Aquachloroiridium (III)-catalyzed oxidation of some unsaturated acids in acetone by acidic quinolinium fluorochromate

Kinetic investigation in Ir(III)-catalyzed oxidation of fumaric acid (FA) and crotonic acid (CA) in an acidified solution of quinolinium fluorochromate (QFC) has been studied in the temperature range of 30–45 °C. First-order kinetics was observed in the case of catalyst Ir(III) as well as oxidant QFC. The order of reaction with respect to substrate (unsaturated acids) was found to be zero. Increase in [Cl^?] showed fractional negative order. The influence of [H⁺] and ionic strength on the rate was found to be insignificant. The main product of oxidation of fumaric acid (FA) and crotonic acid (CA) were identified as pyruvic acid and acetone, respectively. The reaction has been studied in ten different solvents. The first-order rate constant had no effect with decrease in the dielectric constant of the medium. The values of rate constants observed at four different temperatures (30, 35, 40 and 45 °C) were utilized to calculate the activation parameters. A suitable mechanism in conformity with the kinetic observations has been proposed and the rate law has been derived on the basis of obtained data. A transient complex formed between Ir^III and oxidant in a slow and rate-determining step, further reacts with substrate to give the products in a series of fast steps.     

Unveiling the Importance of π‐Stacking in Borrowing‐Hydrogen Processes Catalysed by Iridium Complexes with Pyrene Tags

This work describes the preparation of a series of pyrene‐tagged N‐heterocyclic carbene complexes of iridium, and their use in two benchmark borrowing hydrogen reactions: the reduction of ketones by transfer hydrogenation and the β‐alkylation of secondary alcohols with primary alcohols. The detailed study of these homogeneously catalysed reactions reveals several important implications regarding the strong influence of the pyrene tags in the catalysts. First, the catalytic activity is partially inhibited by addition of an external amount of pyrene, but only when pyrene‐tagged catalysts and aromatic substrates are used. Second, the rate order of the reaction is highly dependent on the nature of the substrates and the ligand. When pyrene‐tagged catalysts and aromatic substrates are used, the reaction follows a zero‐order dependence on the concentration of the substrate. All other combinations afford a second‐order rate in the substrates. And third, the presence or absence of the pyrene functionality in the catalyst also influences the reaction order with respect to the concentration of the catalyst. Pyrene‐containing catalysts display a fractional rate order of below 1. Finally, two pyrene‐tagged catalysts were supported onto reduced‐graphene oxide (rGO), and used as heterogeneous catalysts. While the dimetallic catalyst was effectively recycled 12 times, the monometallic catalyst maintained its activity for only three runs.     

Unified mechanistic concept of electrophilic aromatic nitration: convergence of computational results and experimental data

The mechanism of electrophilic aromatic nitration was revisited. Based on the available experimental data and new high-level quantum chemical calculations, a modification of the previous reaction mechanism is proposed involving three separate intermediates on the potential energy diagram of the reaction. The first, originally considered an unoriented pi-complex or electron donor acceptor complex (EDA), involves high electrostatic and charge-transfer interactions between the nitronium ion and the pi-aromatics. It explains the observed low substrate selectivity in nitration with nitronium salts while maintaining high positional selectivity, as well as observed oxygen transfer reactions in the gas phase. The subsequent second intermediate originally considered an oriented "pi-complex" is now best represented by an intimate radical cation-molecule pair, C(6)H(6)(+)(*)()/NO(2), that is, a SET complex, indicative of single-electron transfer from the aromatic pi-system to NO(2)(+). Subsequently, it collapses to afford the final sigma-complex intermediate, that is, an arenium ion. The proposed three discrete intermediates in electrophilic aromatic nitration unify previous mechanistic proposals and also contribute to a better understanding of this fundamentally important reaction. The previously obtained ICR data of oxygen transfer from NO(2)(+) to the aromatic ring are also accommodated by the proposed mechanism. The most stable intermediate of this reaction on its potential energy surface is a complex between phenol and NO(+). The phenol.NO(+) complex decomposes affording C(6)H(6)O(+)(*)/PhOH(+) and NO, in agreement with the ICR results.     

Influence of ignored and well-known zone distortions on the separation performance of proteins in capillary free zone electrophoresis with special reference to analysis in polyacrylamide-coated fused silica capillaries in various buffers. I. Theoretical studies

Distortion of the starting zone upon its electrophoretic migration toward the detection window gives rise to both symmetrical zones caused by diffusion, sedimentation in the horizontal section of the capillary and the curvature of the capillary, and asymmetrical zones having their origin in Joule heating, sedimentation in the vertical section of the capillary, pH and conductivity differences between the sample zone and the surrounding buffer, solute adsorption onto the capillary wall, and association-dissociation of complexes between the analyte and a buffer constituent or between analytes. Interestingly and importantly a theoretical study shows that moderate pH and conductivity differences as well as adsorption and all of the above interactions when they are characterized by a fast on/off kinetics do not increase the zone broadening (or only slightly), because the sharpening of one boundary of the zone is about the same as the broadening of the other boundary. In addition the peak symmetry caused by a conductivity difference is in most experiments counteracted by a pH difference. The experimentally determined plate numbers in the absence of electroosmosis exceeded one million per meter in some experiments (Part II). These plate numbers are among the highest reported [Z. Zhao, A. Malik, M.L. Lee, Anal. Chem. 65 (1993) 2747; M. Gilges, K. Kleemiss, G. Schomburg, Anal. Chem. 66 (1994) 2038; H. Wan, M. Ohman, L.G. Blomberg, J. Chromatogr. A 924 (2001) 591 (plate numbers determined in the presence of electroosmosis may be higher, although the width of the zone in the capillary may be larger) [p. 680 in S. Hjertén, Electrophoresis 11 (1990) 665]). Capillary free zone electrophoresis is perhaps the only separation method, which, under optimum conditions, gives a plate number not far from the theoretical limit. A prerequisite for this high performance is that the polyacrylamide-coated capillary is washed with 2 M HCl between the runs and stored in water over night (Part II). The difference between the experimentally determined total variance and the sum of the calculated variances originating from the width of the starting zone, longitudinal diffusion, Joule heating, sedimentation in the vertical section of the capillary, curvature of the capillary (i.e., the sum of all other variances) was in our most successful experiments about 28% of the variance of diffusion. The zone broadening, 2sigma, caused by diffusion was estimated at 0.77 mm. The total zone width (2sigma) calculated from the experimentally determined plate number was as small as 1 mm when the migration distance was 40 cm. Accordingly, the only efficient way to reduce drastically the total zone width is to decrease the analysis time and, thereby, the diffusional broadening. An important finding was that the variance originating from the loops of the capillary is not always negligible in high-performance runs. Therefore, one should employ straight capillaries and avoid CE apparatus with cartridges that require a strong curvature of the capillary, common in most commercial instruments. Mathematical formulas have been derived for the sedimentation of the solute zone, the enrichment factor, and the migration time in experiments where the solute is dissolved in a dilute running buffer. This zone sharpening method gave very narrow starting zones (0.04-0.4 mm). However, upon high dilution of the buffer the enrichment becomes so strong that part of the sample zone probably sediments out of the capillary; the almost inevitable change in pH may decrease the mobility of the proteins and, thus, cause the enrichment factor to become still lower than expected. Diffusion of the protein in the very narrow starting zone (located close to the tip of the capillary) and sometimes the thermal expansion of the buffer in the capillary contributes to additional loss of protein in the enrichment step. In some buffers, the interaction between the protein and the buffer constituents is so slow that the peaks become broad. Therefore, different types of buffers should be tested when high resolution is required. The relation sigma2 (the variance of the interaction between a protein and the buffer constituents) = constant x u (the mobility) seems to be valid for all proteins in the applied sample, at least when they have similar molecular masses. To facilitate the understanding of the progress of a free zone electrophoresis experiment, we have discussed in simple terms how the concentrations of the background electrolytes become rearranged during a run and why the difference between the mobilities of the proteins and the mobilities of the background electrolyte determines whether a peak exhibits fronting or tailing. A theoretical analysis of zone broadening in capillary zone electrophoresis, chromatography, and electrochromatography indicates that electrochromatography in homogeneous gels might be the only chromatographic technique which can compete in performance with free electrophoresis. Using an equation, valid not only for electrophoresis, but also for chromatography and centrifugation, the mobility of a concentration boundary has been calculated for the first time and was, as expected, low. Equations based on the Kohlrausch regulating function do not permit such calculations. Another regulating function (the H function) and some of its characteristics are briefly discussed. The theoretical discussions in this paper and the experimental studies in Part II show that high-performance electrophoresis deserves its prefix when the runs are designed to give minimum zone broadening. Some guidelines are given to facilitate this optimization. The plate numbers are so high that the resolution cannot be increased by more than 30% even if they approach the theoretically maximum values.     

Investigation of the copper binding site and the role of histidine as a ligand in riboflavin binding protein

Riboflavin Binding Protein (RBP) binds copper in a 1:1 molar ratio, forming a distinct well-ordered type II site. The nature of this site has been examined using X-ray absorption and pulsed electron paramagnetic resonance (EPR) spectroscopies, revealing a four coordinate oxygen/nitrogen rich environment. On the basis of analysis of the Cambridge Structural Database, the average protein bound copper-ligand bond length of 1.96 A, obtained by extended x-ray absorption fine structure (EXAFS), is consistent with four coordinate Cu(I) and Cu(II) models that utilize mixed oxygen and nitrogen ligand distributions. These data suggest a Cu-O 3N coordination state for copper bound to RBP. While pulsed EPR studies including hyperfine sublevel correlation spectroscopy and electron nuclear double resonance show clear spectroscopic evidence for a histidine bound to the copper, inclusion of a histidine in the EXAFS simulation did not lead to any significant improvement in the fit.     

Effect of the irrigation with residual wastewaters on microbial soil activity of the ornamental flowers (<Emphasis Type="Italic">Dahlia pinnata)</Emphasis> cultures monitored by isothermal calorimetry

A microcalorimetric method was applied to study microbial soil activity of ornamental flower (Dahlia pinnata) plantations when irrigated with potable water and wastewaters. The samples were irrigated with potable water PW sample (reference) and treated wastewaters from Municipal Wastewater Treatment Station of Asa Norte in Brasilia City (Brazil). Three different water treatments were applied to irrigate soil samples, named TW1, TW2, and TW3 samples. The increase of the microbial soil activity observed in TW1 sample must have occurred because of the high amount of organic waste dissolved in wastewater used for irrigation. This rise indicates that the present treated wastewater can affect natural life cycle. However, only a low alteration in microbial soil activity was observed in the TW2 and TW3 samples, which suggests that these wastewater treatments can be normally used to irrigate soils without bringing environmental consequences, once they offer a great opportunity to upgrade and protect the environment.     

PDMS extraction bars for the determination of volatile aromatic hydrocarbons in water and wastewater

In this study, the preparation and application of extraction bars of PDMS were investigated to preconcentrate and determine benzene, toluene, ethylbenzene, and xylene in water and wastewater by means of HPLC with fluorescence detection. Aliquot samples from hospital wastewater were used as the model effluent. The independent variables for the sorptive extraction were as follows: ionic strength (added amounts of NaCl); pH; temperature and time of absorption; temperature and time of desorption. Under optimized conditions, by using a factorial design, the suspended extraction bars could allow the determination of benzene, toluene, ethylbenzene, and xylene (1.20 ± 0.05 μg/L; 10.40 ± 0.02 μg/L; 1.80 ± 0.04 μg/L; 15.9 ± 0.04 μg/L, respectively) in hospital effluent (fortified samples), by recoveries of 71.9 ± 4.9 to 74.8 ± 5.6%. This procedure represents an innovation that eliminates the time‐consuming stage of vacuum microfiltration, and allows the determination of volatile organic compounds by HPLC. As far as we know, this procedure is original and represents an important contribution to the field.     

Ruthenium(III) catalysed oxidation of glycerol by acidified KBrO3: a kinetic study

Kinetic investigations on the Ru^III-catalysed oxidation of glycerol by an acidified solution of KBrO₃ in the presence of Hg(OAc)₂ as a scavenger have been carried out in the 30–50 °C range. First order kinetics in the lower KBrO₃ concentration range tended to zero order at higher concentrations. The reaction follows zero order kinetics in glycerol and [H⁺]; the order is one with respect to [Ru^III]. An increase in [Cl^–] showed a positive effect, while addition of NaClO₄ has a negligible effect on the reaction rate. Hg(OAc)₂ and D₂O have an insignificant effect on the reaction rate. A suitable mechanism in conformity with the kinetic observations has been proposed and thermodynamic parameters computed.     

Protective Effects of PollenAid Plus Soft Gel Capsules’ Hydroalcoholic Extract in Isolated Prostates and Ovaries Exposed to Lipopolysaccharide

Pollen extract represents an innovative approach for the management of the clinical symptoms related to prostatitis and pelvic inflammatory disease (PID). In this context, the aims of the present work were to analyze the phenolic composition of a hydroalcoholic extract of PollenAid Plus soft gel capsules, and to evaluate the extract’s cytotoxic effects, in human prostate cancer PC3 cells and human ovary cancer OVCAR-3 cells. Additionally, protective effects were investigated in isolated prostate and ovary specimens exposed to lipopolysaccharide (LPS). The phytochemical investigation identified catechin, chlorogenic acid, gentisic acid, and 3-hydroxytyrosol as the prominent phenolics. The extract did not exert a relevant cytotoxic effect on PC3 and OVCAR-3 cells. However, the extract showed a dose-dependent inhibition of pro-inflammatory IL-6 and TNF-α gene expression in prostate and ovary specimens, and the extract was effective in preventing the LPS-induced upregulation of CAT and SOD gene expression, which are deeply involved in tissue antioxidant defense systems. Finally, a docking approach suggested the capability of catechin and chlorogenic acid to interact with the TRPV1 receptor, playing a master role in prostate inflammation. Overall, the present findings demonstrated anti-inflammatory and antioxidant effects of this formulation; thus, suggesting its capability in the management of the clinical symptoms related to prostatitis and PID.     

Total synthesis of 8,12-iso-iPF3alpha-VI, an EPA-derived isoprostane: stereoselective introduction of the fifth asymmetric center

[reaction: see text] A new and stereoselective approach for the synthesis of all-syn isoprostanes is reported. This method, which is based on acid-catalyzed Diels-Alder reaction, allows the introduction of the side chain with a predetermined stereochemistry of the hydroxy group. The first total synthesis of an eicosapentaenoic acid (EPA)-derived iP, 8,12-iso-iPF3alpha-VI 10, was performed using this approach.