Ligands L1 Research Articles

Metal-Organic Cage Receptors for Encapsulation and Sensing of Bile Acids.

Developing synthetic supramolecular receptors to solubilize, scavenge, recognize, encapsulate, and sense steroids is challenging. Despite a limited number of receptors having affinity with steroids, none exists to bind steroidal bile acids selectively. Herein, we report a C2-symmetric metal-organic cage [Pd6L24]12+ and an expanded version of the Fujita cage [Pd6L14]12+, built with a conformationally flexible ligand L2, accessed through coordination-driven self-assembly. We examined both cages for steroid recognition in water: both have certain shared characteristics and distinctive features. [Pd6L14]12+ binds hydrophobic bile acids and other steroids by forming a 1:1 complex. In contrast, the expanded [Pd6L24]12+ cage exhibits an affinity for amphiphilic bile acids and selective steroids to encapsulate them as dimers, promoted by cooperative interguest hydrogen bonding. [Pd6L24]12+ has a 5 times stronger solubility enhancement ability for cholic acid compared to [Pd6L14]12+. Further, the expanded [Pd6L24]12+ cage can selectively sense bile acids in nanomolar detection limits through indicator displacement assay by employing sulforhodamine 101 (SR101).

New Ru(II)-p-cymene compounds bearing indomethacin and indomethacin-pyridineamide ligands: synthesis, characterization, computational studies and investigation of their interactions with the Human Serum Albumin

The research interest in ruthenium(II) organometallic compounds has continually increased due to their promising performance in biological assays targeting diverse medicinal applications. This work reports the interactions of the [Ru(II)-η6-p-cymene] framework with the indomethacin (HL1) drug and with its modified analogue indomethacin-pyridineamide (L2). Two new half-sandwich organometallics, [Ru(η6-p-cymene)(L1)Cl] (1) and [Ru(η6-p-cymene)(L2)Cl2] (2), were successfully synthesized and fully characterized by ESI-MS, NMR, ATR-FTIR and UV/VIS spectroscopy. The chemical and electronic structures were corroborated by DFT computational calculations. Compound 2 was chemically stable, keeping the L2 ligand in the coordination sphere in coordinating solvents, and was investigated for the interaction with the Human Serum Albumin (HSA) protein by fluorescence quenching studies. This compound acted as a quencher to the intrinsic protein fluorescence, mainly through binding-related quenching (static) mechanism, showing high value for the apparent association constant (Ka). The analysis of the thermodynamic parameters revealed spontaneous process, presenting low temperature dependence, with electrostatic forces playing a key role in the HSA-compound 2 adduct binding. Site competitive studies suggested that the organometallic 2 may compete for the binding site of ibuprofen (subdomain IIIA) and also for the binding site of Ru(III) naked ion (subdomain IB or IIA). Molecular docking simulations showed that both Ru(II)-arenes may interact through hydrogen bonding with arginine residues, and exhibit high affinity for the microenvironment located in subdomains IIIA and IB. These findings suggest that the HSA protein might be a potential carrier for these Ru(II)-organometallic compounds in the blood plasma.

Precise Post‐Synthetic Modification of Heterometal‐Organic Capsules for Selectively Encapsulating Tetrahedral Anions

AbstractPost‐synthetic modification plays a crucial role in precisely adjusting the structure and functions of advanced materials. Herein, we report the self‐assembly of a tubular heterometallic Pd3Cu6L16 capsule that incorporates Pd(II) and CuL1 metalloligands. This capsule undergoes further modification with two tridentate anionic ligands (L2) to afford a bicapped Pd3Cu6L16L22 capsule with an Edshammer polyhedral structure. By employing transition metal ions, acid, and oxidation agents, the bicapped capsule can be converted into an uncapped one. This uncapped form can then revert back to the bicapped structure on the addition of Br− ions and a base. Interestingly, introducing Ag+ ions leads to the removal of one L2 ligand from the bicapped capsule, yielding a mono‐capped Pd3Cu6L16L2 structure. Furthermore, the size of the anions critically influences the precise control over the post‐synthetic modifications of the capsules. It was demonstrated that these capsules selectively encapsulate tetrahedral anions, offering a novel approach for the design of intelligent molecular delivery systems.

Spectroscopic properties, crystal structure, Hirshfeld surface analysis and DFT study of a new Cu(II) complex based on quinazolinone O,N,O-donor ligand

A quinazolinone-based Schiff base ligand 3-[(2‑hydroxy-5-methoxybenzylidene)amino]-2-(2‑hydroxy-5-methoxyphenyl)-2,3-dihydroquinazolin-4-one (L1) and its new mononuclear copper(II) complex [Cu(L1)Cl(H2O)] (1) were synthesised and fully characterised by various spectroscopic techniques (NMR, FTIR, UV–Vis) and single-crystal X-ray diffraction study. The aspherical model of the crystal structure of the ligand L1 as well as of the copper(II) complex 1 was refined by the Hirshfeld Atom Refinement method. The crystal structure of the copper(II) complex shows the existence of a substitution disorder at the position of the water molecule, which represents two different complex molecules [Cu(L1)Cl(H2O)] (1a) and [Cu(L1)Cl] (1b) with different coordination polyhedra around the copper atom. The majority of the mononuclear complex [Cu(L1)Cl(H2O)] (1a) in the crystal structure contains a coordinated water molecule, but the minority in the crystal structure contains a mononuclear complex [Cu(L1)Cl] (1b) and a water molecule is outside the coordination sphere around the copper atom. The crystal structure of complex 1 showed a penta-coordinated (1a) or tetra-coordinated (1b) Cu atom in the shape of a tetragonal pyramid (1a) or square planar (1b) formed by a chloride atom in the equatorial plane, and a Schiff base bound as an O,N,O-tridentate ligand, and an additional water molecule in the axial position (only 1a). A detailed analysis of the intermolecular interactions was investigated using three-dimensional 3D Hirshfeld surfaces and their associated two-dimensional 2D fingerprint plots. Hirshfeld surface analysis was performed for both crystal structures. Furthermore, theoretical DFT analysis has been performed in order to interpret the experimental data. In order to obtain high quality DFT data, we present here a new basis set B1MH, which is an extension of the LanL2DZ basis with incorporated polarisation and diffusion functions for heavy atoms (C, N, O, Cl and Cu) and added ECPs for Cl and Cu atoms. The presented B1MH basis set allowed us to obtain better theoretical results than those previously published.

Precise Post-Synthetic Modification of Heterometal-Organic Capsules for Selectively Encapsulating Tetrahedral Anions.

Post-synthetic modification plays a crucial role in precisely adjusting the structure and functions of advanced materials. Herein, we report the self-assembly of a tubular heterometallic Pd3Cu6L16 capsule that incorporates Pd(II) and CuL1 metalloligands. This capsule undergoes further modification with two tridentate anionic ligands (L2) to afford a bicapped Pd3Cu6L16L22 capsule with an Edshammer polyhedral structure. By employing transition metal ions, acid, and oxidation agents, the bicapped capsule can be converted into an uncapped one. This uncapped form can then revert back to the bicapped structure on the addition of Br- ions and a base. Interestingly, introducing Ag+ ions leads to the removal of one L2 ligand from the bicapped capsule, yielding a mono-capped Pd3Cu6L16L2 structure. Furthermore, the size of the anions critically influences the precise control over the post-synthetic modifications of the capsules. It was demonstrated that these capsules selectively encapsulate tetrahedral anions, offering a novel approach for the design of intelligent molecular delivery systems.

Segmented Template-Directed Self-Assembly of Giant Truncated Triangular Supramolecules.

The template-directed strategy has been extensively employed for the construction of supramolecular architectures. However, with the increase in the size and complexity of these structures, the synthesis difficulty of the templates escalates exponentially, thereby impeding the widespread application of this strategy. In this study, two truncated triangles T1 and T2 were successfully self-assembled through a novel segmented template strategy by segmenting the core triangular template into portions. Two metallo-organic ligands L2 and L3 were designed and synthesized by dividing the central stable triangle into three separate parts and incorporating them into the precursor ligands, which served as templates to guide the self-assembly process with ligands L1 and L4, respectively. The assembled structures were unambiguously characterized by multidimensional and multinuclear NMR (1H, COSY, NOESY), multidimensional mass spectrometry analysis (ESI-MS and TWIM-MS), and transmission electron microscopy (TEM). Moreover, we observed the formation of fiberlike nanotubes from single-molecule triangles by hierarchical self-assembly.

Silver(I) complexes with diorganochalcogen ligands of type (2-MeC6H4CH2)2E (E = S, Se). Synthesis, structure and antiproliferative activity

Silver(I) complexes of types [Ag(X){E(CH2C6H4Me-2)2}] [E = S, X = CF3SO3 (1), NO3 (2), ClO4 (3); E = Se, X = CF3SO3 (4), NO3 (5), ClO4 (6)] and [Ag(X){E(CH2C6H4Me-2)2}2] [X = CF3SO3, E = S (7), Se (8); X = ClO4, E = S (9), Se (10)] were prepared by reacting the diorganochalcogenides (2-MeC6H4CH2)2E [E = S (L1), Se (L2)] with the appropriate silver(I) salt in a 1:1 and a 2:1 molar ratio, respectively. The ligands and the Ag(I) complexes were characterized by multinuclear NMR spectroscopy (1H, 13C{1H}, 19F{1H}, 77Se{1H}, as appropriate), ESI+ mass spectrometry, elemental analysis and IR spectroscopy. The crystal and molecular structures of the ligand L1 and the complexes 2, 5, 7, 8 and 9 were determined by single-crystal X-ray diffraction. The molar conductivity of the reported metal complexes showed their behaviour as 1:1 electrolytes in solution, while in solid state the inorganic anionic ligand is coordinated to silver by OAg bonds. Preliminary results showed that the silver(I) complexes bearing triflato ligands have in vitro promising antiproliferative activity against the murine melanoma B16.F10 cells.

A Dinuclear Copper(II) Complex Electrochemically Obtained via the Endogenous Hydroxylation of a Carbamate Schiff Base Ligand: Synthesis, Structure and Catalase Activity.

In the present work, we report a neutral dinuclear copper(II) complex, [Cu2(L1)(OH)], derived from a new [N,O] donor Schiff base ligand L1 that was formed after the endogenous hydroxylation of an initial carbamate Schiff base H2L coordinated with copper ions in an electrochemical cell. The copper(II) complex has been fully characterized using different techniques, including X-ray diffraction. Direct current (DC) magnetic susceptibility measurements were also performed at variable temperatures, showing evidence of antiferromagnetic behavior. Its catalase-like activity was also tested, demonstrating that this activity is affected by temperature.

Synthesis of Manganese(II), Iron(III), and Vanadium(IV) Complexes with New Schiff Bases and their Spectroscopic and Thermal Studies and Evaluation of their Antimicrobial Activity

Heterocyclic 3-acetyl coumarin with hydrazide derivatives and their metal complexes are a substantial family of pharmaceutical drugs used to treat infection, anti-inflammatory issues, diabetes, and neurological disorders in the field of medicinal chemistry. Cyclization of 5- floro-2-furaldehyde, ethyl acetoacetate, and urea or thiourea by LaCl3.7H2O, addition of hydrazine to form amine derivatives were performed, and respective Schiff base derivatives (L1, L2) were produced by adding acetyl coumarin in an ethanolic solution at ambient temperature. New ligands and its complexes of the V (IV), Fe (III) and Mn (II) ions were characterized using (FT-IR, UV, MS) and nuclear magnetic resonance (1H-NMR) as well as elemental analysis (CHN). The synthesized complexes chelate with ligands L1, L2 via (N, O2) atoms. The structural geometry of the complexes was illustrated in the solid phase using FT-IR and UV-VIS spectroscopy, elemental analysis (CHNS), and flame atomic absorption, in addition to magnetic susceptibility and conductivity measurement. The antibacterial activity of the newly prepared ligands and their metal complexes was evaluated against Pseudonomous aerugionosa as a gram negative and Bacillus subtilis as a gram positive microorganism. Moreover, the antifungal activity against two fungi Aspergillus flavus, and Saccharomyces cerevisiae was studied for all compounds. The coordinated ligands significantly increased their bactericidal and fungicidal action compared to the free ligands, which did not exhibit any activity against the selected fungal and bacterial strains. The results focused on the synergetic relationship between the metal ion and the ligand, in addition to the structural variation.

Structural, stability and relaxation features of lanthanide‐complexes designed for multimodal imaging detection of enzyme activities

AbstractLanthanide complexes of DO3A‐derivative ligands bearing a pyridine‐carbamate (L1) or pyridine‐amine (L2) arm have potential interest in the design of enzymatically activated imaging probes. Solid‐state X‐ray structures for CeL1 and YbL2 both demonstrate twisted square antiprismatic geometry, with the metal ion in a nine‐ or an eight‐coordinate environment, respectively. As assessed by pH‐potentiometry, in solution lanthanide ions form more stable complexes with the nonadentate L1 than with the octadentate L2 ligand (logKML=18.7–21.1 vs. 16.7–18.6, respectively), while stability constants are similar for L1 and L2 chelates of Mg2+, Ca2+, Zn2+ or Cu2+. The kinetic inertness of GdL1 is exceptionally high, with an estimated dissociation half‐life of ~108 h at pH 7.4, while LnL2 (Ln=Ce, Gd, Yb) complexes have 3–4 orders of magnitude faster dissociation, related to the presence of the protonatable, non‐coordinating amine function. The water exchange rate determined for the monohydrated GdL2 (kex298=1.3×106 s−1) shows a threefold decrease with respect to GdDOTA, as a consequence of a reduction in the negative charge and in the steric crowding around the water binding site, both important in dissociatively activated water exchange processes.

Exfoliation of a Coordination Polymer Based on a Linear π-Conjugated Ligand into an Ultrathin Nanosheet for Glyphosate Sensing.

Owing to the large-scale consumption of pesticides and their potential threats to the environment and human health, the development of sensing materials for pesticides has attracted considerable attention in recent years. In this work, a novel Cd(II)-based coordination polymer (CP) with the formula [Cd(H2O)2(L)]·DMF (Cd-1, DMF = N,N-dimethylformamide, H2L = 4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic acid) was synthesized under solvothermal conditions. Structural analysis revealed that coordination between central Cd2+ cations and the ligand L2- formed two-dimensional (2D) networks, which were further assembled by noncovalent hydrogen bonds into a three-dimensional (3D) supramolecular framework. Through ultrasonic treatment in isopropyl alcohol, Cd-1 was exfoliated to afford an ultrathin CP-based 2D nanosheet (Cd-1-NS) with a thickness of less than 1.8 nm. Compared to the bulk materials, the prepared Cd-1-NS exhibited enhanced fluorescence emission properties and superior sensing performance toward glyphosate (Glyph) in water with high selectivity, sensitivity, anti-interference, fast response, and good recyclability via the turn-off effect. The limit of detection (LOD) of Cd-1-NS for Glyph was as low as 41 nM (7 ppb) in the low-concentration range of 0-2.4 μM. In addition, the Cd-1-NS also showed excellent practicability and reliability for the detection of Glyph in real samples, including lake water, tap water, cabbage, and watermelon skin, and could realize the rapid visualized sensing of Glyph residues on the surfaces of vegetables and fruits.

Interaction of Asn297-Linked Glycan Ligands with the Fc Fragment of the Immunoglobulin Class G1: A Molecular Dynamics Simulation Study.

The allosteric modulation of the homodimeric H10-03-6 protein to glycan ligands L1 and L2, and the STAB19 protein to glycan ligands L3 and L4, respectively, has been studied by molecular dynamics simulations and free energy calculations. The results revealed that the STAB19 protein has a significantly higher affinity for L3 (-11.38 ± 2.32 kcal/mol) than that for L4 (-5.51 ± 1.92 kcal/mol). However, the combination of the H10-03-6 protein with glycan L2 (1.23 ± 6.19 kcal/mol) is energetically unfavorable compared with that of L1 (-13.96 ± 0.35 kcal/mol). Further, the binding of glycan ligands L3 and L4 to STAB19 would result in the significant closure of the two CH2 domains of the STAB19 conformation with the decrease of the centroid distances between the two CH2 domains compared with the H10-03-6/L1/L2 complex. The CH2 domain closure of STAB19 relates directly to the formation of new hydrogen bonds and hydrophobic interactions between the residues Ser239, Val240, Asp265, Glu293, Asn297, Thr299, Ser337, Asp376, Thr393, Pro395, and Pro396 in STAB19 and glycan ligands L3 and L4, which suggests that these key residues would contribute to the specific regulation of STAB19 to L3 and L4. In addition, the distance analysis revealed that the EF loop in the H10-03-6/L1/L2 model presents a high flexibility and partial disorder compared with the stabilized STAB19/L3/L4 complex. These results will be helpful in understanding the specific regulation through the asymmetric structural characteristics in the CH2 and CH3 domains of the H10-03-6 and STAB19 proteins.

Old Acquaintances and Novel Complex Structures for the Ni(II) and Cu(II) Complexes of bis-Chelate Oxime-Amide Ligands.

In the process of systematically studying the methylhydroxyiminoethaneamide bis-chelate ligands with polymethylene spacers of different lengths, L1-L3, and their transition metal complexes, a number of new Ni(II) and Cu(II) species have been isolated, and their molecular and crystal structures were determined using single-crystal X-ray diffraction. In all of these compounds, the divalent metal is coordinated by the ligand donor atoms in a square-planar arrangement. In addition, a serendipitously discovered new type of neutral Ni(II) complex, where the propane spacer of ligand L2 underwent oxidation to the propene spacer, and one of the amide groups was oxidised to the ketoimine, is also reported. The resulting ligand L2' affords the formation of neutral planar Ni(II) complexes, which are assembled in the solid state on top of each other, and yield two polymorphic structures. In both structures, the resulting infinite, exclusively parallel metal ion columns in ligand insulation may serve as precursor materials for sub-nano-conducting connectors. Overall, this paper reports the synthesis and characterisation of seven new anionic, cationic, and neutral Ni(II) and Cu(II) complexes, their crystal structures, as well as experimental and computed UV-Vis absorption spectra for two structurally similar Ni(II) complexes, yellow and red.

Synthesis, structure, theoretical calculation and antibacterial property of two novel Zn(II)/Ni(II) compounds based on 3, 5-dichlorosalicylaldehyde thiocarbamide ligand

Two new compounds namely [Zn(L1)phen]31 and Ni(L1)phen(MeOH) 2 (L1 = 3, 5-dichlorosalicylaldehyde thiosemicarbazone) were synthesized by the slow evaporation method at room temperature. The structure of ligand L1 was determined using 1H NMR and 13C NMR spectra. X-ray single crystal diffraction analysis revealed that compounds 1–2 can form 3D supramolecular network structures through π···π stacking and hydrogen bonding interactions. The DFT calculation shows that the coordination of ligand and metal is in good agreement with the experimental results. Hirshfeld surface analysis revealed that H…H and Cl…H interactions were the predominant interactions in compounds 1–2. Energy framework analysis indicated that dispersion energy played a dominant role in the energy composition of compounds 1–2. The inhibitory effects of compounds 1–2 against Escherichia coli (E. coli) and Methicillin-resistant Staphylococcus aureus (MRSA) were tested using the paper disk diffusion method (1: E. coli: 18 mm, MRSA: 17 mm, 2: E. coli: 15 mm, MRSA: 16 mm). Ion releasing experiments were conducted to assess the ion release capacity of compounds 1–2 (Zn2+, 4 days, 38.33 µg/mL; Ni2+, 4 days, 29.12 µg/mL). Molecular docking demonstrated the interaction modes of compounds 1–2 with UDP-N-acetylenolpyruvoylglucosamine reductase (MurB) and dihydrofolate reductase (DHFR) in bacteria, involving hydrophobic, stacking, hydrogen bonding and halogen bonding interactions. The generation of reactive oxygen species (ROS) in bacteria under the presence of compounds 1–2 were evaluated using a fluorescent dye known as dichlorodihydrofluorescein diacetate (DCFH-DA). Potential antibacterial mechanisms of compounds 1–2 were proposed.

Organoplatinum Chemistry Related to Alkane Oxidation: The Effect of a Nitro Substituent in Ligands Having an Appended Phenol Group

The organoplatinum chemistry of the ligands 2-C5H4N-CH2-NH-C6H3-2-OH-5-X (L1, X = H; L3, X = NO2) and 2-C5H4N-CH=N-C6H3-2-OH-5-X (L2, X = H; L4, X = NO2), which contain an appended phenol substituent, is described. Comparisons are made between the ligands with amine or imine groups (L1, L3 vs. L2, L4) and ligands with X = H or NO2 (L1, L2 vs. L3, L4), and major differences are observed. Thus, on reaction with the cycloneophylplatinum(II) complex [{Pt(CH2CMe2C6H4)(μ-SMe2)}2], ligands L1, L2 and L4 give the corresponding platinum(II) complexes [Pt(CH2CMe2C6H4)(κ2-N,N′-L)], containing a Pt··HO hydrogen bond, whereas L3 gives a mixture of isomeric platinum(IV) hydride complexes [PtH(CH2CMe2C6H4)(κ3-N,N′,O-L3-H)], which are formed by oxidative addition of the phenol O-H bond and which react further with oxygen to give [Pt(OH)(CH2CMe2C6H4)(κ3-N,N′,O-L3-H)]. The differences in reactivity are proposed to be due to the greater acidity of the nitro-substituted phenol groups in L3 and L4 and to the greater ability of the deprotonated amine ligand L3 over L4 to stabilize platinum(IV) by adopting the fac-κ3-N,N′,O-L3-H coordination mode.

Trivial positional isomerism in ligands triggering different properties in Fe(II)-metallopolymers; design, synthesis, and characterization.

The tunable molecular scaffold of organic moieties in metallopolymers generates variation in their properties, but what could be the minimal change that can produce variation in the properties of these macromolecules is still untouched. This research has meticulously explored the trivial change in the molecular scaffold of the ligand capable of making a mammoth difference in the nonvolatile memory and coordination pattern in two metallopolymers. The significance of this research lies in the fact that it demonstrates how a slight change in the organic building block can significantly alter the memristive and fluorescence properties of iron(II) metallopolymers, opening up new possibilities for their design and synthesis. Two novel positional isomeric ligands and their corresponding iron(II)-polymers were synthesized and thoroughly characterized using NMR, XRD, ATR-IR, FESEM, AFM and other techniques. Bright orange solid and solution state fluorescence was observed both in the solid and solution states for ligand L2 (3,3'-bis((E)-(pyridin-3-ylimino)methyl)-[1,1'-biphenyl]-4,4'-diol), while ligand L1 (3,3'-bis((E)-(pyridin-2-ylimino)methyl)-[1,1'-biphenyl]-4,4'-diol) showed blue fluorescence in the solution state only. A robust memristive property for Fe(II)-L1-poly with a high current ON/OFF ratio of 104, remarkable random access behaviour, and a long retention time greater than 35 000 seconds was observed while its counterpart was entirely silent. Both polymers showed solution-state electrochromism. These synthesised metallopolymers also showed good specific capacitance in the range of 50-60 F g-1 with a remarkable retention of 98% of the initial value even after 5000 charge-discharge cycles. The AFM and FESEM micrographs revealed the formation of long polymer nano-rods, which correlates with the NMR, ATR-IR, and XRD results. The difference in the properties of polymers generated by such a slight change in the organic building block forces different coordination patterns of these two ligands around the same central metal ion, and this is also evident in all the characterization methods.

Chemical fixation of atmospheric CO2 in tricopper(II)-carbonato complexes with tetradentate N-donor ligands: reactive intermediates, probable mechanisms, and catalytic and magneto-structural studies.

In the present era, the fixation of atmospheric CO2 is of significant importance and plays a crucial role in maintaining the balance of carbon and energy flow within ecosystems. Generally, CO2 fixation is carried out by autotrophic organisms; however, the scientific community has paid substantial attention to execute this process in laboratory. In this report, we synthesized two carbonato-bridged trinuclear copper(II) complexes, [Cu3(L1)3(μ3-CO3)](ClO4)3 (1) and [Cu3(L2)3(μ3-CO3)](ClO4)3 (2) via atmospheric fixation of CO2 starting with Cu(ClO4)2·6H2O and easily accessible pyridine/pyrazine-based N4 donor Schiff base ligands L1 and L2, respectively. Under very similar reaction conditions, the ligand framework embedded with the phenolate moiety (HL3) fails to do so because of the reduction of the Lewis acidity of the metal center, inhibiting the formation of a reactive hydroxide bound copper(II) species, which is required for the fixation of atmospheric CO2. X-ray crystal structures display that carbonate-oxygen atoms bridge three copper(II) centers in μ3syn-anti disposition in 1 and 2, whereas [Cu(HL3)(ClO4)] (3) is a mononuclear complex. Interestingly, we also isolated an important intermediate of atmospheric CO2 fixation and structurally characterized it as an anti-anti μ2 carbonato-bridged dinuclear copper(II) complex, [Cu2(L2)2(μ2-CO3)](ClO4)2·MeOH (2-I), providing an in-depth understanding of CO2 fixation in these systems. Variable temperature magnetic susceptibility measurement suggests ferromagnetic interactions between the metal centers in both 1 and 2, and the results have been further supported by DFT calculations. The catalytic efficiency of our synthesized complexes 1-3 was checked by means of catechol oxidase and phenoxazinone synthase-like activities. While complexes 1 and 2 showed oxidase-like activity for aerobic oxidation of o-aminophenol and 3,5-di-tert-butylcatechol, complex 3 was found to be feebly active. ESI mass spectrometry revealed that the oxidation reaction proceeds through the formation of complex-substrate intermediations and was further substantiated by DFT calculations. Moreover, active catalysts 1 and 2 were effectively utilized for the base-free oxidation of benzylic alcohols in the presence of air as a green and sustainable oxidant and catalytic amount of TEMPO in acetonitrile. Various substituted benzylic alcohols smoothly converted to their corresponding aldehydes under very mild conditions and ambient temperature. The present catalytic protocol showcases its environmental sustainability by producing minimal waste.

Self-assembly of conformation-adaptive dihydrophenazine-based coordination cages.

In this study, we designed and synthesized three conformation-adaptive Pd2L4- and Pd3L6-type coordination cages based on three dihydrophenazine-based ligands with different lengths. Interestingly, the shorter ligands L1 and L2 self-assembled into Pd2L4-type coordination cages while the longer ligand L3 formed Pd3L6-type one, mainly driven by the anion template effect. All coordination cages were confirmed through single-crystal X-ray diffraction, and their structural conformations underwent great changes compared with those of their corresponding ligands. Moreover, the conformational changes also significantly affected their photophysical and electrochemical properties which were distinct from their parent ligands.

Synthesis of bis(oxazoline)-based rare-earth metal complexes and their catalytic performance in the polymerization of isoprene and polar ortho-methoxystyrene.

A series of bis(oxazoline) rare-earth metal dialkyl complexes [(L)Ln(CH2SiMe3)2(THF)n] (L = L1 (dimethyl-substituted bis(oxazoline) ligand), Ln = Y (1-Y), Lu (1-Lu), Sc (1-Sc), n = 1; L = L2 (phenyl-substituted bis(oxazoline) ligand), Ln = Y (2-Y), Lu (2-Lu), Sc (2-Sc), n = 2) was successfully prepared. NMR spectroscopy and X-ray diffraction indicated that all the complexes ligated with a C2 symmetric bis(oxazoline) and two trimethylsilylmethyl ligands. In the presence of borate and triisobutyl aluminium, these complexes exhibited high catalytic activity for the polymerization of isoprene, yielding the polymer with high cis-1,4-regularity (up to 99.9%) and high molecular weight. Moreover, these ternary catalytic systems also served as efficient initiators for the polymerization of polar ortho-methoxystyrene. However, atactic polymers in all the cases were isolated despite the C2 symmetric geometry of bis(oxazoline) ligands.

Unravelling the mechanism of apoptosis induced by copper(II) complexes of NN2-pincer ligands in lung cancer cells.

The invention of efficient chemotherapeutic drugs is essential for human health and development. Keeping this in mind, a series of copper(II) pincer complexes, 1-4, of ligands L1(H) = 2-morpholino-N-(quinolin-8-yl)acetamide, L2(H) = 2-di-n-propylamino-N-(quinolin-8-yl)acetamide, L3(H) = 2-di-n-butylamino-N-(quinolin-8-yl)acetamide and L4(H) = 2-di-n-benzylamino-N-(quinolin-8-yl)acetamide have been synthesized, characterized, and utilized for inhibiting cancer proliferation. Complexes 1-4 showed very efficient activity against lung (A549) and breast (MCF-7) cancer cells, which are the most frequently diagnosed cancers according to the WHO. Among them, 1 was highly active against lung cancer cells with an IC50 value of 8 μM, showing no toxicity towards common L929 fibroblast cell lines (IC50 > 1000 μM). Moreover, AO-EB staining inferred that this cellular demise was attributed to apoptosis, which was determined to be 25.91% of cells by flow cytometry at the IC50 concentration. Furthermore, carboxy-H2DCFDA staining revealed the involvement of ROS in the mechanism. Interestingly, JC-1 dye staining revealed a change in the potential of the mitochondrial membrane, which indicates the enhanced production of ROS in mitochondria. A deep search for the mechanism through in silico studies guided us to the fact that complexes 1-4 might perturb the function of complex I in mitochondria. Furthermore, the studies can be expanded towards clinical applications mainly with morpholine appended complex 1.