π–π Stacking Interaction in an Oxidized CuII–Salen Complex with a Side-Chain Indole Ring: An Approach to the Function of the Tryptophan in the Active Site of Galactose Oxidase

In order to gain new insights into the effect of the π–π stacking interaction of the indole ring with the Cu^II–phenoxyl radical as seen in the active form of galactose oxidase, we have prepared a Cu^II complex of a methoxy-substituted salen-type ligand, containing a pendent indole ring on the dinitrogen chelate backbone, and characterized its one-electron-oxidized forms. The X-ray crystal structures of the oxidized Cu^II complex exhibited the π–π stacking interaction of the indole ring mainly with one of the two phenolate moieties. The phenolate moiety in close contact with the indole moiety showed the characteristic phenoxyl radical structural features, indicating that the indole ring favors the π–π stacking interaction with the phenoxyl radical. The UV/Vis/NIR spectra of the oxidized Cu^II complex with the pendent indole ring was significantly different from those of the complex without the side-chain indole ring, and the absorption and CD spectra exhibited a solvent dependence, which is in line with the phenoxyl radical–indole stacking interaction in solution. The other physicochemical results and theoretical calculations strongly support that the indole ring, as an electron donor, stabilizes the phenoxyl radical by the π–π stacking interaction.     

Recent Advances in One-Electron-Oxidized CuII–Diphenoxide Complexes as Models of Galactose Oxidase: Importance of the Structural Flexibility in the Active Site

The phenoxyl radical plays important roles in biological systems as cofactors in some metalloenzymes, such as galactose oxidase (GO) catalyzing oxidation of primary alcohols to give the corresponding aldehydes. Many metal(II)–phenoxyl radical complexes have hitherto been studied for understanding the detailed properties and reactivities of GO, and thus the nature of GO has gradually become clearer. However, the effects of the subtle geometric and electronic structural changes at the active site of GO, especially the structural change in the catalytic cycle and the effect of the second coordination sphere, have not been fully discussed yet. In this Review, we focus on further details of the model studies of GO and discuss the importance of the structural change at the active site of GO.     

Function–Topology Relationship in the Catalytic Hydrolysis of a Chemical Warfare Simulant in Two Zr-MOFs

Owing to their high surface area, high concentration of active metal sites, and water stability, zirconium(VI)-based metal–organic frameworks (Zr-MOFs) have shown excellent activity in the hydrolysis of organophosphorus nerve agents (OPNs). In this regard, for the first time, two topologically different Zr-MOFs (Zr-fcu-tmuc and Zr-bcu-tmuc, constructed from the same organic and inorganic building blocks; fcu=face-centered cubic, bcu=body-centered cubic) have been rationally chosen to investigate the effect of network topology on the catalytic hydrolysis of the nerve agent simulant, dimethyl 4-nitrophenyl phosphate (DMNP). A remarkable enhancement in the hydrolysis rate of DMNP was observed with Zr-bcu-tmuc, reducing the half-life more than three-fold compared with Zr-fcu-tmuc. Greater accessibility of the active Zr^VI sites in the 8-connected bcu net compared with the 12-connected fcu leads to a faster hydrolysis of DMNP on Zr-bcu-tmuc. Interestingly, the higher activity of Zr-bcu-tmuc was also confirmed by its higher fluorescence sensitivity towards DMNP (limit of detection (LOD)=0.557 μm ) compared with Zr-fcu-tmuc (LOD=1.09 μm ). The results show that controlling the desired topology of Zr-MOFs is a useful strategy for improving their performance in the detection and catalytic detoxification of OPNs.     

Catalytic Activity of Polymetalorganosiloxanes Supported on Silica in the Metathesis of a C–Cl Bond

The catalytic activity of structurally different Cu- and Ni-containing polymetalorganosiloxanes supported on silica was studied using the reaction of C–Cl bond metathesis in the carbon tetrachloride–saturated hydrocarbon (n-decane) system as an example. Catalysts with low metal contents were found to exhibit the highest activity; an increase in the metal content resulted in a decrease in both conversion and specific activity. At the initial portions of kinetic curves, the reaction was described by first-order rate equations with respect to n-decane; the reaction was of fraction order with respect to CCl₄and catalyst. The activation energy of the process in the n-decane–carbon tetrachloride system on a copper-containing network catalyst was 23 ± 2 kcal/mol. The mechanism of catalysis on immobilized catalysts from the above class is discussed.     

Site of protonation of nicotine and nornicotine in the gas phase: pyridine or pyrrolidine nitrogen?

The gas-phase basicities (GBs) of nornicotine, nicotine, and model pyrrolidines have been measured by FT-ICR. These experimental GBs are compared with those calculated (for the two sites of protonation in the case of nicotine and nornicotine) at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p) level, or those estimated from substituent effects on the GBs of 2-substituted pyrrolidines, 2-substituted N-methylpyrrolidines, and 3-substituted pyridines. It is found that, in contrast to the Nsp(3) protonation in water, in the gas phase nornicotine is protonated on the pyridine nitrogen, because the effects of an intramolecular CH.Nsp(3) hydrogen bond and of the polarizability of the 3-(pyrrolidin-2-yl) substituent add up on the Nsp(2) basicity, while the polarizability effect of the 2-(3-pyridyl) substituent on the Nsp(3) basicity is canceled by its field/inductive electron-withdrawing effect. The same structural effects operate on the Nsp(3) and Nsp(2) basicities of nicotine, but here, the polarizability effect of the methyl group puts the pyrrolidine nitrogen basicity very close to that of pyridine. Consequently, protonated nicotine is a mixture of the Nsp(3) and Nsp(2) protonated forms.     

Removal of Toluene from Industrial Gas by Adsorption–Plasma Catalytic Process: Comparison of Closed Discharge and Ventilated Discharge

Degradation of adsorbed toluene over 13X zeolite, 5A molecular sieve and Al₂O₃ by non-thermal plasma was investigated. Different discharge modes, including closed and ventilated discharge were compared. The carbon balance and COx yield of 13X zeolite were increased by 17.6 and 19.4% by ventilated discharge, respectively, compared with closed discharge. But for 5A molecular sieve and Al₂O₃, the carbon balance and COx yield by closed discharge were greater than those by ventilated discharge. It meant that the closed discharge was more suitable for low-concentration of VOC and the residence time of reactants would be prolonged. Removal of high-concentration VOC by ventilated discharge was more appropriate because of more reactive oxygen species generated. Furthermore, the effect of discharge background gas was studied. Removal of adsorbed toluene over Co/13X by oxygen and air with different flow rate as background gas were compared. The removal efficiency was reduced as flow rate of background gas increased. The oxygen-discharge was more efficiency for toluene oxidation and inhibited the generation of nitrogen oxides.     

A New Conformation of a Water Hexamer Chain and its Reversible Formation/Removal in the Host Channel by Gas–Solid Reaction

Crystal structure determinations of, in most cases, hydrated, alkali metal derivatives of the dicarboxylic acids, 2,2′-bipyridine-3,3′-dicarboxylic acid (H²BDC) and chelidamic acid (4-hydroxypyridine-2,6-dicarboxylic acid, H²CHEL) show numerous similarities, such as in the predominance of O-coordination in generating solid state polymers in which parallel arrays of the essentially planar ligand ring units are apparent, though not necessarily indicative of conventional π-stacking interactions, and some unanticipated differences. In particular, all species derived from chelidamic acid, including its diammonium compound, appear to be complexes of the partially deprotonated pyridone form of this ligand. In both systems, close contacts between atoms constituting the aromatic entities take a variety of forms depending upon the associated metal.     

Characterization of a heavy oil–propane system in the presence or absence of asphaltene precipitation

When a light hydrocarbon solvent is injected into a heavy oil reservoir under a sufficiently high reservoir pressure, asphaltene precipitation occurs so that the heavy oil is in situ deasphalted during a hydrocarbon solvent-based heavy oil recovery process. The physicochemical properties of this in situ deasphalted heavy oil are rather different from those of the original crude oil in the heavy oil reservoir. In this paper, a heavy oil sample is saturated with a typical light hydrocarbon solvent (i.e., propane) under different saturation pressures in a see-through windowed high-pressure saturation cell. The heavy oil–propane system is characterized by measuring and comparing several important physicochemical properties of the propane-saturated heavy oil samples under different saturation pressures and the flashed-off heavy oil samples, such as the solubility, oil-swelling factor, density, viscosity, asphaltene content, hydrogen and carbon aromaticities. When the heavy oil is saturated with propane at P ≤ 780 kPa and T = 20.8 °C, there is no observable asphaltene precipitation and deposition under a microscope camera. The respective properties of the propane-saturated heavy oil samples taken from the upper and lower parts of the saturation cell are measured and found to be essentially the same within the experimental errors so that the entire system is considered to be almost homogeneous. If the saturation pressure is increased to P = 850 kPa, strong asphaltene precipitation occurs and some large asphaltene particles are deposited onto the bottom of the saturation cell. In this case, the heavy oil is deasphalted and the flashed-off heavy oil has lower density, viscosity, asphaltene content, hydrogen and carbon aromaticities than those of the original heavy crude oil.     

Simple Transformation of Hierarchical Hollow Structures by Reduction of Metal–Organic Frameworks and Their Catalytic Activity in the Oxidation of Benzyl Alcohol

Metal–organic framework (MOF)-based derivatives have been found to be promising heterogeneous catalysts for organic transformations. Herein, hollow-structure Cu-MOFs derived by reduction of Cu₃(BTC)₂ (BTC=1,3,5-benzenetricarboxylate; denoted as RCB) were prepared by using hydrazine hydrate as a reducing agent under various conditions. The influence of hydrazine hydrate induced the structure of Cu₃(BTC)₂ and led to dynamic variation in the interior and exterior as well as oxidation states of the Cu ion. The synthesized materials were characterized by SEM, TEM, N₂ sorption isotherms, XRD, and XPS. The product of the catalytic reaction was observed by GC-MS. In addition, the prepared RCBs were found to have excellent catalytic activity and selectivity for benzyl alcohol oxidation when assisted by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).     

Catalytic oxidation of alcohols to aldehydes or ketones using osmium–oxo complexes with sulfoxides or N-methylmorpholine-N-oxide as the co-oxidant: a comparative study

A catalytic amount of osmium tetroxide in association with sulfoxides or N-methylmorpholine-N-oxide can be used to catalyse the oxidation of primary and secondary alcohols to their corresponding carbonyl compounds.     

Analysis of soluble intermediates in the lithium–sulfur battery by a simple in situ electrochemical probe

This paper describes a simple setup using a thin, insulated platinum wire as an in situ electrochemical probe for analysis of the soluble polysulfide intermediates formed and consumed during the course of the discharge process of a lithium–sulfur cell. The probe, sharing common reference and counter electrodes with the cell, can be used to follow the changes in concentration of polysulfides in the electrolyte. The results herein both support and complement more advanced techniques studied elsewhere for understanding the dominant processes occurring in the cell.     

Development of a procedure for the multi-element determination of trace elements in wine by ICP–MS

An inductively coupled plasma mass spectrometric (ICP–MS) procedure has been developed for the determination of trace elements in wine. The procedure consists in simple 1+1 dilution of the wine and semi-quantitative analysis (without external calibration) using In as internal standard. Thirty-one elements at concentrations ranging from 0.1 mg mL^–1 to 0.5 ng mL^–1 can be determined by ICP–MS analysis with and without digestion. It was investigated whether a matrix effect observed for EtOH in the wine matrix can be overcome by application of a micro-concentric nebulizer with a membrane desolvator (MCN 6000). The results obtained for the MCN 6000 are compared with those obtained by use of a conventional Meinhard nebulizer. It is shown that the observed matrix effect can only be compensated by use of an internal standard for the Meinhard nebulizer, but not for the MCN 6000. Results for ICP–MS are compared with those obtained by total reflection X-ray fluorescence spectrometry (TXRF).     

Preparation of Amorphous Silica-Alumina Using the Sol–Gel Method and its Reactivity for a Matrix in Catalytic Cracking

Amorphous silica-aluminas were prepared by the sol–gel method using organic templates such as carboxylic acid and the gel skeletal reinforcement method. Their reactivities as a matrix for the catalytic cracking were investigated. Malic acid (MA) was used as a catalyst for the sol–gel method, an organic template and a reagent for the dispersion of Al. When the ratio of MA/TEOS (tetraethoxysilane) increased from 0.22 to 1.22, surface area, pore volume and pore diameter increased and the mesopore was formed at 1.22. Their average BET pore diameters for 0.22 and 1.22 of MA/TEOS were 2.0 to 5.1 nm, respectively. Although conversions of n-dodecane were around 20% or less with single amorphous silica-aluminas, both single beta-zeolite and the mixed catalysts of zeolite and amorphous silica-aluminas showed much higher activity. Further, the mixed catalyst using silica-alumina with mesopore (MAT(MA122-5)) exhibited the higher ratio of multi-branched paraffin to single branched paraffin in the gasoline franction of products (C5–C11) than the mixed catalysts using silica-alumina with only micropore and silica with mesopore or single zeolite. In the gel skeletal reinforcement method, tetraethoxy orthosilicate (TEOS) was used as not only a precursor of silica but also an agent which reinforces the skeleton of silica-gel to prepare an aerogel and extremely large mesopores were formed for resultant silicas and silica-aluminas. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume reached 30 nm and 3.1 cm³/g, respectively, in the N₂ adsorption measurement by the BJH method, indicating that most of pores for this silica consisted of mesopores. In catalytic clacking reaction of n-dodecane, the mixed catalyst prepared by beta-zeolite and silica-alumina with large mesopore exhibited not only the comparable activity to that for single zeolite but also the unique selectivity where large amounts of branched products were formed. When the catalyst beds of silica-alumina and zeolite were separated, the reference silica-alumina (ref.SA) → zeolite system exhibited the higher activity and the product selectivity close to those for MAT(ref.SA). It is likely that the primary cracking of n-dodecane on silica-alumina would occur to produce the primary cracked product which effectively reacted with zeolite and inhibited the coke formation by overcracking.     

Is anthracene cofactor or spectator for the thermolysis of anthracenyl acylnitroso cycloadducts in the presence of a diene?

Acylnitroso species are very reactive dienophiles broadly used in organic synthesis. They are traditionally prepared from the oxidation of hydroxamic acids at low temperature. When this strategy fails, acylnitroso compounds may be generated from other stable sources, for example, their (9,10-dimethyl)anthracenyl cycloadducts. The thermolysis of such compounds performed in the presence of a diene leads generally to the corresponding hetero Diels-Alder (HD-A) cycloadduct in high yield with concomitant release of anthracene. The most widely accepted mechanism is the postulated slow release of acylnitroso via a retro Diels-Alder process, although the anthracenyl acylnitroso cycloadducts bear intrinsic structural features suggesting another pathway, that is, an exchange process. By using computational chemistry, we have hereby clarified the exact role of anthracene in this reaction.     

Catalytic Cracking of a Mixture of Vacuum Gas Oil and Vegetable Oil in the Presence of Mixed Mg–Al Oxide of Various Compositions

Russian Journal of Applied Chemistry - Effect of mixed Mg–Al oxides contained in catalysts on the distribution of target products formed in cracking of a mixture of vacuum gas oil with...     

Does Fibronect in Influence the Determination of Circulating Immune Complexes by Means of a Clq-Enzyme Immunoassay?

Abstract

Fibronect in was shown to bind to solid-phase C1q and to inhibit the binding of aggregated lgG in an C1q-solid-phase enzyme immunoassay in the absence of human serum. In the presence of human serum the determination of aggregated lgG and circulating immune complexes is not influenced by fibronectin in this assay. Therefore, we suggest that fibronectin does not affect the determination of immune complexes in serum specimens by C1q binding assays.     

The Effect of Preliminary Treatment on the Catalytic Activity of Cobalt–Silica Gel Catalysts in the Complete Oxidation of Methane

The effect of temperature in multiple oxidative–reductive treatments on the activity of cobalt–silica gel catalysts in the complete oxidation of methane is studied. A decrease in the temperature of oxidative–reductive treatments from 500°C to 300°C results in an irreversible decrease in the activity of samples prepared by the impregnation of SiO₂with cobalt nitrate. A sample prepared from cobalt acetate and calcined at 500°C shows a lower activity, which was close to the activity of samples prepared from nitrates and calcined at 300°C.     

Catalytic Conversion of Glycerol in the Presence of Ni/F–Al2O3 Catalyst

Russian Journal of Physical Chemistry A - It is shown that glycerol hydrogenation in the presence of Ni/F–Al2O3 catalyst leads to the formation of simple alcohols ethanol and propanol-1. The...