Dissociation dynamics and thermochemistry of tin species, (CH3)4Sn and (CH3)6Sn2, by threshold photoelectron-photoion coincidence spectroscopy

The dissociative photoionization of tetramethyltin (Me?Sn) and hexamethylditin (Me?Sn?) has been investigated by threshold photoelectron-photoion coincidence (TPEPICO). Ions are energy-selected, and their 0 K dissociation onsets are measured by monitoring the mass spectra as a function of ion internal energy. Me?Sn(+) dissociates rapidly by methyl loss, with a 0 K onset of E? = 9.382 ± 0.020 eV. The hexamethylditin ion dissociates slowly on the time scale of the experiment (i.e., during the 40 μs flight time to the detector) so that dissociation rate constants are measured as a function of the ion energy. RRKM and the simplified statistical adiabatic channel model (SSACM) are used to extrapolate the measured rate constants for methyl and Me?Sn(?) loss to their 0 K dissociation onsets, which were found to be 8.986 ± 0.050 and 9.153 ± 0.075 eV, respectively. Updated values for the heats of formation of the neutral Me?Sn and Me?Sn? are used to derive the following 298.15 K gas-phase standard heats of formation, in kJ·mol?1: Δ(f)H(m)(o)(Me?Sn(+),g) = 746.3 ± 2.9; Δ(f)H(m)(o)(Me?Sn?(+),g) = 705.1 ± 7.5; Δ(f)H(m)(o)(Me?Sn(?),g) = 116.6 ± 9.7; Δ(f)H(m)(o)(Me?Sn,g) = 123.0 ± 16.5; Δ(f)H(m)(o)(MeSn(+),g) = 877.8 ± 16.4. These energetic values also lead to the following 298.15 K bond dissociation enthalpies, in kJ·mol?1: BDE(Me?Sn-Me) = 284.1 ± 9.9; BDE(Me?Sn-SnMe?) = 252.6 ± 14.8.     

Fully automated determination of 74 pharmaceuticals in environmental and waste waters by online solid phase extraction-liquid chromatography-electrospray-tandem mass spectrometry

The present work describes the development of a fully automated method, based on on-line solid-phase extraction (SPE)-liquid chromatography-electrospray-tandem mass spectrometry (LC-MS-MS), for the determination of 74 pharmaceuticals in environmental waters (superficial water and groundwater) as well as sewage waters. On-line SPE is performed by passing 2.5 mL of the water sample through a HySphere Resin GP cartridge. For unequivocal identification and confirmation two selected reaction monitoring (SRM) transitions are monitored per compound, thus four identification points are achieved. Quantification is performed by the internal standard approach, indispensable to correct the losses during the solid phase extraction, as well as the matrix effects. The main advantages of the method developed are high sensitivity (limits of detection in the low ng L⁻¹ range), selectivity due the use of tandem mass spectrometry and reliability due the use of 51 surrogates and minimum sample manipulation. As a part of the validation procedure, the method developed has been applied to the analysis of various environmental and sewage samples from a Spanish river and a sewage treatment plant.     

Decorating poly(alkyl aryl-ether) dendrimers with metallacarboranes

A new family of polyanionic poly(alkyl aryl-ether) metallodendrimers decorated with four and eight cobaltabisdicarbollide units have been obtained in high yield by the ring-opening reaction of cyclic oxonium [3,3'-Co(8-(C(2)H(4)O)(2)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))] with alkoxides formed by deprotonation of terminal alcohols in the α,α'-bis[3,5-bis(hydroxymehyl)phenoxy]-p-xylene, α,α'-bis[3,5-bis(hydroxymehyl)phenoxy]-m-xylene, α,α'-bis[3,5-bis-[3,5-bis(hydroxymethyl)phenoxy]methylen]phenoxy]-p-xylene, and α,α,'-bis[3,5-bis-[3,5-bis(hydroxymethyl)phenoxy]methylen]phenoxy]-m-xylene dendrimers. The crystal structure of the precursor α,α'-bis[3,5-bis(chloromethyl)phenoxy]-p-xylene is also described. Final products are fully characterized by FTIR, NMR, UV-vis spectroscopies and elemental analysis. For metallodendrimers, the UV-vis absorptions have been a good tool for estimating the experimental number of cobaltabisdicarbollide units peripherally attached to the dendrimeric structure and consequently to corroborate the complete functionalization of the dendrimers.     

Preparation and Characterization of Interpenetrating Polymer Hydrogels Based on Poly(acrylic acid) and Poly(vinyl alcohol)

Interpenetrating polymer hydrogels (IPHs) of Poly (vinyl alcohol) (PVA) and Poly (acrylic acid) (PAAc) have been prepared by a sequential method: crosslinked PAAc chains were formed in aqueous solution by crosslinking copolymerization of acrylic acid and N, N′-methylenebisacrylamide in the presence of PVA. The application of freezing-thawing cycles (F-T cycles) leads to the formation of a PVA hydrogel within the synthesized PAAc hydrogel. The swelling and the viscoelastic properties of the prepared IPHs were evaluated on the basis of the structural features obtained from solid state ¹³C-NMR spectroscopy.     

A simple method for simultaneous determination of nine triazines in drinking water

A simple, effective, and economic method for determination of nine triazines (ametryn, atrazine, cyanazine, prometryn, propazine, simazine, simetryn, terbuthylazine, and terbutryn) in drinking water based on solid-phase extraction (SPE) followed by high-performance liquid chromatography-diode array detection (HPLC-DAD) was developed. A specialized solid phase (Oasis HLB) was used, and the parameters that may affect the efficiency of SPE were optimized. The limits of detection (ranged from 0.010 to 0.023 µg L^?1) were satisfactory and allow the determination of triazines at the levels required by European Union legislation. Repeatability (2.4–7.6%) and intermediate precision (0.9–11.0%) calculated at 0.1 µg L^?1 (legislation level) were adequate. The accuracy calculated as the average recovery of spiked tap and mineral waters was higher than 86% for all compounds. The developed method also could be used for undergraduate laboratory experiments because it acquaints students with solution preparation, solid phase extraction procedure, and HPLC-DAD technique.     

Synthesis and characterization of zirconogermanates

Six new zirconogermanates have been prepared under hydrothermal conditions using amines as bases. There are four new structure types (ASU-n) with a common motif of ZrGe(5). ASU-23 is a layered structure: ZrGe(3)O(8)(OH)F.[C(10)H(26)N(4)].H(2)O, space group P2(1)/n, a = 6.7957(8) A, b = 12.700(1) A, c = 24.293(3) A, beta = 97.936(2) degrees, V = 2076.4(4) A(3). ASU-24 is a pillared layered structure: Zr(3)Ge(6)O(18)(OH(2),F)(4)F(2).[C(6)H(18)N(2)].[C(6)H(17)N(2)](2).2H(2)O, space group P2(1)/n, a = 7.4249(3) A, b = 25.198(1) A, c = 11.3483(5) A, beta = 90.995(1) degrees, V = 2122.9(2) A(3). This material has the lowest framework density (FD) of any oxide material that we are aware of (FD = 8.48 metal atoms/nm(3)). Two other materials form three-dimensional open-frameworks, ASU-25: ZrGe(3)O(9).[C(3)H(12)N(2)], space group P112(1)/a, a = 13.1994(4) A, b = 7.6828(2) A, c = 11.2373(3) A, gamma = 91.233(3) degrees, V = 1139.29(5) A(3). The other is ASU-26: ZrGe(3)O(9).[C(2)H(10)N(2)], space group Pn, a = 13.7611(3) A, b = 7.7294(2) A, c = 11.2331(3) A, beta = 104.793(1) degrees, V = 1155.21(4) A(3). ASU-25 is related to the mineral umbite K(2)ZrSi(3)O(9).H(2)O. The germanium equivalent has been prepared through the inorganic route: K(2)ZrGe(3)O(9).H(2)O, space group P2(1)2(1)2(1), a = 13.6432(6) A, b = 7.4256(3) A, c = 10.3973(4) A, V = 1053.33(8) A(3). The structural relationships between ASU-25 and its inorganic counterpart are described. The thermal decomposition of the germanium umbite generated the cyclic trigermanate K(2)ZrGe(3)O(9), analogue of the mineral wadeite, crystallizing in the orthorhombic system, a = 7.076 A, b = 12.123 A, c = 10.451 A, V = 904.5 A(3).     

Effect of substrate inhibition and cooperativity on the electrochemical responses of glucose dehydrogenase. Kinetic characterization of wild and mutant types

Thanks to its insensitivity to dioxygen and to its good catalytic reactivity, and in spite of its poor substrate selectivity, quinoprotein glucose dehydrogenase (PQQ-GDH) plays a prominent role among the redox enzymes that can be used for analytical purposes, such as glucose detection, enzyme-based bioaffinity assays, and the design of biofuel cells. A detailed kinetic analysis of the electrochemical catalytic responses, leading to an unambiguous characterization of each individual steps, seems a priori intractable in view of the interference, on top of the usual ping-pong mechanism, of substrate inhibition and of cooperativity effects between the two identical subunits of the enzyme. Based on simplifications suggested by extended knowledge previously acquired by standard homogeneous kinetics, it is shown that analysis of the catalytic responses obtained by means of electrochemical nondestructive techniques, such as cyclic voltammetry, with ferrocene methanol as a mediator, does allow a full characterization of all individual steps of the catalytic reaction, including substrate inhibition and cooperativity and, thus, allows to decipher the reason that makes the enzyme more efficient when the neighboring subunit is filled with a glucose molecule. As a first practical illustration of this electrochemical approach, comparison of the native enzyme responses with those of a mutant (in which the asparagine amino acid in position 428 has been replaced by a cysteine residue) allowed identification of the elementary steps that makes the mutant type more efficient than the wild type when cooperativity between the two subunits takes place, which is observed at large mediator and substrate concentrations. A route is thus opened to structure-reactivity relationships and therefore to mutagenesis strategies aiming at better performances in terms of catalytic responses and/or substrate selectivity.     

Synthesis and electro‐optical characterization of new conducting PEDOT/Au‐nanorods nanocomposites

This paper describes a new strategy to obtain PEDOT/Au‐nanorods nanocomposites with different PEDOT: Au ratio. A polymeric ionic liquid (PIL) was used as stabilizer during the chemical synthesis of PEDOT dispersions. PEDOT/Au‐nanorods dispersions in organic media were obtained. Electrochemical characterization of PEDOT/Au‐nanorods nanocomposites revealed that the addition of Au nanorods modified the electroactivity of the conducting films by reducing the oxidation potential from +0.33 to +0.23 V (versus Ag/AgCl). Optical contrast (ΔT%) of the films decreased from 17% for neat PEDOT films to 8% for PEDOT/Au‐nanorods nanocomposites films (3:1 (v/v)) while switching times (from 1 to 4 sec) were similar to neat PEDOT. Conductivity of the films increased from 0.027 S/cm for neat PEDOT to 0.691 S/cm for PEDOT/Au‐nanorods nanocomposites. Nanoscale morphology and contact potential of PEDOT/Au‐nanorods nanocomposites were investigated in detail by Scanning Force Microscopy. Electrical measurements show a clear contact potential difference between the ITO substrate and the PEDOT/Au‐nanorods film. On the film, no contact potential inhomogeneity is observed indicating that the Au‐nanorods are uniformly dispersed in the film. Copyright © 2010 John Wiley & Sons, Ltd.     

Fast determination of oleic acid in pork by flow injection analysis/mass spectrometry

In some Mediterranean products such as olive oil or ham, oleic acid is the most abundant component of the total fat. Due to the large volume of trade in these products, it may be necessary to analyze oleic fatty acids in high numbers of samples in short periods of time. However, using classic lipid analysis techniques, it is not always possible to cope with these high demands. To solve this problem, a high-throughput analytical method for oleic fatty acid quantification in pork is presented. The purpose of the method is to avoid liquid chromatography processes using a flow injection analysis (FIA) system based on electrospray ionization mass spectrometry. The use of pentadecanoic fatty acid as an internal standard overcame matrix effects. The oleic FIA technique could be used as a suitable method for discriminating carcass samples for selection and labeling by oleic acid content when large numbers of pork samples must be processed in a short period of time.     

The effect of the addition of SBA-15 to the slow pyrolysis of tobacco studied by heart-cutting GC/MC

Journal of Thermal Analysis and Calorimetry - The composition of evolved slow pyrolysis products under inert and oxidising atmospheres of reference tobacco from the University of Kentucky and its...