Zinc(II)-MOF: A Versatile Luminescent Sensor for Selective Molecular Recognition of Flame Retardants and Antibiotics.

An exceptional Zinc(II)-organic framework with the formula [{Zn(L4-py)(bdc)}·DMF]n (Zn-MOF) has been constructed solvothermally using a novel linker L4-py {2,7-bis(3-(pyridin-4-ylethynyl)phenyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone}, coligand H2bdc (1,4-benzenedicarboxylic acid), and ZnBF4·xH2O. The ligand L4-py has been fabricated after functionalization of NDA (1,4,5,8-naphthalenetetracarboxylic dianhydride) core with 3-(pyridin-4-ylethynyl)phenyl group. The single-crystal X-ray analysis reveals that Zn-MOF exhibits a comprehensive three-dimensional (3D) framework architecture and features (4)-connected uninodal dia; 4/6/c1; sqc6 topology with point symbol {66} and two-dimensional (2D) + 2D, parallel polycatenation. Notably, Zn-MOF displayed excellent fluorescence phenomenon and stability in water as well as in methanol solvents and was harnessed as a versatile sensor, demonstrating selective and sensitive molecular recognition of flame retardants and antibiotics. Notably, Zn-MOF displayed 57 and 49.5% quenching efficiency for the flame-retardant pentabromophenol (PBP) and 3,3',5,5'-tetrabromobisphenol A (TBPA), respectively. Whereas an outstanding 90% quenching efficiency was observed for antibiotics, tetracycline (TC) and secnidazole (SD). The mechanistic investigations of this luminescence quenching suggest that this might be primarily occurring via the Fourier resonance energy transfer (FRET) and photoinduced electron transfer (PET) mechanisms, which might be assisted by the competitive absorption and host-guest interactions. The π-electron-rich framework structure of sensor Zn-MOF activates this mechanism.

Metal-Organic Framework-Based Selective Molecular Recognition of Organic Amines and Fixation of CO2 into Cyclic Carbonates.

Synthesis and structural depiction of two new metal-organic frameworks (MOFs), namely, [{Zn(L)(oba)}·4H2O]α (Zn-MOF-1) and [{Cd1/2(L)1/2(nipa)1/2(H2O)1/2}·(DMF)1/2(H2O)]α (Cd-MOF-2) (where L = N2,N6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide, 4,4'-H2oba = 4,4'-oxybisbenzoic acid, and 5-H2nipa = 5-nitroisophthalic acid) are reported. Both Zn-MOF-1 and Cd-MOF-2 have been prepared by reacting ligand L and coligand 4,4'-H2oba or 5-H2nipa with the respective dihydrates of Zn(OAc)2 and Cd(OAc)2 (OAc = acetate). Crystal structure X-ray analysis discloses that Zn-MOF-1 displays an overall 2D → 3D interpenetrated framework structure. The topological analysis by ToposPro suggests a (4)-connected uninodal sql topology with a point symbol of {44·62} having 2D + 2D parallel polycatenation. However, crystal packing of Cd-MOF-2 adapted a porous framework architecture and was topologically simplified as (3,4)-connected binodal 2D net. In addition, both Zn-MOF-1 and Cd-MOF-2 were proved to be multifunctional materials for the recognition of organic amines and in the fixation of CO2 to cyclic carbonates. Remarkably, Zn-MOF-1 and Cd-MOF-2 showed very good fluorescence stability in aqueous media and have shown 98 and 97% quenching efficiencies, respectively, for 4-aminobenzoic acid (4-ABA), among all of the researched amines. The mechanistic study of organic amines recognition proposed that fluorescence quenching happened mainly through hydrogen-bonding and π-π stacking interactions. Additionally, cycloaddition of CO2 to epoxide in the presence of Zn-MOF-1 and Cd-MOF-2 afforded up to 96% of cyclic carbonate within 24 h. Both Zn-MOF-1 and Cd-MOF-2 exhibited recyclability for up to five cycles without noticing an appreciable loss in their sensing or catalytic efficiency.

Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso-Hydroxylation of Arylboronic Acids.

We report the synthesis and structural characterization of two coordination polymers (CPs), namely; [{Zn(L)(DMF)4 } ⋅ 2BF4 ]α (1) and [{Cd(L)2 (Cl)2 } ⋅ 2H2 O]α (2) (where L=N2 ,N6 -di(pyridin-4-yl)naphthalene-2,6-dicarboxamide). Crystal packing of 1 reveals the existence of channels running along the b- and c-axis filled by the ligated DMF and lattice anions, respectively. Whereas, crystal packing of 2 reveals that the metallacycles of each 1D chain are intercalating into the groove of adjacent metallacycles resulting in the stacking of 1D loop-chains to form a sheet-like architecture. In addition, both 1 and 2 were exploited as multifunctional materials for the detection of nitroaromatic compounds (NACs) as well as a catalyst in the ipso-hydroxylation of aryl/heteroarylboronic acids. Remarkably, 1 and 2 showed high fluorescence stability in an aqueous medium and displayed a maximum 88% and 97% quenching efficiency for 4-NPH, respectively among all the investigated NACs. The mechanistic investigation of NACs recognition suggested that the fluorescence quenching occurred via electron as well as energy transfer process. Furthermore, the ipso-hydroxylation of aryl/heteroarylboronic acids in presence of 1 and 2 gave up to 99% desired product yield within 15 min in our established protocol. In both cases, 1 and 2 are recyclable upto five cycles without any significant loss in their efficiency.

A highly active copper catalyst for the hydrogenation of carbon dioxide to formate under ambient conditions.

Carbon dioxide (CO2) is an important reactant and can be used for the syntheses of various types of industrially important chemicals. Hence, investigation concerning the conversion of CO2 into valuable energy-rich chemicals is an important and current topic in molecular catalysis. Recent research on molecular catalysts has led to improved rates for conversion of CO2 to energy-rich products such as formate, but the catalysts based on first-row transition metals are underdeveloped. Copper(i) complexes containing the 1,1'-bis(di-tert-butylphosphino) ferrocene ligand were found to promote the catalytic hydrogenation of CO2 to formate in the presence of DBU as the base, where the catalytic conversion of CO2via hydrogenation is achieved using in situ gaseous H2 (granulated tin metal and concentrated HCl) to produce valuable energy-rich chemicals, and therefore it is a promising, safe and simple strategy to conduct reactions under ambient pressure at room temperature. Towards this goal, we report an efficient copper(i) complex based catalyst [CuI(dtbpf)] to achieve ambient-pressure CO2 hydrogenation catalysis for generating the formate salt (HCO2-) with turnover number (TON) values of 326 to 1.065 × 105 in 12 to 48 h of reaction at 25 °C to 80 °C. The outstanding catalytic performance of [CuI(dtbpf)] makes it a potential candidate for realizing the large-scale production of formate by CO2 hydrogenation.

Synthetic, spectral, structural and catalytic activity of infinite 3-D and 2-D copper(ii) coordination polymers for substrate size-dependent catalysis for CO2 conversion.

Two copper(ii) coordination polymers, viz. [Cu2(OAc)4(µ4-hmt)0.5]n (1) and [Cu{C6H4(COO-)2}2]n·2C9H14N3 (2), have been synthesized solvothermally and characterized. The solid-state structure reveals that 1 is an infinite three-dimensional (3D) motif with fused hexagonal rings consisting of Cu(ii) and hmt in a µ4-bridging mode, while 2 is an infinite two dimensional (2D) motif containing Pht-2 in a µ1-bridging mode. CP 1 has a two-fold interpenetrated diamondoid network composed of 4-connected sqc6 topology with the point symbol of {66}, while 2 has a Shubnikov tetragonal plane network possessing a 4-connected node with an sql topology with a point symbol of {44·.62}-VS [4·4·4·4·*·*]. Both CPs 1 and 2 serve as efficient catalysts for CO2-based chemical fixation. Moreover, 1 demonstrates one of the highest reported catalytic activity values (%yield) among Cu-based MOFs for the chemical fixation of CO2 with epoxides. 1 shows high efficiency for CO2 cycloaddition with small epoxides but its catalytic activity decreases sharply with the increase in the size of epoxide substrates. The catalytic results suggested that the copper(ii) motif-catalyzed CO2 cycloaddition of small substrates had been carried out within the framework, while large substrates could not enter into the framework for catalytic reactions. The high efficiency and size-dependent selectivity toward small epoxides on catalytic CO2 cycloaddition make 1 a promising heterogeneous catalyst for carbon fixation and it can be used as a recoverable stable heterogeneous catalyst without any loss of performance. The solvent-free synthesis of the cyclic carbonate from CO2 and an epoxide was monitored by in situ FT-IR spectroscopy and an exposed Lewis-acid metal site catalysis mechanism was proposed.

Synthesis and photophysical properties of pyridyl conjugated triazole appended naphthalenediimide derivatives.

A series of three substituted triazole appended NDI-derivatives, 2,7-bis(3,5-di(pyridin-X-yl)-4H-1,2,4-triazol-4-yl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (where X = 2, NDI-PyTz-1; 3, NDI-PyTz-2; and 4, NDI-PyTz-3), were designed, synthesized and well characterized using various analytical and spectroscopic techniques. All the three NDI-PyTz derivatives exhibit decent electronic properties as suggested by DFT, cyclic voltammetry and fluorescence studies. In particular, NDI-PyTz-1 demonstrated the generation of a stable anion radical [NDI-PyTz-1]˙-.

EGFR, HER2 target based molecular docking analysis, in vitro screening of 2, 4, 5-trisubstituted imidazole derivatives as potential anti-oxidant and cytotoxic agents.

In our endeavor towards the development of potent molecules for cancer diseases, we have designed and synthesized a series of 2,4,5-trisubstituted imidazole derivatives (B1-B24) and characterized by using various spectroscopic techniques. All these compounds are further evaluated for their in vitro anti-cancer, anti-oxidant activities and molecular docking studies against EGFR, HER2 protein receptors. The in vitro anti-cancer activity analysis reveals that compounds B11 and B16 were found to be effective scaffolds against the tested human cancer cell lines IMR-32, A549 and HeLa. Particularly, B16 and B11 showed effective cytotoxicity against A549 and IMR-32 with IC50 values of 09.521±0.54µM and 10.294±0.43µM, respectively. Moreover, compounds B17, B18 and B23 showed potent activity towards the anti-oxidant screening with IC50 values of 5.87±1.73µM, 6.29±1.27µM and 4.95±1.81µM, respectively compared to standard ascorbic acid. Molecular docking was performed against the EGFR, HER2 protein receptors to provide more insight into their mechanism of interaction by comparing with standard EGFR, HER2 inhibitors like Gefitinib (EFGR), Lapatanib (EGFR), Afitinib (HER2) and Canertinib (HER2). Compounds B15, B16, B11 and B10 were exhibiting their minimum binding energies. Out of the aforementioned docked molecules, B15 and B16 showed the best binding energies of -11.15kcalmol-1, -10.70kcalmol-1 and -10.49kcalmol-1, -10.12kcalmol-1 against EGFR and HER2 protein receptors, respectively. The molecular docking results are well corroborated with the in vitro anti-cancer activity finding.

Design, synthesis and biological evaluation of 8-substituted-6-hydrazonoindolo[2,1-b]quinazolin-12(6H)-one scaffolds as potential cytotoxic agents: IDO-1 targeting molecular docking studies.

Herein, we have reported the synthesis of 18 novel 8-substituted tryptanthrin analogues based on our earlier work. All these tryptanthrin analogues were well characterized by 1H &13C NMR, FT-IR, Mass Spectrometry and Elemental Analysis. All these 8-substituted analogues were screened for their anti-oxidant activity by DPPH radical scavenging assay. Out of all the tested compounds, T11, T12, T17 and T18 showed potent anti-oxidant activity. The anti-cancer activity have been performed by using MTT assay protocol and their results depicts that compounds having the 4-pyridyl or 4-carboxyphenyl substituents at the 8th position of the tryptanthrin framework are found to be the most promising cytotoxic agent against A549, MCF-7 and HeLa human cancer cell lines compared to others as well as with the standard drug cisplatin. Moreover, the comparative molecular docking studies against the three protein receptors IDO1, EGFR and HER2 strongly suggested that IDO1 is the best target protein, which exhibits lowest binding energies of -11.73 and -11.61kcalmol-1 for T11 and T12 scaffolds, respectively towards the in vitro anti-cancer activity.

A Functional Zn(II) Metallacycle Formed from an N-Heterocyclic Carbene Precursor: A Molecular Sensor for Selective Recognition of Fe3+ and IO4- Ions.

We have reported the synthesis and structural characterization of a unique Zn(II) metallacycle (1) and its utilization as a fluorescent probe for the shape-specific selective recognition (turn-off) of Fe3+ and IO4- ions. The relevant Stern-Volmer graphs indicate that the recognitions of Fe3+ and IO4- ions are examples of diphasic and monophasic quenchings, respectively. The title metallacycle has been prepared by the reaction of a novel N-heterocyclic carbene precursor, 1,3-bis(2,6-diisopropyl-4-(pyridin-4-yl)phenyl)-1H-imidazol-3-ium chloride/bromide (L), and zinc(II) chloride salt. Notably, the ligand itself did not show any type of recognition for any ions. DFT calculations were performed on L and metallacycle 1 using the geometric parameters, obtained from their single-crystal X-ray diffraction data, to understand the electronic structures of the ligand and macrocycle. The detection limit for the recognition of the Fe3+ ion was determined to be 2.5 × 10-6 mol/L, and that for IO4- ion was found to be 6.3 × 10-5 mol/L.

Crystal structure of (E)-4-hy-droxy-6-methyl-3-{1-[2-(4-nitro-phen-yl)hydrazinyl-idene]eth-yl}-2H-pyran-2-one.

The title compound, C14H13N3O5 (HMNP), was synthesized by the simple condensation of p-nitro-phenyl-hydrazine with de-hydro-acetic acid (DHA) in a 1:1 molar ratio in ethanol. HMNP has been characterized by using FT-IR, 1H and 13C NMR and UV-Vis spectroscopic and single-crystal X-ray diffraction techniques. The crystal packing reveals strong hydrogen bonds between the NH group and the carbonyl O atom of di-hydro-pyran-one moiety, forming chains along [101]. The thermal stability of the synthesized compound was confirmed by thermogravimetric analysis and it was found to be stable up to 513 K. The UV-Vis spectrum shows the presence of a strong band at λmax 394 nm. 1H NMR and single-crystal X-ray analyses confirmed the presence of the enol form of the ligand and dominance over the keto form. The crystal studied was a non-merohedral twin with the refined ratio of the twin components being 0.3720 (19):0.6280 (19).

Novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues as cytostatic agents: Synthesis, crystal structure, biological evaluation and molecular docking studies.

A series of novel substituted hydrazono indolo[2,1-b]quinazoline-6,12-dione analogues have been synthesized and screened for their in vitro cytotoxic and antimicrobial activities. Among all the target compounds, 3c exhibited the most potent inhibitory activity against three cancer cell lines MCF-7, A549, HeLa with IC50 values 07.14±1.285µM, 09.18±0.968µM and 10.57±0.581µM respectively, while maintaining low toxicity towards non-cancer originated cell line, HEK-293. The detailed studies about molecular interactions with probable target protein indoleamine 2,3-dioxygenase (IDO1) were done by using docking simulations. The results from docking models are in consistent with the experimental in vitro cytotoxic activity conclusions i.e. 3c shows the highest binding energy -11.25kcal/mol. Furthermore, antimicrobial studies revealed that the compound 3e has shown excellent anti bacterial activity against four tested strains and the compounds 3b, 3e and 3f have shown good anti fungal activity against two tested organisms as compared with their standard drugs.

Manganese- and cobalt-based coordination networks as promising heterogeneous catalysts for olefin epoxidation reactions.

We demonstrate the synthesis of Mn(2+)- and Co(2+)-based coordination networks using two Co(3+)-based metalloligands differing by the position of the appended arylcarboxylate groups. The structural analyses reveal topologically distinct networks with pores of variable dimensions allowing facile diffusion of substrates and/or reagents. All four networks function as heterogeneous catalysts for the olefin epoxidation reactions using tert-butyl-hydroperoxide without any requirement of solvent or additive. Control and optimization experiments illustrate recyclable network-based catalysts that make them attractive candidates for the "greener" oxidation chemistry processes.

Molecularly designed architectures--the metalloligand way.

Designed materials offer noteworthy applications which are often architecture dependent. Despite knowing such a fact, one of the major challenges faced by the scientific community is to find ways to predict and, if possible, control the resultant architecture of a network. If such an exercise is fruitful, it creates enormous opportunities to synthesize exotic materials with tailor-made applications. Any network is composed of individual molecules and the transition from a single molecule to a network can be achieved through several routes taking advantage of synthetic chemistry. There exists a molecular building block at the heart of such a transition which mediates such a process from a single molecule to a network. Although a large number of building blocks have created assorted materials, utilization of a well-defined coordination complex as the building block (i.e., metalloligand) is unique for the construction of a designed architecture. A coordination complex as the building block offers structural rigidity that places the auxiliary functional groups to a pre-organized conformation. Such auxiliary functional groups could then coordinate a secondary metal ion or be involved in the self-assembly via weak interactions, such as hydrogen bonds. This review focuses on the recent progress achieved through assorted molecular building blocks towards generating ordered networks. Broadly, two classes of metalloligands will be discussed: those offering hydrogen bond sensitive functional groups and those tendering coordination bond responsive groups. Nevertheless, the result is the construction of networks of a highly-ordered nature in both cases. The present review is expected to provide new strategies for constructing functional materials through metalloligands for challenging and practical applications.

Three-dimensional {Co(3+)-Zn2+} and {Co(3+)-Cd2+} networks originated from carboxylate-rich building blocks: syntheses, structures, and heterogeneous catalysis.

The present work shows the utilization of Co(3+) complexes appended with either para- or meta-arylcarboxylic acid groups as the molecular building blocks for the construction of three-dimensional {Co(3+)-Zn(2+)} and {Co(3+)-Cd(2+)} heterobimetallic networks. The structural characterizations of these networks show several interesting features including well-defined pores and channels. These networks function as heterogeneous and reusable catalysts for the regio- and stereoselective ring-opening reactions of various epoxides and size-selective cyanation reactions of assorted aldehydes.

Cobalt complexes appended with p- and m-carboxylates: two unique {Co(3+)-Cd2+} networks and their regioselective and size-selective heterogeneous catalysis.

Co(3+) complexes appended with arylcarboxylate groups act as molecular building blocks to afford {Co(3+)-Cd(2+)} networks. These networks function as the heterogeneous and reusable catalysts for regio- and stereoselective ring opening of epoxides and size-selective cyanation of aldehydes.

Two-dimensional {Co(3+)-Zn2+} and {Co(3+)-Cd2+} networks and their applications in heterogeneous and solvent-free ring opening reactions.

We report the synthesis and structural characterization of two-dimensional {Co(3+)-Zn(2+)} and {Co(3+)-Cd(2+)} heterobimetallic networks and their catalytic applications in heterogeneous and solvent-free ring opening reactions of various epoxides.