Showing papers in "Journal of Chemical Sciences in 2016"

Bader’s Theory of Atoms in Molecules (AIM) and its Applications to Chemical Bonding

Abstract: In this perspective article, the basic theory and applications of the “Quantum Theory of Atoms in Molecules” have been presented with examples from different categories of weak and hydrogen bonded molecular systems.

Pd immobilized on modified magnetic Fe 3 O 4 nanoparticles: Magnetically recoverable and reusable Pd nanocatalyst for Suzuki-Miyaura coupling reactions and Ullmann-type N -arylation of indoles

Abstract: The Pd supported on amidoxime (AO)-functionalized Fe3O4 (Fe3O4/AO/Pd) hybrid material was used as an effective and recyclable nanocatalyst in Suzuki-Miyaura coupling reactions. The catalyst was very effective for the Suzuki-Miyaura reaction of aryl halides (Ar–I, Ar–Br, Ar–Cl) with phenylboronic acid and conversion was excellent in most cases. The yields of the products were in the range from 7–98%. The catalyst showed good stability and could be recovered and reused for six reaction cycles without a significant loss in its catalytic activity. Also, a wide range of N-arylated indoles are selectively synthesized through intermolecular C(aryl)–N bond formation from the corresponding aryl iodides and indoles through Ullmann-type coupling reactions in the presence of the prepared catalyst.

Molecular electrostatic potential analysis of non-covalent complexes

Abstract: Ab initio MP4/Aug-cc-pvDZ//MP2/6-311 ++g(d,p) level interaction energy (Eint) and molecular electrostatic potential analysis (MESP) of a large variety of non-covalent intermolecular complexes, viz. tetrel, chalcogen, pnicogen, halogen, hydrogen, dihydrogen and lithium bonded complexes have been reported. The electronic changes associated with the non-covalent complex formation is monitored in terms of MESP minimum (V m i n ) in the free and complexed states of the donor and acceptor molecules as well as in terms of MESP at the donor and acceptor atoms (V n ) of the free monomers and complexes. The change in V min or V n on the donor molecule (ΔV min(D) or ΔV n(D)) during complex formation is proportional to its electron donating ability while such a change on the acceptor molecule (ΔV min(A) or ΔV n(A)) is proportional to its electron accepting ability. Further, the quantities ΔΔV min=ΔV min(D) −ΔV min(A) and ΔΔV n=ΔV n(D) −ΔV n(A) have shown strong linear correlations with Eint of the complex (Eint values fall in the range 0.7 to 46.2 kcal/mol for 54 complexes) and suggest that the intermolecular non-covalent interactions in a wide variety of systems can be monitored and assessed in terms of change in MESP due to complex formation in the gas phase. With the incorporation of solvent effect in the calculation, charged systems showed significant deviations from the linear correlation. The MESP based analysis proposes that the large variety of intermolecular non-covalent complexes considered in this study can be grouped under the general category of electron donor-acceptor (eDA) complexes.

Direct synthesis of dimethyl carbonate from CO 2 and methanol over CeO 2 catalysts of different morphologies

Abstract: The direct synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) and methanol is an attractive approach towards conversion of the greenhouse gas - CO2 into value-added chemicals and fuels. Ceria (CeO2) catalyzes this reaction. But the conversion efficiency of CeO2 is enhanced when the byproduct water in the reaction medium is separated by employing trapping agents like 2-cyanopyridine (2-CP). In this work, the influence of morphology of CeO2 on the direct synthesis of DMC in presence of 2-CP is reported. CeO2 catalysts of cube, rod, spindle and irregular morphology (Ce - C, Ce - R, Ce - S and Ce - N, respectively) were prepared, characterized and studied as catalysts in the said reaction conducted in a batch mode. Among all, Ce - S shows superior catalytic performance with nearly 100 mol% of DMC selectivity. Catalytic activity correlates with the concentration of acid and base sites of medium strength as well as defect sites. Ce - S has an optimum number of these active sites and thereby shows superior catalytic performance.

Cycloisomerization of acetylenic oximes and hydrazones under gold catalysis: Synthesis and cytotoxic evaluation of isoxazoles and pyrazoles

Abstract: The synthesis of substituted isoxazoles and pyrazoles through a general cycloisomerization methodology has been reported. The capability of gold(III) chloride to promote cycloisomerization of both α, β-acetylenic oximes and α, β-acetylenic hydrazones is the centrepiece of the strategy. A range of acetylenic precursors were investigated to afford 28 examples of the products with good to excellent chemical yields. Selected compounds were screened for their cytotoxic potential towards COLO320 cancer cell lines. The IC50 values of the tested compounds were in the micromolar range, with the best compound, 5-(6-Methoxy-naphthalen-2-yl)-3-phenyl-isoxazole (3h) displaying an IC50 of 38.9 μM. For this compound, the crystal structure in complex with Aurora-A kinase was obtained which revealed details of its binding mode within the active site with a free energy of binding -9.54 kcal/mol.

On the electrocatalytic activity of nitrogen-doped reduced graphene Oxide: Does the nature of nitrogen really control the activity towards oxygen reduction?

Abstract: Synthesis of metal-free electrocatalyst for the cathodic reduction of oxygen is of great interest for fuel cell and metal-air battery applications. The heteroatom-doped graphene/reduced graphene oxide (rGO) is very promising and the nitrogen-doped rGO (N-rGO) is emerging as a new inexpensive electrocatalyst for oxygen reduction reaction (ORR). Herein, we describe the effect of the chemical nature and amount of nitrogen in N-rGO towards ORR in acidic solution. Four different samples of N-rGO with different nitrogen content were synthesized by simple chemical route. The chemical nature and nitrogen content were analyzed with X-ray photoelectron spectroscopic measurements. The electrocatalytic performance of the catalyst was examined by cyclic and hydrodynamic voltammetric studies. All the N-rGO samples favor 4-electron pathway for the reduction of oxygen in acidic solution. The onset potential and kinetic current density depends on the nature of the doped nitrogen. It is demonstrated that the chemical nature and the amount of nitrogen actually control the ORR activity. The N-rGO which contains a large amount of pyridinic nitrogen with N/C ratio of 0.074 has high catalytic activity. The carbon bonded to pyridinic nitrogen could be a possible catalytic site in ORR. Our studies suggest that the graphitic nitrogen does not significantly influence the electrocatalytic activity of N-rGO.

Synthesis and characterization of Polyindole and its catalytic performance study as a heterogeneous catalyst

Abstract: The catalytic performance study of polyindole as a heterogeneous catalyst is reported for the synthesis of 3,3’-arylmethylene-bis-1H-Indole derivatives using various substituted aldehydes and indole under reflux reaction condition with good to excellent yield. Polyindole was synthesized by chemical oxidative polymerization using citric acid as a dopant. The synthesized polymer was well characterized by various spectroscopic techniques like FT-IR, XRD, FESEM, etc. The XRD pattern confirms the partially crystalline nature of polyindole. The FESEM images of polyindole revealed the formation of irregularly shaped particulate nature with size in the range of 0.2 to 6 micron. In FT-IR spectrum, the major peak at ∼ 3400 cm−1 indicates N-H stretching and at 1564 −1624 cm −1 indicates C-C stretching of benzenoid ring of indole. The presence of peak at ∼ 3400 cm−1 indicates that the polymerization does not occur at nitrogen. The present protocol has certain advantages like recyclability, low loading of the catalyst, low-cost and efficient use of polyindole as a heterogeneous catalyst.

Pyrone-based Cu(II) complexes, their characterization, DFT based conformational drift from square planar to square pyramidal geometry and biological activities

Abstract: This work deals with the synthesis and characterization of a series of three N-Dehydroacetic acid-4-phenyl-3-thiosemicarbazide (H2dha-ptsc) Schiff base Cu(II) complexes based on combined experimental and theoretical approach, having the general composition formula as [Cu(dha-ptsc)(L-L)], where L-L is H2O, 2,2-bipyridine (bipy) or 1,10-phenanthroline (phen). H2O containing complex acts as origin for the latter two complexes and in due course, the geometry of the complex changes from square planar to square pyramidal. DFT calculations were carried out for both the geometrical forms. B3LYP/LANL2DZ level of theory was used to carry out the required computations. From the overall DFT computations, square pyramidal geometry was found to be more stable as compared to the square planar conformation for the complexes under investigation. Super oxide dismutation, thermal behaviour and electrochemical activity were also studied. The results have shown satisfactory super oxide scavenging potential, high degree of thermal resistance and efficient redox properties for the title complexes. Moreover, charge analysis and nonlinear optical properties were computed to establish a comprehensive note of atomic constituents differing in nature of charge delocalization.

Green synthesis and catalytic application of curcumin stabilized silver nanoparticles

Abstract: An ultrasonication based green synthesis approach was used to prepare curcumin-stabilized silver nanoparticles (c-AgNPs) Nanoparticles thus obtained were characterized by UV-Visible spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) Two different size distributions of c-AgNPs were obtained by changing the ratio of curcumin to silver salt precursor These c-AgNPs were used as catalysts in the catalytic reduction of p-nitrophenol to p-aminophenol The c-AgNPs with narrower size distribution exhibited better catalytic activity as well as lower activation energy Variation of apparent rate constant with the reactant concentration agreed with the Langmuir-Hinshelwood (LH) model Consequently, the surface rate constant related to the rate-determining step and the respective adsorption constants of p-nitrophenol and of borohydride were determined as per this model

Recognition of self-assembled water-nitrate cluster in a Co(III)-2,2 ′ -bipyridine host: Synthesis, X-ray structure, DNA cleavage, molecular docking and anticancer activity

Abstract: A mononuclear cobalt(III) complex [Co(bpy)2Cl2]NO3⋅2H2O (1) (bpy = 2,2′-bipyridine) has been synthesized and crystallographically characterized. Self-assembly of the lattice water molecules from rectangular tetrameric water cluster interacts with nitrate anion along the c-axis forming a six membered hexagonal water-nitrate cluster. It presents a new mode of association of water molecules with nitrate molecules which is not predicted theoretically or found experimentally. The molecule effectively cleaves bacterial genomic DNA and shows important cytotoxicity against human hepatocarcinoma cell (HepG2).

Synthesis, characterization and studies on antioxidant and molecular docking of metal complexes of 1-(benzo[d]thiazol-2-yl)thiourea

Abstract: In the present study, a new thiourea derivative bearing benzothiazole ligand, 1-(benzo[d]thiazol-2-yl)thiourea (btt) and its ternary metal (Cu(II), Co(II) and Ni(II)) complexes were synthesized. The structural characterization was carried out by micro analysis, IR, 1H-NMR, EPR, UV-Visible spectral analyses, molar conductance and thermal analysis studies. Spectral studies of complexes revealed that the metal complexes have distorted octahedral geometry. Molecular modelling study was performed to evaluate the recognition of target compounds at the 3MNG binding pocket. The docking results revealed that copper complex selectively binds to the crucial amino acid residues in the active site of 3MNG. The in vitro antioxidant activity of the ligand and its metal complexes was assayed by radical scavenging activity (DPPH, H2O2 and NO) and ferric reducing antioxidant power (FRAP) methods. The ligand showed moderate antioxidant activity whereas the metal complexes exhibited better antioxidant activity than that of the ligand. The results of the four methods proved that the copper complex is the most potent antioxidant among all the tested compounds.

An efficient and convenient synthesis of N -substituted amides under heterogeneous condition using Al(HSO 4 ) 3 via Ritter reaction

Abstract: An efficient and inexpensive synthesis of N-substituted amides from the reaction of aliphatic and aromatic nitriles with various benzylic alcohols (secondary and tertiary) and tert-butyl alcohol by refluxing nitromethane via the Ritter reaction catalyzed by aluminum hydrogen sulfate [Al(HSO4)3] is described. The catalyst which is an air-stable, cost-effective solid acid could be readily recycled by filtration and reused four times without any significant loss of its activity.

A heterogeneous catalyst, SiO2-ZnBr2: An efficient neat access for α-aminophosphonates and antimicrobial activity evaluation

Abstract: An efficient, environmentally benign and green method was developed for the synthesis of α-aminophosphonates by one-pot three-component reaction (Kabachnik-Fields reaction) of amine (4-(4-chlorophenoxy)aniline), aldehydes and diethyl phosphite using catalyst, SiO2-ZnBr 2 under solvent-free conditions. The developed method under conventional conditions was further optimized in microwave and ultrasonication methods. A series of α-aminophosphonates, diethyl (4-(4-chlorophenoxy)phenylamino)(aryl/ heteroaryl)methylphosphonates was synthesized to check the generality. The catalyst, SiO2-ZnBr2 afforded good yields of products in all the methods in the range of 85–97% but variation was observed in reaction time. Microwave irradiation method took very less time (4–8 min) as compared with ultrasonication (35–52 min) and conventional (2–3 h) conditions. The major advantages are simple and mild conditions, short reaction times, high yield of the product with purity, use of cheap catalyst and reusability of the catalyst until to three times without significant loss of activity. Antibacterial and antifungal activities were evaluated for the title compounds (50 and 100 μg/mL) including minimum inhibitory concentrations. A few of the newly synthesized α-aminophosphonates exhibited promising antimicrobial activity at lower MIC values in the range of 15.0–25.0 μg/mL and closer to the standards (5–12 μg/mL).

Why are Hydrogen Bonds Directional

Abstract: The recent IUPAC recommendation on the definition of hydrogen bonding points out that directionality is a defining characteristic of a hydrogen bond and the angle ∠X-H-Y is generally linear or 180∘. It also suggests that the X-H⋯Y angle be greater than 110∘ for an interaction to be characterized as a hydrogen bond but does not provide any rationale for the same. This article reports a rationale for limiting the angle, based on the electron density topology using the quantum theory of atoms in molecules. Electron density topology for common hydrogen bond donors HF, HCl, HBr, HNC, HCN and HCCH are reported in this work. These calculations lead to an interesting observation that the atomic basins of H atom in all these donor molecules are limited justifying the restriction of hydrogen bond angle. Moreover, similar analysis on some hydrogen bonded complexes confirms that beyond this angle the acceptor atom Y starts interacting with the atomic basin on X. However, conclusions based on bond lengths and angles have to be treated with care and as the IUPAC recommendation points out that independent ‘evidence for bond formation’ in every case is important.

Unprecedented hetero-geometric discrete copper(II) complexes: Crystal structure and bio-mimicking of Catecholase activity

Abstract: An unprecedented solid of coper(II) complexes, [Cu(dpa)2NCS]2[Cu(dpa)2(NCS)2](ClO4)2 (1) [dpa = 2,2′-dipyridylamine; SCN = thiocyanate], has been synthesized and crystallographically characterized with the aim to study the catecholase activity. The Cu(II) complex mimics the full catalytic cycle of the active site of catechol oxidase enzyme in acetonitrile medium with a turnover number of 4.788×103 h −1 along with the production of semiquinone radical and hydrogen peroxide. In situ generation of Cu(I) species in the catalytic pathway of catechol oxidation was established by electrochemical study and further confirmed by electron paramagnetic resonance (EPR) spectroscopy.

An efficient synthesis of pyrazolo[1,5-a]pyrimidines and evaluation of their antimicrobial activity

Abstract: A series of new pyrazolo[1,5-a]pyrimidine derivatives has been synthesized by using 7-hydrazinyl- 5-methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile 1 and 7-amino-5-methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile 2 as precursors. The pyrazolo[3,4-d] pyrimidines 3a–b have been synthesized by a three-step reaction starting with 1. Compound 1 was utilized for the synthesis of dioxopyrrolidindolinylamio-pyrazolo-pyrimidines 4a–b, and dioxoisoindolin-pyrazolo-pyrimidines 4c–d. Also, compounds 4a-dwere synthesized using deep eutectic solvents (DES). This method using DES provides several advantages such as benign environment, high yield, scalable and simple work-up procedure. Similarly, the cyclocondensation of 2 with α-acetyl- γ-butyrolactone afforded pyrazolo-pyrido-pyrimidine 5 and dihydrofuro-pyrido-pyrazolo-pyrimidine 6. All synthesized compounds were screened for antimicrobial activity.

A computational study on structure, stability and bonding in Noble Gas bound metal Nitrates, Sulfates and Carbonates (Metal = Cu, Ag, Au)

Abstract: A density functional theory based study is performed to investigate the noble gas (Ng = Ar-Rn) binding ability of nitrates, sulfates and carbonates of noble metal (M). Their ability to bind Ng atoms is assessed through bond dissociation energy and thermochemical parameters like dissociation enthalpy and dissociation free energy change corresponding to the dissociation of Ng bound compound producing Ng and the respective salt. The zero-point energy corrected dissociation energy values per Ng atom for the dissociation process producing Ng atom(s) and the corresponding salts range within 6.0–13.1 kcal/mol in NgCuNO3, 3.1–9.8 kcal/mol in NgAgNO3, 6.0–13.2 kcal/mol in NgCuSO4, 3.2–10.1 kcal/mol in NgAgSO4, 5.1–11.7 kcal/mol in Ng2Cu2SO4, 2.5–8.6 kcal/mol in Ng2Ag2SO4, 8.1–19.9 kcal/mol in Ng2Au2SO4, 5.7–12.4 kcal/mol in NgCuCO3, 2.3–8.0 kcal/mol in Ng2Ag2CO3 and 7.3–18.2 kcal/mol in Ng2Au2CO3, with a gradual increase in moving from Ar to Rn. For a given type of system, the stability of Ng bound analogues follows the order as Au > Cu > Ag. All dissociation processes are endothermic in nature whereas they become endergonic as well in most of the cases of Kr-Rn bound analogues at 298 K. Natural population analysis along with the computation of Wiberg bond indices, and electron density analyses provide insights into the nature of the Ng-M bonds. The Ng-M bonds can be represented as partial covalent bonds as supported by the different electron density descriptors.

Molecular docking, MM/GBSA and 3D-QSAR studies on EGFR inhibitors

Abstract: Epidermal growth factor receptor (EGFR) is the first growth factor receptor proposed as a target for cancer therapy. Molecular modeling protocols like molecular docking, molecular mechanics/generalized born surface area (MM/GBSA) calculations and three dimensional-quantitative structure activity relationship (3D-QSAR) studies were performed on 45 molecules to understand the structural requirements for EGFR tyrosine kinase inhibitors. Conformation for all the molecules obtained from molecular docking were used as is for 3D-QSAR analysis. Comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models were obtained by performing partial least square analysis on 35 training molecules and these models were validated using 10 test moleucles. The models showed good statistical results in terms of r 2, q $^{2}_{\text {loo}}$ and r $^{2}_{\text {pred}}$ values. Information rendered from 3D-QSAR model and sitemap analysis was used to optimize lead molecule to design prospective inhibitors. Improvement in EGFR binding affinity can be achieved by substitutional modification on phenyl ring attached to alkynyl group with bulkier hydrogen bond donor and acceptor substituents that can increase favourable interaction with the receptor.

Synthesis and characterization of gold nanoparticles incorporated bentonite clay for electrocatalytic sensing of arsenic(III)

Abstract: In the present manuscript, a simple and easy route to synthesize bentonite (bt) clay-supported gold nanoparticles (Au NPs) is reported (represented as Au-bt). Application of this new environmentally benign material in electrocatalytic determination of arsenite (As(III)) was studied. The successful synthesis and incorporation of Au NPs into the bt clay is supported by spectroscopic, microscopic and electrochemical methods. The synthesized Au-bt material was used to modify glassy carbon electrode (GC) by the evaporation of Au-bt aqueous suspension dropped on the surface of the GC (GC/Au-bt). Cyclic voltammetry and chronoamperometry studies of As(III) solutions were performed with this GC/Au-bt electrode which act as efficient platform for the electro-oxidation of As(III) to As(V) at a very low overpotential. Kinetic parameters were evaluated for the oxidation of As(III) at the GC/Au-bt platforms. A wide linear calibration range for the determination of As(III) from 1 to 1700 μM was obtained with high reproducibility and stability. A limit of detection, 0.1 μM was achieved with high sensitivity. Additionally, it showed a good selectivity for the determination of As(III) in the presence of copper(II) and other interfering ions suggesting a promising new route for trace level determination of As(III) in neutral conditions.

On the issues of resolving a low melting combination as a definite eutectic or an elusive cocrystal: A critical evaluation

Abstract: Cocrystals and eutectics are different yet related crystalline multi-component adducts with diverse applications in pharmaceutical and materials fields. Recently, they were shown to be alternate products of cocrystallization experiments. Whereas a cocrystal shows distinct diffraction, spectroscopic and thermal signatures as compared to parent components, the hallmark of a eutectic is its low melting nature. However, in certain cases, there can be a problem when one resorts to design a cocrystal and assess its formation vis-A -vis a eutectic. In the absence of a gold standard method to make a cocrystal, it is often difficult to judge how exhaustive should the cocrystallization trials be to ensure the accomplishment of a desired/putative cocrystal. Further, a cocrystal can manifest with intermolecular interactions and/or crystal structure similar to that of its parent compounds such that the conventional diffraction and spectroscopic techniques will be of little help to conclusively infer the formation of cocrystal in the lack of single crystals. Such situations combined with low melting behavior of a combination brings the complication of resolving the combination as a cocrystal or eutectic since now both the adducts share common features. Based on the curious case of Caffeine-Benzoic acid combination, this study aims to unfold the intricate issues related to the design, formation and characterization of cocrystals and eutectics for a way forward. The utility of heteronuclear seeding methodology in establishing a given combination as a cocrystal-forming one or a eutectic-forming one in four known systems is appraised.

Development of an electrochemical DNA biosensor for detection of specific Mycobacterium tuberculosis sequence based on poly(L-glutamic acid) modified electrode

Abstract: An electrochemical DNA biosensor was developed by avidin-biotin interaction of a biotinylated probe and avidin-attached, poly(L-glutamic) acid coated pencil graphite electrode (PGA/PGE) for detection of specific Mycobacterium tuberculosis DNA sequence. The discrimination of fully complementary hybridization and mismatch hybridization was carried out by electrochemical reduction current of Meldola’s Blue (MDB) in square wave voltammetry (SWV). The calibration graph of the DNA biosensor was linear between 1.5–12.5 nM and the detection limit was calculated as 1.3 nM. The proposed biosensor successfully discriminated short and long oligonucleotides related to DNA sequence of Mycobacterium tuberculosis in optimal condition.

Role of Lanthanide-Ligand bonding in the magnetization relaxation of mononuclear single-ion magnets: A case study on Pyrazole and Carbene ligated Ln I I I (Ln=Tb, Dy, Ho, Er) complexes

Abstract: Ab initio CASSCF + RASSI-SO + SINGLE_ANISO and DFT based NBO and QTAIM investigations were carried out on a series of trigonal prismatic M(BcMe)3 (M = Tb(1), Dy(2), Ho(3), Er(4), [BcMe]−= dihydrobis(methylimidazolyl)borate) and M(BpMe)3 (M = Tb(1a), Dy(2a), Ho(3a), Er(4a) [BpMe]−= dihydrobis(methypyrazolyl)borate) complexes to ascertain the anisotropic variations of these two ligand field environments and the influence of Lanthanide-ligand bonding on the magnetic anisotropy. Among all the complexes studied, only 1 and 2 show large Ucal (computed energy barrier for magnetization reorientation) values of 256.4 and 268.5 cm−1, respectively and this is in accordance with experiment. Experimentally only frequency dependent χ” tails are observed for complex 1a and our calculation predicts a large Ucalof 229.4 cm−1 for this molecule. Besides these, none of the complexes (3, 4, 2a, 3a and 4a) computed to possess large energy barrier and this is affirmed by the experiments. These observed differences in the magnetic properties are correlated to the Ln-Ligand bonding. Our calculations transpire comparatively improved Single-Ion Magnet (SIM) behaviour for carbene analogues due to the more axially compressed trigonal prismatic ligand environment. Furthermore, our detailed Mulliken charge, spin density, NBO and Wiberg bond analysis implied stronger Ln...H–BH agostic interaction for pyrazole analogues. Further, QTAIM analysis reveals the physical nature of coordination, covalent, and fine details of the agostic interactions in all the eight complexes studied. Quite interestingly, for the first time, using the Laplacian density, we are able to quantify the prolate and oblate nature of the electron clouds in lanthanides and this is expected to have a far reaching outcome beyond the examples studied.

Anodization of Aluminium using a fast two-step process

Abstract: Ultra-fast two-step anodization method is developed for obtaining ordered nano-pores on aluminium (Al) foil. First anodization was carried out for 10 min, followed by 3 min of second anodization at high voltage (150 V) compared to previous reports of anodization times of 12 h (40-60 V). The pore dimensions on anodized alumina are 180 nm for pore diameter and 130 nm for inter-pore distance. It was evident that by increasing the anodization voltage to 150 V, the diameter of the pores formed was above 150 nm. The electrolyte and its temperature affect the shape and size of the pore formation. At lower anodization temperature, controlled pore formation was observed. The anodized samples were characterized using the field emission scanning electron microscope (FE-SEM) to determine the pore diameter and inter-pore distance. Using UV-Visible spectroscopy, the reflectance spectra of anodized samples were measured. The alumina (Al2O3) peaks were identified by x-ray diffraction (XRD) technique. The x-ray photo electron spectroscopy (XPS) analysis confirmed the Al 2p peak at 73.1 eV along with the oxygen O 1s at 530.9 eV and carbon traces C 1s at 283.6 eV.

Amine-functionalized magnetic nanoparticles as robust support for immobilization of Lipase

Abstract: Preparation of magnetic nanoparticles with controlled size and shape along with modulation of their surface properties via introduction of functional groups holds great prospect in the field of nanotechnology. Superparamagnetic, aqueous dispersible iron oxide nanoparticles (Fe3O4) with amine-functionalized surface were prepared through solvothermal method, using poly(ethylene imine) (PEI), ethanolamine (EA), and 2,2 ′-(ethylenedioxy)bis(ethylamine) (EDBE) as amine precursors. These aminated nanoparticles were used as support for the immobilization of lipase, an important industrial enzyme. Lipase was immobilized via glutaraldehyde coupling agent. These functionalized nanoparticles were characterized by XRD, FTIR, TEM, FESEM and VSM analysis. The maximum activity was obtained for the lipase immobilized on EDBE modified Fe3O4 nanoparticles. The lipase immobilized on EDBE-Fe3O4 depicted 83.9% relative activity with respect to the same amount of free lipase. Moreover, lipase immobilized on EDBE-Fe3O4 nanoparticles demonstrated good thermal and storage stability, and easy reusability. The kinetic parameters of lipase immobilized on EDBE-Fe3O4 were compared with those of free lipase and the apparent Michaelis-Menten constant of immobilized lipase was found to be nearly same as that of free lipase.

Carbene →N+ Coordination Bonds in Drugs: A Quantum Chemical Study

Abstract: Coordination chemistry of bonds between main group elements and electron donating ligands as in L →E (where E is electron acceptor centre like C0, Si0, N1, P1, As1, B1 and L is an electron donating N-heterocyclic carbene) has been recently gaining attention. Many important drugs have nitrogen atom as an electron acceptor center and can be represented by two general formulae: (L →N←L)⊕ and L →N-R. Divalent N1 compounds possess two lone pairs at central nitrogen and low nucleophilicity associated with them is found to be of importance. In this article, electronic structure analysis of drug molecules like picloxydine, chlorhexidine, and moroxydine was performed at B3LYP/6-311 ++G(d,p) level of theory. Evaluation of electron localization function (ELF), molecular orbitals, charge density, nucleophilicity, proton affinity and complexation energy estimation confirms the presence of coordination bonds (L →N←L)⊕ in the above mentioned drug molecules in their cationic state. Further, electronic structure analysis of drugs like clonidine, apraclonidine, brimonidine and xylazine indicated the presence of electronic structure similar to L →N-R systems.

Mn(II) complexes with bipyridine, phenanthroline and benzoic acid: Biological and catalase-like activity

Abstract: Five mononuclear Mn(II) complexes, [Mn(phen)2(ClO4)2] (1), [Mn(phen)3](ClO4)2(H2CO3)2(2), [Mn(bipy)2(ClO4)2] (3), [Mn(bipy)3](ClO4)2) (4), and Mn(phen)2(ba)(H2O)](ClO4)(CH3OH) (5), where bipy = 2,2’-bipyridine, phen = 1,10-phenanthroline, and ba = benzoic acid were prepared and characterized by X-ray, IR and UV-Vis spectroscopies, and their catalase-like and biological activities were studied. The presence of two different types and the number of chelating NN-donor neutral ligands allowed for analysis of their effects on the catalase and biological activities. It was observed that the presence and number of phen ligands improved the activity more than the bipy ligand. Complexes 1 and 2, which contain more basic phen ligands, disproportionate H2O2 faster than complexes 3 and 4, which contain less basic bipy ligands. The in vitro antimicrobial activities of all the complexes were also tested against seven bacterial strains by microdilution tests. All the bacterial isolates demonstrated sensitivity to the complexes and the antifungal (anticandidal) activities of the Mn(II) complexes were remarkably higher than the reference drug ketoconazole.

Effects of dimethyl sulfoxide on the hydrogen bonding structure and dynamics of aqueous N-methylacetamide solution

Abstract: Effects of dimethyl-sulfoxide (DMSO) on the hydrogen bonding structure and dynamics in aqueous N-methylacetamide (NMA) solution are investigated by classical molecular dynamics simulations. The modifications of structure and interaction between water and NMA in presence of DMSO molecules are calculated by various site-site radial distribution functions and average interaction energies between these species in the solution. It is observed that the aqueous peptide hydrogen bond interaction is relatively stronger with increasing concentration of DMSO, whereas methyl-methyl interaction between NMA and DMSO decreases significantly. The DMSO molecule prefers to interact with amide-hydrogen of NMA even at lower DMSO concentration. The lifetimes and structural-relaxation times of NMA-water, water-water and DMSO-water hydrogen bonds are found to increase with increasing DMSO concentration in the solution. The slower translational and rotational dynamics of NMA is observed in concentrated DMSO solution due to formation of stronger inter-species hydrogen bonds in the solution.

PtNi nanoparticles embedded in porous silica microspheres as highly active catalysts for p -nitrophenol hydrogenation to p -aminophenol

Abstract: Supported Pt-based alloy nanoparticles have attracted greater attention in catalysis due to their high activity, reduced cost, and easy recycling in chemical reactions. In this work, mesoporous SiO2 microspheres were employed as support to immobilize PtNi alloy nanocatalysts with different mass ratios of Pt and Ni (1:0, 3:1, 1:1, 1:3 and 0:1) by a facile in situ one-step reduction in the absence of any capping agent. SEM, EDS, TEM, FTIR, XRD, ICP-AES, XPS and nitrogen adsorption/desorption analysis were employed to systematically investigate the morphology and structure of the obtained SiO2 microspheres and SiO2/PtNi nanocatalysts. Results show that uniform PtNi nanoparticles can be homogeneously and firmly embedded into the surface of SiO2 microspheres. When the as-prepared SiO2/PtNi nanocatalysts were used in the reduction process of p-nitrophenol to p-aminophenol, the nanocatalyst with Pt and Ni mass ratio of 1:3 showed the highest catalytic activity (TOF of 5.35 × 1018 molecules⋅g −1⋅s −1) and could transform p-nitrophenol to p-aminophenol completely within 5 min. The SiO2/PtNi nanocatalyst can also maintain high catalytic activity in the fourth cycle, implying its excellent stability during catalysis.

Catalytic decomposition of N2O over CeO2 supported Co3O4 catalysts

Abstract: This work was aimed to design efficient catalysts for N2O decomposition at low temperatures. Cobalt oxide (Co3O4) was prepared by hydrothermal, precipitation and combustion methods and tested for N2O decomposition. It was found that the catalysts prepared by solution combustion synthesis were most active for this reaction. Subsequently, a series of ceria (CeO2) supported Co3O4 catalysts (xCeCo) were prepared by solution combustion method and used them for N2O decomposition. All the catalysts were characterized by analytical methods like XRD, TEM, BET, XPS, UV-Vis, Raman and H 2-TPR. It was found that 10 and 20 wt..% loading of CeO2 on Co3O4 promoted the activity of Co3O4 towards N2O decomposition, whereas, higher loading of CeO2 reduced the activity. Typical results indicated that addition of CeO2 increases the surface area of Co3O4, and improves the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step for the N2O decomposition over Co3O4 spinel catalysts. Optimal CeO2 loading can increase both dispersion and surface area of Co3O4 catalysts and weaken the Co–O bond strength to promote N2O decomposition.

Synthesis, crystal structures, spectroscopic characterization and in vitro antidiabetic studies of new Schiff base Copper(II) complexes

Abstract: Two new Schiff base copper(II) complexes, [CuL1(tmen)] (1) and [Cu $_{\mathrm {2}}\mathrm {L}_{\text {2}}^{\text {2}}$ (tmen)] (2) {where, H $_{\mathrm {2}}\textit {L}^{\mathrm {1}}=$ N-(salicylidene)-L-valine, H $_{\mathrm {2}}\textit {L}^{\mathrm {2}}=$ N-(3,5-dichlorosalicylidene)-L-valine and tmen = N,N,N $^{\prime }$ ,N $^{\prime }$ -tetramethylethylene-1,2-diamine} have been synthesized and characterized by molar conductance, elemental analyses, VSM-RT, UV-Vis, FTIR, EPR, and CD spectra. Both the complexes were structurally characterized by single crystal XRD. The crystal structure of complex 1 displays a distorted square pyramidal geometry in which Schiff base is coordinated to the Cu(II) ion via ONO-donor in the axial mode, whereas, the chelating diamine displays axial and equatorial mode of binding via NN-donor atoms. The crystal structure of the complex 2 reveals a syn-anti mode of carboxylate bridged dinuclear complex, in which, the coordination geometry around Cu(1) is square pyramid and distorted square planar around Cu(2). The target complexes were screened for in vitro antidiabetic activity. Both the complexes showed good inhibitory activity for α-amylase and α-glucosidase.