Experimental and computational studies of selective recognition of Hg2+ by amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene: species characterization in solution and that in the isolated complex, including the delineation of the nanostructures

Amide linked lower rim 1,3-dibenzimidazole derivative of calix[4]arene, L has been shown to be sensitive and selective to Hg(2+) in aqueous acetonitrile solution based on fluorescence spectroscopy, and the stoichiometry of the complexed species has been found to be 1:1. The selectivity of L toward Hg(2+) has been shown among 11 M(2+) ions, viz., Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+), Ca(2+), and Mg(2+) studied, including those of the mercury group and none of these ions impede the recognition of Hg(2+) by L. Role of the solvent on the recognition of Hg(2+) has been demonstrated. The role of calix[4]arene platform and the benzimidazole moieties in the recognition of Hg(2+) by L has been delineated upon performing such studies with five different molecules of relevance as reference molecular systems. The binding cores formed by the receptor L and the reference compounds have been established based on the single crystal XRD structures, and the preferential metal ion binding cores have been discussed. The binding of Hg(2+) with L has been further established based on (1)H and (13)C NMR, ESI MS, absorption, and fluorescence lifetime measurements. Some of these techniques have been used to establish the stoichiometry of the species formed. The complex species formed between L and Hg(2+) have been isolated and characterized and found to be 1:1 species even in the isolated complex. Whereas transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) provided the nanostructural behavior of L, the TEM and SEM demonstrated that the mercury complex has different characteristics when compared to L. The TEM, SEM, and powder XRD studies revealed that whereas L is crystalline, that of the mercury complex is not, perhaps a reason for not being able to obtain single crystals of the complex. Binding characteristics of Hg(2+) toward L have been established based on the DFT computational calculations.     

Nanostructured Cu and Cu@Cu(2)O core shell catalysts for hydrogen generation from ammonia-borane

Copper nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. Oxidation of the SMAD prepared copper colloids resulted in Cu@Cu(2)O core shell structures (7.7 +/- 1.8 nm) or Cu(2)O nanoparticles depending on the reaction conditions. The nano Cu, Cu@Cu(2)O core shell, and Cu(2)O particles were found to be catalytically active for the generation of hydrogen from ammonia-borane either via hydrolysis or methanolysis reaction.     

Kinetics and mechanism of electrochemical oxygen reduction using Platinum/clay/Nafion catalyst layer for polymer electrolyte membrane fuel cells

This work demonstrates the use of amino functionalized Mg-phyllosilicate clay/Nafion nanocomposite film embedded with Pt nanoparticles (Pt/AC/N) for catalyzing oxygen reduction reaction (ORR) in sulphuric acid medium. Pt/AC/N nanocomposite films were surface characterized using transmission electron microscope. Cyclic and linear scan voltammetry studies were carried out under hydrodynamic conditions taking rotating-ring disc electrode (RRDE) as the working electrode. The effects of clay content, Pt mass loading, electrode rotation rate, and temperature on the ORR kinetics were studied. The Tafel slopes were found to vary between 118 and 126 mV dec⁻¹ indicating a good ORR kinetics. The exchange current density values calculated after mass transfer correction ranged from 5.8 × 10⁻⁷ to 2.4 × 10⁻⁶ A cm⁻². From the RRDE disc currents, Koutecky-Levich plots were constructed and the ORR mechanism was found to follow a four electron path with minimum H₂O₂ formation of ∼1.6%. The effect of temperature on ORR kinetics was found at 25, 40, and 50 °C. The energy of activation calculated to be 7.68 kJ mol⁻¹ and comparable to the standard Pt/C catalyzed ORR systems.     

Conformational mapping and energetics of saccharide-aromatic residue interactions: implications for the discrimination of anomers and epimers and in protein engineering

Aromatic residues play a key role in saccharide-binding sites. Experimental studies have given an estimate of the energetics of saccharide-aromatic residue interactions. In this study, dependence of the energetics on the mutual position-orientation (PO) of saccharide and aromatic residue has been investigated by geometry optimization of a very large number (164) of complexes at MP2/6-31G(d,p) level of theory. The complexes are of Tyr and Phe analogs with α/β-D-Glc, β-D-Gal, α-D-Man and α/β-L-Fuc. A number of iso-energy POs are found for the complexes of all six saccharides. Stacking and non-stacking modes of binding are found to be of comparable strengths. In general, complexes of p-OHTol are stronger than those of Tol, and those dominated by OH···O interactions are more stable than ones dominated by CH···π interactions. The strengths of OH···O/π interactions, but not those of CH···π, show large variations. Even though an aromatic residue has a large variety of POs to interact with a saccharide, distinct preferences are found due to anomeric and epimeric differences. An aromatic residue can interact from either the a- or b-face of Glc, but only through the b-face with Gal, its C4-epimer. In contrast, stacking interaction with Man (C2-epimer of Glc) requires the participation of the -CH(2)OH group and free rotation of this group, as is observed in solution, precludes all modes of stacking interactions. It is also found that an aromatic residue can be strategically placed either to discriminate or to accommodate (i) anomers of Glc and of Fuc and (ii) Gal/Fuc. Thus, analysis of the optimized geometries of by far the largest number of complexes, and with six different saccharides, at this level of theory has given insights into how Nature cleverly uses aromatic residues to fine tune saccharide specificities of proteins. These are of immense utility for protein engineering and protein design studies.     

Synthesis and charge transport studies of stable, soluble hexacenes

Acenes larger than pentacene are predicted to possess enticing electronic properties, but are insoluble and prone to rapid decomposition. Utilizing a combination of functionalization strategies, we present stable, solution-processable hexacenes and an evaluation of their hole and electron transport properties.     

COSMO-RS Based Predictions for the Extraction of Lignin from Lignocellulosic Biomass Using Ionic Liquids: Effect of Cation and Anion Combination

A total of 34 cations belonging to 6 classes and 34 anions resulting in 1156 possible combinations are screened using the quantum chemical based COSMO-RS (COnductor-like Screening MOdel for Real Solvents) model. The Hildebrand solubility parameter (?? _H) is calculated using the predicted infinite dilution activity coefficient (?? ^??) of lignin in ionic liquids at 303.15 K. Initial benchmarking is performed by predicting the Hildebrand solubility parameter of lignin in ionic liquids. Comparison with literature values involving 12 ILs gives the average root mean square deviation (RMS) as 10.15?%. Except for anions based on hexafluorophosphate [PF₆], bis(oxalato(2)borate) [BOB], tetracyanoborate [B(CN)₄] and bis(trifluoromethylsulfonyl)amide [BTA], all the cation?Canion combinations have calculated solubility parameters equal to that of lignin at 303.15 K, indicating high solubilities for lignin.     

16-electron elongated dihydrogen complex stabilized by agostic interaction

A 16-electron dicationic dihydrogen complex [Ru(eta2-H...H)(PP)2][OTf]2 [4; PP = (C6H5CH2)2PCH2CH2P(CH2C6H5)2] has been prepared and characterized by protonating the precursor hydride complex [Ru(H)(PP)2)][OTf] (2) using HOTf. The hydride and dihydrogen complexes are stabilized via agostic interaction of the ortho C-H fragment of the phenyl ring on the benzyl group. The intact nature of the H-H bond in this derivative was established from the short spin-lattice relaxation time and the observation of a substantial J(H,D) of 22.0 Hz for the HD isotopomer. The H-H bond distance calculated from J(H,D) is 1.05 A, which falls under the category of elongated dihydrogen ligands.     

A novel method of synthesizing solid phase adsorbent silica modified with xylenol orange: application for separation, pre-concentration and determination of uranium in calcium rich hydro-geochemical samples and sea water—Part 1

A novel, single-step route has been developed for the synthesis of solid phase adsorbent silica modified with xylenol orange. The addition of cationic surfactant cetyl tri-methylammonium bromide during the synthesis of the adsorbent supports the formation of a stable coating of xylenol orange on silica. The adsorbent showed no signs of degradation in contact with organic solvents and with solutions of varying pH between 1 and 9. This adsorbent has been used for separation and pre-concentration of uranium from hydro-geochemical samples with high calcium content and from sea water. Quantitative sorption of uranium was observed above pH 3 and complete desorption can be achieved using 0.2 M sodium pyrophosphate solution. The uranium content in the extract was determined by laser fluorimetric technique. The equilibration time is 30 min. The sorption capacity of the adsorbent for uranium is 10 mg g^?1. An enrichment factor of 50 was obtained by this procedure taking 500 mL of sample solution. Uranium concentrations down to 0.05 ng mL^?1 can be determined after pre-concentration using this method. The relative standard deviation at an 0.1 ng mL^?1 level is ±15%.     

Antiproliferative Efficacy of N-(3-chloro-4-fluorophenyl)-6,7-dimethoxyquinazolin-4-amine,DW-8, in Colon Cancer Cells Is Mediated by Intrinsic Apoptosis

A novel series of 4-anilinoquinazoline analogues, DW (1–10), were evaluated for anticancer efficacy in human breast cancer (BT-20) and human colorectal cancer (CRC) cell lines (HCT116, HT29, and SW620). The compound, DW-8, had the highest anticancer efficacy and selectivity in the colorectal cancer cell lines, HCT116, HT29, and SW620, with IC₅₀ values of 8.50 ± 2.53 µM, 5.80 ± 0.92 µM, and 6.15 ± 0.37 µM, respectively, compared to the non-cancerous colon cell line, CRL1459, with an IC₅₀ of 14.05 ± 0.37 µM. The selectivity index of DW-8 was >2-fold in colon cancer cells incubated with vehicle. We further determined the mechanisms of cell death induced by DW-8 in SW620 CRC cancer cells. DW-8 (10 and 30 µM) induced apoptosis by (1) producing cell cycle arrest at the G2 phase; (2) activating the intrinsic apoptotic pathway, as indicated by the activation of caspase-9 and the executioner caspases-3 and 7; (3) nuclear fragmentation and (4) increasing the levels of reactive oxygen species (ROS). Overall, our results suggest that DW-8 may represent a suitable lead for developing novel compounds to treat CRC.     

Cosmological Parameters from Planck Data in SU(2)CMB,Their Local ΛCDM Values,and the Modified Photon Boltzmann Equation

A review of the spatially flat cosmological model SU(2)_CMB, minimally induced by the postulate that the cosmic microwave background (CMB) is subject to an SU(2) rather than a U(1) gauge principle, is given. Cosmological parameter values, which are determined from the Planck CMB power spectra at small angular scales, are compared to their values in spatially flat ΛCDM from both local and global extractions. As a global model SU(2)_CMB leans toward local ΛCDM cosmology and is in tension with some global ΛCDM parameter values. Spectral antiscreening / screening effects in SU(2)_CMB radiance are presented within the Rayleigh– Jeans regime in dependence on temperature and frequency. Such radiance anomalies can cause CMB large-angle anomalies. Therefore, it is pointed out how SU(2)_CMB modifies the Boltzmann equation  for the perturbations of the photon phase space distribution at low redshift and why this requires to the solve the ℓ-hierarchy on a comoving momentum grid (q-grid) for all z.