Determination of aflatoxins B1, G1, B2 and G2 in medicinal herbs by liquid chromatography-tandem mass spectrometry

An easy method for the determination of aflatoxins B1, G1, B2 and G2 in Rhammus purshiana by LC coupled to mass spectrometry has been developed. Aflatoxins were extracted with a mixture of methanol and water and then it was purified by solid-phase clean-up using a polymeric sorbent, not described previously, for the determination of these toxins. The eluted extract was injected into the chromatographic system using a reversed-phase C18 short column with an isocratic mobile phase composed of methanol-water (30:70). A single-quadruple mass spectrometry using an electrospray ionization source operating in the positive ion mode was used to detect aflatoxins due to derivatization presenting several disadvantages. Recoveries of the full analytical procedure were 110% for aflatoxin B1, 89% for aflatoxin B2, 81% for aflatoxin G1 and 77% for aflatoxin G2. Detection limit (S/N = 3) was 10 ng and quantification limit (S/N = 10) was 25 ng, calculated as amount in medicinal herb.     

The use of DSC to characterize structural relaxation in thermosetting polymers

Structural relaxation in different epoxy-anhydride and epoxy-diamine resins has been investigated by differential scanning calorimetry using annealing and cooling rate experiments. The annealing experiments lead to the determination of enthalpy loss,H, at an equivalent annealing temperatureT _a=T _g-20, and for periods of annealing time, t_a, between 1 h and 4 months. The variation ofH with logt_a, defines a relaxation rate per decade,rrpd, which is very sensitive to changes of the epoxy network. The cooling rate experiments allow the determination of the apparent activation energy,h ^*. The effect of the degree of crosslinking, the addition of a reactive diluent, which acts as flexibilizer, and the length of cross-link onrrpd and h^* was studied.Financial support has been provided by DGICYT (Project no.PB93/1241). The authors are grateful to CIBA-GEIGY for supplying the epoxies and hardeners, and to HUNTSMAN CORPORATION EUROPE for supplying the JEFFAMINE*, J.M.H. wishes to acknowledge assistance for a sabbatical period from theMinisterio de Education y Ciencia.     

Complexes of Cu2(μ‐OAc)4(H2O)2 with 1,10‐Phenanthroline and Comparison with those of 2,2′‐Bipyridine. Crystal Structure of the Dimer [Cu(OAc)2(phen)](μ‐H2O)

The two complexes of composition Cu₂(OAc)₄(phen)(H₂O)₂ ( 1 ) andCu₂(OAc)₄(phen)₂(H₂O) ( 2 ) have been synthesized and characterized by chemical analysis and IR and electronic spectroscopies. Compound 2 has the structure of a dimer with a phenanthroline molecule and two monodentate acetate groups coordinated to each copper atom and a water molecule as the only bridging ligand between them. Each copper atom has a distorted square‐planar pyramidal coordination, determined by two oxygen atoms at 1.94(3) and 1.959(3) Å, two nitrogen atoms at 2.023(4) Å and the oxygen atom of the bridging water molecule at 2.289(2) Å. The distance between the two copper atoms is of 4.29 Å and the angle Cu(1)‐O(3)‐Cu(1A) 139.2(2)°. The water molecule is involved in two intramolecular hydrogen bonds with non coordinated oxygen atoms. The distance between the molecules of phenanthroline is 3.75 Å. Magnetic and EPR results for Cu₂(OAc)₄(phen)(H₂O)₂ ( 1 ), Cu₂(OAc)₄(phen)₂(H₂O) ( 2 ), Cu₂(OAc)₄(bipy) ( 3 ) and Cu₂(OAc)₄(bipy)₂(H₂O)₂ ( 4 ) have been analysed and compared. For 1 and 3 an antiferromagnetic dimer unit [Cu₂(μ‐OAc)₄] with 2J = ?325 and ?292 cm^?1, respectively, and other two copper atoms without significant magnetic interaction are present. Triplet signals are detected in the EPR spectra. In 2 and 4 there is no practically magnetic exchange and the orthorhombic signals are observed in the EPR spectra.     

Excess molar volumes and enthalpies for the binary systems propyl propanoate + o-xylene, m-xylene, and p-xylene at 298.15 K

This paper reports excess molar enthalpies, H_m^E, and excess molar volumes, V_m^E, of the binary systems {propyl propanoate + o-xylene}, {propyl propanoate + m-xylene} and {propyl propanoate + p-xylene} at the temperature 298.15 K and atmospheric pressure, over the whole composition range. V_m^E was calculated from the experimental measurement of the corresponding densities, while H_m^E was measured directly. The excess magnitudes were correlated to a Redlich-Kister type equation. Finally, we will discuss the results of the three mixtures studied here and by comparison with other binary systems containing propyl propanoate and a benzene-based compound previously published.     

Ferromagnetic exchange in a dinuclear copper(II) complex mediated by a methanolate bridging ligand

The copper(II) complex Cu(2)L(OMe)(H(2)O)(3), [middle dot]3H(2)O [H(3)L = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine] was obtained and recrystallised in methanol to yield crystals of [[Cu(2)L(OMe)]](2).2.5MeOH.4H(2)O, 1.2.5MeOH.4H(2)O. Its single X-ray study shows that it contains two crystallographically different but chemically equivalent dinuclear [Cu(2)L(OMe)] 1 molecules in the asymmetric unit cell. The copper atoms of each dinuclear moiety are in distorted square-pyramidal environments, with both pyramids sharing an apical phenolate and a basal methanolate oxygen atom. Magnetic characterisation of 1.3H(2)O shows a quite strong intramolecular ferromagnetic coupling between both metal atoms. Extended Huckel calculations reveal that the intradinuclear magnetic interaction seems to be mediated by the exogenous methanolate bridging ligand.     

Reflections on the calculation and publication of potentiometrically-determined formation constants

Calculation and reporting procedures are described, which aim to improve the quality and comparability of published formation constant values obtained by glass-electrode potentiometry. Ways in which the processing of data by computer optimization programs can be standardized are the main concern, particularly in respect of improving the usefulness of equilibrium data through incorporation into large publically available databases. These recommendations may be particularly valuable to researchers beginning in this field as well as to those who determine formation constants only occasionally.     

Spirolactams as conformationally restricted pseudopeptides: synthesis and conformational analysis

The synthesis of 1-(tert-butoxycarbonyl)-7-[1-(tert-butoxycarbonyl)-3-methylbutyl]-6-oxo-1,7-diazaspiro[4.5]decanes (S,S)-1a and (S,R)-1b is described. Derivatives 17a,b and 19a are prepared for use in peptide synthesis as constrained surrogates of the Pro-Leu and Gly-Leu dipeptides. The Ac-[Gly-Leu]-Met-NH(2) derivatives (S,S,S)-2a and (S,R,S)-2b, with the tripeptidic C-terminal region present in tachykinins, are also synthesized. Conformational analyses of these tripetide analogues by NMR experiments and molecular modeling calculations show that both (S,S,S)-2a and (S,R,S)-2b epimers are gamma-turn/distorted type II beta-turn mimetics.     

Practical synthesis of a dithiane-protected 3',5'-dialkoxybenzoin photolabile safety-catch linker for solid-phase organic synthesis.

The solution-phase preparation of the 3',5'-dialkoxybenzoin photolabile safety-catch linker 16 is described. Pivotal to this convenient synthesis is the selection of appropriate orthogonal protecting groups for the alkoxy functionalities present. The new linker can be readily loaded onto any standard amine-terminating resin under peptide-coupling conditions, without the need to protect the secondary alcohol functionality, and subsequently loaded with substrate. Alternatively, the loading efficiency of sterically hindered substrates can be enhanced by preloading the semiprotected linker variant 10 in solution prior to immobilization onto the resin. This second generation of benzoin photolabile safety-catch linkers provides greater control of both linker loading and resin attachment and should prove to be a more versatile and convenient form of the linker.     

Volatile compounds of red and white wines by headspace--solid-phase microextraction using different fibers

The behavior of four fibers [polydimethylsiloxane (PDMS), PDMS-divinylbenzene (DVB), carboxen (CAR)-PDMS, PDMS-DVB-CAR), is tested for the analysis of volatile compounds of white and red wine. The PDMS-DVB-CAR fiber is the most appropriate to obtain the most wide volatile profile of wines. The better extraction conditions are 40 min at 35 degrees C. Satisfactory data about the reproducibility and uptake are obtained for more than 40 volatile compounds of red and white wine.