Octahedral Geometry Research Articles

Synthesis, Characterization, Cytotoxicity, Biological Evaluation, DFT Calculations, and Molecular Docking of a Novel Schiff Base and Its Pt(IV) Complex

ABSTRACTA novel Schiff base ligand derived from 1,2,4‐triazole‐3‐thione was synthesized and complexed with platinum (IV) ion to enhance its bioactivity. Characterization techniques, including FTIR, NMR, UV‐Vis, and mass spectrometry, confirmed the formation of Schiff base molecule and revealed that its Pt(IV) complex has an octahedral geometry. The antibacterial and antifungal activity of the synthesized compounds was evaluated against Staphylococcus epidermidis, Pseudomonas aeruginosa, Candida albicans, and Aspergillus flavus, with the metal complex outperforming the ligand. The antioxidant properties were evaluated using a DPPH assay, with the Pt(IV) complex demonstrating superior radical‐scavenging ability. Cytotoxicity studies via MTT assays on MCF‐7 breast cancer cells showed dose‐dependent reductions in cell viability, with the Pt(IV) complex inducing enhanced antiproliferative effects compared with the ligand. DFT calculations were performed to investigate the electronic properties of the compounds, and molecular docking studies were conducted against the alpha estrogen receptor (PDB ID: 3ERT) to predict their binding affinities. The results demonstrated that the Pt(IV) complex exhibited higher biological activity than the free ligand, suggesting its potential as an effective therapeutic agent.

The relative impact of ligand flexibility and redox potential on the activity of Cu superoxide dismutase mimics.

Two copper(II) complexes, [Cu(salbn)] and [Cu(py2bn)(OAc)]ClO4, formed with the Schiff-base ligands 1,4-bis(salicylidenamino)butane (H2salbn) and 1,4-bis(pyridin-2-ylmethyleneamino)butane (py2bn), have been prepared and characterized in solid state and in solution, and their ability to catalyse the dismutation of O2˙- has been evaluated in homogeneous medium and immobilized in a mesoporous matrix. The crystal structures show that [Cu(salbn)] possesses a distorted square-planar geometry, while [Cu(py2bn)(OAc)]ClO4 adopts a cis-distorted octahedral geometry. The two complexes experience structural changes in solution, and different spectroscopies were used to examine them. Moreover, their redox potentials are strongly affected by the solvent. In water, the complexes exist as [Cu(salbn)(H2O)] and [Cu(py2bn)(H2O)]2+ with Cu(II)/Cu(I) reduction potential at -361 mV and -229 mV, respectively, well different from redox potentials measured in acetonitrile. Although with a more unfavourable redox potential, [Cu(salbn)(H2O)] reacts with O2˙- faster than [Cu(py2bn)(H2O)]2+, with catalytic rate constants of 3.3 × 107 and 2.9 × 107 M-1 s-1, respectively, at pH = 7.8. Both complexes exhibit higher superoxide dismutase activity than the analogues with a shorter central alkyl chain. The observed catalytic rates essentially correlate with the ligand flexibility, rather than with the redox potential, which is also supported by the slower O2˙- dismutation rate when the complexes are immobilized by encapsulation into the channels of well-ordered mesoporous SBA-15 silica where the pore modifies the complex structures and restraints the ligand rearrangement.

Folded pseudochiral Fermi surface in 4Hb-TaSe2 from band hybridization with a charge density wave

Abstract Stacking of strongly-correlated 2D materials is opening the possibility to demonstrate novel electronic or magnetic ordering phenomena. In this regard the intrinsic polytypism of tantalum dichalcogenides has emerged as a platform to generate clean and controllable material interfaces. Here, we report on the Fermi surface of 4Hb-TaSe2, a polytype which consists of alternately stacked layers with octahedral (T) and trigonal prismatic (H) coordination of tantalum in the Se-Ta-Se layers. The material is known to host a charge density wave (CDW) phase with star clusters in the T-layers, intercalated by metallic H-layers, but its momentum resolved electronic structure remains undetermined. Using selective area angle resolved photoemission spectroscopy on the T termination combined with ab initio calculations, we unveil a finely structured Fermi surface arising from band folding in the reconstructed Brillouin zone caused by the CDW star clusters. The star-shaped Fermi surface is rotated away from the high-symmetry directions of the normal phase, and exhibits pseudochirality. Theoretical analysis supports the metallic nature of the system and interlayer interactions leading to hybridization. The work provides a detailed overview on the impact of band hybridization with the CDW on the Fermi surface of a material for new phases of quantum matter.

New Ru(III) 2,6-Bis(2-benzimidazolyl)Pyridine Complexes Bearing p-sub-Benzyl Thiosemicarbazones Schiff Base: Synthesis, Characterization, DNA Binding and Anti-cancer Activity.

The six mononuclear Schiff's base Ru(III) complexes viz., [Ru(BZP)(LA)2].2NO3 (MRA), [Ru(BZP)(LB)2].2NO3 (MRB), [Ru(BZP))(LC)2].2NO3 (MRC), [Ru(BZP))(LD)2].2NO3 (MRD), [Ru(BZP)(LE)2].2NO3 (MRE) and [Ru(BZP)(LF)2].2NO3 (MRF), [(BZP = 2,6-bis(2-benzimidazolyl)pyridin], were synthesized using of p-sub-benzylthiosemicarbazones (BTS) [(Sub = 4-NO2 (LA), 4-N(CH3)2 (LB), 4-Cl (LC), 4-OCH3 (LD), 4-OCH2Ph (LE), 4-OH (LE)] and 4-OH (LF), as an ancillary ligand. The thiosemicarbazones ligands (LA-LF) were obtained by the condensation of p-substituted benzaldehyde and thiosemicarbazide. These complexes were characterized by elemental analysis, IR, ESR, ESI-MS, electronic absorption spectroscopy. The geometry was optimized by theoretical calculation using DFT and structure reveals that MRA-MRF adopt octahedral geometry. Further, the complexes were examined for anticancer against Leukemia cancer cell line K562 and shown significant responses to these cells. Moreover, DNA binding studies were studied with all complexes MRA-MRF and the binding constant (Kb) were found 1.54 x 104, 2.87 x 104, 1.67 x 104, 1.98 x 104 and 1.59 x 104, respectively. It was found that DNA binds in intercalation mode which is also validate by the Docking studies.

Zhonghongite, Cu29(As,Sb)12S33, a new mineral from the high-sulfidation vein of Jiama porphyry system, Tibet, China

Abstract Zhonghongite (IMA2023-046), ideally Cu29(As,Sb)12S33, is a new mineral discovered in the high-sulfidation vein of the Jiama deposit (E 91°45′, N 29°42′), southern Tibet, China. It forms complex intergrowths with watanabeite and tennantite-tetrahedrite, creating veined or massive aggregates ranging from millimeters to centimeters. Single crystals of zhonghongite are anhedral, and their sizes range from several micrometers to ∼100 μm. The mineral is gray with a black streak and metallic luster. It is brittle, with uneven fractures, and has a calculated density of 4.925 g/cm3. The average values of electron microprobe analyses (wt%) are: Cu 42.19, As 11.11, Sb 16.09, S 25.45, Hg 3.73, Mn 0.67, and Te 0.28. The empirical formula, based on 33 sulfur apfu, is (Cu27.60Hg0.77Mn0.51Fe0.07Ag0.02)Σ28.97(As6.16Sb5.49Te0.09)Σ11.74S33. In zhonghongite, the substitution of Sb for As is limited, with the atomic ratio of As/(As+Sb) ranging from 0.457 to 0.629. Hg, Mn, and Fe, with minor Cu, are divalent and serve for charge balance. Zhonghongite is orthorhombic, space group F2mm (42), a = 10.37741(5) Å, b = 14.69821(9) Å, c = 36.7645(2) Å, and V = 5607.66(5) Å3. The crystal structure was solved and refined by single-crystal X-ray diffraction with a final R1 = 0.0235 for 27 028 (2467 unique) reflections. It is composed of individual AsS3 tripyramids and clustered As4S7 tripyramids, CuS4 tetrahedra, and CuS3 planar triangles, connected through corner S atoms in tetrahedral coordination and octahedral coordination with Cu and/or As. The structure is a derivative of a tetrahedrite-type structure. Zhonghongite was formed under high-temperature conditions and is classified as an intermediate-sulfidation state mineral.

Diamagnetic, binary Sulfide Ba3Sc2S6 – with Infinite [ScS6/2] Chains as structural Element

The ternary sulfide, Ba3Sc2S6, was synthesized by the conventional high-temperature solid-state technique in an inert atmosphere, utilizing sealed silica ampules with low internal pressure of Ar gas. The crystal structure was determined by single crystal X-ray diffraction and can be described by a trigonal crystal lattice with rhombohedral symmetry, Rc (No. 167), with powder diffraction unit cell parameters a = 12.0402(1) Å and c = 13.3893(2) Å. The compound crystallizes with the K4CdCl6-type structure, which has been used to describe homologous sulfides. This crystal structure shares features with the 2H perovskites but contains infinite 1D chains, Niggli notation , consisting of alternating, distorted octahedra and trigonal prisms connected by face-sharing. Ba3Sc2S6 is diamagnetic, as determined from magnetic susceptibility measurements. UV-Vis spectroscopy data suggest a direct bandgap of about 2.9 eV. Further, DFT calculations reveal a band gap of about 1.8 eV and 2.9 eV using the PBE and the HSE06 functional, respectively, of which the latter agrees perfectly with UV-Vis observations.

Berndlehmannite: A new V-bearing sulfide mineral from the black shale-hosted Zhongcun vanadium deposit, South China

Abstract Berndlehmannite, Cu(CrV)S4, is a newly identified V-bearing sulfide mineral discovered in the black shale-hosted Zhongcun vanadium deposit, South China. It is abundant in a phosphatic nodule-rich layer and is commonly mineralogically associated with roscoelite, quartz, and framboidal pyrite. Berndlehmannite exhibits black color in hand specimens with a black streak and it comprises subhedral grains that vary in size from 20 to 120 μm. The mineral is opaque with a cream-colored polished surface under reflected light. It has a Mohs hardness of 3½ with a {111} perfect cleavage, and its calculated density is 4.17 g·cm−3. Berndlehmannite is cubic, with space group Fd-3m; the unit-cell parameters determined from powder data are a = 9.8585(22) Å, V = 958.1(6) Å3, and Z = 8. The unit-cell parameters by single-crystal X-ray diffraction are a = 9.8374(2) Å, V = 952.01(6) Å3, Z = 8, and the final value of R is 0.015. The mineral is a member of the carrollite subgroup within the thiospinel group, featuring (Cr,V)S6 in octahedral coordination and CuS4 in tetrahedral coordination. The calculated empirical formula from electron-probe microanalysis is (Cu+0.99Zn0.02)Σ1.01(Cr3+0.87V4+1.00Sb0.07As0.04)Σ1.98S4.01 with an average V content of 17.0 wt%. It has the highest V component compared to other V-bearing minerals in black shales and may provide new insight into the vanadium enrichment mechanism in black shales. Berndlehmannite is named to honor Bernd Lehmann (1950- ), Professor emeritus of Economic Geology at Technische Universität Clausthal, Germany.

Synthesis, Characterization, and Toxicity Studies of Azo Dye Ligand for Metal Assessment in Different Brands of Lipsticks in Iraq

This research project focuses on the synthesis and characterization of a novel azo ligand, 4- CMBP, derived from 2-amino-6-methylbenzothiazole, and its complexes with Co(III) and Ni(II) ions. The study aims to investigate the structural and biological properties of the ligand and its complexes, with a particular emphasis on their potential applications in environmental and health sectors. The ligand and its complexes were characterized using techniques such as melting point measurements, nuclear magnetic resonance, mass spectrometry, Fourier-transform infrared spectroscopy, UV-Vis spectroscopy, elemental analysis, atomic absorption spectroscopy, molar conductivity, and magnetic susceptibility measurements. Biological activities were evaluated through the removal percentages of Co(III) and Ni(II) from eleven popular brands of lipsticks in the Iraqi market, antimicrobial screening against bacteria and fungi, in silico ADMET predictions, and anticancer activity tests in human liver cancer cell lines. Characterization confirmed the successful synthesis of the ligand and the formation of octahedral complexes with Co(III) and Ni(II) ions. The analysis revealed nickel concentrations ranging from 0.36 to 3.08 ppm, with varying safety implications. Antimicrobial screening showed promising activity, and in silico predictions indicated favorable oral bioavailability. The ligand and its complexes exhibited significant anticancer activity against liver cancer cell lines. The study successfully synthesized and characterized the azo ligand 4-CMBP and its metal complexes, highlighting their intriguing geometries and promising biological activities, with potential applications in environmental remediation, antimicrobial agents, and anticancer therapeutics.

New Layered Boride NiPtB2-x (x = 0.5) with a Ternary Derivative Structure of MoB.

A novel ternary boride, NiPtB2-x (x = 0.5), was obtained by argon-arc melting of the elements followed by annealing at 750 °C. It exhibits a new structure type with the space group Imma (a = 2.9835(3) Å, b = 3.0470(3) Å, c = 15.3843(3) Å; Z = 4; single-crystal X-ray data) and displays distinct layers of condensed [BNi6] and [BPt6] (and [Pt6]) trigonal prisms with mutually perpendicular axes. Atoms of Pt and Ni from adjacent layers interlink to form empty tetragonal pyramids and tetrahedra. Two boron atom positions form two orthogonal zigzag chains; however, one boron position exhibits a partial boron occupancy. Considering B-deficiency, the platinum boride substructure in NiPtB2-x quantitatively corresponds to a trigonal prismatic slab in the Pt2B structure, while the nickel boride partial structure is consistent with the CrB-type NiB binary. Cell parameters and atomic coordinates of NiPtB2-x and Pt2B were refined in the scope of generalized gradient approximation. Chemical bonding analysis by means of the electron localizability approach, supported by Bader charge analysis, reveals a strong electron contribution of Ni atoms for stabilization of the boron zigzag chains, wherein boron atoms are bonded covalently. Bonding within the platinum boride partial structures in the studied compounds varies depending on the atom coordination of boron: from covalent in both the NiPtB2-x structure and trigonal prismatic slabs in Pt2B to mixed metallic with covalent contributions in [BPt6] octahedra in Pt2B. Electrical resistivity measurements characterize NiPtB2-x as a metal with no phase transitions in the temperature range from 2 to 300 K, in concord with electronic band structure calculations and specific heat measurements. The compound is characterized by a positive Hall coefficient at 20 K. This work unveils a new elemental space on realizing novel layered boride structural arrangements and provides a reference for future experiments.

Novel azo-based benzimidazole Schiff base ligand and its Co(II), Ni(II) Cu(II) complexes: computational and biological studies

A novel azo-based benzimidazole Schiff base ligand (FDSBI) was synthesized by the condensation reaction of 2-aminobenzimidazole with 4-fluorodiazenyl-salicylaldehyde. The ligand and its metal complexes were studied by elemental analysis, spectral analysis, and magnetic susceptibility measurement. The absorption spectra of the complexes evidence octahedral geometry. The structural properties of the Schiff base and its metal complexes were also proved by the treatment of density functional theory (DFT) calculation. Thermogravimetric analysis proved the coordinated and lattice water molecules. Cyclic voltammetry technique has been used to study the redox behavior of the copper (II) complex. The in vitro antibacterial and antifungal activities of the Schiff base and its coordinated compounds were screened against bacterial species (Staphylococcus aureus, Salmonella typhi, Escherichia coli, Bacillus subtilis) and Fungi (Candida albicans, Aspergillus niger) using well diffusion method. The obtained results have suggested that the metal complexes showed significant biological activity than ligand. The in vitro antioxidant activity of both the ligand and its metal (II) complexes was assessed through the utilization of the DPPH stable free radical. The result shows that the ligand possesses better antioxidant properties than metal (II) complexes. The second harmonic generation efficiency was analyzed for the ligand, demonstrating its potential application in nonlinear optical material.

Exploring the Antiplasmodial and Antimicrobial Potential of Transition Metal(II) Complexes Bearing Hydrazone Ligands: Insights From Molecular Docking and ADMET Studies

ABSTRACTIn the search of antiplasmodium agents, the hydrazone ligands, that is, (2‐hydroxy‐5‐nitrobenzylidene)benzo[b]thiophene‐2‐carbohydrazone (H2L1)/(3,5‐dichloro‐2‐hydroxybenzylidene)benzo[b]thiophene‐2‐carbohydrazone (H2L2) and their Co(II), Ni(II), Cu(II), and Zn(II) metal complexes were synthesized. All the compounds were well characterized by wide range of spectral and physical techniques, that is, FT‐IR, 1H NMR, 13C NMR, ESR, mass spectrometry, UV‐Vis, XRD, SEM‐EDAX, molecular conductivity, and thermal studies (TG‐DTA). The coordination by O‐phenolic, O‐enolic, and N‐azomethine donor atoms and three aqua ligands to metal(II) ions was confirmed by various physicochemical techniques, affirming the octahedral geometry of the metal complexes. Biological evaluation of the synthesized compounds involved assessing by their antiplasmodium potency utilizing microassay and antimicrobial activities using serial dilution technique. The Cu(II) (5, 6) and Zn(II) (9, 10) metal complexes significantly inhibited the growth of parasitic ailments caused by Plasmodium falciparum 3D7 strain and also exhibited remarkable antimicrobial effectiveness against diseases caused by microbes comparable with the standard drugs (ciprofloxacin and fluconazole). Moreover, theoretical study including molecular docking was employed utilizing 3,5‐dihydroxy‐2‐naphthoic acid (PDB:1U5A) P. falciparum protein receptor to validate the antiplasmodium effectiveness of the most potent H2L1 hydrazone ligand (1) and their complexes (3–6). This analysis indicated that the docked compounds could serve as a promising drug candidate for malaria. whereas the ADMET profiling authenticated the drug‐like features of compounds 1 and 3–6. Thus, this research provides fresh perspectives for in vivo study of the compounds with minor developments.

Artificial Neural Network-Based Validation, DFT, Thermal and Biological Evaluation of 4-Aminoantipyrine-Derived Ru(III) Complexes.

New methodologies have been evaluated for validating analytical characterization with artificial neural networks (ANNs). Compared to previous machine learning models, these provide more accurate and automated results with high testing accuracy. The Schiff base ruthenium complexes used in the proposed study were synthesized using 4-aminoantipyrine derivatives. 4-Aminoantipyrine is a biologically active pharmacophore. The geometry of the complexes was confirmed by IR, electronic, and magnetic measurements. XRD analysis pointed out the nanocrystalline behavior of the chelates. The molecular structures have been optimized using DFT calculations. The ruthenium complexes are one of the main chemotherapeutic agents in anticancer therapy over platinum drugs due to a wide range of peculiarities. Complexes exhibit octahedral geometry as confirmed by magnetic measurements exhibiting more biological activity. The complexes are redox active depicting high biological potency. The Ru chelates also display high photocatalytic efficiency. The chelates also adhere to Lipinski's rule of five as evidenced from mole inspiration calculations. Among the chelates, RuL3 exhibits high anticancer potency suggesting a valuable candidate for the treatment of cancer. RuL5 has high antibacterial efficiency, and RuL4 complex possesses high antifungal activity. The chelates may serve as potential antimicrobial agents.

An unusual chiral-at-metal mechanism for BINOL-metal asymmetric catalysis

Chiral binaphthols (BINOL)-metal combinations serve as powerful catalysts in asymmetric synthesis. Their chiral induction mode, however, typically relies on multifarious non-covalent interactions between the substrate and the BINOL ligand. In this work, we demonstrate that the chiral-at-metal stereoinduction mode could serve as an alternative mechanism for BINOL-metal catalysis, based on mechanistic studies of BINOL-aluminum-catalyzed asymmetric hydroboration of heteroaryl ketones. Theoretical calculations reveal that an octahedral stereogenic-at-metal aluminum alkoxide species is the most stable species within the reaction system, and also is the catalytic relevant intermediate, promoting the stereo-determining hydroboration reaction through a ligand-assisted hydride transfer mechanism rather than the conventional hydroalumination mechanism. These computations reproduce the experimental selectivities and also rationalize the stereoinduction mechanism, which arises from the aluminum-centered chirality induced by chiral BINOL ligands during diastereoselective assembly. The reliability of the proposed mechanism could be verified by the single-crystal X-ray diffraction characterization of the octahedral aluminum alkoxide complex. Additional NMR and Electronic Circular Dichroism (ECD) experiments elucidated the behavior of the hexacoordinated aluminum alkoxide in the solution phase. We anticipate that these findings will extend the applicability of BINOL-metal catalysis to a broader range of reactions.

Understanding non-reducible N2 in the mechanism of Mo-nitrogenase.

In my proposed mechanism of Mo-nitrogenase there are two roles for separate N2 molecules. One N2 diffuses into the reaction zone between Fe2 and Fe6 where a strategic gallery of H atoms can capture N2 to form the Fe-bound HNNH intermediate which is then progressively hydrogenated through intermediates containing HNNH2, NH and NH2 entities and then two NH3 in sequence. The second N2 can be parked in an N2-pocket about 3.2 Å from Fe2 or bind end-on at the exo coordination site of Fe2. This second N2 is outside the reaction zone, not exposed to H atom donors, and so is 'non-reducible'. Here density functional calculations using a 485+ atom model describe the thermodynamics for non-reducible N2 moving between the N2-pocket and the exo-Fe2 position, for the resting state and 19 intermediates in the mechanism. The entropy component is estimated and included. The result is that for all intermediates with ligation by H or NHx at the endo-Fe2 position the free energy for association of non-reducible N2 at exo-Fe2 is negative. There remains some uncertainty about the status of exo-Fe2-N2 during the step in which H2 exchanges with the incoming reducible N2, where at least two unbound molecules are present. At Fe2 it is evident that attainment of octahedral coordination stereochemistry dominates the binding thermodynamics for non-reducible N2. Possibilities for experimental support of these computational conclusions are discussed.

Experimental Investigation of Cadmium Isotope Fractionation during Adsorption on Montmorillonite and Kaolinite.

Cadmium (Cd) isotopes have recently emerged as novel tracers of Cd sources and geochemical processes. Widespread clay minerals play a key role in Cd migration due to their strong adsorption capacity, but the mechanism of Cd isotope fractionation during adsorption onto clay minerals is poorly understood. Here, we experimentally investigated the adsorption mechanisms of Cd on montmorillonite (2:1) and kaolinite (1:1) by using extended X-ray absorption fine structure (EXAFS) spectroscopy. Our results show that lighter Cd isotopes are preferentially adsorbed on clay minerals, with Δ114/110Cddissolved-adsorbed values of 0.03 ± 0.02‰ for montmorillonite and 0.03 ± 0.03‰ for kaolinite. These values are independent of the pH, initial Cd concentration, and ionic strength. EXAFS indicate that the adsorbed Cd forms octahedral outer-sphere surface complexes with an average Cd-O bond length of 2.25-2.26 Å, identical to Cd-O bonding environment in the Cd(NO3)2 solution. Our results demonstrate that the extent of Cd isotope fractionation is constrained by structural changes (including the bond length and coordination number) in surface complexes. These findings suggest that Cd adsorption on clay minerals has a minimal impact on the variability of Cd isotopic compositions in soils and sediments, implying that variations in Cd isotope ratios in soils and sediments primarily reflect changes in Cd sources.

Solvent-Driven Self-Assembly of Discrete Ni(II)-Azide Complexes: Unraveling Unusual Behavior in Mimicking Jack Bean Urease.

The well-known inhibitory strength of 3d metal Schiff base complexes against urease enzymes has long been acknowledged, but their untapped potential to act as ureolytic mimics of active metallobiosites remained unexplored. To break the new ground, we present pyrrolidine-based mononuclear Ni(II)-azide complex 1 {[NiL(HL)(N3)]·1.5(H2O)} using the N,N,O donor ligand, namely (E)-4-bromo-2-(((2-(pyrrolidin-1-yl)ethyl)imino)methyl)phenol. The initial spectrophotometric analysis showed catalytic inefficiency in methanol since it undergoes unexpected ligand dissociation to generate a new octahedral nickel complex (INC), catalyzing condensation to form BrTz. Notably, complex 1 was subjected to self-assembly in DMF into UV-responsive tetranuclear complex 2 {[NiL(H2O)(N3)]4} and structurally characterized using single-crystal XRD. Furthermore, complex 2 was utilized as a functional urease model, demonstrating catalytic efficiency in urea hydrolysis with the estimation of the liberated ammonia and CO2 in MeOH. The mechanistic pathway was speculated to proceed via the hydrogen bonding of urea with bridging azides, facilitating coordination with the nickel center. Moreover, it significantly inhibited hydrolysis in the presence of external NBPTO [N-(n-butyl)thiophosphoric triamide], guanidine, etc., revealing its potential for precise catalytic control. To the best of our knowledge, this is the first report of the urease-mimicking activity of the tetranuclear Ni(II) complex and elucidating the mechanism through detailed chemical analysis.

Sustainable synthesis of benzimidazole-based Schiff base using reusable CaAl2O4 nanophosphors catalyst: Insights into metal(II) complexes and DNA interactions

This article presents a new and facile method for the synthesis of Schiff base compounds with a benzimidazole group using a low-cost and reusable calcium aluminate nanophosphorus catalyst (CaAl2O4). This approach avoids harmful solvents and reactants, supporting a more environmentally friendly synthesis process. The catalyst maintained its activity and heterogeneity over four cycles with minimal loss of efficiency. The synthesis process was straightforward and eliminated the need for column chromatography. The Schiff base ligand (HL=(E)-N-((6-(thiophen-2-yl)pyridin-2-yl)methylene)-1H-benzo[d]imidazol-2-amine)) was synthesized by the reaction of 6-(thiophen-2-yl)pyridine-2-carbaldehyde with 1H-benzimidazole-2-amine. Subsequently, metal(II) complexes of Co(II), Ni(II), and Cu(II) were prepared using this ligand. Structural analysis of both the ligand and its metal complexes was carried out using various physicochemical and spectroscopic methods. Ni(II) and Co(II) complexes were found to adopt an octahedral geometry, while the Cu(II) complex exhibited a square-planar structure. Binding studies with calf thymus DNA (CT-DNA) at pH 7.2 were performed using UV-visible spectroscopy, viscosity measurements, and thermal denaturation studies and showed that the metal complexes intercalate into the DNA and produced a distinct binding pattern. Molecular docking simulations with AutoDock Vina provided insights into the interaction of these complexes with the B-DNA dodecamer. Furthermore, the ligand and its metal complexes showed UV-visible photonuclease activity against pUC19 DNA. Agarose gel electrophoresis showed that the metal complexes exhibit photoinduced nuclease activity, confirming their ability to cleave DNA upon exposure to light.

Structural characterization of pyruvic oxime dioxygenase, a key enzyme in heterotrophic nitrification.

Nitrification by heterotrophic microorganisms is an important part of the nitrogen cycle in the environment. The enzyme responsible for the core function of heterotrophic nitrification is pyruvic oxime dioxygenase (POD). POD is a non-heme, Fe(II)-dependent enzyme that catalyzes the dioxygenation of pyruvic oxime to produce pyruvate and nitrite. To analyze the catalytic mechanism of POD, the crystal structure of POD from Alcaligenes faecalis (AfPOD) was determined at 1.76 Å resolution. The enzyme is a homotetramer, and the subunit structure is homologous to those of class II aldolases, in particular, a zinc-dependent L-fuculose-1-phosphate aldolase. The active site of the subunit is located at the bottom of a cleft formed with an adjacent subunit. The iron ion at the active site is coordinated by three histidines and three water molecules in an octahedral geometry. The putative oxygen tunnel was connected between the active site and the central cavity of the tetramer. The N-terminal region of AfPOD, which is essential for catalytic activity, is disordered in the crystal. Structure prediction with AlphaFold2 combined with mutational experiments suggested that the disordered N-terminal region adopts an α-helix conformation and participates in the formation of the active site. The catalytic mechanism of the dioxygenase reaction by POD is discussed on the basis of the molecular docking model.IMPORTANCEOur knowledge of nitrification has increased considerably in recent decades with the discovery of new nitrifying microorganisms and the characterization of their biochemical processes. Some heterotrophic bacteria and fungi are known to show nitrification activities, but the molecular mechanisms have been poorly understood. Here, we performed a structural characterization of pyruvic oxime dioxygenase (POD), a key enzyme in heterotrophic nitrification that produces nitrite from ammonia using pyruvic oxime as an intermediate. Structural and enzymatic analyses revealed that POD is a unique dioxygenase with features such as an aldolase backbone, an N-terminal α-helix, and an oxygen tunnel. Our results provide insights not only into the molecular mechanisms but also into the design of specific inhibitors of heterotrophic nitrification.

Influence of Iodine Substitutions on the Photophysical Properties of Rhenium(I) Tricarbonyl Complexes With Pyridine Schiff Base (PSB‐IHB)

ABSTRACTThis theoretical investigation aims to evaluate the influence of iodine substitutions on the phenolic moiety of the pyridine Schiff bases harboring an intramolecular hydrogen bond (PSB‐IHB) ancillary ligand within the monocationic. fac‐[Re(CO)3(N,N)(PSB‐IHB)]+ architecture on photophysical properties, particularly emission range. Optimized structures of two Re(I) tricarbonyl complexes (C1 and C2) were analyzed, revealing a distorted octahedral coordination geometry. Geometric parameters were compared with experimental data from analogous complexes. NBO analysis confirmed the presence of intramolecular hydrogen bonds (IHBs) in both singlet and triplet states, providing significant stabilization. Theoretical calculations predicted three distinct absorption bands for all complexes in dichloromethane, indicating substantial electronic delocalization between the pyridinic and phenolic rings via the azomethine group. These findings underscore the crucial role of delocalization and donor–acceptor interactions in stabilizing Re(I) tricarbonyl complexes and their impact on photophysical properties. Emissions calculated for the C1 and C2 complexes were observed within the range of 632–643 nm. The presence of IHBs was found to be essential for modulating photophysical properties, with emissions attributed to ligand‐to‐ligand charge transfer transitions.

Bis{µ-(2,2′-bipyridine-1κ2N,N′)-(6,6′-dicarbonyl-1κ2O,O′:2κO′)bis(N,N-diethylthioureato-2κS)}(acetato-1κO)(µ-acetato-1κO:2-κO′)(methanol-2κO)thoriumnickel

Reactions of 2,2′-bipyridine-6,6′-dicarbonyl-bis(N,N-diethylthiourea), H2Lbipy, with a mixture of thorium nitrate hydrate and nickel acetate hydrate in methanol with NEt3 as a supporting base yield brown single crystals of the bimetallic complex [ThNi(Lbipy)2(CH3COO)2(MeOH)]. Two 2,2′-bipyridine-centered bis(aroylthioureato) ligands connect the metal atoms in a way that the thorium atom is coordinated by two O,N,N,O donor atom sets, while the nickel atom establishes two S,O chelate rings in its equatorial coordination plane. The metal atoms are connected by a bridging acetato ligand, and their coordination spheres are completed by one methanol ligand (nickel) and a monodentate acetato ligand (thorium). A distorted octahedral coordination environment is established around the Ni2+ ion, while the Th4+ ion is in first approximation a 10-coordinate with a diffusely defined coordination polyhedron.