Building robust calibration models for the analysis of estrogens by gas chromatography with mass spectrometry detection

Five hormonal growth promotants (diethylstilbestrol, hexestrol, dienestrol, 17-β-estradiol and 17-α-ethynylestradiol) have been analysed by gas chromatography with mass spectrometry detection (GC/MS, SIM mode) for four non-consecutive days. The aim is to build models with stable predictions. The strategies applied are internal standardization and global models carried out by gathering signals recorded on several days. Two models were examined: univariate models (with standardized peak area) and PARAFAC2 (the analyte scores were standardized by the scores of the internal standard). Internal standardization has been proved to be efficient for both models of dienestrol and ethynylestradiol. The mean relative error in absolute value when samples recorded on a different day to the calibration set are quantified by PARAFAC2 is 7.00% and 7.11% for dienestrol and ethynylestradiol, respectively. For diethylstilbestrol and estradiol, internal standardization was combined with global calibration models built with signals recorded under several sources of variability (different days). Thus predictions become steadier over time and in the estradiol example, errors decrease from 33.10% to 9.76%. The mean relative error in absolute value with PARAFAC2 updated models oscillates between 6.34% for ethynylestradiol and 10.74% for diethylstilbestrol. For univariate updated models errors range from 6.42% to 14.19% for ethynylestradiol and estradiol respectively. The combination of both strategies has been proved to be efficient independently of the analyte and of the signal order.     

Unified synthesis of eudesmanolides,combining biomimetic strategies with homogeneous catalysis and free-radical chemistry

[reaction: see text] A general procedure for the synthesis of both 12,6- and 12,8-eudesmanolides has been developed. The key step is the titanocene-catalyzed radical cyclization of accessible epoxygermacrolides. The novel reagent 2,4,6-trimethyl-1-trimethylsilylpyridinium chloride, both compatible with oxiranes and capable of regenerating Cp(2)TiCl(2) from Cp(2)Ti(Cl)H and Cp(2)Ti(Cl)OAc, played an important role in the catalytic cycle leading to exocyclic alkenes.     

Identification and quantification of enrofloxacine in poultry feeding water through excitation emission fluorescence and three-way PARAFAC calibration

In this work an excitation emission molecular fluorescence technique with PARAFAC calibration is proposed for enrofloxacine determination in feeding water from poultry farms. In accordance with the working criteria of the 2002/657/EC European Decision, the proposed method has a capability of detection, CCbeta, of 6.8 microg l(-1), for both probabilities of false positive and false negative of 5%. The accuracy of the method is demonstrated and its precision is 1.7 microg l(-1), expressed as standard deviation. This method allows one to identify and determine the quantity of enrofloxacine present in water samples from poultry farms without it being necessary to determine the possible interferents, nor separate them in a step previous to calibration.     

Characterization and Crystal Structure of some Schiff Base Copper(II) Complexes derived from Enantiomeric Pairs of Chiral Amines

Copper(II) complexes of three chiral enantiomeric pairs of o‐hydroxy Schiff bases derived from (R)‐(+)‐1‐phenylethylamine and (S)‐(‐)‐1‐phenylethylamine, were prepared and characterized. Elemental analyses, specific rotation, i.r., electronic, cd and mass spectra,and some X‐ray crystal structures were obtained. The X‐ray study of four complexes shows that the geometry around the metal atom is distorted square planar. Epr studies of all these complexes in DMF solution at 77 K suggest that their geometries in solution are slightly different to that observed in the solid state by X‐ray crystallography. Although, cd spectra only show charge transfer absorptions, the data confirm the enantiomeric character of the three pairs of the obtained complexes.     

Gas chromatographic determination of the fatty-acid content of heat-treated green beans

A gas chromatographic method that employs flame ionization detection, a DB-Wax capillary column with helium as the carrier gas, and a split-splitless (1:15) injector was used to determine the effects of different heat treatments on the fatty-acid content of whole green beans (Phaseolus vulgaris, L.). A one-step-extraction-methylation method was used to obtain fatty acid methyl esters from raw and steamed, boiled, pressure-cooked, and microwave-cooked green beans. The fatty-acid profile changed slightly, but heat treatment produced an increase in the fatty-acid content.     

Spectrophotometric determination of zinc with 1-(2-pyridylmethylidene)-5-(salicylidene)thiocarbohydrazone

The absorbance of the yellow complex formed in pH 4.8 acetate buffer is measured at 410 nm in 40% (v/v) dimethylformamide. The molar absorptivity is 68 000 l mol^?1 cm^?1. The effect of interferences is discussed, and the method is applied to zinc in tap water and standard alloys.     

Kinetics and mechanisms of homogeneous catalytic reactions. Part 3. Regioselective,catalysed [RuH(CO)(NCMe)2(PPh3)2]BF4 reduction of quinoline

Summary A kinetic study of the regioselective homogeneous hydrogenation of quinoline (Q) to 1,2,3,4-tetrahydroquinoline (THQ) was carried out using the cationic complex [RuH(CO)(NCMe)₂(PPh₃)₂]BF₄ (1) as the precatalyst. The experimentally determined rate law wasr = {k ₂ K ₁/(1+K ₁[H₂])}[Ru₀][H₂]², which becomesr = {k ₂ K ₁[Ru₀]–[H₂]² at low hydrogen concentrations (k ₂ K ₁ = 28.5M ^–2 s^–1 at 398 K). The corresponding activation parameters were found to be H = 42 + 6 kJ mol^–1, S = – 115 ± 2JK^–1mol^–1 and G = 92 ± 8 kJ mol^–1. Complex(1) was found to react with Q in CHCl₃ under reflux to yield [RuH(CO)(NCMe)(N-Q)(PPh₃)₂]BF₄ (2) which was also isolated from the hydrogenation runs. These experimental findings, together with the results ofab initio self-consistent-field molecular orbital calculations on the free organic molecules involved, are consistent with a mechanism involving a rapid and reversible partial hydrogenation of(2) to yield the corresponding dihydroquinoline (DHQ) species [RuH(CO)(NCMe)(DHQ)(PPh₃)₂]BF₄ (4), followed by a rate-determining second hydrogenation of DHQ to yield [RuH(CO)(NCMe)(THQ)(PPh₃)₂]BF₄ (3).     

Supramolecular aggregates between carboxylate anions and an octaaza macrocyclic receptor

The 28-membered octaazamacrocycle Me2[28]py2N6 was used as a receptor for the molecular recognition of aromatic and aliphatic carboxylate substrates. The receptor-substrate binding behaviour of (H6Me2[28]py2N6)6+ with an aliphatic (-O2C(CH2)nCO2-, n=0 to 4) and an aromatic (phthalate, isophthalate, terephthalate, 4,4'-dibenzoate, benzoate, 3- and 4-nitrobenzoate) series of carboxylate anions was evaluated by 1H NMR spectroscopy (carried out in DMSO-d6 at 300 K). Two association constants were found for most of the studied cases, except for 3- and 4-nitrobenzoate for which only K1 was determined. For oxalate, malonate, benzoate and dibenzoate anions only the beta2 constants could be obtained. The values of the first association constant cover a range from 2.86 to 3.69 (log units), and the second stepwise constant from 2.15 to 2.89 (also in log units). No special selectivity was found but the highest values were determined for adipate and the lowest for the monoprotic 3- and 4-nitrobenzoates. Single crystal X-ray structures of H6Me2[28]py2N6 6+ with terephthalate, 1, and 4,4'-dibenzoate (2) were determined showing supramolecular entities with general formula (H6Me2[28]py2N6).(substrate)2(PF6)2.4H2O. These anions are the building blocks of an extensive 3-D network of hydrogen bonds.