Proton positions in the Mn(2+) binding site of concanavalin A as determined by single-crystal high-field ENDOR spectroscopy

High-field (95 GHz) pulsed EPR and electron-nuclear double resonance (ENDOR) techniques have been used for the first time to determine coordinates of ligand protons of a high-spin metal center in a protein single crystal. The protein concanavalin A contains a Mn(2+) ion which is coordinated to two water molecules, a histidine residue, and three carboxylates. Single crystals of concanavalin A were grown in H(2)O and in D(2)O to distinguish the exchangeable water protons from the nonexchangeable protons of the imidazole group. Distinct EPR transitions were selected by performing the ENDOR measurements at different magnetic fields within the EPR spectrum. This selection, combined with the large thermal polarization achieved at 4.5 K and a magnetic field of approximately 3.4 T allowed us to assign the ENDOR signals to their respective M(S) manifolds, thus providing the signs of the hyperfine couplings. Rotation patterns were acquired in the ac and ab crystallographic planes. Two distinct crystallographic sites were identified in each plane, and the hyperfine tensors of two of the imidazole protons and the four water protons were determined by simulations of the rotation patterns. All protons have axially symmetric hyperfine tensors and, by applying the point-dipole approximation, the positions of the various protons relative to the Mn(2+) ion were determined. Likewise, the water protons involved in H-bonding to neighboring residues were identified using the published, ultrahigh-resolution X-ray crystallographic coordinates of the protein (Deacon et al. J. Chem. Soc., Faraday Trans. 1997, 93(24), 4305-4312).     

Efficient and versatile catalysis for β-alkylation of secondary alcohols through hydrogen auto transfer process with newly designed ruthenium(II) complexes containing ON donor aldazine ligands

A new series of ruthenium(II) carbonyl complexes, [RuCl(CO)(EPh₃)₂(L_1-2)] (1–4) (E = P or As; H₂L₁ = salicylaldazine, H₂L₂ = 2-hydroxynaphthaldazine), have been assembled from ruthenium(II) precursors [RuHCl(CO)(EPh₃)₃] and bidentate ON donor Schiff base ligands (H₂L_1-2). Both ligands and their new ruthenium(II) complexes have been characterized by elemental analyses, spectroscopic methods (UV, IR, NMR (¹H, ¹³C, ³¹P) as well as ESI mass spectrometry. The molecular structures of H₂L₁ and 1 have been confirmed by single crystal X-ray diffraction. Based on the above studies, an octahedral coordination geometry around the metal center has been proposed for 1–4. To investigate the catalytic effectiveness of 1–4, the complexes have been used as catalysts in β-alkylation of secondary alcohols with primary alcohols and synthesis of quinolines. The effect of solvent, time, base, catalyst loading, and substituent of the ligand moiety on the reaction was studied. Notably, 1 was a more efficient catalyst toward alkylation of a wide range of alcohols and quinolines synthesis. The reusability of the catalyst was checked and the results showed up to six catalytic runs without significant loss of activity.     

Spectral studies of methyl‐p‐hydroxy benzoate: An organic nonlinear optical crystalline material

The single crystals of Methyl‐p‐Hydroxy Benzoate (MHB) were grown by solution growth technique and characterized by X‐ray diffraction (single crystal), density, melting point, UV‐Vis, FT‐IR and FT‐Raman techniques. Electron Paramagnetic Resonance (EPR) spectra of Cu²⁺: MHB were recorded and the spin Hamiltonian parameters were evaluated. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of γ-ray-irradiated conducting polymer electrolyte and its application of dye-sensitized solar cells to building window glass system

Journal of Solid State Electrochemistry - In the present study, γ-ray-irradiated and un-irradiated PVA/PPy/KI/I2 conducting polymer electrolytes have been prepared for dye-sensitized solar...     

Future perspective of nanoparticle interaction-assisted laser desorption/ionization mass spectrometry for rapid, simple, direct and sensitive detection of microorganisms

The introduction of nanoparticles into mass spectrometric research greatly influenced the applicability of this technique into various omics. Surface-modified or functionalized nanoparticles (NPs) have recently extended the use of mass spectrometry into microorganism research. We survey the application of unmodified NPs, for microorganism research, on the basis of our expertise in this area within the recent years in this decade. The use of unmodified NPs in mass spectrometry, especially with respect to microorganisms, is an untreaded research area, which we have ventured to probe and have been fruitful. On the basis of our experience, we provide an insight into the principle behind the use of unmodified NPs and provide guidelines to be followed to obtain significant results. We also brief the current scenario of nanoparticle interaction-assisted laser desorption/ionization mass spectrometry (NPILDI-MS) for rapid, simple, direct and sensitive detection of microorganisms on the basis of our past and present reports, quoting examples of successful application of this technique. Finally, we address the future of the NPILDI-MS technique and the tools needed to reach those visions.     

Hamilton cycle decompositions of the tensor products of complete bipartite graphs and complete multipartite graphs

In this paper, it is shown that the tensor product of the complete bipartite graph, K_r,r,r≥2, and the regular complete multipartite graph, , is Hamilton cycle decomposable.     

Fabrication and characterization of poly 2-napthol orange film modified electrode and its application to selective detection of dopamine

The present work is based on the use of a redox mediator containing an azo group for the selective determination of dopamine in the presence of uric acid and ascorbic acid by electrochemical method. A modified electrode was prepared by electrochemical polymerization of the poly 2-napthol orange film (P2NO) on the paraffin wax-impregnated graphite electrode (PIGE) by applying potential between ?0.6 and 0.8 V at scan rate of 50 mV s^?1 for 30 segments. The modified P2NO film electrode was characterized by ATR-IR spectroscopy, FE-SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), hydrodynamic voltammetry (HDV), and chronoamperometry (CA). The P2NO film modified electrode exhibited selective determination of dopamine in the presence of uric acid and ascorbic acid, and the electrocatalytic activity for oxidation of dopamine was excellent. The linear range for the determination of dopamine was 0.6 to 250 μM with a limit of detection of 0.13 μM. The modified P2NO electrode showed good stability and reproducibility. The modified electrode was used for real sample analysis such as human blood serum, rat blood serum, and pharmaceutical samples (dopamine hydrochloride injection). The results obtained were found to be satisfactory.     

A comparative study on the mode of interaction of different nanoparticles during MALDI‐MS of bacterial cells

We propose the benefits of preincubation during nanoparticle‐assisted bacterial analysis, where the bacteria are grown along with the nanoparticles. We were able to obtain a two to ten fold enhancement of bacterial signals in 3 h compared to the generally used methodology followed in previous literature. The previous literature method required a long time (18 h) to obtain such an enhancement. We probe the interactions of two bacteria, Staphylococcus aureus and Pseudomonas aeruginosa, with Ag, NiO, Pt TiO₂ and ZnO nanoparticles via transmission electron microscopy, ultraviolet spectroscopy and matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry (MS). Based on these results, we propose a mechanism for interaction of these five nanoparticles with bacteria. Two mechanisms were observed for the interactions: (1) Mechanism A is proposed for the Pt and NiO NPs which functioned based on affinity for bacterial cells. (2) Mechanism B was proposed for the bactericidal NPs such as TiO₂, ZnO and Ag NPs. The results indicate that the success of the unmodified NPs in MALDI‐MS bacterial studies lies in following the ideal protocol for incubation at the ideal concentrations. Copyright © 2013 John Wiley & Sons, Ltd.     

Phytochemical mediated gold nanoparticles and their PTP 1B inhibitory activity

Current discovery demonstrates the rapid formation of gold nanoparticles with guavanoic acid a phytochemical of Psidium guajava (Pg). The pharmacological capabilities of the phytochemicals present in the leaves of Pg and their ability to generate gold nanoparticles is presented herein. The new genre of green nanoparticles exhibit remarkable Protein Tyrosine Phosphatase 1B (PTP 1B) inhibitory activity and in vitro stability in various physiological medium including saline, histidine, cysteine, bovine serum albumin (BSA), human serum albumin (HSA) and buffers (pH 5, 7 and 9). It is predicted that this new technology will be felt greatly in several routes of pharmaceuticals.     

Photocatalytic and bactericidal activities of hydrothermally synthesized nanocrystalline Cd-doped ZnO

Nanocrystalline Cd-doped ZnO has been obtained by hydrothermal synthesis and characterized by powder X-ray diffraction, energy dispersive X-ray spectrum, high resolution scanning electron micrographs and UV–visible diffuse reflectance, photoluminescence and electrochemical impedance spectra. Cd-doping by hydrothermal method decreases the grain size and destroys the microstructure. Although doping does not modify the band gap it suppresses the deep level emission, decreases the charge-transfer resistance and increases the capacitance. Cd-doping enhances the photocatalytic and bactericidal activities.