Selective sensing of picric acid using a Zn(II)-metallacycle: experimental and theoretical validation of the sensing mechanism and quantitative analysis of sensitivity in contact mode detection.

A combination of N,N',N''-tris(3-pyridyl)-1,3,5-benzenetricarboxamide (L1) and p-chlorobenzoic acid (HL2) with Zn(NO3)2·6H2O resulted in the formation of a dinuclear metallacycle [ZnL1(L2)2(DMF)2]2 (1(DMF)4). In 1(DMF)4, the Zn(II) centre adopts a square pyramidal geometry, while one of the pyridyl N out of the three pyridyl groups in L1 remained uncoordinated. Solvated DMF molecules are present in 1(DMF)4. The structural and chemical nature of 1(DMF)4 is effective for it to act as a potential fluorescent probe for the detection of nitroaromatic compounds. It is observed that the probe, 1(DMF)4, could selectively detect picric acid (PA) among various aromatic compounds in solution (DMSO), while the solid state (contact mode) detection showed a positive sensing response for the nitrophenols (PA: 87% quenching efficiency, 2,4-dinitrophenol (2,4-DNP): 57% quenching efficiency and 4-nitrophenol (4-NP): 40% quenching efficiency). The limit of detection (LOD) of PA by the probe in DMSO was found to be 6.8 × 10-11 M while the LOD in contact mode detection was estimated to be 0.49 ng cm-2. The mechanism of selective detection of PA by 1(DMF)4 in DMSO was analyzed through photophysical studies, 1H-NMR experiments and also by density functional theory (DFT) calculations. The effective overlap of the absorption spectrum of 1(DMF)4 and emission spectrum of PA in DMSO suggests that the Förster resonance energy transfer (FRET) is responsible for quenching phenomena in DMSO. The DFT calculations and molecular docking studies showed the adduct formation due to the favorable interactions between 1(DMF)4 and PA in DMSO, while negligible interactions were observed between 1(DMF)4 with other aromatic compounds. The experimental and DFT studies showed that the efficient sensing ability of PA by 1(DMF)4 in the solid-state was due to photoelectron transfer (PET) and FRET phenomena described herein.

Tailored Inorganic-Organic Architectures via Metalloligands.

This article discusses the design principles and strategies and the structural outcome of various supramolecular architectures constructed by utilizing well-defined coordination complexes as the metalloligands. We have included selected examples of metalloligands, offering either pyridyl or arylcarboxylic acid groups as the appended functional groups, for illustrating the construction of their supramolecular architectures. Both geometrical position and the number of the appended functional groups emerging from a metalloligand were found to critically regulate the structural aspects and dimensionality of the resultant material. The article concludes by delineating the structure-directing lessions as well as the potential applications of the metalloligand-based supramolecular architectures for the generation of next-level materials.

Molecular Assemblies Offering Hydrogen-Bonding Cavities: Influence of Macrocyclic Cavity and Hydrogen Bonding on Dye Adsorption.

This work presents a set of Hg macrocycles of amide-phosphine-based ligands offering H-bonding cavities of different dimensions. Such macrocycles are shown to selectively adsorb anionic dyes followed by neutral dyes as well as Prontosil, a biologically relevant antibiotic, within their cavities with the aid of H-bonding-assisted encapsulation. Kinetic experiments supported by spectroscopic and docking studies illustrate the importance of the cavity structure as well as H-bonds for the selective adsorption of dyes.

Synthesis, In Silico Study, and Anti-Cancer Activity of Thiosemicarbazone Derivatives.

Thiosemicarbazones are known for their biological and pharmacological activities. In this study, we have synthesized and characterized 3-Methoxybenzaldehyde thiosemicarbazone (3-MBTSc) and 4-Nitrobenzaldehyde thiosemicarbazone (4-NBTSc) using IR, 1HNMR and 13C NMR. The compound's in vitro anticancer activities against different cell lines were evaluated. Molecular docking, Insilco ADMET, and drug-likeness prediction were also done. The test compounds showed a comparative IC50 and growth inhibition with the standard drug Doxorubicin. The IC50 ranges from 2.82 µg/mL to 14.25 µg/mL in 3-MBTSc and 2.80 µg/mL to 7.59 µg/mL in 4-NBTSc treated cells. The MTT assay result revealed, 3-MBTSc inhibits 50.42 and 50.31 percent of cell growth in B16-F0 and EAC cell lines, respectively. The gene expression showed that tumor suppressor genes such as PTEN and BRCA1 are significantly upregulated in 7.42 and 5.33 folds, and oncogenes, PKC, and RAS are downregulated -7.96 and -7.64 folds, respectively in treated cells. The molecular docking performed on the four targeted proteins (PARP, VEGFR-1, TGF-ß1, and BRAFV600E) indicated that both 4-NBTSc and 3-MBTSc potentially bind to TGF-ß1 with the best binding energy of -42.34 Kcal/mol and -32.13 Kcal/mol, respectively. In addition, the test compound possesses desirable ADMET and drug-likeness properties. Overall, both 3-MBTSc and 4-NBTSc have the potential to be multitargeting drug candidates for further study. Moreover, 3-MBTSc showed better activity than 4-NBTSc.

Supramolecular catalysis: the role of H-bonding interactions in substrate orientation and activation.

Hydrogen bonding plays significant roles in various biological processes during substrate orientation and binding and therefore assists in assorted organic transformations. However, replicating the intricate selection of hydrogen bonds, as observed in nature, in synthetic complexes has met with only limited success. Despite this fact, recent times have seen the emergence of several notable examples where hydrogen bonds have been introduced in synthetic complexes. A few such examples have also illustrated the substantial role played by the hydrogen bonds in influencing and often controlling the catalytic outcome. This perspective presents selected examples illustrating the significance of hydrogen bonds offered by the coordination and the organometallic complexes that aid in providing the desired orientation to a substrate adjacent to a catalytic metal center and remarkably assisting in the catalysis.

Half-Sandwich Ruthenium Complexes of Amide-Phosphine Based Ligands: H-Bonding Cavity Assisted Binding and Reduction of Nitro-substrates.

We present synthesis and characterization of two half-sandwich Ru(II) complexes supported with amide-phosphine based ligands. These complexes presented a pyridine-2,6-dicarboxamide based pincer cavity, decorated with hydrogen bonds, that participated in the binding of nitro-substrates closer to the Ru(II) centers, which is further supported with binding and docking studies. These ruthenium complexes functioned as the noteworthy catalysts for the borohydride mediated reduction of assorted nitro-substrates. Mechanistic studies not only confirmed the intermediacy of [Ru-H] in the reduction but also asserted the involvement of several organic intermediates during the course of the catalysis. A similar Ru(II) complex that lacked pyridine-2,6-dicarboxamide based pincer cavity substantiated its unique role both in the substrate binding and the subsequent catalysis.

Architectural and catalytic aspects of designer materials built using metalloligands of pyridine-2,6-dicarboxamide based ligands.

This perspective presents the design, synthesis and crystal structures of a large number of architectures constructed using assorted metalloligands of pyridine-2,6-dicarboxamide based ligands. The metalloligands offered various appended functional groups, whereas design strategies included varying both their position and number. A combination of these parameters resulted in the development of assorted architectures including discrete trinuclear and tetranuclear complexes as well as 1D/2D/3D coordination polymers. The metalloligand strategy not only assisted in the construction of ordered crystalline materials with varied dimensionalities but also judiciously allowed the incorporation of Lewis acidic and redox-active secondary metals in the resultant architectures. As a result, such designer architectures illustrated their noteworthy role both as homogenous and heterogeneous catalysts in different organic transformation reactions.

Zn- and Cd-based Coordination Polymers Offering H-Bonding Cavities: Highly Selective Sensing of S2 O7 2- and Fe3+ Ions.

We present two ZnII - and CdII -based coordination polymers (CPs), L-Zn and L-Cd, offering H-bonding-based cavities of varying dimensions. Both CPs were used for the highly selective detection of S2 O7 2- and Fe3+ ions where H-bonding based cavities played an important role. Fluorescence quenching, competitive binding studies and binding parameters substantiated significant recognition of S2 O7 2- and Fe3+ ions by both CPs.

Size-Selective Detection of Picric Acid by Fluorescent Palladium Macrocycles.

This work presents the synthesis and characterization of two palladium-based fluorescent macrocycles offering hydrogen-bonding cavities of contrasting dimensions. Both palladium macrocycles function as chemosensors for the detection of nitroaromatics, whereas the larger macrocycle not only illustrates nanomolar detection of picric acid but also transports its significant amount from an aqueous to an organic phase.