Ramesh C. Deka

In situ generated copper nanoparticle catalyzed reduction of 4-nitrophenol

In situ generated Cu nanoparticles catalyze the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 very efficiently at room temperature with good recyclability up to four cycles. The precursor compound, formed by hydrothermal treatment of copper chloride with urea at 120 °C for 6 h, produces Cu nanoparticles on reduction with NaBH4 during the course of the reaction. The synthesized precursor and the catalyst are characterized by various analytical techniques such as XRD, FTIR, TGA, SEM-EDX, TEM, and UV-visible spectroscopy.

Enhanced Catalytic Activity of Zeolite Encapsulated Fe(III)-Schiff-Base Complexes for Oxidative Coupling of 2-Napthol

Iron(III) Schiff-base complexes of general formula [Fe(L)(2)Cl]·2H(2)O, where L = N,Ń-bis(salicylidene)ethylenediamine and N,Ń-disalicylidene-1,2-phenylenediamine have been encapsulated within various alkali exchanged zeolites viz. LiY, NaY, and KY by flexible ligand method. The encapsulated complexes are characterized by EDX, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), FT-IR, UV-vis, diffuse reflectance spectroscopy (DRS), electron spin resonance spectroscopy (ESR) and cyclic voltammetry studies. The diffuse reflectance UV-vis spectra of encapsulated complexes show a dramatic red shift of the charge transfer band with increasing electropositivity of the exchangeable cations. The electrochemical analysis predicts the shifting of the reduction potential toward negative values with increasing size of the alkali exchanged cations. The zeolite encapsulated Schiff-base complexes of iron are found to be catalytically active toward the oxidative coupling of 2-napthol. Metal complexes incorporated in potassium exchanged zeolite-Y are found to be more effective for catalytic conversion of 2-naphthol to binaphthol and induces higher selectivity toward the R-conformation. The catalytic conversion of 2-napthol to BINOL is found to depend on the reduction potential of the catalyst, with a more negative reduction potential being better for the catalytic conversion. Density functional calculation is being carried out on both the neat Fe-Salen and Fe-Salophen complexes and those encapsulated in NaY zeolite to investigate change in structural parameters, energies of the HOMO and LUMO, and global hardness and softness. Fukui functions, as local descriptors, are used to analyze the hard-hard interaction at a particular site of the complexes.

Stability of small Pdn (n=1–7) clusters on the basis of structural and electronic properties: A density functional approach

Density functional calculations within the generalized gradient approximation have been used to investigate the lowest energy electronic and geometric structures of neutral, cationic, and anionic Pd(n) (n=1-7) clusters in the gas phase. In this study, we have examined three different spin multiplicities (M=1, 3, and 5) for different possible structural isomers of each neutral cluster. The calculated lowest energy structures of the neutral clusters are found to have multiplicities, M=1 for Pd(1), Pd(3), Pd(5), Pd(6), and Pd(7), while M=3 for Pd(2) and Pd(4). We have also determined the lowest energy states of cationic and anionic Pd(n) (n=1-7) clusters, formed from the most stable neutral clusters, in three spin multiplicities (M=2, 4, and 6). Bond length, coordination number, binding energy, fragmentation energy, bond dissociation energy, ionization potential, electron affinity, chemical hardness, and electric dipole moment of the optimized clusters are compared with experimental and other theoretical results available in the literature. Based on these criteria, we predict the four-atom palladium cluster to be a magic-number cluster.

Reaction intermediates of CO oxidation on gas phase Pd4 clusters: a density functional study.

Density functional theory (DFT) studies have revealed the energetically favorable reaction paths for oxidation of CO on Pd(4) cluster. Adsorption of various species such as O(2), 2O, O, CO, CO(2), and coadsorbate combinations, including O(2)+CO, 2O+CO, O+CO, and O+CO(2) on neutral, cationic, and anionic Pd(4) clusters were investigated. The results indicate that Pd(4)(+) and Pd(4) are more effective for catalyzing CO in comparison with Pd(4)(-). It is further observed that dissociated oxygen is a superior oxidant for CO oxidation on Pd(4)(q) (q = 0, 1, -1) than molecular and atomic oxygen.

First principles calculation on the structure and electronic properties of BNNTs functionalized with isoniazid drug molecule

One-dimensional nanostructures such as nanowires and nanotubes are stimulating tremendous research interest due to their structural, electronic and magnetic properties. We perform first principles calculation using density functional theory on the structural, and electronics properties of BNNTs adsorbed with isoniazid (INH) drug via noncovalent functionalization using the GGA/PBE functional and DZP basis set implemented in SIESTA program. The band structure, density of states and projected density of states (PDOS) plots suggest that isoniazid prefers to get adsorbed at the hollow site in case of (5,5) BNNT, whereas in (10,0) BNNT it favours the bridge site. The adsorption energy of INH onto (5,5) BNNT is smaller than in (10,0) BNNT which proposes that (10,0) BNNT with a larger radius compared to (5,5) BNNT is more favourable for INH adsorption as the corresponding distortion energy will also be quite lower. Functionalization of (5,5) and (10,0) BNNTs with isoniazid displays the presence of new impurity states (dispersionless bands) within the HOMO–LUMO energy gap of pristine BNNT leading to an increase in reactivity of the INH/BNNT system and lowering of the energy gap of the BNNTs. The PDOS plots show the major contribution towards the dispersionless impurity states is from INH molecule itself rather than from BNNT near the Fermi energy region. To summarize, noncovalent functionalization of BNNTs with isoniazid drug modulates the electronic properties of the pristine BNNT by lowering its energy gap with respect to the Fermi level, as well as demonstrating the preferential site selectivity for adsorption of isoniazid onto the nanotube sidewalls of varying chirality.

Role of ligand to control the mechanism of nitric oxide reduction of copper(II) complexes and ligand nitrosation.

The nitric oxide reactivity of two copper(II) complexes, 1 and 2 with ligands L(1) and L(2), respectively, [L(1) = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, L(2) = 5,5,7-trimethyl-[1,4]-diazepane] have been studied. The copper(II) center in complex 1 was found to be unreactive toward nitric oxide in pure acetonitrile; however, it displayed reduction in methanol solvent in presence of base. The copper(II) center in 2, in acetonitrile solvent, on exposure to nitric oxide has been found to be reduced to copper(I). The same reduction was observed in methanol, also, in case of complex 2. In case of complex 1, presumably, the attack of nitric oxide on the deprotonated amine is the first step, followed by electron transfer to the copper(II) center to afford the reduction. Alternatively, first NO coordination to the Cu(II) followed by NO(+) migration to the secondary amine is the most probable in case of complex 2. The observation of the transient intermediate in UV-visible and FT-IR spectroscopy prior to reduction in case of complex 2 also supports this possibility. In both cases, the reduction resulted into N-nitrosation; in 1, only mononitrosation was observed whereas complex 2 afforded dinitrosation as major product along with a minor amount of mononitrosation. Thus, it is evident from the present study that the macrocyclic ligands prefer the deprotonation pathway leading to mononitrosation; whereas nonmacrocyclic ones prefer the [Cu(II)-NO] intermediate pathway resulting into nitrosation at all the available sites of the ligand as major product.

Porous CuO nanostructure as a reusable catalyst for oxidative degradation of organic water pollutants

A precursor mediated route is developed for the synthesis of a porous CuO nanostructure based on the hydrothermal method using copper chloride dihydrate and urea, followed by calcination at 400 °C for 4 h. The structural and morphological characteristics of the synthesized oxide are examined by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, UV-visible spectroscopy and BET surface area analyses. The CuO nanostructure is utilized for the catalytic oxidative degradation of both cationic (methylene blue) and anionic (methyl orange) dye pollutants, respectively. It exhibits excellent catalytic performance with good reusability up to the fourth cycle of the degradation reaction. It also provides a new route for promising dye degradation in wastewater treatment.

Anticancer activity of nucleoside analogues: A density functional theory based QSAR study

In the present work multiple linear regression analyses were performed to build QSAR models for nucleoside analogous using density functional theory (DFT) and molecular mechanics (MM+) based descriptors in both gas and solvent phases. The QSAR models for 14 carbocyclic analogues of nucleosides against murine leukemia cell line (L1210/0) and human T-lymphocyte cell lines (Molt4/C8 and CEM/0) explain more than 90% of the variances in the activity data along with higher values of

Ab initio study on the noncovalent adsorption of camptothecin anticancer drug onto graphene, defect modified graphene and graphene oxide

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