Unraveling Multicopper [Cu3] and [Cu6] Clusters with Rare μ3-Sulfato and Linear μ2-Oxido-Bridges as Potent Antibiofilm Agents against Multidrug-Resistant Staphylococcus aureus

In this research article, two multicopper [Cu3] and [Cu6] clusters, [Cu3(cpdp)(μ3-SO4)(Cl)(H2O)2]·3H2O (1) and [Cu6(cpdp)2(μ2-O)(Cl)2(H2O)4]·2Cl (2) (H3cpdp = N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol), have been explored as potent antibacterial and antibiofilm agents. Their molecular structures have been determined by a single-crystal X-ray diffraction study, and the compositions have been established by thermal and elemental analyses, including electrospray ionization mass spectrometry. Structural analysis shows that the metallic core of 1 is composed of a trinuclear [Cu3] assembly encapsulating a μ3-SO42- group, whereas the structure of 2 represents a hexanuclear [Cu6] assembly in which two trinuclear [Cu3] motifs are exclusively bridged by a linear μ2-O2- group. The most striking feature of the structure of 2 is the occurrence of an unusual linear oxido-bridge, with the Cu3-O6-Cu3' bridging angle being 180.00°. Whereas 1 can be viewed as an example of a copper(II)-based compound displaying a rare μ3:η1:η1:η1 bridging mode of the SO42- group, 2 is the first example of any copper(II)-based compound showing an unsupported linear Cu-O-Cu oxido-bridge. Employing variable-temperature SQUID magnetometry, the magnetic susceptibility data were measured and analyzed exemplarily for 1 in the temperature range of 2-300 K, revealing the occurrence of antiferromagnetic interactions among the paramagnetic copper centers. Both 1 and 2 exhibited potent antibacterial and antibiofilm activities against methicillin-resistant Staphylococcus aureus (MRSA BAA1717) and the clinically isolated culture of methicillin-resistant S. aureus (MRSA CI1). The mechanism of antibacterial and antibiofilm activities of these multicopper clusters was investigated by analyzing and determining the intracellular reactive oxygen species (ROS) generation, lipid peroxidation, microscopic observation of cell membrane disruption, membrane potential, and leakage of cellular components. Additionally, 1 and 2 showed a synergistic effect with commercially available antibiotics such as vancomycin with enhanced antibacterial activity. However, 1 possesses higher antibacterial, antibiofilm, and antivirulence actions, making it a potent therapeutic agent against both MRSA BAA1717 and MRSA CI1 strains.

Monomeric copper(II) complexes with unsymmetrical salen environment: Synthesis, characterization and study of biological activities

Three new ONNO-donor tetradentate unsymmetrical salen ligands were synthesized by using o-phenyl diamine with substituted salicylaldehydes followed by a two-step reaction methodology. These three ligands by reaction with Cu(OAc)2.4H2O produced three new monomeric Cu(II) complexes, [CuII(L1-3)] (1-3). Elemental analysis, IR, UV-vis, NMR, and HR-ESI-MS techniques were used to analyze and characterize all the synthesized ligands and their corresponding metal complexes. Molecular structures of 1-3 were confirmed by the single-crystal-XRD analysis. Furthermore, the DNA binding ability of these complexes was checked through UV-vis, fluorescence spectroscopy, and also by circular dichroism studies. All the complexes were found to show an intercalation mode of binding with the Kb value in the range of 104-105 M-1. Finally, 1-3 was tested against two malignant (HeLa and A549) and non-cancerous (NIH-3T3) cell lines to check their in vitro antiproliferative activities. Among all, 1 is the most cytotoxic of the series having IC50 values of 5.7 ± 0.9 and 6.0 ± 0.3 μM against HeLa and A549 cell lines, respectively. This result is also consistent with the DNA binding order. Furthermore, the apoptotic mode of cell death of all the complexes was also evaluated by DAPI, AO/EB, and Annexin V-FITC/PI double staining assays.

Anticancer activity of Ni(II) and Zn(II) complexes based on new unsymmetrical salophen-type ligands: synthesis, characterization and single-crystal X-ray diffraction

The discovery of new coordination compounds with anticancer properties is an active field of research due to the severe side effects of platinum-based compounds currently used in chemotherapy. In the search for new agents for the treatment of cancer, unsymmetrical N2O2-tetradentate ligand (H2L1 and H2L2) and their Ni(II) and Zn(II) asymmetric complexes (NiII-L1-2 and ZnII-L1-2) have been synthesized and fully characterized. 1H NMR studies revealed that the ligands and complexes were stable in mixtures of DMSO : D2O (9 : 1). Complementary UV-Vis studies confirmed that ZnII derivatives also exhibit high stability in mixtures DMSO : buffer (6 : 4) after 24 h. Single-crystal X-ray diffraction studies confirmed the molecular structures of H2L1, H2L2, NiII-L1, and NiII-L2. At the molecular level, complexes were completely planar without significant distortions of the square-planar geometry according to τ4 parameter. Furthermore, the crystalline structures revealed non-classical intermolecular interactions of the C-H⋯O and the Ni⋯Ni type. The ligands and complexes were screened against the human osteosarcoma (MG-63), human colon cancer (HCT-116), breast cancer (MDA-MB-231) cell lines, and non-cancerous cells (L929). H2L1 and H2L2 ligands not caused cytotoxic effects at a concentration of 100 μM, while NiII-L2, ZnII-L1, and ZnII-L2 complexes induce cytotoxic effects in all cell lines. NiII-L2 was a more active complex against MG-63 (3.9 ± 1.5) and HCT-116 (3.4 ± 1.7) cell lines with IC50 values in the low micromolar range. In addition, this compound was 10-, 5-, and 11-fold more potent than cisplatin in MG-63 (39 ± 1.8), HCT-116 (17.2), and MDA-MB-231 (131 ± 18), respectively. Three complexes exhibited great selectivity for tumoral cells with SI values ranging from 1.6 to 7.4.

Exploring a new family of designer copper(II) complexes of anthracene-appended polyfunctional organic assembly displaying potential anticancer activity via cytochrome c mediated mitochondrial apoptotic pathway

The present article describes the systematic study on design and synthesis, physicochemical properties and spectroscopic features, and potential anticancer activities of a family of novel copper(II)-based designer metal complexes [Cu₂(acdp)(μ-Cl)(H₂O)₂] (1), [Cu₂(acdp)(μ-NO₃)(H₂O)₂] (2) and [Cu₂(acdp)(μ-O₂CCF₃)(H₂O)₂] (3) of anthracene-appended polyfunctional organic assembly, H₃acdp (H₃acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol). Synthesis of 1-3 was accomplished under facile experimental conditions, preserving their overall integrity in solution. The incorporation of polycyclic anthracene skeleton within the backbone of organic assembly increases lipophilicity of resulting complexes, thereby dictating the degree of cellular uptake with improved biological activity. Complexes 1-3 were characterized by elemental analysis, molar conductance, FTIR, UV-Vis absorption/fluorescence emission titration spectroscopy, PXRD and TGA/DTA studies, including DFT calculations. The cellular cytotoxicity of 1-3 when studied in HepG2 cancer cell line showed substantial cytotoxic effects, whereas no such cytotoxicity was observed when exposed to normal L6 skeletal muscle cell line. Thereafter, the signaling factors involved in the process of cytotoxicity in HepG2 cancer cells were investigated. Alteration of cytochrome c and Bcl-2 protein expression levels along with modulation of mitochondrial membrane potential (MMP) in the presence of 1-3, strongly suggested the possibility of activating mitochondria-mediated apoptotic pathway involved in halting the cancer cell propagation. However, when a comparative assessment on their bio-efficacies was made, 1 showed higher cytotoxicity, nuclear condensation, DNA binding and damage, ROS generation and lower rate of cell proliferation compared to 2 and 3 in HepG2 cell line, indicating that the anticancer activity of 1 is significantly higher than that of 2 and 3.

Ancillary-Ligand-Assisted Variation in Nuclearities Leading to the Formation of Di-, Tri-, and Tetranuclear Copper(II) Complexes with Multifaceted Carboxylate Coordination Chemistry

The self-assembly of a carboxylate-based dinucleating ligand, N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (H₃cpdp), and copper(II) ions in the presence of various exogenous ancillary ligands results in the formation of the new dinuclear complex [Cu₂(cpdp)(μ-Hisophth)]₄·2H₂isophth·21H₂O (1), trinuclear complex [Cu₃(Hcpdp)(Cl)₄] (2), and tetranuclear complex [Cu₄(cpdp)(μ-Hphth)(μ₄-phth)(piconol)(Cl)₂]·3H₂O (3) (H₂phth = phthalic acid; H₂isophth = isophthalic acid; piconol = 2-pyridinemethanol; Cl^- = chloride). In methanol-water, the reaction of H₃cpdp with CuCl₂·2H₂O at room temperature leads to the formation of 2. On the other hand, 1 and 3 have been obtained by carrying out the reaction of H₃cpdp with CuCl₂·2H₂O/m-C₆H₄(CO₂Na)₂ and CuCl₂·2H₂O/o-C₆H₄(CO₂Na)₂/piconol, respectively, in methanol-water in the presence of NaOH at ambient temperature. All three complexes have been characterized by elemental analysis, molar electrical conductivity and magnetic moment measurements, FTIR, UV-vis spectroscopy, and PXRD, including single-crystal X-ray structural analyses. The molecular structure of 1 is based on a μ-alkoxide and μ-isophthalate-bridged dimeric [Cu₂] core; the structure of 2 represents a trimeric [Cu₃] core in which a μ-alcohol-bridged dinuclear [Cu₂] unit is exclusively coupled with a [CuCl₂] species by two μ:η¹:η¹-syn-anti carboxylate groups forming a triangular motif; the structure of 3 embodies a tetrameric [Cu₄] core, with two copper(II) ions in a distorted-octahedral coordination environment, one copper(II) ion in a distorted-trigonal-bipyramidal coordination environment, and the other copper(II) ion in a square-planar coordination environment. In fact, 2 and 3 represent rare examples of copper(II)-based multinuclear complexes showing outstanding features of rich coordination chemistry: (i) using a symmetrical dinucleating ligand, trinuclear complex 2 is generated with four- and five-coordination environments around copper(II) ions; (ii) the unsymmetrical tetranuclear complex 3 is obtained by using the same ligand with four-, five- and six-coordination environments around copper(II) ions; (iii) tetracopper(II) complex 3 shows four different bridging modes of carboxylate groups simultaneously such as μ:η², μ:η¹:η¹, μ₃:η²:η¹:η¹, and μ₄:η¹:η¹:η¹:η¹, the μ₄:η¹:η¹:η¹:η¹ mode of phthalate being unprecedented. The formation of these [Cu₂], [Cu₃], and [Cu₄] complexes can be controlled by changing the exogenous ancillary ligands and pH of the reaction solutions, thus allowing an effective tuning of the self-assembly. The magnetic susceptibility measurements suggest that the copper centers in all three complexes are antiferromagnetically coupled. The thermal properties of 1-3 have been investigated by thermogravimetric and differential thermal analytical (TGA and DTA) techniques, indicating that the decomposition of all three complexes proceeds via multistep processes.

Design, Synthesis, and Herbicidal Activity of Thioether Containing 1,2,4-Triazole Schiff Bases as Transketolase Inhibitors

Transketolase (TK) represents a potential target for novel herbicide development. To discover novel TK inhibitors with potency against resistant weeds, 36 thioether compounds containing 1,2,4-triazole Schiff bases were designed and synthesized for herbicidal activity evaluation. The results demonstrated that compounds 5av and 5aw provided excellent weed control with inhibition of over 90% against the tested weeds, even at concentrations as low as 100 mg/L in vitro. In addition, compounds 5av and 5aw exhibited higher postemergence herbicidal activity than all of the positive controls against the tested weeds at 50-90 g [active ingredient (ai)]/ha in a greenhouse, while being safe for crops of maize and wheat at 90 g (ai)/ha. Fluorescent binding experiments of At TK indicated that compounds 5av and 5aw had strong TK inhibitory activity and could tightly bind with the enzyme At TK. Also, molecular docking analyses revealed that the structures of compounds 5av and 5aw were suitable for TK inhibitory activity. Taken together, these results suggested that compounds 5av and 5aw were promising herbicide candidates for weed control in wheat and maize fields targeting TK.

Potential Third-Order Nonlinear Optical Response Facilitated by Intramolecular Charge Transfer in a Simple Schiff Base Molecule: Experimental and Theoretical Exploration

A Schiff base, namely, 4-[(2-hydroxy-3-methoxybenzylidene) amino] benzoic acid (L1), has been synthesized by the condensation reaction. It has been characterized by Fourier transform infrared spectroscopy , UV-vis spectroscopy, single-crystal X-ray diffraction, and DFT/B3LYP calculations. Single-crystal X-ray crystallographic analysis revealed that L1 exists in the zwitterionic (N-H···...O) form. The supramolecular interactions were investigated by Hirshfeld surface analysis. In addition, third-order nonlinear optical (NLO) properties of L1 were also investigated. The nonlinear refractive index (n2), nonlinear absorption coefficient (β), and the third-order NLO susceptibility (χ(3)) have been estimated at different concentrations and at different laser powers using close and openaperture Z-scan data. The values of the parameters were found to be varying almost linearly with concentration and power. The present study revealed the utility of the material for various optoelectronic devices such as optical switches, optical data storage devices, and optical sensors. The optical limiting study reveals that this material can also be exploited as an instrument protector from unwanted laser illumination. Furthermore, the NLO behavior of L1 has also been studied by B3LYP/6-311++G(d,p) results.

Interplay of weak noncovalent interactions in alkoxybenzylidene derivatives of benzohydrazide and acetohydrazide: a combined experimental and theoretical investigation and lipoxygenase inhibition (LOX) studies

Three hydrazide-based Schiff bases have been synthesized and characterized by IR, UV-vis and X-ray diffraction methods. A detail analysis of intermolecular interactions has been performed by Hirshfeld surface analysis and DFT calculations.

Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands

Chemistry of Schiff base (SB) ligands began in 1864 due to the discovery made by Hugo Schiff (Schiff, H., Justus Liebigs Ann. der Chemie 1864, 131 (1), 118-119). However, there is still a vivid interest in coordination compounds based on imine ligands. The aim of this paper is to review the most recent concepts on construction of homo- and hetero-oligonuclear Schiff base coordination compounds narrowed down to the less frequently considered complexes of platinum group metals (PGM). The combination of SB and PGM in oligonuclear entities has several advantages over mononuclear or polynuclear species. Such complexes usually exhibit better electroluminescent, magnetic and/or catalytic properties than mononuclear ones due to intermetallic interactions and frequently have better solubility than polymers. Various construction strategies of oligodentate imine ligands for coordination of PGM are surveyed including simple imine ligands, non-innocent 1,2-diimines, chelating imine systems with additional N/O/S atoms, classic N2O2-compartmental Schiff bases and their modifications resulting in acyclic fused ligands, macrocycles such as calixsalens, metallohelical structures, nano-sized molecular wheels and hybrid materials incorporating mesoionic species. Co-crystallization and formation of metallophilic interactions to extend the mononuclear entities up to oligonuclear coordination species are also discussed.

Intermolecular interactions in antipyrine-like derivatives 2-halo-N-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)benzamides: X-ray structure, Hirshfeld surface analysis and DFT calculations

Based on experimental and computational data, a complex network of intermolecular interactions has been rationalized for antipyrine compounds.