Lipase-catalyzed preparation of corticosteroid 17α-esters endowed with antiandrogenic activity

Several 17α-monoesters of cortexolone and its Δ⁹-derivative are endowed with antiandrogenic activity. Their synthesis can be accomplished by means of a lipase-catalyzed chemoselective alcoholysis of the corresponding 17α,21-diesters.     

Headspace sampling of the volatile fraction of vegetable matrices

The evolution of vapour phase sampling of the volatile fraction of vegetable matrices, or of products directly related to them, over the period 1996-2007 is reviewed. High concentration capacity headspace (HCC-HS) and dynamic headspace (D-HS) techniques, that is headspace sampling approaches where the analytes in the vapour phase are concentrated into a sorbent, an adsorbent or a solvent, are considered. Advantages, disadvantages and applications to the vegetable field of several successful techniques based on these approaches are critically presented, including in-tube sorptive extraction (INCAT, HS-SPDE), headspace sorptive extraction (HSSE), solid-phase aroma concentrate extraction (SPACE), large surface area HCC-HS sampling (MESI, MME, HS-STE), headspace liquid-phase microextraction (HS-LPME) and dynamic headspace samplings (D-HS). The developments necessary to overcome some of the limits of the above approaches and techniques are also discussed in view of their application to new fields.     

Determination of aflatoxins in hazelnuts by various sample preparation methods and liquid chromatography-tandem mass spectrometry

A sensitive and reliable liquid chromatography-tandem mass spectrometric with electrospray ionization method for determining aflatoxins in hazelnuts has been developed. Three different extraction techniques, such as homogenization, ultrasonic extraction, and matrix solid phase dispersion have been tested and compared in terms of recovery, matrix effect, accuracy and precision. Ultrasound extraction was the most performing sample preparation method. Absolute recoveries for analytes and I.S. ranged from 93 to 101%. Accuracy and precision were calculated using matrix matched calibration, and ranged 91-102% and 2-11%, respectively. CC alpha and CC beta for aflatoxin B1 (EU limit=2 microg/kg) were 2.15 and 2.33 microg/kg, respectively. A ruggedness test performed on three other matrices demonstrated that sonication time was critical and a matrix matched calibration must be constructed for every sort of matrix.     

How important are temperature effects for cluster polarizabilities?

State-of-the-art first-principle all-electron density functional theory calculations on small sodium clusters are performed to study the temperature dependency of their polarizabilities. For this purpose Born-Oppenheimer molecular dynamics simulations with more than 100,000 time steps (>200 ps) are recorded employing gradient corrected functionals in combination with a double-zeta valence polarization basis set. For each cluster 18 trajectories between 50 and 900 K are collected. The cluster polarizabilities are then calculated along these trajectories employing a triple-zeta valence polarization basis set augmented with field-induced polarization functions. The analysis of these calculations shows that the temperature dependency of the sodium cluster polarizabilities varies strongly with cluster size. For several clusters characteristic changes in the polarizability per atom as a function of temperature are observed. It is shown that the inclusion of finite temperature effects resolves the long-standing mismatch between calculated and measured sodium cluster polarizabilities.     

Chiral expression at the solid-liquid interface: a joint experimental and theoretical study of the self-assembly of chiral porphyrins on graphite

The chiral organization of an enantiopure functional molecule on an achiral surface has been studied with the aim of understanding the influence of stereogenic centers on the self-assembly in two dimensions. A chiral tetra meso-amidophenyl-substituted porphyrin containing long hydrophobic tails at the periphery of the conjugated pi-electron system was prepared for this purpose. Scanning tunneling microscopy (STM) images of the compound at the graphite-heptanol interface reveal a chiral arrangement of the molecules, with the porphyrin rows tilted by 13 degrees with respect to the normal to the graphite axes. In terms of molecular modeling, a combination of molecular dynamics simulations on systems constrained by periodic boundary conditions and on unconstrained large molecular aggregates has been applied to reach a quantitative interpretation on both the density of the layer and its orientation with respect to the graphite surface. The results show clearly that (i) the methyl groups of the stereogenic point toward the graphite surface and (ii) the porphyrin molecules self-assemble into an interdigitated structure where the alkyl chains align along one of the graphite axes and the porphyrin cores are slightly shifted with respect to one another. The direction of this shift, which defines the chirality of the monolayer, is set by the chirality of the stereogenic centers. Such an arrangement results in the formation of a dense chiral monolayer that is further stabilized by hydrogen bonding with protic solvents.     

Tricarbonyl rhenium(I) complexes containing a bridging 2,5-diphenyl-1,3,4-oxadiazole ligand: structural, spectroscopic, electrochemical, and computational characterization

The three complexes [Re2(mu-X1)(mu-X2)(CO)6(mu-ppd-kappaN3:kappaN4)] (X1, X2 ) H, 1; X1 ) H, X2 ) Cl, 2; X1, X2 ) Cl, 3; ppd) 2,5-diphenyl-1,3,4-oxadiazole) have been synthesized by different routes, involving the reaction of [Re4(mu3-H)4(CO)12]with ppd for 1, the reaction of 1 with HCl for 2, and the reaction of [ReCl(CO)5] with ppd for 3. The three complexes possess a different number of valence electrons, so the formal Re-Re bond order varies from 2 to 1 to 0 in complexes 1, 2, and 3, respectively. This is reflected in the Re-Re bond distance (277.9, 297.9, and 358.5 pm in the same series)and in the stability of the complexes in the coordinating solvent acetonitrile (t1/2 for ppd displacement 13.6, 4.5, and 3.7 h,for 1, 2, and 3, respectively). Both experimental and calculated structures indicates that coordination induces a distortion from planarity of the diphenyloxadiazole moiety due to the interaction of the equatorial carbonyls with the bridging ppd,which increases on going from 1 to 2 to 3 (dihedral angle between the oxadiazole and the phenyl rings 18.4 degrees, 23.3 degrees, and 45.0 degrees, respectively). The UV spectra show pi-pi* transitions of the oxadiazole ligand (which shift to higher energy on increasing the distortion from the planarity, from 252 to 267 nm) and metal-to-ligand charge transfer absorptions (from 300 to 362 nm). Upon irradiation between 340 and 380 nm, complex 2 only features a weak broad emission at 527 nm(phi)0.02%), whereas upon excitation at 300 nm, the emission typical of free ppd is observed, suggesting photodissociation.Cyclic voltammetry investigations in acetonitrile showed that the three complexes exhibit ligand-centered irreversible reduction peaks (from -1.83 to -1.93 V vs Fc+|Fc), shifted to more positive values with respect to free ppd (-2.50 V). The shift however is smaller than in the analogous derivatives containing 1,2-diazines, suggesting a smaller electron depletion of the heterocycle ligand upon coordination. The complexes also show a metal-centered, bi-electronic, irreversible oxidation peak (from 1.05 to 1.37 V vs Fc+/Fc). A combined density functional and time-dependent density functional (TD DFT)study allowed us to understand the factors affecting the stability of the three complexes and to rationalize their electrochemical and photophysical properties in terms of their electronic structure.     

Mycoestrogen determination in cow milk: Magnetic solid‐phase extraction followed by liquid chromatography and tandem mass spectrometry analysis

Recently, magnetic solid‐phase extraction has gained interest because it presents various operational advantages over classical solid‐phase extraction. Furthermore, magnetic nanoparticles are easy to prepare, and various materials can be used in their synthesis. In the literature, there are only few studies on the determination of mycoestrogens in milk, although their carryover in milk has occurred. In this work, we wanted to develop the first (to the best of our knowledge) magnetic solid‐phase extraction protocol for six mycoestrogens from milk, followed by liquid chromatography and tandem mass spectrometry analysis. Magnetic graphitized carbon black was chosen as the adsorbent, as this carbonaceous material, which is very different from the most diffuse graphene and carbon nanotubes, had already shown selectivity towards estrogenic compounds in milk. The graphitized carbon black was decorated with Fe₃O₄, which was confirmed by the characterization analyses. A milk deproteinization step was avoided, using only a suitable dilution in phosphate buffer as sample pretreatment. The overall process efficiency ranged between 52 and 102%, whereas the matrix effect considered as signal suppression was below 33% for all the analytes even at the lowest spiking level. The obtained method limits of quantification were below those of other published methods that employ classical solid‐phase extraction protocols.     

Presence of thiamine pyrophosphate in mammalian peroxisomes

Background

Thiamine pyrophosphate (TPP) is a cofactor for 2-hydroxyacyl-CoA lyase 1 (HACL1), a peroxisomal enzyme essential for the α-oxidation of phytanic acid and 2-hydroxy straight chain fatty acids. So far, HACL1 is the only known peroxisomal TPP-dependent enzyme in mammals. Little is known about the transport of metabolites and cofactors across the peroxisomal membrane and no peroxisomal thiamine or TPP carrier has been identified in mammals yet. This study was undertaken to get a better insight into these issues and to shed light on the role of TPP in peroxisomal metabolism.

Results

Because of the crucial role of the cofactor TPP, we reanalyzed its subcellular localization in rat liver. In addition to the known mitochondrial and cytosolic pools, we demonstrated, for the first time, that peroxisomes contain TPP (177 ± 2 pmol/mg protein). Subsequently, we verified whether TPP could be synthesized from its precursor thiamine, in situ, by a peroxisomal thiamine pyrophosphokinase (TPK). However, TPK activity was exclusively recovered in the cytosol.

Conclusion

Our results clearly indicate that mammalian peroxisomes do contain TPP but that no pyrophosphorylation of thiamine occurs in these organelles, implying that thiamine must enter the peroxisome already pyrophosphorylated. Consequently, TPP entry may depend on a specific transport system or, in a bound form, on HACL1 translocation.     

H2O nucleation around Au+

First principles electronic structure calculations have been carried out to investigate the ground state geometry, electronic structure, and the binding energy of [Au(H2O)n]+ clusters containing up to 10 H2O molecules. It is shown that the first coordination shell of Au+ contains two H2O molecules forming a H2O-Au+-H2O structure with C2 symmetry. Subsequent H2O molecules bind to the previous H2O molecules forming stable and fairly rigid rings, each composed of 4 H2O molecules, and leading to a dumbbell structure at [Au(H2O)8]+. The 9th and the 10th H2O molecules occupy locations above the Au+ cation mainly bonded to one H2O from each ring, leading to structures where the side rings are partially distorted and forming structures that resemble droplet formation around the Au+ cation. The investigations highlight quantum effects in nucleation at small sizes and provide a microscopic understanding of the observed incremental binding energy deduced from collision induced dissociation that indicates that [Au(H2O)n]+ clusters with 7-10 H2O molecules have comparable binding energy. The charge on the Au+ is shown to migrate to the outside H2O molecules, suggesting an interesting screening phenomenon.     

A sensitive confirmatory method for aflatoxins in maize based on liquid chromatography/electrospray ionization tandem mass spectrometry

A liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for measurement of aflatoxins B1, B2, G1, and G2 in maize is described. Aflatoxins (AFs) were extracted from 1 g samples by using tri-portions of acetonitrile/water (80:20, v/v) (10 + 7 + 7 mL), and 2/5 of the extract diluted to 500 mL by water was cleaned up with a 100 mg Carbograph-4 cartridge. After the addition of the internal standard AFM1, the final extract was analyzed by LC/ESI-MS/MS in positive ion mode using multiple reaction monitoring with a triple-quadrupole instrument. A C(18) column thermostatted at 45 degrees C with a mobile phase gradient of acetonitrile/water with 2 mmol/L ammonium formate was used. Although the matrix suppression effect was negligible, quantitation was achieved by an external calibration procedure using matrix-matched standard solutions to improve accuracy. Sample recoveries at four spiking levels ranged from 81 to 101% (relative standard deviation (RSD) 相似文献