Ultra‐performance liquid chromatography MS/MS method for the determination of parabens in compost from sewage sludge: Comparison of the efficiency of two extraction techniques

The efficiency of two extraction techniques—ultrasound‐assisted extraction and pressurized liquid extraction—are compared and evaluated in the determination of parabens in compost samples. The extraction parameters for each technique were accurately optimized. The selected compounds were detected and quantified using ultra‐performance LC MS/MS, operating in negative ESI and in SRM mode. The analytes were separated in less than 5 min. Ethylparaben (ring‐¹³C₆ labeled) was used as an internal standard. Two selective, sensitive, and accurate analytical methods were developed and validated. The LODs of the methods ranged from 3 to 7 ng/g and the LOQs from 10 to 23 ng/g, while inter‐ and intraday variability was under 6% in all cases. The methods were validated separately by using matrix‐matched calibration and recovery assays with spiked samples. Recovery rates ranged from 94.0 to 105.0%. Compost samples were taken from different composting plants. Although the statistical comparison demonstrated no statistically significant differences between the two extraction techniques, the method based on pressurized liquid extraction was more sensitive than the ultrasound extraction based method.     

Thermal synthesis and structural characterization of the orthorhombic Th2(PO4)(P3O10)

Polycrystalline thorium(IV) phosphate-triphosphate, Th₂(PO₄)(P₃O₁₀) (1), was obtained by (NH₄)₂Th(PO₄)₂·H₂O (2) heating from room temperature to 1,273 K. 1 crystallizes in the orthorhombic space group Pn2₁ a (a = 11.6846(2) Å, b = 7.1746(1) Å, c = 12.9320(3) Å, Z = 4). Combining powder synchrotron X-ray diffraction data and DFT geometry optimization, a structural model is proposed for 1. The structure is built on ThO₈ polyhedral chains along the b-axis. PO₄ ^3? and P₃O₁₀ ^5? groups coexist in the structure and the latter group forms non-linear chains. Cohesion of the structure is made by the linkage of ThO₈ chains by PO₄ and P₃O₁₀ groups. Thermal transformation from 2 to 1 was monitored by thermogravimetric analysis (activation energy as a function of the extent of conversion was obtained from Kissinger–Akahira–Sunose (KAS) isoconversional method) and powder X-ray thermo-diffraction. For 2, the dehydration process takes place in two steps, with the apparition of a layered intermediate phase, (NH₄)₂Th(PO₄)₂·nH₂O (0 < n < 1, d = 6.42 Å), previously to the formation of (NH₄)₂Th(PO₄)₂ (d = 6.31 Å). The condensation process produces an amorphous material that crystallizes to α-ThP₂O₇ (3) when the temperature increases. At 1,273 K, 3 slowly transforms to 1.     

Ethanol reforming on Co(0001) surfaces: a density functional theory study

A computational study using density functional theory is carried out to investigate the reaction mechanism of ethanol steam reforming on Co(0001) surfaces. The adsorption properties of the reactant, possible intermediates, and products are carefully examined. The reaction pathway and related transition states are also analyzed. According to our calculations, the reforming mechanism primarily consisting of dehydrogenation steps of ethanol, ethoxy, methanol, methoxy, and formic acid, is feasible on Co(0001) surfaces. It is also found that the reaction of formaldehyde yielding formic acid and hydrogen may not be an elementary reaction. The dehydrogenation of ethoxy possesses the highest barrier and is accordingly identified as the rate-determining step.     

A versatile metal-organic framework for carbon dioxide capture and cooperative catalysis

A multi-functional MOF was constructed from Cu paddlewheel motifs and a judiciously designed novel ligand bearing carboxylate, pyridine, and amide groups. exhibits selective adsorption of CO(2) over CH(4) and excellent catalytic activity in a tandem one-pot deacetalization-Knoevenagel condensation reaction as a cooperative catalyst.     

Perfluorobutane sulfonic acid hydration and interactions with O2 adsorbed on Pt3

The side chain of NAFION, a proton conductive membrane used as electrolyte in low-temperature fuel cells, is modeled with perfluorobutane sulfonic acid. Density functional theory is used to characterize structures and energetics of hydration of the model system interacting with a proton solvated with up to 24 water molecules and analyze interactions of some of these hydrated complexes with O(2) adsorbed on Pt(3). It is found that at least three water molecules are needed to ionize the sulfonic acid, and higher degrees of hydration induce the formation of cages where the water molecules are held together via complex hydrogen-bond networks. The interaction between the complex formed by the ionized acid and the hydrated proton, in contact with a bridge-adsorbed O(2)-Pt(3), promotes the protonation of the adsorbed O(2). Upon protonation, the O(2)-Pt(3) system evolves from hydrophobic to hydrophilic behavior, which may facilitate further interfacial contact.     

Dissolution of oxygen reduction electrocatalysts in an acidic environment: density functional theory study

Density functional theory is employed to determine the reaction thermodynamics of a group of chemical and electrochemical reactions chosen to investigate the dissolution of metal atoms from oxygen reduction reaction catalysts in an acid medium. Once a set of thermodynamically allowed reactions is established, those reactions are selected to investigate the relative stabilities of Pt atoms and of other transition metal atoms (Ir, Pd, Rh, Ni, and Co) toward the dissolution reactions. The dissolution reactions that are found thermodynamically favorable are electrochemical and involve adsorbed oxygenated compounds that are intermediate species of the oxygen reduction reaction. Iridium is found to be the most stable among the various pure metals in comparison to Pt. Most of the metals alloyed with Pt cause a decrease of the Pt stability against dissolution, except for Ni, which does not affect it. On the other hand, the influence of Pt on the stability of the second metal in the alloy follows the same trend as in pure metal catalysts, with Ir being the most stable. When both atoms in a PtM alloy are involved in dissolution reactions, alloyed Ir is also found more stable than Pt in a given dissolution reaction, and the same behavior is found in alloyed Co for most of the reactions studied.     

Adsorption and dissociation of H2O2 on Pt and Pt-alloy clusters and surfaces

The adsorption of H(2)O(2) on Pt and Pt-M alloys, where M is Cr, Co, or Ni, is investigated using density functional theory. Binding energies calculated with a hybrid DFT functional (B3PW91) are in the range of -0.71 to -0.88 eV for H(2)O(2) adsorbed with one of the oxygen atoms on top Pt positions of Pt(3), Pt(2)M, and PtM(2), and enhanced values in the range of -0.81 to -1.09 eV are found on top Ni and Co sites of the Pt(2)M clusters. Adsorption on top sites of Pt(10) yields a weaker binding of -0.48 eV, whereas on periodic Pt(111) and Pt(3)Co(111) surfaces, H(2)O(2) generally dissociates into two OH radicals. On the other hand, attempts to attach H(2)O(2) on bridge sites cause spontaneous dissociation of H(2)O(2) into two adsorbed OH radicals, suggesting that stable adsorptions on bridge sites are not possible for any of the clusters or extended surfaces that are being studied. We also found that the water-H(2)O(2) interaction reduces the strength of the adsorption of H(2)O(2) on these clusters and surfaces.     

The o-xylylene protecting group as an element of conformational control of remote stereochemistry in the synthesis of spiroketals

Protection of trans-1,2-diol segments as cyclic o-xylylene ethers strongly favours diequatorial over diaxial dispositions; the possibility of using this grouping for remote control of the stereochemistry in the synthesis of spiroketals is here demonstrated by the stereoselective synthesis of tricyclic spirodisaccharides (di-D-fructose dianhydrides).     

Superconnectivity of regular graphs with small diameter

A graph is superconnected, for short super-κ, if all minimum vertex-cuts consist of the vertices adjacent with one vertex. In this paper we prove for any r-regular graph of diameter D and odd girth g that if D≤g−2, then the graph is super-κ when g≥5 and a complete graph otherwise.