Dillip Kumar Chand

A remarkable upfield shift of the pyα protons of complexed 2,2′-bipyridine in [cis-Pd(bpy)(NO3)2] is observed which is considered to originate from the anisotropic influence of suitably positioned coordinated nitrate anions around the Pd(II) centre of the molecule. A typical complexation-induced downfield shift is observed for the NH2 protons in [cis-Pd(en)(NO3)2] where 'en' stands for ethylenediamine. © 2006 Elsevier Ltd. All rights reserved.

An unanticipated anion-water cluster is assembled by one bromide and three highly-ordered “water tetramers” within the cavity of a receptor, providing a perfect C 3 symmetric propeller-shaped bromide-water cluster of [Br(H2O)12]-. © 2012 The Royal Society of Chemistry.

Ring-opening polymerization (ROP) of maleic anhydride (MA) or L-Lactide (L-LA) with tert-butyl glycidyl ether (tBGE) were carried out in the presence of Ti and Zr complexes of benzoxazole substituted 8-hydroxyquinoline ligands (1a-3a and 1b-3b), delivering nearly alternative P(tBGE-co-MA) and block-like P(tBGE)-b-PLLA co-polymers with high molecular weight (Mn) and narrow to broad molecular weight distributions (Mw/Mn). The molecular structures of the Ti and Zr complexes (1a and 3b) were confirmed by single-crystal X-ray diffraction analysis. The Zr complex 3b exhibited superior reactivity and produced copolymers within one hour at 80 °C in dry toluene (Mn,GPC = 14–40 Kg mol-1 and Mw/Mn = 1.19–1.55). In case of P(tBGE-co-MA) copolymer synthesis, the polymer arm with tBGE fraction was building faster (82–100 unit%) compared to MA (52–99 unit%). In contrast, incorporation of L-LA was higher (82–99 unit%) compared to tBGE insertion (20–60 unit%) in P(tBGE)-b-PLLA copolymer synthesis.

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 14 days 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 36 h. These results suggest that PLA/HPG/Cur nanofibers can be a potential wound patch dressing for acute and chronic wound applications.

A series of designed binuclear palladium(II)-based self-assemblies, [Pd2(en)2(L)2](NO3)4, 1a; [Pd2(tmeda)2(L)2](NO3)4, 2a; [Pd2(bpy)2(L)2](NO3) 4, 3a; and [Pd2(phen)2(L)2](NO 3)4, 4a, are synthesized. These complexes are obtained in good to excellent yields by equimolar combination of the nonchelating bidentate ligand bis(4-pyridylmethyl)piperazine, L, with the corresponding cis-protected palladium(II) component, that is, Pd(N-N)(NO3)2, under suitable reaction conditions. The cis-protecting N-N units used are ethylenediamine (en), tetramethylethylenediamine (tmeda), 2,2′-bipyridyl (bpy), and 1,10-phenanthroline (phen). The complexes 1a-4a are well-characterized by 1H NMR, H-H COSY, and HSQC, and the molecular compositions have been established by ESI-MS. The molecular structures are confirmed for the complexes [Pd2(tmeda)2(L) 2](ClO4)4, 2b; [Pd2(bpy) 2(L)2](ClO4)4, 3b; and [Pd 2(phen)2(L)2](NO3)4, 4a, by the single-crystal X-ray diffraction technique. In the cases of the complexes 3b and 4a, the crystal packing diagrams display a unique one-dimensional predefined organization of molecules by intermolecular π-π interactions using the strategically located π-surfaces of the cis-protecting units. This organization resembles a set of toppled dominos. A given set exhibits further interactions with the neighboring sets in the packing pattern that are influenced by the nature of the N-N moiety, for example, bpy or phen. However, no such arrangement is observed in the case of the complex 2b due to the lack of a π-surface at the cis-protecting moiety. © 2013 American Chemical Society.

An efficient pathway to synthesize biaryls and terphenyls through ligand-free palladium nanoparticles (PdNPs) catalyzed Suzuki cross-coupling reactions has been developed. Mild reaction conditions, high yields of desired products, absence of inert atmosphere and short reaction times are the notable features of this method. © 2012 Elsevier B.V.

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 ε-caprolactone (ε-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.

A pyridine/aniline appended unsymmetrical bidentate ligand N-(4-(4-aminobenzyl)phenyl)nicotinamide, investigated in this work has two well-separated coordination sites. Combination of the ligand with cis-protected palladium(II) (i.e., PdL′) and palladium(II) in separate reactions produced the corresponding Pd2L′2Lun2 and extremely rare Pd2Lun4 type self-assembled binuclear complexes, respectively. Notably, both varieties of complexes are prepared from a common ligand system. Two diastereomers (i.e., (2,0) and (1,1)-forms) are possible for Pd2L′2Lun2 type complex, whereas four diastereomers (i.e., (4,0), (3,1), trans(2,2), and cis(2,2)-forms) can be imagined for the Pd2Lun4 type complex. However, exclusive diastereoselectivity was observed, and the complexes formed belong to (1,1)-Pd2L′2Lun2 and cis(2,2)-Pd2Lun4 forms. The diastereomers are predicted from NMR study in solution and DFT calculations in gas-phase and implicit-solvent media; however, single-crystal structures of both the complexes provided unambiguous support. The rare Pd2Lun4 type complex is studied in further detail. Parameters like counteranion, concentration, temperature, and stoichiometry of metal to ligand did not influence the diastereoselectivity in complex formation. DFT calculations show the cis(2,2) form to be the most stable, followed by the (3,1) isomer. The lowest conformational strain in the bound ligand strands in the cis(2,2)-arrangement along with optimal intermolecular interactions makes it the energetically most stable of all the isomers. Molecular dynamics (MD) simulations were carried out to visualize the self-assembly process toward the formation of Pd2Lun4 type complex and the free energy difference between the cis(2,2) and (3,1) isomers. Snapshots of MD simulation elucidate the step-by-step progress of complexation leading to the cis(2,2)-isomer.

The simple combination of PdII with the tris-monodentate ligand bis(pyridin-3-ylmethyl) pyridine-3,5-dicarboxylate, L, at ratios of 1:2 and 3:4 demonstrated the stoichiometrically controlled exclusive formation of the "spiro-type" Pd1L2 macrocycle, 1, and the quadruple-stranded Pd3L4 cage, 2, respectively. The architecture of 2 is elaborated with two compartments that can accommodate two units of fluoride, chloride, or bromide ions, one in each of the enclosures. However, the entry of iodide is altogether restricted. Complexes 1 and 2 are interconvertible under suitable conditions.

New multinuclear discrete heteroleptic complexes have been synthesized by mixing Pd(II), 2,2′-bipyridine and N,N′-(1,2-phenylene) diisonicotinamide in a single pot as a new approach. A dimeric molecular rhombus and a trimer in equilibrium are obtained where the dimer is the major product. Similar equilibrium is also observed when classical method is employed for the synthesis. The equilibrium is shifted exclusively in favour of the dimer upon addition of benzene. The complexes are characterized by NMR and ESI-MS methods. Crystal structure of the benzene encapsulated rhombus is presented. © 2010 Elsevier Ltd.