Application of the Specific Ion Interaction Theory → the Solubility Product and First Hydrolysis Constant of Europium

The specific ion interaction theory (SIT) was applied to the first hydrolysis constants of Eu(III) and solubility product of Eu(OH)₃ in aqueous 2, 3 and 4 mol⋅dm⁻³ NaClO₄ at 303.0 K, under CO₂-free conditions. Diagrams of pEu_aq versus pC_H were constructed from solubilities obtained by a radiometric method, the solubility product log₁₀ K_{sp, Eu(OH)3}^I {Eu(OH)_3(s) Eu_aq³⁺+ 3OH_aq⁻ } values were calculated from these diagrams and the results obtained are log₁₀ K_sp,Eu(OH)3^I = − 22.65 ± 0.29, −23.32 ± 0.33 and −23.70 ± 0.35 for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. First hydrolysis constants {Eu_aq³⁺+H₂O Eu(OH)_(aq)²⁺+H⁺ } were also determined in these media by pH titration and the values found are log₁₀β_Eu,H^I = − 8.19 ± 0.15, −7.90 ± 0.7 and −7.61 ± 0.01 for ionic strengths of 2, 3, and 4 mol⋅dm⁻³ NaClO₄, respectively. Total solubilities were estimated taking into account the formation of both Eu³⁺ and Eu(OH)²⁺ (7.7 < pC_H < 9) and the values found are: 1.4 × 10⁻⁶ mol⋅dm⁻³, 1.2 × 10⁻⁶ mol⋅dm⁻³ and 1.3 × 10⁻⁶ mol⋅dm⁻³, for ionic strengths of 2, 3 and 4 mol⋅dm⁻³ NaClO₄, respectively. The limiting values at zero ionic strength were extrapolated by means of the SIT from the experimental results of the present research together with some other published values. The results obtained are log₁₀ K_{sp, Eu(OH)3}^o = − 23.94 ± 0.51 (1.96 SD) and log₁₀β_Eu,H⁰ = − 7.49 ± 0.15 (1.96 SD).     

New method for determination of ochratoxin A in beer using zinc acetate and solid-phase extraction silica cartridges

A new method for the determination of ochratoxin A (OTA) in beer has been developed. The new method has been compared with a reference method currently accepted as AOAC official first action. The limits of detection and quantification of the proposed method were 0.0008 and 0.0025 ng/ml, respectively, while they were 0.0025 and 0.0075 ng/ml, respectively, in the AOAC method used as reference. The recovery levels in the 0.025-0.40 ng OTA/ml spiking range for the proposed and the reference methods were 80.6-87.6% and 78.2-83.8%, respectively. The relative standard deviations of recoveries were 2.6-7.5% for the proposed method and 0.7-6.1% for the reference method. Passing and Bablok regression analysis of recovery data obtained by the proposed method versus data obtained by the reference method on an OTA-spiked beer sample showed good correlation (r2 = 0.9993), while the slope and intercept were 1.049 and -0.0013, respectively. The advantage of the proposed method is the low cost of the materials used in sample preparation because expensive immunoaffinity columns are not needed to clean-up samples while it maintains or even increases the good performance of the reference method. The proposed method was applied to 69 beer samples from different geographic origins (national and imported) but purchased in the Spanish market. They were found to be contaminated with OTA in the range from 0.008 to 0.498 ng/ml (average: 0.070 ng/ml). Five samples surpassed the limit recommended by the European Union (0.2 ng OTA/g).     

Calorimetric and computational study of 1,4-dithiacyclohexane 1,1-dioxide (1,4-dithiane sulfone)

This work reports the enthalpies of formation in the condensed and gas state of 1,4-dithiacyclohexane 1,1-dioxide (1,4-dithiane sulfone, 5), derived from the enthalpy of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. The theoretically estimated enthalpy of formation was calculated from high-level ab initio molecular orbital calculations at the G2(MP2) level. The theoretical calculations appear to be in very good agreement with experiment. A comparison of the conversion of thiane sulfone 3 to 1,3-dithiane sulfone 4 and 1,4-dithiane sulfone 5 clearly shows the 1,3 isomer to be 6.7 kJ mol(-1) less stable, probably owing to diminished electrostatic repulsion between the sulfur heteroatoms in 1,4-sulfone 5.     

Size effect in thiol and amine binding to small Pt nanoparticles

A study was carried out to compare the binding affinities of 1-dodecanethiol and dodecylamine for small Pt nanoparticles. The results showed that the affinity of thiol for Pt nanoparticles increases with increasing particle size whereas the affinity of amine for Pt nanoparticles decreases. The divergence in binding affinities has resulted in differences in catalytic activities of thiol- and amine-protected Pt nanoparticles in the room temperature electro-oxidation of methanol (a fuel cell reaction). It was therefore possible for the larger Pt nanoparticles to be catalytically more active than the smaller Pt nanoparticles up to a certain critical size, before the surface area effects of nanoparticles become noticeable.     

A stereoselective synthesis of 6,6,6-trifluoro-L-daunosamine and 6,6,6-trifluoro-L-acosamine

A short synthesis of 6,6,6-trifluoro-L-acosamine 15 and 6,6,6-trifluoro-L-daunosamine 19 has been accomplished. The pyranose ring system of these carbohydrate analogues was formed by a hetero-Diels-Alder reaction of vinylogous imide 11 and ethyl vinyl ether which gave adduct 12a in 40% yield. Hydroboration gave 13 and subsequent hydrogenolytic removal of the (R)-2-phenylethyl chiral auxiliary gave ethyl 6,6,6-trifluoro-L-acosaminide 14. Acid hydrolysis furnished target 15. Glycoside 13 was N-trifluoroacetylated to give 16, the structure was confirmed by single crystal X-ray diffraction. The C-4 stereochemistry of 16 was inverted by Swern oxidation of the 4-OH group, and subsequent borohydride reduction to give 17. Hydrogenolytic removal of the auxiliary gave ethyl-6,6,6-trifluoro-L-daunosaminide 18. Acid hydrolysis provided 19.     

Trace analysis of antibacterial tylosin A, B, C and D in honey by liquid chromatography-electrospray ionization-mass spectrometry

A new LC-ESI-MS method was developed for the determination of residues of the antibacterial tylosins A, B, C and D in honey. The procedure employed an SPE on polymeric cartridges for the isolation of tylosins from diluted honey. Chromatographic separation of the tylosins was performed on a C18 column (150 x 4.60 mm2 ID, 5 microm) using a ternary gradient made of formic acid 1% in water (solvent A), methanol (solvent B) and ACN (solvent C) as mobile phase, at 30 degrees C and at a flow rate of 0.8 mL/min. Average analyte recoveries for the studied compounds ranged from 89 to 106% in replica sets of fortified honey samples. The detection limits for the four drugs studied were between 2 and 3 microg/kg. The developed method has been applied to the analysis of tylosin residues in honey from veterinarian treated beehives fed with the technical product, which contains the four compounds and is a new candidate antibiotic to treat American foulbrood disease of honey bee colonies.     

Universal and discriminative detection using a miniaturized pulsed discharge detector in comprehensive two-dimensional GC

A miniaturized pulsed discharge detector (Mini-PDD) has been successfully demonstrated for comprehensive 2-D GC (GC x GC) analysis of pyrolysis gasoline and the pyrolysis GC x GC analysis of a polyethylene copolymer. The detector cell volume of the Mini-PDD is reduced to 25% of the Valco plug-in PDD D-3. An n-C11 peak width at base is 96 ms for the Mini-PDD, about 23% larger than a peak width of 78 ms detected by a flame ionization detector (FID). The Mini-PDD has sufficient response time for most GC x GC applications. When Mini-PDD is operated in helium photoionization mode (Mini He-PDD), it is a universal detector for both inorganic and organic compounds. This is especially useful when detection of water is needed in GC x GC applications. When krypton is doped in the helium discharge gas (Mini Kr-PDD), it can suppress signals of compounds having higher ionization potentials and enhance relative signal intensities of aromatic compounds. The determination of aliphatic to aromatic hydrocarbon ratios is essential to the operation of petroleum crackers. Comparison of the signal from two modes of the Mini-PDD is a simple and fast way to verify the location of aromatics in comprehensive 2-D gas chromatograms.     

Urea-, thiourea-, and guanidine-linked glycooligomers as phosphate binders in water

Beta-(1-->6)-linked pseudodi- and pseudotrisaccharides incorporating alternating pseudoamide-type (urea, thiourea, guanidine) intersaccharide bridges have been prepared and evaluated as phosphate binders in water. The monosaccharide subunits induce the Z,Z rotameric form at the pseudoamide segments, thus favoring their participation in bidentate hydrogen-bond interactions with oxoanions. Moreover, the conformational properties about the anomeric C-1-N bonds and the sugar C-5--C-6 bonds privilege orientations that facilitate both the desolvation of the incoming anionic guest and the stabilization of the complex by cooperative interactions. Measurable association constants (K(as)) toward dimethyl and, especially, phenyl phosphate were obtained from NMR titration experiments for both series of glucooligomers, the binding affinity being strongly dependent on the nature of the pseudoamide functionality. Guanidinium derivatives, for which charge neutralization was expected to contribute to phosphate binding, were superior to the neutral thiourea and urea derivatives (K(as) = 48-60 M(-1) for 1:1 complexes with phenyl phosphate dianion). Interestingly, the thiourea oligomers exhibited association constants of the same order of magnitude (K(as) = 25-40 M(-1)), much higher than those observed for the urea analogues (K(as) = 2-3 M(-1)), which is ascribed to a less efficient solvation of the thiocarbonyl derivatives.     

Controlled synthesis of (S,S)-2,7-diaminosuberic acid: a method for regioselective construction of dicarba analogues of multicystine-containing peptides

A method to facilitate regioselective formation of multiple dicarba isosteres of cystine is described. A sequence of ruthenium-catalyzed cross metathesis and rhodium-catalyzed hydrogenation of nonproteinaceous allylglycine derivatives has been developed to achieve high-yielding and unambiguous formation of diaminosuberic acid derivatives. Allylglycine derivatives readily undergo ruthenium-catalyzed metathesis and hydrogenation to yield diaminosuberic acid derivatives in near quantitative yield. Under the same experimental conditions, prenylglycine was found to be inert to both Grubbs' and Wilkinson's catalyzed metathesis and hydrogenation, respectively, but was readily activated for metathesis via cross metathesis with Z-butene. Subsequent cross metathesis of the metathesis-formed crotylglycine derivative, followed by hydrogenation, yielded the second diaminosuberic acid derivative in excellent yield.