Dillip Kumar Chand

A molybdenum based metallomicellar catalyst for controlled and selective sulfoxidation reactions in aqueous medium

A surfactant based molybdenum system that exhibits catalytic activity for sulfoxidation reactions of various organic sulfides in aqueous medium has been developed and comprehensively characterized using IR, XRD, NMR, ESI-MS, DLS and TEM. The catalyst showcases remarkable selectivity for the preparation of both sulfoxides and sulfones in the range of good to excellent yields. Furthermore, the catalyst showed a high degree of tolerance towards various sensitive functional groups such as hydroxyl, acetal, aldehyde, amine, imine, oxime, cyano and alkene.

Visual colorimetric detection of TNT and 2,4-DNT using as-prepared hexaazamacrocycle-capped gold nanoparticles

The dual role of a hexaazamacrocyclic ligand L in the effective reduction of Au3+ to Au0 and stabilization of the ensuing gold nanoparticles (AuNPs) is successfully demonstrated. The molar ratio of ligand L to Au3+ is found to be very important for the effective stabilization of the AuNPs. The as-prepared amine-capped AuNPs in the instant visual colorimetric detection of the TNT and 2,4-DNT under easy-to-adopt conditions is established. The naked eye detection of the analytes with an instant color change at concentrations as low as 476 fM is observed. Colorimetric analysis supported the detection of TNT and 2,4-DNT using the nanosensor with the LOD of 1.55 × 10−13 ± 2.02 × 10−13 M and 3.79 × 10−13 ± 3.65 × 10−13 M respectively.

Polyaromatic molecular peanuts

Mimicking biological structures such as fruits and seeds using molecules and molecular assemblies is a great synthetic challenge. Here we report peanut-shaped nanostructures comprising two fullerene molecules fully surrounded by a dumbbell-like polyaromatic shell. The shell derives from a molecular double capsule composed of four W-shaped polyaromatic ligands and three metal ions. Mixing the double capsule with various fullerenes (that is, C60, C70 and Sc3N@C80) gives rise to the artificial peanuts with lengths of ∼3 nm in quantitative yields through the release of the single metal ion. The rational use of both metal–ligand coordination bonds and aromatic–aromatic π-stacking interactions as orthogonal chemical glue is essential for the facile preparation of the multicomponent, biomimetic nanoarchitectures.

Group 4 alkoxide complexes containing [NNO]-type scaffold: synthesis, structural characterization and polymerization studies

A series of Ti(IV), Zr(IV) and Hf(IV) complexes are synthesized by complexation of [NNO]-type tridentate Schiff base ligands {2-amino-3-((E)-(2-hydroxybenzylidene)amino)maleonitrile}, L1(H)2; {2-amino-3-((E)-(2-hydroxy-3,5-dimethylbenzyl-idene)amino)maleonitrile}, L2(H)2 and {2-amino-3-((E)-(3-(tert-butyl)-2-hydroxy-5-methylbenzylidene)amino)maleonitrile}, L3(H)2 with suitable group 4 metal alkoxides. The ligands are derived by the mono-condensation of diaminomaleonitrile and salicylaldehyde derivatives. All the complexes are found to be dinuclear on the basis of their NMR and MS spectral data. Three of the nine complexes are structurally characterized by single crystal X-ray diffraction studies. The crystal structures confirmed the dinuclear nature of these complexes. The metal centers of the dinuclear core are connected through two bridging alkoxy groups. The coordination environment of a metal center comprises one unit of a di-deprotonated ligand, one unit of a terminal alkoxide and two units of the bridging alkoxide groups, so as to form distorted octahedral complexes. The catalytic activities of these complexes were investigated towards the ring-opening polymerization (ROP) of e-caprolactone (e-CL) and rac-lactide (rac-LA) in bulk. These complexes were found to be highly active catalysts for the production of PCL [poly(caprolactone)] and PLA [poly(lactic acid)] with a high rate of conversion. The strong electron withdrawing cyano groups present in these complexes rationalized the high polymerization activity. The polymers exhibited narrow molecular weight distributions (MWDs). Furthermore, the isolated PLAs were remarkably heterotactic-rich with maximum Pr = 0.80, by using an Hf catalyst with tert-butyl substituent on the ortho-position of the phenolic moiety. These complexes are moderately active towards the ring-opening homopolymerization of rac-epoxides, such as rac-cyclohexene oxide (rac-CHO), rac-propylene oxide (rac-PO) and rac-styrene oxide (rac-SO). These complexes exhibited good activity in ethylene polymerization upon activation with co-catalyst MAO and with a bulky substituent on the ortho-position of the phenolic moiety of the catalysts.

Cage‐to‐Cage Cascade Transformations

A series of Pd2 L4 -type binuclear self-assembled coordination cages (1-4), where L stands for a nonchelating bidentate ligand, were prepared. The strategies adopted for the synthesis of the cages were: combination of Pd(II) with 1) a selected ligand or 2) subcomponents of the ligand. Highly efficient cage-to-cage transformation reactions are demonstrated by suitable covalent modification (from 1 to 2 or 3 or 4) or ligand-exchange reactions (from 1 to 2 or 3 or 4; from 2 to 3 or 4). Thus, new cascade transformations (from 1 to 2 to 3; from 1 to 2 to 4) are achieved beautifully.

Synthesis and characterization of curcumin loaded PLA—Hyperbranched polyglycerol electrospun blend for wound dressing applications

This study is aimed to develop curcumin (Cur) incorporated electrospun nanofibers of a blend of poly (lactic acid) (PLA) and hyperbranched polyglycerol (HPG) for wound healing applications. Both the polymers are synthesized and fabricated by electrospinning technique. The produced nanofibers were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Colorimetry (DSC) and Thermogravimetric Analysis (TGA). Electrospun scaffolds (PLA/HPG/Cur) exhibits very high hydrophilicity, high swelling and drug uptake and promotes better cell viability, adhesion and proliferation when compared to PLA/Cur electrospun nanofibers. Biodegradation study revealed that the morphology of the nanofibers were unaffected even after 14days immersion in Phosphate Buffered Saline. In vitro scratch assay indicates that migration of the cells in the scratch treated with PLA/HPG/Cur is complete within 36h. These results suggest that PLA/HPG/Cur nanofibers can be a potential wound patch dressing for acute and chronic wound applications.

A two-dimensional polydodecameric water–chloride cluster enfolding (Hg–Cl–Hg)+ concealed cascade cryptate

An intriguing phenomenon of a hitherto unknown type of cavity induced “reductive encapsulation” using Hg(II) and a homoditopic octaaza cryptand is described. The crystal structure of the complex offers a new type of grid-like polydodecameric water–chloride cluster, {[(H2O)12(Cl)]1−}n, that renders the highest number of water molecules per chloride reported thus far.

Role of peripheral phenanthroline groups in the self-assembly of self-assembled molecular triangles

AbstractSelf-assembled molecular triangles [Pd3(phen)3(imidazolate)3](NO3)3, 1a and [Pd3(phen)3 (imidazolate)3](PF6)3, 1b are prepared by the combination of imidazole with Pd(phen)(NO3)2 and Pd(phen) (PF6)2, respectively. Imidazole was deprotonated during the complexation reactions and the imidazolate so formed acted as a bis-monodentate bridging ligand to form the bowl-shaped trinuclear architectures of 1a/b. Relative orientation of the imidazolate moieties can be best described as syn,anti,antias observed in the crystal structure of 1b. However, in solution state, slow conformational changes are assumed on the basis of 1HNMR spectral data. The molecular triangles are crafted with three peripheral phen units capable of π−π stacking interactions. Well-fashioned intermolecular π−π interactions are observed in the solid-state, wherein further self-assembly of already self-assembled triangle is observed. Graphical AbstractSelf-assembly of the self-assembled molecular triangle [Pd3(phen)3(imidazolate)3](PF6)3 is observed in the solid-state where the triangular panels are packed by utilizing intermolecular π−π interactions in a chain like fashion.

Self-assembly of self-assembled molecular triangles

AbstractA rare variety of self-assembled molecular triangle [Pd3(bpy)3(imidazolate)3](NO3)3, 1 is prepared by the combination of Pd(bpy)(NO3)2 with imidazole, at 1:1 ratio, in acetonitrile-water. Deprotonation of imidazole happened during the course of the complexation reaction where upon the metallomacrocycle is formed. The bowl-shaped trinuclear architecture of 1 is crafted with three peripheral bpy units capable of π−π stacking interactions. While the solution state structure of 1can be best described as a trinuclear complex, in the solid-state well-fashioned intermolecular π−π and CH- π interactions are observed. Thus, in the solid-state further self-assembly of already self-assembled molecular triangle is witnessed. The triangular panels are arranged in a linear manner utilizing intermolecular π−π interactions where upon two out of three bpy units of each molecule participated in the chain formation. Graphical AbstractA rare variety of self-assembled molecular triangle [Pd3(bpy)3(imidazolate)3](NO3)3, 1 is prepared by the combination of Pd(bpy)(NO3)2 with imidazole, at 1:1 ratio. In the solid-state, the triangular panels are packed by utilizing intermolecular π–π and CH-π interactions.

Coordination polymers via self-assembly of silver(I) and cis-bis-nitrile-oxa-bowl derivatives

A series of silver(I)-based coordination polymers (AgCPs) have been synthesized using three new nonchelating cis-bis-nitrile derivatives of oxa-bowls, L1–L3, as ligand components. The ligands are designed to provide conformational restrictions as well as semi-rigid directionality to the coordination vectors extended from the nitrile functionalities. The steric bulks around the oxa-bowl spacer moieties are gradually escalated to study their influence on the topologies of the ensuing AgCPs. Two silver salts i.e. AgSbF6 and AgPF6 are used to check the influence of anions on the structural architectures. Ziz-zag-sheet type 2-D AgCPs are formed with the ligands L1 and L2 possessing less steric bulk. All the metal centres are found to be tetracoordinated by nitrile-nitrogens of the same sheet giving distorted-bisphenoidal geometries. Additional short interactions of the silver(I) centres of a given sheet with the oxygen of the oxa-bowls belonging to the neighbouring stacked sheets are observed. The bulky ligand L3 behaved differently where the metal centres are tetracoordinated although only two of the ligating units are derived from the nitrile nitrogens and the remaining two are from, depending upon the counter anion, the counter anion/oxygen of oxa-bowls or two water molecules. The overall arrangements in the AgCPs of L3 are of the 2-D carpet type (for SbF6− ion) composed of interconnected chains, and 1-D ladder type (for PF6− ion) constructed from two chains. Cation–π interactions are found between the aromatic part of L3 of a given chain and the silver(I) of the adjacent chain that are interdigitated.