Hydrolysis of mefenpyrdiethyl: an analytical and DFT investigation

The hydrolysis of the herbicide safener mefenpyrdiethyl (1-(2, 4-dichlorophenyl)-4, 5-dihydro-5-methyl-1H-pyrazole-3,5-dicarboxylic acid diethyl ester) was investigated in aqueous solutions in the pH range from 2 to 9 and the temperature range from 298 to 323 K. The kinetics of hydrolysis were pseudo first order and were found to be strongly pH and temperature dependent. While near-constant in acidic medium, the hydrolysis rates strongly increased in alkaline pH, and total hydrolysis was observed at pH 11. Two main hydrolysis products, mefenpyrethyl (monoester) and mefenpyr (dicarboxylic acid) were isolated by ultrahigh-pressure liquid chromatography (UHPLC) and characterized using high-resolution Fourier transform ion cyclotron resonance mass spectroscopy (ICR-FT/MS) as well as ¹H, ¹³C and 2D NMR analyses. Additionally, a density functional theory (DFT) investigation explained the stability of the pesticide at pH 7 and the high reactivity of the pesticide in alkaline medium. The key nucleophilic reaction partner is hydroxyl ions instead of neutral water molecules. Furthermore, the calculated activation barrier for hydrolysis in alkaline medium is in agreement with the extrapolated and experimentally determined activation barrier at pH 14.     

Sweeping and new on-line sample preconcentration techniques in capillary electrophoresis

Sweeping is a powerful on-line sample preconcentration technique that improves the concentration sensitivity of capillary electrophoresis (CE). This approach is designed to focus the analyte into narrow bands within the capillary, thereby increasing the sample volume that can be injected, without any loss of CE efficiency. It utilizes the interactions between an additive [i.e., a pseudostationary phase (PS) or complexing agent] in the separation buffer and the sample in a matrix that is devoid of the additive used. The accumulation occurs due to chromatographic partitioning, complexation or any interaction between analytes and the additive through electrophoresis. The extent of the preconcentration is dependent on the strength of interaction involved. Both charged and neutral analytes can be preconcentrated. Remarkable improvements—up to several thousandfold—in detection sensitivity have been achieved. This suggests that sweeping is a superior and general approach to on-line sample preconcentration in CE. The focusing mechanism of sweeping under different experimental conditions and its combination with other on-line preconcentration techniques are discussed in this review. The recently introduced techniques of transient trapping (tr-trapping) and analyte focusing by micelle collapse (AFMC) as well as other novel approaches to on-line sample preconcentration are also described.

Adsorption of dodecyltrimethylammonium bromide and sodium bromide on gold studied by liquid chromatography and flow adsorption microcalorimetry

Here, we report on a new aspect of the adsorption of Br- on the surface of gold. The adsorption of dodecyltrimethylammonium bromide (C12TABr) from aqueous solutions onto macroporous gold particles was studied by continuous flow frontal analysis solid/liquid chromatography and flow adsorption microcalorimetry. The material balance and enthalpy balance of adsorption and the change in the solution pH were measured simultaneously. Initially, Br- is irreversibly bound to high-affinity surface sites counterbalanced by the adsorption of H+ from the aqueous phase. The surface speciation is accompanied by the formation of C12TAOH, which in turn results in a significant pH increase in the bulk solution. The net process was found to be strongly exothermic (-280 kJ.mol(-1)), which is indicative of the occurrence of chemisorption. The specific adsorption of Br- is followed by the reversible adsorption of C12TABr to produce a firmly bound monolayer in a head-to-surface arrangement (-53 kJ.mol(-1)). In a relatively narrow range of the surface coverage, various composite structures may develop on the top layer and eventually transform to full-cylindrical surface aggregates. The surface aggregation was found to be reversible, with an enthalpy change of -11 kJ.mol(-1). The importance of the specific binding of Br- to the surface of gold was confirmed by measurement of the initial adsorption of NaBr on the microparticles. The initial adsorption was found to be irreversible, with an enthalpy change of approximately -240 kJ.mol(-1). This process involved the formation of an AuBr-/H+ electric double layer at the gold/water interface, accompanied by a dramatic increase in the solution pH due to the release of a copious amount of OH- in the bulk liquid phase.     

Salmonella surveillance in Australia--created from adversity

A national scheme of Salmonella surveillance emerged in Australia as a direct result of high-profile outbreaks in 1977. A typing laboratory in Victoria put together a working model using the computer technology available at the time. The evolving information-gathering system has stood the test of time and has provided an invaluable bank of information covering isolations from humans and other sources. The databases have been used effectively in detecting trends and outbreaks and have assisted in the solution of public health problems--even extending internationally. The way in which this has been done and the lessons learned are described.     

Theoretical interpretation of Grimme's spin-component-scaled second order Møller-Plesset theory

It is shown that spin-component-scaled second order M?ller-Plesset theory proposed by Grimme [J. Chem. Phys. 118, 9095 (2003)] can be interpreted as a two-parameter scaling of the zero order Hamiltonian, a generalization of the approach reported by Feenberg [Phys. Rev. 103, 1116 (1956)].     

Behavior of human serum albumin on strong cation exchange resins: I. Experimental analysis

Experiments with human serum albumin on the strong cation exchange resin Fractogel EMD SE Hicap (M) were carried out. Even though human serum albumin was used at high purity, two peaks in gradient elution experiments occurred. The obtained data can be explained by considering that human serum albumin binds to Fractogel EMD SE Hicap (M) in two different binding conformations: the protein adsorbs instantaneously in the first conformation and then changes into the second one with a kinetic limitation. The two-peak behavior of human serum albumin was analyzed in detail, especially at various gradient lengths, concentrations and temperatures. Breakthrough curves were performed at four modifier concentrations and three velocities. The characteristic adsorption behavior, found for gradient experiments, was confirmed by the breakthrough curves. The two-peak elution pattern of human serum albumin was also found for other strong cation exchange resins, but not for weak cation exchange resins. It is concluded that the described behavior is peculiar for the interaction of human serum albumin with the strong cation exchange ligand of the resin.     

A Convenient One-Pot Synthesis of Phosphino-Dipeptide Analogs

A general "one-pot" synthetic method is described for the preparation of phosphinodipeptides of type 1 , in 60-80% overall yield, allowing the variation of the substituents in f and/or g position to the phosphorus atom and also in f position to the nitrogen atom.     

A comprehensive self-consistent spectrophotometric acidity scale of neutral Brønsted acids in acetonitrile

For the first time, the self-consistent spectrophotometric acidity scale of neutral Br?nsted acids in acetonitrile (AN) spanning 24 orders of magnitude of acidities is reported. The scale ranges from pK(a) 3.7 to 28.1 in AN. The scale includes 93 acids that are interconnected by 203 relative acidity measurements (DeltapK(a) measurements) and contains compounds with gradually changing acidities, including representatives from all of the conventional families of OH (alcohols, phenols, carboxylic acids, sulfonic acids), NH (anilines, diphenylamines, disulfonimides), and CH acids (fluorenes, diphenylacetonitriles, phenylmalononitriles). The CH acids were particularly useful in constructing the scale because they do not undergo homo- or heteroconjugation processes and their acidities are rather insensitive to traces of water in the medium. The scale has been fully cross-validated: the relative acidity of any two acids on the scale can be found by combining at least two independent sets of DeltapK(a) measurements. The consistency standard deviation of the scale is 0.03 pK(a) units. Comparison of acidities in many different media has been carried out, and the structure-acidity relations are discussed. The large variety of the acids on the scale, its wide span, and the quality of the data make the scale a useful tool for further acidity studies in acetonitrile.     

Characterization of trimetallic Pt-Pd-Au/CeO2 catalysts combinatorial designed for methane total oxidation

In the present work, the role and the effect of platinum and gold on the catalytic performance of ceria supported tri-metallic Pt-Pd-Au catalysts have been studied. The optimum composition of these tri-metallic supported catalysts has been discovered using methods and tools of combinatorial catalyst library design. Detailed catalytic, spectroscopic and physico-chemical characterization of catalysts in the vicinity of the optimum in the given compositional space has been performed. The temperature-programmed oxidation of methane revealed that the addition of Pt and Au to Pd/CeO2 catalyst resulted in higher conversion values in the whole investigated temperature range compared to the monometallic Pd catalyst. The time-on-stream experiments provided further evidence for the high-stability of tri-metallic catalysts compared to the monometallic one. Kinetic studies revealed the stronger adsorption of methane on Pt-Pd/CeO2 catalysts than over Pd/CeO2. XPS analysis showed that Pt and Au stabilize Pd in a more reduced form even under condition of methane oxidation. FTIR spectroscopy of adsorbed CO and hydrogen TPD measurements provided indirect evidences for alloying of Pt and Au with Pd. CO chemisorption data indicated that tri-metallic catalysts have increased accessible metallic surface area. It is suggested that advantageous catalytic properties of tri-metallic Pt-Au-Pd/CeO2 catalysts compared to the monometallic one can be attributed to (i) suppression of the formation of ionic forms of Pd(II), (ii) reaching an optimum ratio between Pd0 and PdO species, and (iii) stabilization of Pd in high dispersion. The results also indicate that Pd0 - PdO ensemble sites are required for methane activation.     

Preface

Foundations of Computational Mathematics -