.H2O > [Cu(PyCHD)2]ClO4.H2O > PCHD > PyCHD.

Enantiomeric Complexes Based on Ruthenium(III) and 2,2'-Biimidazole: X-ray Structure and Magnetic Properties

We have prepared and characterized two Ru(III) compounds based on the 2,2'-biimidazole (H2biim) ligand, namely, a single complex of formula cis-[RuCl2(H2biim)2]Cl·4H2O (1) and a racemic mixture of formula {cis-[RuCl2(H2biim)2]Cl}2·4H2O (2), which contains 50% of Ru(III) complex 1. Both compounds crystallize in the monoclinic system with space groups C2 and P21 for 1 and 2, respectively. These complexes exhibit the metal ion bonded to four nitrogen atoms from two H2biim molecules and two chloride ions, which balance part of the positive charges in a distorted octahedral geometry. Significant differences are observed in their crystal packing, which leads to the observation of differences in their respective magnetic behaviors. Despite having imidazole rings in both compounds, π-π stacking interactions occur only in the crystal structure of 2, and the shortest intermolecular Ru···Ru separation in 2 is consequently shorter than that in 1. Variable-temperature dc magnetic susceptibility measurements performed on polycrystalline samples of 1 and 2 reveal different magnetic behaviors at low temperatures: while 1 behaves pretty much as a magnetically isolated mononuclear Ru(III) complex with S = 1/2, 2 exhibits the behavior of an antiferromagnetically coupled system with S = 0 and a maximum in the magnetic susceptibility curve at approximately 3.0 K.

Antifungal activity of Co(II) and Cu(II) complexes containing 1,3-bis(benzotriazol-1-yl)-propan-2-ol on the growth and virulence traits of fluconazole-resistant Candida species: synthesis, DFT calculations, and biological activity

Relevant virulence traits in Candida spp. are associated with dimorphic change and biofilm formation, which became an important target to reduce antifungal resistance. In this work, Co(II) complexes containing a benzotriazole derivative ligand showed a promising capacity of reducing these virulence traits. These complexes exhibited higher antifungal activities than the free ligands against all the Candida albicans and non-albicans strains tested, where compounds 2 and 4 showed minimum inhibitory concentration values between 15.62 and 125 μg mL-1. Moreover, four complexes (2-5) of Co(II) and Cu(II) with benzotriazole ligand were synthesized. These compounds were obtained as air-stable solids and characterized by melting point, thermogravimetric analysis, infrared, Raman and ultraviolet/visible spectroscopy. The analysis of the characterization data allowed us to identify that all the complexes had 1:1 (M:L) stoichiometries. Additionally, Density Functional Theory calculations were carried out for 2 and 3 to propose a probable geometry of both compounds. The conformer Da of 2 was the most stable conformer according to the Energy Decomposition Analysis; while the conformers of 3 have a fluxional behavior in this analysis that did not allow us to determine the most probable conformer. These results provide an important platform for the design of new compounds with antifungal activities and the capacity to attack other target of relevance to reduce antimicrobial resistance.

Investigation of antituberculosis, antimicrobial, anti-inflammatory efficacies of newly synthesized transition metal(II) complexes of hydrazone ligands: structural elucidation and theoretical studies

Tuberculosis disease is a serious threat to humans and spreading quickly worldwide, therefore, to find a potent drug, the synthesis of hydrazone ligands endowed Co(II), Ni(II), Cu(II), Zn(II) metal complexes were carried out and well characterized by numerous spectral and analytical techniques. The octahedral geometry of the complexes was confirmed by spectral analysis. Further, in vitro antituberculosis efficacy of the compounds (1-10) revealed that complexes (6), (9), (10) have highest potency to control TB malformation with 0.0028 ± 0.0013-0.0063 ± 0.0013 µmol/mL MIC value while Zn(II) complex (10) (0.0028 ± 0.0013 µmol/mL) has nearly four time potent to suppress TB disease in comparison of streptomycin (0.0107 ± 0.0011 µmol/mL). The antimicrobial and anti-inflammatory evaluations revealed that the complex (10) is more active with lowest MIC (0.0057-0.0114 µmol/mL) and IC50 (7.14 ± 0.05 µM) values, correspondingly which are comparable with their respective standard drugs. Furthermore, the theoretical studies such as molecular docking, DFT, MESP and ADMET were employed to authenticate the potency of HL2 hydrazone ligand (2) and its metal complexes (7-10) which revealed that the zinc(II) complex (10) might be utilized as novel drug candidate for tuberculosis dysfunctions. So, the present research gives a new insight for in vivo investigation of the compounds.

Multispectroscopic Studies on HSA Interaction, DFT Calculations, Molecular Docking, and Antimicrobial Activities of Imine‐ Functionalized Tris(hydroxymethyl)aminomethane Derivatives

Following recent work on new Tris hydroxymethyl aminomethane Schiff base derivatives were synthesized and characterized by using NMR (1H, 13C, and depth), FT‐IR, and Mass spectroscopy. The crystal structure of STB has been determined by X‐ray diffraction analysis. The binding interaction of the 3 chemically synthesized molecules with human serum albumin has been examined under the pH=7.40 through UV‐visible absorption and fluorescence spectroscopy analysis. The result obtained from the fluorescence experiment (1014) suggests a static mechanism of quenching. By utilizing fluorescence spectroscopy to determine the binding constant (Kb=106), it was determined which ligands have the highest affinity for HSA and that these ligands had changed the structure of HSA. Through hydrophobic interactions, the ligands bind to HSA on site I (subdomain II), according to thermodynamic parameters like enthalpy change (ΔHo), entropy change (ΔSo), and Gibbs free energy change (ΔGo). The result of 3D fluorescence spectra also showed that albumin conformational changes were brought on by these ligands. The results of the experiments were supported by DFT and molecular docking of ligands with HSA. Escherichia coli, Stap. aureus, Aspergillus niger, and Aspergillus flavus were tested for antimicrobial activity against the synthesized compounds respectively.

Recent insights into antibacterial potential of benzothiazole derivatives

Antimicrobial resistance (AMR) is a worldwide concern among infectious diseases due to increased mortality, morbidity and treatment cost. According to WHO 2019 report, among the 32 antibiotics in the clinical trials, only six were classified as innovative and containing novel moiety. The remaining antibiotics from this list contain previously known moiety (WHO AMR 2019). Therefore, the development of novel antibiotics to control resistance problems is crucial. Benzothiazole derivatives are of great interest due to their wide range of biological activities and medicinal applications. Reported data indicated that benzothiazole derivatives displayed antibacterial activity by inhibiting the dihydroorotase, DNA gyrase, uridine diphosphate-n-acetyl enol pyruvyl glucosamine reductase (MurB), peptide deformylase, aldose reductase, casdihydrofolate reductase, enoyl acyl carrier protein reductase, dialkylglycine decarboxylase, dehydrosqualene synthase, dihydropteroate synthase and tyrosine kinase. The present review analyzed the synthesis, structure-activity relationship (SAR) and mechanism of action studies of benzothiazole derivatives as antibacterial agents reported by various research groups in the last five years (2018-2022). Different patents on the antimicrobial activity of benzothiazole derivatives have also been summarized. The finding of the present review will be beneficial for the researchers in the development of novel antibacterial molecules based on benzothiazole moiety.

Graphical Abstract

Synthesis, Structural Characterization, Hirshfeld Surface Analysis, and Antibacterial Study of Pd(II) and Ni(II) Schiff Base Complexes Derived from Aliphatic Diamine

A Schiff base bearing two methyl substituents, namely, 6,6'-((1E,1'E)-((2,2-dimethylpropane-1,3-diyl) bis(azanylylidene)) bis(methanylylidene)) bis(2-methylphenol) [H₂AD1Me] was synthesized and characterized through physicochemical and spectroscopic analyses. Then, the Schiff base was complexed with Pd(II) and Ni(II) to form [Pd(AD1Me)] and [Ni(AD1Me)], respectively. Both metal complexes were successfully obtained and characterized through several analyses, viz., melting point, elemental analysis, molar conductivity, magnetic susceptibility, FTIR, ¹H NMR, UV-vis, and single crystal X-ray diffraction. A quantitative analysis of the intermolecular interactions in the crystal structures has been performed using Hirshfeld surface analysis. Both metal complexes were crystallized in a monoclinic crystal system with the space group of P2₁/c. Additionally, the deprotonated phenolic oxygen atom (O1/O2) and azomethine nitrogen atom (N1/N2) of the ligand chelate the Pd(II) and Ni(II) ions, forming a slightly distorted square-planar complex containing three six-membered rings encircling the metal core with dsp² hybridization. The shift of ν(C=N) to a higher frequency in FTIR by 26-28 cm^-1 indicated that the complexation to Pd(II) and Ni(II) through the azomethine N was established. It was further supported through the shifting of the azomethine proton signal to higher or lower chemical shifts with Δδ = 0.43-1.15 ppm in ¹H NMR. In addition, the shifting of the n-π*(C=N) band in UV-vis spectra with Δλ = 24-40 nm indicated the involvement of azomethine nitrogen in the complexation. All the compounds showed no significant antibacterial activity against three bacterial strains, namely, Staphylococcus aureus subsp. aureus Rosenbach (ATCC 6538), Streptococcus mutans Clarke (ATCC 700,610), and Proteus vulgaris (ATCC 6380), as the percent growth inhibition calculated was less than 90%.

Exploration of Pull-Push Effect for Novel Photovoltaic Dyes with A-π-D Design: A DFT/TD-DFT Investigation

The π-rich versus π-poor units in 4,6-di(thiophen-2-yl)pyrimidine (DTB) alternating the π-backbone of solar cells dyes have been extended with a push-pull technique to lower their HOMO-LUMO energy gap and to increase Intramolecular Charge Transfer (ICT). Density functional theory was used to optimize the ground state molecular geometries of newly designed dyes (DTB1-DTB6). Time Dependent DFT (TD-DFT) was used to simulate the Uv-vis spectral values at the maximum absorbance values ranging between 481-535 nm. These values were red shifted from DTB value of experimental (333 nm) and theoretical (346 nm). however, their computed absorbance and fluorescence spectra revealed a bathochromic shift of them upon an increasing the solvent polarity. Different DFT functionals such as (B3LYP, CAM-B3LYP, B97XD, and APFD) were employed to choose their proper use Uv-visible analysis to reveal an unexpected coherence at the B3LYP level with experimental values. As a result, the B3LYP with most diffused basis sets of 6-31G + (d,p) were used for further calculations. The parameters of Global Chemical reactivities revealed that all the dyes had a softer nature with their softness value range of 0.27-0.41. their Ionization Potentials (IP) ranged between 6.21-8.10 eV to comply that the new dyes had good electron donating potentials. With a good electron injection potential of -1.47-1.74 eV, aluminum can be the best electrode, while Au is excellent towards a hole injection operation which had the potential range of 1.79-3.68 eV. For Natural Bond Orbital (NBO) assessment, (N14)LP → (F16-F28)π* with stabilization energy of 42.55 kcal/mol was noted for DTB4. Their Second order hyperpolarizability [Formula: see text] values as their Nonlinear Optical (NLO) response ranged between 59.16-232.11 debye-angstrom^-1 which were almost 6 times higher than the reference DTB (8.47D). The NLO attributes has also shown that a dyes with its small bandgap was related with higher hyperpolarizability values. Because of the decreased reorganization frequencies, newly discovered derivatives with electron transfer qualities might be comparable to or equivalent to those of commonly used electron transmission materials.

Correlating the charge transfer efficiency of metallic sulfa-isatins to design efficient NLO materials with better drug designs

The present study presents synthesis, characterization and first principle studies on metal chelates, (1-12), of sulfonamide-isatin reacted ligands (S¹-S³). All the products were evaluated by various physical and spectral (UV, IR, NMR, MS) means. The octahedral geometry for Co⁺², Ni⁺² and Zn⁺², while square planner geometry for Cu⁺² chelates were confirmed by their spectroscopic and magnetic data. Their physical chemistry investigation show the ability of aromatic rings to stabilize sulfonamide rings across NH-π interactions at their optimized geometries. The nonlinear optical response for all the compounds disclosed that the z-axis has the most contributions. An efficient electron injection and hole studies for Au and Al electrodes having the energies of - 0.1-3.1 and 0.0-11.8 eV respectively were noted. Their bioactive character was shown by global reactivity calculated from FMO energy gaps. The enzyme inhibitory results were found to be 45-61% and IC₅₀ = 102-122 µL, for compound (4), (10), (8), (5) and (12) against the amylase, protease, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) respectively The antibacterial findings showed significant action having 11-17 mm for (2), (7) and (10) for bacterial species, Escherichia coli and Micrococcus luteus. The DPPH and ferric reducing power assay was used to evaluate the antioxidant capacity with 49.0 ± 0.09-66.2 ± 0.08% and IC₅₀ = 102.3-122.4 µL range. In comparison to ligands, the results showed that all metal chelates had higher bioactivity. The chelation was the primary cause of their increased bioactivity. These findings suggested that such metal-based compounds might be used as antimicrobial, and antioxidant options in future to cope drug resistance.