Complexes 2c Research Articles

Alkylaluminium complexes supported by Schiff base as pre-catalysts in hydroboration of alkynes and nitriles

Dinuclear Schiff base aluminium complexes (C1, C2) were synthesized from salicylaldehyde derivatives and 2-aminopyridine. Complexes C1 and C2 were characterized by NMR and single-crystal X-ray diffraction. Subsequently, the catalytic activity of C1 as a pre-catalyst for the hydroboration of alkynes and nitriles was investigated. It exhibited good functional group tolerance towards both terminal alkynes and nitriles under solvent-free and low-load conditions. The potential mechanism for the C1-catalyzed reaction of alkynes and nitriles with HBpin are proposed by the NMR spectroscopy of the intermediates.

Unveiling the therapeutic potential of organotellurium(IV) Schiff base complexes through structural elucidation, antimalarial, antioxidant and antimicrobial studies

Infectious diseases have long been a formidable adversary to human health and well-being, presenting a persistent global challenge with far-reaching implication for individuals, communities and societies at large. Thus, with the aim of a combating agent against malarial and oxidant causing ailments, the newly synthesized Organotellurium(IV) complexes with a hydroxynaphthaldehyde Schiff base ligand are proposed in the present research. The structures of the complexes were established through various physical and spectral analysis. The weak electrolytic (8.77 to 35.08 ohm−1 cm2 mol−1) and crystalline nature of the compounds were demonstrated by molar conductivity and TGA, respectively. The ligand and complexes (7a-7f) shows molecular ion peaks at m/z 458.3563, 726.1039, 713.6978, 727.6179, 799.4780, 771.3178 and 799.3978 amu which were well consistent with their formula, revealing formation of compounds. The shifting of ligand's azomethine peak (7.74 ppm) and disappearance of naphthyl hydroxyl proton (12.28 ppm) in 1H NMR spectra confirmed the chelation of ligand with metal ion in proposed manner. In the FT-IR spectra, the complexation of ligand with metal ion was confirmed by disappearance of hydroxyl group (3355 cm−1) band and shifting of C = N (1245 cm−1) and CO (1632 cm−1) band whereas appearance of Te-O (of 285–293 cm−1) and Te-N (458–467 cm−1) bands, revealed the bonding of metal with metal and octahedral nature of the complexes. Optimized structures, HOMO-LUMO energies and associated chemical reactivity descriptors of the compounds were computed by DFT calculations. The in vitro studies demonstrate that the complexes 7c (1.06 ± 0.11 μM) and 7f (1.22 ± 0.05 μM) exhibited moderate inhibition of the Plasmodium falciparum 3D7 strain, complexes 7a (100.96 ± 0.32 μg/mL) and 7d (96.32 ± 0.40 μg/mL) demonstrated the highest free radical quenching ability. Complex 7c displayed the highest antibacterial actions, whereas 7f exhibited the highest antifungal actions against the tested pathogens. Molecular docking and ADMET studies demonstrated enhanced binding affinity of the complexes compared to the Schiff base and their drug-like qualities.

Synthesis and structural characterization of picolinamide and thiol chelated Pt(II) complexes: Their kinetics & mechanism and theoretical approach

Picolinamide is a versatile chelating ligand and it reveals peculiar behaviour for metal chelation, particularly for its amide group. The bonding mode of N & O donor centres of an amide group depends on the metal ion, their associated charge and the other associated ligands in metal complexes. Picolinamide (pica) based Pt(II) complex C1 to C4 were synthesized and their bonding mode with Pt(II) was established by different spectroscopic analyses and theoretical approaches for their structural importance and potential anticancer activity. The complex [Pt(pica)Cl2]; C1 was synthesized and its hydrolyzed product [Pt(pica)(OH2)2](ClO4)2; C2 was obtained from hydrolysis of complex C1. The kinetic and mechanistic study for the interaction of complex C2 with l-cysteine (l-cys) and N-acetyl-l-cysteine (N-ac-l-cys) was performed in pseudo-first-order reaction condition to evaluate the rate constants, rate equation, enthalpy of activation (ΔHǂ) and entropy of activation (ΔSǂ). Sulfur chelated complex [Pt(pica)(l-cys)]+; C3 and [Pt(pica)(N-ac-l-cys)]; C4 were obtained when a 1:1 M ratio of C2 and thiol are mixed separately. Theoretical investigation on drug likeness property was evaluated by PASS prediction software. The theoretical approach on structural properties like; structural optimization, HOMO-LUMO energy, TD-DFT simulation, MEP and reactivity descriptors of the complexes were executed and analyzed with the Gaussian09 software package. Molecular docking of the complexes was executed with DNA and BSA.

Ring-Opening Polymerization of Cyclohexene Oxide and Cycloaddition with CO2 Catalyzed by Amine Triphenolate Iron(III) Complexes.

A series of novel amine triphenolate iron complexes were synthesized and characterized using UV, IR, elemental analysis, and high-resolution mass spectrometry. These complexes were applied to the ring-opening polymerization (ROP) of cyclohexene oxide (CHO), demonstrating excellent activity (TOF > 11050 h-1) in the absence of a co-catalyst. In addition, complex C1 maintained the dimer in the presence of the reaction substrate CHO, catalyzing the ring-opening polymerization of CHO to PCHO through bimetallic synergy. Furthermore, a two-component system consisting of iron complexes and TBAB displayed the ability to catalyze the reaction of CHO with CO2, resulting in the formation of cis-cyclic carbonate with high selectivity. Complex C4 exhibited the highest catalytic activity, achieving 80% conversion of CHO at a CHO/C4/TBAB molar ratio of 2000/1/8 and a CO2 pressure of 3 MPa for 16 h at 100 °C, while maintaining >99% selectivity of cis-cyclic carbonates, which demonstrated good conversion and selectivity.

New Architecture Based on Metal-Organic Frameworks and Spin Crossover Complexes to Detect Volatile Organic Compounds.

We present here the encapsulation of a spin crossover complex C1 [FeII(L)] (L: 4-amino-, 2-(2-pyridinylmethylene)hydrazide) inside MOF-808(Zr), a chemically robust Metal-Organic Framework. The compound C1⊂MOF-808 retains its crystallinity as well as a partial porosity compared to pristine MOF and shows solvatochromism under Volatile Organic compounds (VOCs) sorption associated to a spin state change of the guest complex. More specifically, this compound shows an interesting reversible color change under formaldehyde and formic acid vapor sorption and can therefore be considered as a new kind of optical VOCs chemosensor, opening new doors for developing a broad range of VOCs optical sensors.

New silver, rhodium and iridium complexes with anthracene-functionalized N-heterocyclic carbene ligands: Crystal structures, cytotoxicity and fluorescence studies

In the present study, we have synthesized anthracene-functionalized metal complexes to investigate their cytotoxicity and photophysical properties. In this context, firstly, an Ag–NHC (NHC = N-heterocyclic carbene) complex (2a) has been synthesized by the interaction of Ag2O and N-(2-methylbenzyl)-N-((anthracen-9-yl)methyl)benzimidazolium chloride (1a). Corresponding Rh– (3a) and Ir–NHC (4a) complexes have also been synthesized by the transmetalation reaction between 2a and corresponding metal compounds. Additionally, for comparison purposes, an ether-functionalized Ag–NHC complex (2b) with N-(methoxyethyl)-N-((anthracene-9-yl)methyl)benzimidazole-2-ylidene ligand, and [AgL2]NO3 type complex (2c) with a N-coordinated N-((anthracen-9-yl)methyl)benzimidazole ligand have been synthesized. All complexes have been characterized by the combination of NMR and mass spectroscopic techniques, and elemental analyses. Moreover, solid state structures of 2a, 2b and 4a have been determined by the single crystal X-ray diffraction analysis. Cytotoxic potentials of all compounds have been tested against human lung adenocarcinoma alveolar basal epithelial cell line (A549) using the MTT assay, and all complexes performed strong anti-proliferative activity. Stability studies have disclosed that only 1a and 2c are able to retain their structure in the culture medium (DMEM) that biological assays were carried out. Photophysical measurements revealed that all compounds have similar emission bands because of the conjugation of anthracene group. Finally, 1a and 2c have been visualized by fluorescence confocal microscopy to investigate cellular uptake and subcellular distribution of the complexes, and the findings indicated that both compounds dispersed along the cell membranes nuclear regions.

Studies on synthesis and influence of sterically driven Ni(II)-terpyridine (NNN) complexes on BSA/DNA binding and anticancer activity

The present work demonstrates the synthesis, structural diversity and coordination behavior of some selected new Ni(II)-Tpy complexes. The structural analysis revealed the coordination of the selected terpyridine ligands with the core metal atom in two different modes via dimeric species (1:1 fashion) through the Cl-bridging and a bis(Tpy)-Ni complex (2:1 fashion). Perhaps the most striking manifestations of these Ni(II)-Tpy complexes are BSA/DNA binding ability and anticancer activity. In addition, the cytotoxicity studies of Tpy ligand (4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl 5-methylthiophene-2-carboxylate) and the Ni(II) complexes were carried out using lung cancer cell line (A549), breast cancer cell line (MCF-7) and normal cell line (Vero cell). The cytotoxicity results were compared with the cisplatin control group. Notably, bis-terpyridyl complex 3C (R = 4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl 4-isopropoxybenzoate) demonstrates better activity with the IC50 value of 23.13 ± 3 μm for A549 and 22.7 ± 3 for MCF-7. The DFT calculations reveal the significant energy differences of HOMO and LUMO for the ligands and their corresponding Ni(II) complexes. The Tpy ligands and Ni(II)-Tpy complexes were investigated for BSA binding and further all the Ni(II) complexes were analyzed for DNA binding studies.

Palladium(II) NCS‐Pincer Complexes Mediated Regioselective Cross Dehydrogenative Alkenation of 2‐Arylthiophenes

AbstractIn this report, we have synthesized two new NCS pincer ligands by the Schiff base reaction of 3‐((phenylthio)methoxy)benzaldehyde (P) with alkyl amines (tbutylamine (L1) and 1‐adamantylamine (L2)). The palladium pincer complexes (tbutylamine=C1 and 1‐adamantylamine=C2) of these ligands were synthesized by their reaction with PdCl2(CH3CN)2 precursor. The newly synthesized ligands and complexes were characterized using various analytical and spectroscopic techniques such as 1H, 13C{1H} Nuclear Magnetic Resonance (NMR), Ultraviolet–visible (UV‐Visible), Fourier Transform Infrared (FTIR) Spectroscopy, and High‐Resolution Mass Spectrometry (HRMS). The structure of the ligand and its coordination mode with palladium precursor were studied with the help of single‐crystal X‐ray diffraction. The complexes showed distorted square planar geometry around the palladium center. The palladium pincer complexes were used as catalysts for the regioselective cross‐dehydrogenative alkenation of 2‐arylthiophene derivatives. The complex C2, where sterically bulky adamantyl ligand is part of the side arm showed a higher yield of alkenation reaction. Only 2.5 mol% catalyst loading was sufficient to achieve 74–95 % yields of desired products with excellent functional group tolerance under mild reaction conditions. The poisoning experiments (PPh3 and Hg) showed the homogeneous nature of the catalytic process. The plausible mechanism of the reaction was proposed based on the control experiments and time‐dependent HRMS studies.

Novel half-sandwich ruthenium(II) nicotinic hydrazone complexes: An efficient class of catalyst for the N-alkylation of amines with benzyl alcohol via transfer hydrogen mechanism and effective antibacterial agents

A new series of half sandwich ruthenium(II) complexes supported by nicotinic acid hydrazone derivatives of general formula [Ru(ɳ6-p-cymene)(Cl)(L)], where L represents N’-benzylidenenicotinohydrazide (HL1), N’-(naphthalen-1-ylmethylene)nicotinohydrazide (HL2) or N’-(pyren-1-ylmethylene)nicotinohydrazide (HL3) were synthesized and fully characterized. The solid-state molecular structures of ligands and complexes were elucidated with single-crystal X-ray diffraction. The ligands HL1 and HL2 possess monoclinic crystal system with P21/c and C2/c space groups respectively, whereas all the three Ru(II) complexes C1–3 are typical three-legged piano-stool geometries with orthorhombic(Aba2) (C1) and triclinic(P-1) (C2–3) systems respectively. The catalytic activities of these ruthenium complexes in the synthesis of N-alkylated amines were explored. Under optimal reaction condition, the complex C3 was found to be the most efficient catalyst for the N-alkylation of primary to secondary amines using benzyl alcohol. A wide range of substrates have been studied that includes anilines bearing electron withdrawing/electron donating group, fused aromatic, heteroaromatic, alicyclic and aliphatic amines with good to excellent yield. In addition, the antibacterial activity of the complexes were tested against different human pathogenic bacteria, among them C2 complex with naphthyl moiety was found to be the most active one against both Gram-positive (S. aureus and E. faecalis) and Gram-negative (E. coli and K. pneumoniae) bacteria. These two different studies demonstrate the catalytic and biological importance of our newly prepared Ruthenium complex.

Antioxidant Activity and DFT Calculations of Metal Complexes Derived from a Schiff Base Ligand: Synthesis, Characterization, and Biological Evaluation

AbstractMetal complexes derived from Schiff bases are known to have a wide range of applications, spanning the areas of material and medicinal sciences. Herein, a Schiff base ligand, (Z)‐2‐(((4‐chlorophenyl)imino)methyl)naphthalen‐1‐ol HL, was synthesized via a condensation reaction between 2‐hydroxy‐1‐naphthaldehyde and 4‐chloroaniline using methanol as a solvent in the presence of a catalytic amount of formic acid. The obtained ligand was further reacted with Mn(II), Ni(II), and Cu(II) using their acetate salts in a 1 : 2 stoichiometric ratio of metal to ligand to afford complexes C1–C3, respectively. Physicochemical and analytical techniques consisting of FTIR, UV‐Vis, elemental (CHN and metal content), TGA, HRMS, 1H, and 13 C NMR spectroscopy were deployed to establish the formation of the compounds. Results show that the ligand coordinated with the metal ions through the oxygen and nitrogen atoms of the phenolate and azomethine moieties, respectively, forming ON‐type complexes. Furthermore, the free ligand and its complexes were evaluated for their antioxidant activity compared to the standard (ascorbic acid) using an in vitro DPPH radical scavenging assay. From this investigation, C1 demonstrated higher radical scavenging activity than the free ligand, the complexes, and the standard (ascorbic acid). But the ligand has better scavenging activity than C2 and C3 at higher concentrations. DFT was also used to examine the electronic properties of the compounds, and the data obtained corroborated well with the experimental study.

Modes of Interactions with DNA/HSA Biomolecules and Comparative Cytotoxic Studies of Newly Synthesized Mononuclear Zinc(II) and Heteronuclear Platinum(II)/Zinc(II) Complexes toward Colorectal Cancer Cells.

A series of mono- and heteronuclear platinum(II) and zinc(II) complexes with 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine ligand were synthesized and characterized. The DNA and protein binding properties of [ZnCl2(terpytBu)] (C1), [{cis-PtCl(NH3)2(μ-pyrazine)ZnCl(terpytBu)}](ClO4)2 (C2), [{trans-PtCl(NH3)2(μ-pyrazine)ZnCl(terpytBu)}](ClO4)2 (C3), [{cis-PtCl(NH3)2(μ-4,4'-bipyridyl)ZnCl(terpytBu)}](CIO4)2 (C4) and [{trans-PtCl(NH3)2(μ-4,4'-bipyridyl)ZnCl(terpytBu)}](CIO4)2 (C5) (where terpytBu = 4,4',4″-tri-tert-butyl-2,2':6',2″-terpyridine), were investigated by electronic absorption, fluorescence spectroscopic, and molecular docking methods. Complexes featuring transplatin exhibited lower Kb and Ksv constant values compared to cisplatin analogs. The lowest Ksv value belonged to complex C1, while C4 exhibited the highest. Molecular docking studies reveal that the binding of complex C1 to DNA is due to van der Waals forces, while that of C2-C5 is due to conventional hydrogen bonds and van der Waals forces. The tested complexes exhibited variable cytotoxicity toward mouse colorectal carcinoma (CT26), human colorectal carcinoma (HCT116 and SW480), and non-cancerous mouse mesenchymal stem cells (mMSC). Particularly, the mononuclear C1 complex showed pronounced selectivity toward cancer cells over non-cancerous mMSC. The C1 complex notably induced apoptosis in CT26 cells, effectively arrested the cell cycle in the G0/G1 phase, and selectively down-regulated Cyclin D.

Synthesis, Crystal Structures, Genotoxicity, and Antifungal and Antibacterial Studies of Ni(II) and Cd(II) Pyrazole Amide Coordination Complexes.

In this study, we synthesized two coordination complexes based on pyrazole-based ligands, namely 1,5-dimethyl-N-phenyl-1H-pyrazole-3-carboxamide (L1) and 1,5-dimethyl-N-propyl-1H-pyrazole-3-carboxamide (L2), with the aim to investigate bio-inorganic properties. Their crystal structures revealed a mononuclear complex [Ni(L1)2](ClO4)2 (C1) and a dinuclear complex [Cd2(L2)2]Cl4 (C2). Very competitive antifungal and anti-Fusarium activities were found compared to the reference standard cycloheximide. Additionally, L1 and L2 present very weak genotoxicity in contrast to the observed increase in genotoxicity for the coordination complexes C1 and C2.

Spectroscopic characterization, DFT calculations, in vitro pharmacological potentials, and molecular docking studies of N, N, O-Schiff base and its trivalent metal complexes

In this study, trivalent metal complexes of the category: [M(L)(H2O)nCly] obtained from the interaction of metal3+ ion salts with organic N, N, O-Schiff base (HL) (where: HL = 4-{(Z)-((2-{(E)-((2-hydroxyphenyl)methylidene)amino}ethyl)imino)methyl}-2-methoxyphenol; n, y = 1 or 2 and M = Ti(III), Fe(III), Ru(III), Cr(III) and Al(III)) were synthesized and characterized viz molar conductance, FT-IR, and UV–Vis spectroscopies, elemental analyses, thermal analyses (TGA and DTA), and UV–Vis spectroscopy, theoretical calculations. A distorted octahedral structure around the metal ions was proposed based on the obtained experimental and calculated data. Thermal examination of the complexes signposts the step-by-step disintegration to give the final decomposition product as metal oxides. Moreover, DFT calculations were executed utilizing the B3LYP/LANL2DZ theory level, which revealed that the synthesized metal (III) complexes were more stable than the free ligand (HL). The value of ΔE for HL is 4.60 eV while the related values for the complexes of Cr(III) (C1), Ru(III) (C2), Fe(III) (C3), Al(III) (C4), and Ti(III) (C5) are respectively 2.59, 3.68, 3.15, 1.64, and 2.75 eV. Scavenging abilities of DPPH and ABTS radicals by the test compounds revealed promising antioxidant behavior. It was observed that the compounds are proficient DPPH radical scavengers in a dose-dependent configuration. Ru(III); IC50 = 1.69 ± 2.68 µM for DPPH and Ti(III); IC50 = 8.70 ± 2.78 µM for ABTS performed best. Similarly, the complexes demonstrated higher antimicrobial activities compared to HL against the designated strains, while ciprofloxacin acted as a standard antibiotic. Furthermore, the ligand and its most effective complexes C2 and C5 were docked against the targets S. aureus DNA gyrase (2XCT), S. pneumoniae DNA gyrase (5BOD), and E. coli DNA gyrase (5L3J). The binding sites were evaluated and the docking results showed that the studied molecules bind to the targets through classical O—H…O and/or N—H…O hydrogen bonds, as well as via hydrophobic contacts.

Unveiling the biomedical potential of thiophene‐derived Schiff base complexes: A comprehensive study of synthesis, spectral characterization, antimicrobial efficacy, antioxidant activity, and computational insights

In our pursuit of designing potent bioactive compounds, we synthesized six novel tellurium (IV) complexes through the condensation of 5‐methyl‐2‐thiophene carboxaldehyde and p‐nitroaniline. These compounds underwent rigorous investigation using various analytical techniques (TGA, SEM, EDAX, and powder XRD) and spectral analyses (NMR, mass spectrometry, UV–Vis, and FTIR). Spectroscopic analysis suggested an octahedral geometry for the complexes, revealing chelation through the thiophene sulfur and azomethine nitrogen atoms. Thermal analysis indicated a three‐step degradation process, ultimately leaving behind metal oxide as the end product. We conducted in‐vitro antimicrobial screening using the broth micro‐dilution method, highlighting the significant antimicrobial and antioxidant properties of complexes 3c and 3d, as well as the potent antimicrobial activity of 3b and 3f against various bacterial strains, including Candida albicans. To further substantiate our findings, we performed advanced computational analyses, including molecular docking, pharmacophore modeling, DFT, MESP, and ADMET studies. Molecular docking validated our antimicrobial results, whereas pharmacophore models enhanced our understanding of molecular interactions with proteins, potentially identifying novel bioactive compounds. Furthermore, DFT and MESP investigations underscored the superior biological efficacy of tellurium (IV) complexes over thiophene‐derived ligands, emphasizing their potential as therapeutic agents. ADMET analysis revealed their favorable profile as precursors for drug development with minimal adverse effects. In summary, our research seamlessly integrates experimental and theoretical aspects, offering innovative insights into drug design and potential applications in pharmaceuticals. This study represents a significant milestone, paving the way for future advancements in the field of pharmaceutical science.

Transit-oriented development (TOD) in a scattered city: applied study in Brasília, Federal District

This research aims to analyze the territorial urban strategy entitled transit-oriented development (TOD), a methodology originated in the United States, which for at least 30 years has been little discussed and applied in Brazil. Faced with the challenges imposed in the 21st century in terms of sustainability and the projection of upward population growth of Brazilian cities, DOT planning is a viable concrete alternative for the transformation of today's dispersed, distant, and disconnected (3D) cities into future compact, connected and coordinated urban complexes (3C). Thus, based on the characterization of the DOT, it has led to the conclusion that this methodology is suitable for application in Brasília, Federal District, so that mass transport planning in the city would integrate with urban planning, in a fairer and more equitable way.

A novel isatin Schiff based cerium complex: synthesis, characterization, antimicrobial activity and molecular docking studies

In this work, a novel isatin-Schiff base L2 had been synthesized through a simple reaction between isatin and 2-amino-5-methylthio-1,3,4-thiadiazole. The produced Schiff base L2 was then subjected to a hydrothermal reaction with cerium chloride to produce the cerium (III)-Schiff base complex C2. Several spectroscopic methods, including mass spectra, FT-IR, elemental analysis, UV–vis, 13C-NMR, 1H-NMR, Thermogravimetric Analysis, HR-TEM, and FE-SEM/EDX, were used to completely characterize the produced L2 and C2. A computer simulation was performed using the MOE software program to find out the probable biological resistance of studied compounds against the proteins in some types of bacteria or fungi. To investigate the interaction between the ligand and its complex, we conducted molecular docking simulations using the molecular operating environment (MOE). The docking simulation findings revealed that the complex displayed greater efficacy and demonstrated a stronger affinity for Avr2 effector protein from the fungal plant pathogen Fusarium oxysporum (code 5OD4) than the original ligand. The antibacterial activity of the ligand and its Ce3+ complex were applied in vitro tests against different microorganism. The study showed that the complex was found to be more effective than the ligand.

Structural versatility in nickel (II) complexes of a hydrazone ligand based on alloxan: Preparation, spectroscopic, DFT, anticancer, and molecular docking studies

New binary and mixed‐ligand nickel (II) chelates of a hyrdazone ligand (HYQX) carrying alloxan and quinoline moieties were synthesized. Spectroscopic and analytical techniques were effectively used for identifying the composition and structure of the prepared nickel (II) HYQX chelates. The neutral nature of Ni‐HYQX complexes was demonstrated by molar conductivity studies, and magnetic moment values revealed octahedral geometry. The results demonstrated that HYQX behaves as a monoanionic di‐/tridentate chelating agent in all complexes, except nitrato C2 and acetato C4 complexes, which are bi‐ and tri‐nuclear complexes, respectively, with a unique mode of coordination. The thermal decomposition patterns of Ni‐HYQX complexes were investigated in relation to structure, and thermodynamic parameters were successfully calculated. The molecular structural features of HYQX and its Ni (II) chelates were investigated based on density functional theory (DFT) level at B3LYP/6‐311G(d,p) and LanL2dz level. Ni‐HYQX complexes were found to have anticancer action against Ehrlich Ascites Carcinoma. A molecular docking investigation was conducted to determine in what way the title compounds connect to the CDK‐5 inhibitor‐crystal structure of the inhibitor EFP with CDK‐2 (PDB ID: 3IG7) in order to verify their biological activity.

A Neutral Pyridine-Pyrazole-Based N^N*N^N Ligand as a Tetradentate Chromophore for Diverse Transition Metal Cations

Herein, the synthesis and the structural as well as the photophysical characterization of five transition metal complexes bearing a neutral pyridine-pyrazole-based N^N*N^N ligand (L) acting as a tetradentate chelator are reported. The luminophore can be synthesized via two different pathways. An alkyl chain with a terminal tert-butyl moiety was inserted on the bridging nitrogen atom to enhance the solubility of the complexes in organic solvents. Due to the neutral character of L, metal ions with different charges and electronic configurations can be chelated. Thus, complexes with Pt(II) (C1), Ag(I) (C2), Zn(II) (C3), Co(II) (C4) and Fe(II) (C5) were synthesized. Single-crystal X-ray diffraction experiments showed that complex C2 exhibits a completely different structure in the crystalline state if compared with C3 and C5, i.e., depending on the chelated cation. The UV-vis absorption and the NMR spectra showed that the complexes dissociate in liquid solutions, except for the Pt(II)-based coordination compound. Therefore, the photophysical properties of the complexes and of the ligand were studied in the solid state. For the Pt(II)-based species, a characteristic metal-perturbed ligand-centered phosphorescence was traceable, both in dilute solutions as well as in the solid state.

Pd(II) complexes bearing NNS pincer ligands: unveiling potent cytotoxicity against breast and pancreatic cancer.

The continuously increasing rate of breast cancer is one of the major threats to female health worldwide. Recently, palladium complexes have emerged as impressive candidates with effective biocompatibility and anticancer activities. Hence, in the present study, we report a new series of palladium complexes bearing NNS pincer ligands for cytotoxicity studies. The reaction of thiophenol/4-chlorothiophenol/4-methylthiophenol/4-methoxythiophenol with 2-bromo-N-quinolin-8-yl-acetamide in the presence of sodium hydroxide in ethanol at 80 °C gave [C9H6N-NH-C(O)-CH2-S-Ar] [Ar = C6H5 (L1), C6H4Cl-4 (L2), C6H4Me-4 (L3), and C6H4-OMe-4 (L4)]. The corresponding reaction of L1-L4 with Na2PdCl4 in methanol at room temperature for 3 h resulted in complexes [(L1-H)PdCl] (C1), [(L2-H)PdCl] (C2), [(L3-H)PdCl] (C3), and [(L4-H)PdCl] (C4). All new compounds have been characterized by spectroscopic analyses. The structures of complexes C1, C3, and C4 have also been determined from single-crystal X-ray diffraction data. The cytotoxicities of L1-L4 and C1-C4 have been investigated for breast cancer 4T1 and pancreatic cancer MIA-PaCa-2 cells. The IC50 values for complexes C2 and C3 were observed to be comparable to or higher than those of cisplatin. The stressed morphology and cell death of cancerous cells were successfully observed through cellular morphology analysis and the assessment of cytoskeleton damage.

Re(I)[2-aryl-1H-imidazo[4,5-f][1,10]phenanthroline] tricarbonyl chloride complexes for selective cancer therapy via a potential DNA damage mechanism.

Recently, achieving selective cancer therapy with trifling side effects has been a great challenge in the eradication of cancer. Thus, to amplify the cytoselective approach of complexes, herein, we developed a series of Re(I)[2-aryl-1H-imidazo[4,5-f][1,10]phenanthroline] tricarbonyl chloride complexes and screened their potency against HeLa and MCF-7 cell lines together with the evaluation of their toxicity towards a normal kidney cell line (HEK-293). On meticulous investigation, complex [ReI(CO)3Cl(K2-N,N-(2c))] (3c) was found to be the most potent anticancer entity among other complexes. Complex 3c also showed competency to induce apoptosis in MCF-7 cells through G2/M phase cell-cycle arrest in association with the generation of ample reactive oxygen species (ROS), eventually leading to DNA intercalation and internucleosomal cleavage. The order of the cytotoxicity of these complexes depended on their lipophilic character and the electron-withdrawing halogen substitution at the para-position of the phenyl ring in the imidazophenanthroline ligand.