Interfacing metal organic frameworks with polymers or carbon-based materials: from simple to hierarchical porous and nanostructured composites.

In the past few years, metal organic frameworks (MOFs) have been assembled with (bio)polymers and a series of carbon-based materials (graphene, graphene oxide, carbon nanotubes, carbon quantum dots, etc.) leading to a wide range of composites differing in their chemical composition, pore structure and functionality. The objective was mainly to overcome the limitations of MOFs in terms of mechanical properties, chemical stability and processability while imparting novel functionality (electron conductivity, (photo)catalytic activity, etc.) and hierarchical porosity. These composites were considered for numerous applications including gas/liquid adsorption and separation, (photo)catalysis, biomedicine, energy storage, conversion and so on. The performance of such composites depends strongly on their microstructural and physico-chemical properties which are mainly driven by the chemical strategies used to design and process such composites. In this perspective article, we propose to cover this topic and provide a useful survey of recent progress in the synthesis and design of MOFs-carbon material composites. This article will describe the development of composites with increasing complexity in terms of porous architecture, spatial structuration and organisation, and functionality.

Metal-organic frameworks for the capture of α-pinene traces.

A dual computational/experimental approach enabled ranking of the performance of a series of MOFs for α-pinene capture in terms of affinity and uptake. UiO-66(Zr) is demonstrated to be a good candidate for adsorbing α-pinene at sub-ppm levels, while MIL-125(Ti)-NH2 shows ideal performances for abating α-pinene at concentrations encountered in indoor air.

In Operando Spectroscopic Ellipsometry Investigation of MOF Thin Films for the Selective Capture of Acetic Acid.

The emission of polar volatile organic compounds (VOCs) is a major worldwide concern of air quality and equally impacts the preservation of cultural heritage (CH). The challenge is to design highly efficient adsorbents able to selectively capture traces of VOCs such as acetic acid (AA) in the presence of relative humidity (RH) normally found at storage in museums (40-80%). Although the selective capture of VOCs over water is still challenging, metal-organic frameworks (MOFs) possess highly tunable features (Lewis, Bronsted, or redox metal sites, functional groups, hydrophobicity, etc.) suitable to selectively capture a large variety of VOCs. In this context, we have explored the adsorption efficiency of a series of MOFs thin films (ZIF-8(Zn), MIL-101(Cr), and UiO-66(Zr)-2CF3) for the selective capture of AA based on a UV/vis and FT-IR spectroscopic ellipsometry in operando study (2-6% of relative pressure of AA under 40% of RH), namely conditions close to the realistic environmental storage conditions of cultural artifacts. For that purpose, optical quality thin films of MOFs were prepared by dip-coating, and their AA adsorption capacity and selectivity were evaluated under humid conditions by measuring the variation of the refractive index as a function of the vapor pressures while the chemical nature of the coadsorbed analytes (water and AA) was identified by FT-IR ellipsometry. While thin films of ZIF-8(Zn) strongly degraded upon exposure to AA/water vapors, films of MIL-101(Cr) and UiO-66(Zr)-2CF3 present a high chemical stability under those conditions. It was shown that MIL-101(Cr) presents a high AA adsorption capacity due to its high pore volume but exhibits a poor AA adsorption selectivity under humid conditions. In contrast, UiO-66(Zr)-2CF3 was shown to overpass MIL-101(Cr) in terms of AA/H2O adsorption selectivity and AA adsorption/desorption cycling stability because of its high hydrophobic character, suitable pore size for adequate confinement, and specific interactions.

A significantly non-toxic novel Cobalt(III) Schiff base complex induces apoptosis via G2-M cell cycle arrest in human breast cancer cell line MCF-7.

AIMS: Metal complexes have ignited considerable interest in the field of chemotherapy after the serendipitous discovery of cisplatin but the severe toxicity of these platinum-based drugs compelled researchers to search for newer, more effective lesser toxic anticancer drugs. MATERIALS AND METHODS: Structural analysis is done by different physicochemical techniques including X-ray single crystallography. Toxicity study has been done in normal Swiss albino mice. MTT assay assessed cell viability. Apoptosis, cell cycle arrest, and cell proliferation were assessed by FACS using Annexin V-PI, PI, and CFSE staining respectively. Western blot quantifies protein expression. While cell migration was studied by wound healing assay. KEY FINDINGS: One-pot synthesis of a novel mononuclear cobalt(III)-Schiff base complex (1) (>99 % purity) and its complete characterization have been done. Cell viability assay showed that 1 (IC50 = 16.81 ± 1.33 µM) exhibits cytotoxicity at much lower concentration in comparison to oxaliplatin (IC50 = 31.4 ± 0.69 µM) against MCF-7 cells for 24 h of therapy without being overly toxic to human PBMCs (IC50 ≥ 60 µM). Additional in vitro studies demonstrated that 1 induces apoptosis via G2-M cell cycle arrest and reduces cell proliferation as well as cell migration in MCF-7 cells. In vivo subacute toxicity (28 days) and systemic chronic toxicity (40 days) studies were carried out in normal Swiss albino mice showed 1 is significantly nontoxic to the host. SIGNIFICANCE: The readily synthesizable, significantly nontoxic cobalt complex with appreciable anticancer activity implies that it might be an effective chemotherapeutic agent for new-age anti-tumor medication.

Supramolecular Arrangement and DFT analysis of Zinc(II) Schiff Bases: An Insight towards the Influence of Compartmental Ligands on Binding Interaction with Protein.

We report, for the first time, a detailed crystallographic study of the supramolecular arrangement for a set of zinc(II) Schiff base complexes containing the ligand 2,6-bis((E)-((2-(dimethylamino)ethyl)imino)methyl)-4-R-phenol], where R=methyl/tert-butyl/chloro. The supramolecular study acts as a pre-screening tool for selecting the compartmental ligand R of the Schiff base for effective binding with a targeted protein, bovine serum albumin (BSA). The most stable hexagonal arrangement of the complex [Zn-Me] (R=Me) stabilises the ligand with the highest FMO energy gap (ΔE=4.22 eV) and lowest number of conformations during binding with BSA. In contrast, formation of unstable 3D columnar vertebra for [Zn-Cl] (R=Cl) tend to activate the system with lowest FMO gap (3.75 eV) with highest spontaneity factor in molecular docking. Molecular docking analyses reported in terms of 2D LigPlot+ identified site A, a cleft of domains IB, IIIA and IIIB, as the most probable protein binding site of BSA. Arg144, Glu424, Ser428, Ile455 and Lys114 form the most probable interactions irrespective of the type of compartmental ligands R of the Schiff base whereas Arg185, Glu519, His145, Ile522 act as the differentiating residues with ΔG=-7.3 kcal mol-1 .

Synthesis of Mn3O4 nanozymes from structurally characterized phenoxazinone synthase models based on manganese(iii) Schiff base complexes.

Three mononuclear and one hexanuclear manganese(iii) complexes, [Mn(L)(H2O)2]·Cl (1), [Mn(L)(H2O)2]·Br (2), [Mn(L)(H2O)2]·NO3 (3), and [Mn6(L)6(NCS)6] (4), have been synthesized using a Schiff-base ligand, namely (E)-2-((3-(2-hydroxyethylamino)propylimino)methyl)phenol (H2L), and structurally characterized by the usual physicochemical techniques such as UV-Vis, FT-IR, ESI-MS, EPR and single crystal XRD. The structure of complex 4 is unique among all four complexes as the sixth coordination position of manganese is fulfilled by the oxygen atom of a neighbouring unit by covalent interaction. The phenoxazinone synthase like activity of all four complexes has been thoroughly investigated using three different substrates, o-aminophenol (OAP), 2-amino-4-methylphenol (MAP) and 3-amino-4-hydroxybenzoic acid (CAP). All complexes were found to be active towards catalysis and complex 4 showed the highest activity. The EPR study reveals that the oxidative dimerization of the substrates occurred through metal centered redox participation rather than a radical formation pathway. The experimental observations have been supported by DFT calculations to put forward the most probable mechanistic pathways operating in the catalytic cycle. Moreover, Mn3O4 nanoparticles (NPs) having two different morphologies have been synthesized using complexes 1 and complex 4 simply by calcination, respectively, with the aim to prepare nanozymes. These two synthesized NPs were also able to show phenoxazinone synthase like activity and thus complexes 1 and 4 can be claimed as precursors of nanozymes.

Designing of novel zinc(ii) Schiff base complexes having acyl hydrazone linkage: study of phosphatase and anti-cancer activities.

Three asymmetric tridentate acyl hydrazone Schiff base ligands namely L1, L2 and L3 were prepared via condensation of 4-methoxybenzohydrazide with picolinaldehyde, 1-(pyridin-2-yl)ethanone and phenyl(pyridin-2-yl)methanone respectively. Three bio-relevant mononuclear zinc(ii) complexes [Zn(L1)Cl2]·2H2O (1), [Zn(L2)Cl2] (2) and [Zn(L3)Cl2] (3) were synthesized by treatment of zinc(ii) chloride with the corresponding Schiff base ligands and characterised by the usual physicochemical techniques. The solid state structures of complexes 1 and 3 were evaluated by single crystal X-ray analysis. All complexes were able to hydrolyse the P-O bond of the phosphate monoester in 90% (v/v) DMSO-water medium using 4-nitrophenylphosphate (4-NPP) as the model substrate and the trend in their activity is 1≈2 > 3. On considering the highly efficient hydrolysis properties, complexes 1-3 were tested as potential therapeutic agents for cancer using HCT116 (human colorectal carcinoma), HepG2 (human hepatocellular carcinoma) and A549 (human non-small lung carcinoma) cells. Complex 2 showed the highest IC50 values for anti-cancer activity towards all three cell lines among the three complexes and complex 3 showed the least activity as observed in the phosphatase activity study. The internucleosomal degradation of DNA during apoptosis can be detected by cell death detection ELISA. DNA fragmentation that leads to cell death was examined and when induced by complex 2 in HepG2 cells a significant level of DNA fragmentation was observed at regular intervals of time.

Executing a Series of Zinc(II) Complexes of Homologous Schiff Base Ligands for a Comparative Analysis on Hydrolytic, Antioxidant, and Antibacterial Activities.

Six zinc(II) complexes, namely, [Zn(HL1H)Cl2] (1), [Zn(HL1H)Br2] (2), [Zn2(HL1H)2(OH)I2]·I (3), [Zn(HL2)Cl] (4), [Zn2(HL2)Br3] (5), and [Zn(HL2)I] (6) have been manufactured by using two homologous Schiff base ligands H2L1 and H2L2 for the purpose of perlustrating their phosphatase-like activity, antioxidant activity, and antibacterial activity. Complexes 1, 2, 4, and 5 have been reported earlier by us, whereas complexes 3 and 6 have been synthesized and structurally characterized by regular physicochemical methods The hydrolytic property of the six complexes has been evaluated by checking the hydrolysis of the P-O bond of a widely used substrate, namely, disodium salt of (para-nitrophenyl)phosphate (PNPP) in 97.5% (v/v) mixture of N,N-dimethylformamide and water (DMF-water). Complexes 2-5 have profound efficiency toward hydrolysis of phosphate ester bonds, and complexes 1 and 6 were noted to be inactive toward hydrolysis. Complex 3 displayed the highest efficacy among the six complexes. Additionally, antioxidant and antibacterial activities of the complexes were studied thoroughly. A detailed study of their antioxidant property revealed that complex 3 manifested superior radical scavenging activity, thus exhibiting the highest antioxidant property. The antibacterial activity was tested using four investigating bacteria, specifically Listeria monocytogenes ATCC19111, Staphylococcus aureus ATCC 700699, Salmonella typhimurium ATCC 23564, and Escherichia coli ATCC 25922 by determining minimum inhibitory concentration (MIC) values using the microdilution method. Here as well, complex 3 exhibited the highest activity to both Gram positive and Gram negative bacteria. The chemistry behind these experimental findings has been manifested by shedding light upon the structural features of the complexes. The suitable choice of ligand H2L1 where one methylene group is less than its homologous ligand and metal precursor (ZnI2) imparts a unique hydroxo-bridged molecular geometry and 2D hydrogen bonding network which in turn probably enhances the hydrolytic and biological activities of complex 3.

Anion-mediated bio-relevant catalytic activity of dinuclear nickel(ii) complexes derived from an end-off compartmental ligand.

Four dinuclear nickel(ii) complexes, namely [Ni4(L)2(H2O)8(µ2-H2O)2](NO3)6(H2O)6 (1), [Ni2(L)Cl2(µ-Cl)(CH3OH)] (2), [Ni2(L)(OAc)2(H2O)2]Br (3) and [Ni2(L)(H2O)4(µ2-OH)] (H2O)X(I)X (4), have been synthesized using a template synthesis technique by adding nickel(ii) salts (nitrate/chloride/bromide/iodide) to the N4O donor end-off compartmental ligand (HL) obtained via the condensation of 2-(2-pyridyl)ethylamine and 2,6-diformyl-4-isopropyl phenol in methanol. All complexes were characterized with the help of typical physicochemical techniques, and their solid-state structures were assigned from single crystal X-ray analysis. The variable temperature magnetic study reveals that the two nickel centers are antiferromagnetically coupled with J values ranging from -5 to -15 cm-1 in the complexes. The catecholase-like activity of complexes 1-4 was studied using 3,5-di-tert-butylcatechol (3,5-DTBC) as the model substrate in N,N-dimethylformamide (DMF) medium. Complex 1 shows the catecholase activity, while the other complexes were found to be inactive. The phosphatase-like activity of the complexes was also investigated in a 97.5% (v/v) DMF-water mixture using the disodium salt of 4-nitrophenylphosphate (4-NPP) as the model substrate and the reactivity trend was 4 > 1 > 3 > 2. The reasons behind the activity, inactivity and activity trend have been explored. It has been assumed that the anions associated with the complexes are supposed to play a crucial role in the whole event. Complex 1 showed catalytic promiscuity, whereas complexes 2, 3 and 4 should be considered only as the potential hydrolytic catalyst.

A Deep Insight into the Photoluminescence Properties of Schiff Base CdII and ZnII Complexes.

A tridentate N,N,O donor ligand 2,4-dichloro-2-[(2-piperazine-4-yl-ethylimino)-methyl]-phenol (HL) was designed, and eight new ZnII and CdII complexes, namely, [Zn(LH)(SCN)2] (1), [Zn(LH)(N3)2] (2), [Zn(LH)(NO2)2] (3), [Zn(LH)(dca)(OAc)] (4), [Cd2(LH)2(SCN)4] (5), [Cd(LH)(N3)2] (6), [Cd(LH)(NO2)2] (7), and [Cd(LH)(dca)(OAc)] (8) [where dca = dicyanamide anion] were synthesized. Five of them (1, 2, 4, 5, 7) were structurally characterized through single-crystal X-ray diffraction analysis. H-Bonding interactions are found to be the major stabilizing factor for crystallization in the solid state. Experimental and computational studies were performed in cooperation to provide a rationalization of the photoluminescence properties of those complexes. The quantum yields are anion-dependent, with enhanced efficiencies in the following order: LH < Cd-SCN(5) < Cd-dca(8) < Cd-N3(6) < Cd-NO2(7) < Zn-dca(4) < Zn-N3(2) < ZnNO2(3) < ZnSCN(1). By using quantum chemical calculations we rationalized the above trends. Moreover, the diverse lifetimes observed for those eight complexes were also quantitatively explained by considering the subtle competition between different photo-deactivation pathways.

Cooperative influence of pseudohalides and ligand backbone of Schiff-bases on nuclearity and stereochemistry of cobalt(iii) complexes: experimental and theoretical investigation.

Four cobalt(iii) complexes, [Co(HL1)(NCS)2(EtOH)] (1), [Co2(L1)2(N3)2] (2) and [Co(HL2)(NCS)2(EtOH)] (3), [Co(HL2)(N3)2] (4) were synthesized from two Schiff-base ligands namely, (E)-2-((2-(2-hydroxyethylamino)ethylimino)methyl)phenol (H2L1) and (E)-2-((3-(2-hydroxyethylamino)propylimino)methyl)phenol (H2L2), respectively. All the four complexes have been thoroughly characterised by using various physicochemical studies such as UV-Vis, FT-IR, ESI-MS, EPR and single crystal X-ray diffraction. Depending on flexibility of the ligand backbone subtle structural differences are observed in the synthesized complexes. In complex 1 the two thiocyanate ligands are trans to each other whereas in complex 3 they are cis to each other with addition of one additional methylene (-CH2-) group to the ligand system. Complex 2 is dinuclear while complex 4 is mononuclear in the presence of the azide co-anionic ligand. Theoretical studies are carried out in order to rationalize the structural differences observed in the complexes. Catecholase like activity of all the four complexes were performed in N,N-dimethylformamide (DMF) using 3,5-di-tert-butylcatechol (3,5-DTBC) as a model substrate. Complex 2 was found to exhibit the highest activity. Mechanistic investigation of the catecholase like activity revealed the formation of the imine radical during catalytic reactions of complexes 2 and 4 which are further corroborated by the EPR study.

Unveiling the effects of the in situ generated arene anion radical and imine radical on catecholase like activity: a DFT supported experimental investigation.

Two new dinuclear nickel(ii) complexes namely [Ni2(L1)2(OAc)2(H2O)2]·CH3CN (1) and [Ni2(L2)2(SCN)2(CH3OH)2]·CH3OH (2) have been synthesized from the designed Schiff-base ligand 4-bromo-2-[(2-hydroxy-1,1-dimethyl-ethylimino)-methyl]-phenol (HL1) and its reduced analogue 4-bromo-2-[(2-hydroxy-1,1-dimethyl-ethylamino)-methyl]-phenol (HL2), respectively. Both 1 and 2 have been characterised by usual physicochemical techniques (UV-Vis, FT-IR, ESI-MS study and single crystal XRD) and their variable temperature magnetic study has been performed. The nickel(ii) centres in the dinuclear complexes 1 and 2 are antiferromagnetically coupled through participation of the bridging phenoxyl oxygen. In acetonitrile solution both 1 and 2 retain their dinuclear structural integrity as is evident from the ESI-MS study. The catecholase-like activity of 1 and 2 has been performed in acetonitrile medium using 3,5-di-tert-butylcatechol (3,5-DTBC) as a model substrate. Complex 1 shows a higher catalytic activity than that of complex 2. The ESI-MS study suggests that dinuclear species undergo cleaving into a mononuclear entity in the presence of 3,5-DTBC and that mononuclear species are supposed to act as active catalysts in the catalytic cycle. The EPR study of catalytic reactions confirms that organic radicals have been generated during catalysis in both cases. However, in the case of complex 1 catalyzed reaction a single isotropic signal at g = 1.97 is obtained which is most likely due to imine radical formation. On the other hand, for complex 2 catalyzed reaction the spectrum shows a signal with hyperfine splitting (g = 2.11, 2.05 and 1.9), thereby suggesting the generation of a new radical i.e. an arene anion radical in this study on catecholase activity. Extensive DFT calculations have been performed to support the experimental observation and thus to put forward the most probable mechanistic pathways operating in the two cases. The higher efficiency of the imine radical pathway over the arene anion radical has been rationalized by DFT calculations.

Unique mononuclear Mn(II) complexes of an end-off compartmental Schiff base ligand: experimental and theoretical studies on their bio-relevant catalytic promiscuity.

Three new mononuclear manganese(ii) complexes, namely [Mn(HL)2]·2ClO4 (1), [Mn(HL)(N(CN)2)(H2O)2]·ClO4 (2) and [Mn(HL)(SCN)2] (3) [LH = 4-tert-butyl-2,6-bis-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol], have been synthesized and structurally characterized. An "end-off" compartmental ligand (LH) possesses two symmetrical compartments with N2O binding sites but accommodates only one manganese atom instead of two due to the protonation of the imine nitrogen of one compartment. Although all three complexes are mononuclear, complex 1 is unique as it has a 1 : 2 metal to ligand stoichiometry. The catalytic promiscuity of complexes 1-3 in terms of two different bio-relevant catalytic activities namely catecholase and phenoxazinone synthase has been thoroughly investigated. EPR and cyclic voltametric studies reveal that radical formation rather than metal centered redox participation is responsible for their catecholase-like and phenoxazinone synthase-like catalytic activity. A computational approach suggests that imine bond bound radical generation rather than phenoxo radical formation is most likely responsible for the oxidizing properties of the complexes.