A Mets motif peptide found in copper transport proteins selectively binds Cu(I) with methionine-only coordination

Mets motifs, which refer to methionine-rich sequences found in the high-affinity copper transporter Ctr1, also appear in other proteins involved in copper trafficking and homeostasis, including other Ctrs as well as Pco and Cop proteins isolated from copper-resistant bacteria. To understand the coordination chemistry utilized by these proteins, we studied the copper binding properties of a peptide labeled Mets7-PcoC with the sequence Met-Thr-Gly-Met-Lys-Gly-Met-Ser. By comparing this sequence to a series of mutants containing noncoordinating norleucine in place of methionine, we confirm that all three methionine residues are involved in a thioether-only binding site that is selective for Cu(I). Two independent methods, one based on mass spectrometry and one based on rate differences for the copper-catalyzed oxidation of ascorbic acid, provide an effective K(D) of approximately 2.5 microM at pH 4.5 for the 1:1 complex of Mets7-PcoC with Cu(I). These results establish that a relatively simple peptide containing an MX(2)MX(2)M motif is sufficient to bind Cu(I) with an affinity that corresponds well with its proposed biological function of extracellular copper acquisition.     

An electrochemical investigation on (MoO<Subscript>3</Subscript>+PVP+PVA) nanobelts for lithium batteries

Molybdenum trioxide (MoO₃) xerogel films modified with poly(vinyl alcohol)+poly(vinyl pyrrolidone) (PVP+PVA) polyblends were obtained by ion-exchange method with sol-gel technique. Investigations were conducted using X-ray “diffractometry”, Fourier transform infrared spectroscopy, and cyclic voltammetry. The results show that the H atoms in polyblend are H-bonded with the O atoms in the Mo=O bonds of MoO₃ xerogel, which effectively shield the electrostatic interaction between MoO₃ interlayer and Li⁺ ions when MoO₃ xerogel is modified by the intercalation of (PVP+PVA). The reversibility of the insertion/extraction of Li⁺ ions is greatly improved by the modification with polyblend of MoO₃ nanocomposite films. MoO₃ and (PVP+PVA) _x MoO₃ (x = 0, 0.5) nanobelts were obtained by a simple hydrothermal process from MoO₃ sol. The electrochemical cells with configuration Li/(LiPF₆+EC+DMC)/MoO₃ modified by (PVP+PVA) were fabricated and their discharge profiles studied.     

Fluorometric investigation of the interaction of bovine serum albumin with surfactants and 6-mercaptopurine

Fluorescence quenching in solutions of bovine serum albumin has been investigated in the presence of 6-mercaptopurine and ionic surfactants. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of bovine serum albumin by 6-mercaptopurine was dynamic quenching mechanism. The Stern–Volmer quenching model has been successfully applied, and the activation energy of the interaction between 6-mercaptopurine and bovine serum albumin as much as 4.26 kJ mol⁻¹ was calculated. The distance r between donor (bovine serum albumin) and acceptor (6-mercaptopurine) was obtained according to fluorescence resonance energy transfer (FRET). The result of synchronous fluorescence spectra shows that the conformation of bovine serum albumin has been changed at the present of 6-mercaptopurine.     

Speciation of dissolved iron(II) and iron(III) in environmental water samples by gallic acid-modified nanometer-sized alumina micro-column separation and ICP-MS determination

A method has been developed for the speciation of trace dissolved Fe(II) and Fe(III) in water by coupling gallic acid (GA) modified nanometer-sized alumina micro-column separation with inductively coupled plasma mass spectrometry (ICP-MS). The separation of Fe(II) and Fe(III) was achieved based on the obvious difference in reaction kinetics between Fe(II) and Fe(III) with GA. Fe(III) was selectively retained on the micro-column at pH 5.5-6.5, while Fe(II) could not be retained by the micro-column at the whole tested pH range of 1.0-6.5, and passed through the micro-column. The Fe(II) can be determined by ICP-MS directly without preconcentration/separation procedure, while Fe(III) retained on the micro-column was then eluted with 1.0 mL of 1 mol L(-1) HCl and determined by ICP-MS. The parameters affecting the separation of Fe(II) and Fe(III) were investigated systematically and the optimum separation conditions were established. Under the optimized conditions, the detection limits of 0.48 microg L(-1) and 0.24 microg L(-1) with relative standard deviation of 5.6% and 4.3%(C= 5 microg L(-1), n= 7) for Fe(II) and Fe(III) were found, respectively. No obvious effect on the speciation of Fe(II) and Fe(III) was found with the change of the ratio of Fe(II) and Fe(III) from 0 ratio 10 to 10 ratio 0. The proposed method was applied for the determination of trace Fe(II) and Fe(III) in environmental water and the recoveries for spiked samples were found to be in the range of 97-105%.     

Synthesis of a novel hypocrellin B derivative and its photogeneration of semiquinone anion radical

In order to improve the photosensitizing activity of HB further, the complex of 5,8-di-Br-HB with Al(3+) was first designed and synthesized in high yield. 5,8-di-Br-HB forms a 2:1 type (metal-ligand ratio) complex with Al(3+) measured by molar ratio and continuous variation methods. The new photosensitizer was characterized by UV-Vis, IR, 1H NMR and elemental analysis measurements. Based on the above experimental results, we first proposed a polymer-like structural model of the complex. The water-solubility and red absorption of the [Al(2)(5,8-di-Br-HB)Cl(4)](n) complex are both enhanced over hypocrellin B. In addition, the EPR and spectrophotometric measurements demonstrate that semiquinone anion radical of [Al(2)(5,8-di-Br-HB)Cl(4)](n) can be produced by [Al(2)(5,8-di-Br-HB)Cl(4)](n) photosensitization. The generation efficiency of ([Al(2)(5,8-di-Br-HB)Cl(4)](n))(.-) is almost equal to that of HB(.-). These results obtained indicated that [Al(2)(5,8-di-Br-HB)Cl(4)](n)was at least a favorable Type I phototherapeutic agent.     

Structure and Magnetic Properties of a Novel Two‐Dimensional Complex from 1, 3, 5‐Benzenetricarboxylate and Neodymium(III) — {[Nd(1, 3, 5‐benzenetricarboxylate)(H2O)4] · H2O}n

A unique neodymium(III) complex, {[Nd(BTC)(H₂O)₄] · H₂O}_n (BTC = 1, 3, 5‐benzenetricarboxylate), was obtained from the reaction between Nd(ClO₄)₃ · xH₂O and Na₃BTC. Coordination bonds, hydrogen bonds, and π‐π stacking form a supramolecular structure with a novel, two‐dimensional framework. The temperature‐dependent magnetic susceptibilities were analyzed by the Curie‐Weiss law; the following values were found C = 1.32, θ = —18.3 K, respectively.     

Solvent Effects on the Absorption Spectrum of the Product and the Equilibrium Constant for the Proton Transfer Reaction from 1-Phenacylquinolinium Bromide to Amines

The equilibrium constants, K ₂, have been determined for the proton-transfer reactions of 1-phenacylquinolinium ion, PHQ⁺, with several amines {triethylamine (TEA), N,N,N′,N′-tetramethylethylenediamine (ED), N,N,N′, N′-tetramethylpropanediamine (PD), N,N,N′,N′-tetramethylbutanediamine (BD), and 1,8-bis(dimethylamino-naphthalene (DMAN)} in acetonitrile (AN), AN-tetrahydrofuran (THF) and AN-ethanol (EtOH) mixtures. The reaction was followed spectrophotometrically using a stopped-flow technique. The K ₂ value decreased for DMAN and increased for TEA with increasing vol-% of THF in AN-THF mixtures. The changes in the K ₂ value for ED, PD and BD changed in the order: ED, PD and BD from a pattern similar to TEA to a pattern similar to DMAN. The change in the K ₂ value for DMAN with increasing vol-% of THF in AN-THF mixtures was explained by the effect of polarity on the stability of P⁻Q⁺ (the deprotonated product of PHQ⁺). The effect of THF on the K ₂ value is consistent with that of the peak wavelength of the absorption spectrum of P⁻Q⁺. The change in the K ₂ value for TEA, ED, PD and BD depended on the structures of the protonated bases, one of the products for this reaction. The effect of EtOH on the K ₂ value for DMAN was examined in ternary EtOH-THF-AN mixtures that contain different amounts of EtOH and whose relative permittivities were adjusted to that of EtOH. The K ₂ value increased with increasing vol-% of EtOH because of the stabilization of P⁻Q⁺ upon the formation of the hydrogen-bonded complex with EtOH. The absorption spectrum of P⁻Q⁺ demonstrated a blue shift as the vol-% of EtOH increased.     

Double hexagonal chains with minimal total <Emphasis Type="Italic">π</Emphasis>-electron energy

The total energy of all π-electrons in a conjugated hydrocarbon (within the framework of HMO approximation) is the sum of the absolute value of all the eigenvalues of its corresponding graph. In this paper, we consider “double hexagonal chains” as benzenoids constructed by successive fusions of successive naphthalenes along a zig–zag sequence of triples of edges as appear on opposite sides of each naphthalene unit. It is shown that if the fusions are such as to give a polyaceacene then the total π-electron energy is the minimum from among all the double hexagonal chains with the same number of naphthalene units.      

Preparation of spherical spinel LiMn2O4 cathode material for lithium ion batteries

A novel process is proposed for synthesis of spinel LiMn₂O₄ with spherical particles from the inexpensive materials MnSO₄, NH₄HCO₃, and NH₃H₂O. The successful preparation started with carefully controlled crystallization of MnCO₃, leading to particles of spherical shape and high tap density. Thermal decomposition of MnCO₃ was investigated by both DTA and TG analysis and XRD analysis of products. A precursor of product, spherical Mn₂O₃, was then obtained by heating MnCO₃. A mixture of Mn₂O₃ and Li₂CO₃ was then sintered to produce LiMn₂O₄ with retention of spherical particle shape. It was found that if lithium was in stoichiometric excess of 5% in the calcination of spinel LiMn₂O₄, the product had the largest initial specific capacity. In this way spherical particles of spinel LiMn₂O₄ were of excellent fluidity and dispersivity, and had a tap density as high as 1.9 g cm^–3 and an initial discharge capacity reaching 125 mAh g^–1. When surface-doped with cobalt in a 0.01 Co/Mn mole ratio, although the initial discharge capacity decreased to 118 mAh g^–1, the 100th cycle capacity retention reached 92.4% at 25°C. Even at 55°C the initial discharge capacity reached 113 mAh g^–1 and the 50th cycle capacity retention was in excess of 83.8%.     

Dynamically coating the capillary with 1-alkyl-3-methylimidazolium-based ionic liquids for separation of basic proteins by capillary electrophoresis

Ionic substances with melting points close to room temperature are referred to as ionic liquids. Because ionic liquids are environmentally benign and are good solvents for a wide range of both organic and inorganic materials, interest for their potential uses in different chemical processes is increasing. In this paper, a capillary electrophoretic method for the analysis of basic proteins including lysozyme, cytochrome c, trypsinoge, and α-chymotyypsinogen A is reported. The method, in which 1-alkyl-3-methylimidazolium-based ionic liquids are used as the running electrolytes, leads to a surface charge reversal on the capillary wall. The effects of the alkyl group, imidazolium counterion, and the concentration of the ionic liquids were discussed. The optimum buffer system was a 90 mM 1-ethyl-3-methylimidazolium tetrafluoroborate (1E-3MI-TFB) solution. The applied voltage was −15 kV and detection was performed by monitoring absorbance at 240 nm. Baseline separation, high efficiencies, and symmetrical peaks of four proteins were obtained. The R.S.D. values of migration times and peak areas were <0.68 and <3.0%, respectively. The separation mechanism seems to involve association between the imidazolium cations and the proteins.