Determination of total selenium and selenium distribution in the milk phases in commercial cow’s milk by HG-AAS

A procedure has been developed for determining the selenium in cows milk using hydride generation–atomic absorption spectrometry (HG-AAS) following microwave-assisted acid digestion. The selenium distributions in milk whey, fat and micellar casein phases were studied after separating the different phases by ultracentrifugation and determining the selenium in all of them. The detection limits obtained by HG-AAS for the whole milk, milk whey and micellar casein were 0.074, 0.065 and 0.075 g l^–1, respectively. The accuracy for the whole milk was checked by using a Certified Reference Material CRM 8435 whole milk powder from NIST, and the analytical recoveries for the milk whey and casein micelles were 100.9 and 96.9%, respectively. A mass balance study of the determination of selenium in the different milk phases was carried out, obtaining values of 95.5–100.8%. The total content of selenium was determined in 37 milk samples from 15 different manufacturers, 19 whole milk samples and 18 skimmed milk samples. The selenium levels found were within the 8.5–21 g l^–1 range. The selenium distributions in the different milk phases were studied in 14 whole milk samples, and the highest selenium levels were found in milk whey (47.2–73.6%), while the lowest level was found for the fat phase (4.8–16.2%). A strong correlation was found between the selenium levels in whole milk and the selenium levels in the milk components.     

The Configuration of β-Carotene in the Photosystem II Reaction Center

Different pigment extraction procedures and HPLC methods were tested to investigate the geometric configuration of the β-carotene in two forms of the photosystem II reaction center (Dl-D2-cytochrome (Cyt) b559) complex containing one and two β-carotene molecules per two pheophytin a. All the handling steps and HPLC analyses were done in darkness at room temperature and at 4°C. Two different pigment extracts were analyzed, a mixture of chlorophyll a, pheophytin a and 3-carotene, and the isolated p-carotene from that mixture. In both cases only the all-frans-β-carotene was detected. The chromatographic profiles were similar at both temperatures only differing in the retention times that were longer at 4°C. This result was independent of the concentration of photosynthetic starting material. Furthermore, no differences were observed between Dl-D2-Cyt b559 complexes with one and two p-carotene molecules per reaction center. The analysis of the β-carotene chromatographic peak indicated no 15-cis to all-fraws isom-erization occurred during the HPLC chromatography in our experimental conditions. Resonance Raman spectra were also recorded in the isolated Dl-D2-Cyt b559 complex at room and liquid nitrogen temperature with excitation at 514.5 nm from an Ar⁺ laser. Spectra of control preparations showed main bands at 1532, 1264, 1213, 1185, 1154 and 1003 cm^?1 corresponding to the M-trans isomer and confirm previous results. The presence in the reaction center suspension of artificial electron acceptors such as silicomolybdate or 2,5-dibromo-3-methyl-6-iso-propyl-p-benzoquinone that are able to quench ³P680 did not modify the resonance Raman spectra of the native Dl-D2-Cyt b559 complex. The results suggest that no isomerization takes place during the laser irradiation.     

A novel efficient deoxygenation process for N-heteroarene N-oxides

A novel deoxygenation process for N-heteroarene N-oxides is described. The deoxygenation process has been carried out by utilizing some short C-chain alcohols, benzyl alcohol, or 1-phenylethanol as the solvent in the presence of a base, such as sodium alkoxide or sodium hydroxide. A series of N-heteroarene N-oxides was submitted to the developed conditions to provide the corresponding N-heteroarenes with high yield and excellent selectivity. When the deoxygenation is carried out with benzyl alcohol or 1-phenylethanol as the reaction medium, the process can be performed under very mild conditions, at only 30 degrees C. The deoxygenation process is in contrast to several other methods performed without the presence of any transition metal as a catalyst or stoichiometric reagent. DFT calculations suggest that the alkoxide performs a nucleophilic attack on the N-heteroarene in the ortho or para position. This bond is cleaved homolytically with the overall result being that a single electron-transfer step has occurred. The products of this process are an N-heteroarene N-oxide radical anion and an alkoxyl or benzyloxy radical, depending on the solvent that has been used. Successive steps of the mechanism result in an oxygen transfer from the N-oxide to give the deoxygenated N-heteroarene and 1 equiv of the aldehyde, which is the oxidation product of the solvent alcohol.     

LC-PAD Determination of Mescaline in Cactus “Peyote” (Lophophora williamsii)

A reversed-phase column liquid chromatographic method for the separation and quantification of mescaline present in “peyote” has been developed using a Symmetry C₁₈ column and isocratic profile. The method can be utilised for the quantitative determination of other alkaloids. This method is economical in terms of the time taken and the amount of solvent used for each analysis. The validity of the method with respect to analysis was confirmed by comparing the UV spectra of peak with the reference compound (mescaline) using a photodiode array detector. The assay method described is simple, rapid and accurate, and may form part of future drug authentication protocols.     

Selenonium ionic liquid as an efficient catalyst for the synthesis of thioacetals under solvent-free conditions

Acidic ionic liquid butyl ethyl phenyl selenonium tetrafluoroborate, [BEPSe]BF₄, was successfully employed as a catalyst for the synthesis of several dithioacetals in the absence of a solvent. The method is general and selectively afforded thioacetals derived from aldehydes and ketones in good yields.     

Different evolutionary trails in the related genomes Cricetus cricetus and Peromyscus eremicus (Rodentia, Cricetidae) uncovered by orthologous satellite DNA repositioning

Constitutive heterochromatin comprises a substantial fraction of the eukaryotic genomes and is mainly composed of tandemly arrayed satellite DNAs (satDNA). These repetitive sequences represent a very dynamic and fast evolving component of genomes. In the present work we report the isolation of Cricetus cricetus (CCR, Cricetidae, Rodentia) centromeric repetitive sequences from chromosome 4 (CCR4/10sat), using the laser microdissection and laser pressure catapulting procedure, followed by DOP-PCR amplification and labelling. Physical mapping by fluorescent in situ hybridisation of these sequences onto C. cricetus and another member of Cricetidae, Peromyscus eremicus, displayed quite interesting patterns. Namely, the centromeric sequences showed to be present in another C. cricetus chromosome (CCR10) besides CCR4. Moreover, these almost chromosome-specific sequences revealed to be present in the P. eremicus genome, and most interestingly, displaying a ubiquitous scattered distribution throughout this karyotype. Finally and in both species, a co-localisation of CCR4/10sat with constitutive heterochromatin was found, either by classical C-banding or C-banding sequential to in situ endonuclease restriction.The presence of these orthologous sequences in both genomes is suggestive of a phylogenetic proximity. Furthermore, the existence of common repetitive DNA sequences with a different chromosomal location foresees the occurrence of an extensive process of karyotype restructuring somehow related with intragenomic movements of these repetitive sequences during the evolutionary process of C. cricetus and P. eremicus species.     

A micellar electrokinetic chromatography approach using diastereomeric derivatization and a volatile surfactant for the enantioselective separation of selenomethionine

A MEKC methodology with UV detection was developed for the enantioselective separation of selenomethionine (SeMet). The use of (+)‐1‐(9‐fluorenyl)ethyl chloroformate (FLEC) as chiral derivatization reagent to form SeMet diastereomers enabled their subsequent separation using ammonium perfluorooctanoate (APFO) as a volatile pseudostationary phase. The effect of APFO concentration and pH, temperature, injection volume, and derivatization conditions (time and FLEC/SeMet ratio) were evaluated in order to select the best separation conditions. A chiral resolution of 4.4 for DL‐SeMet was achieved in less than 6 min using 100 mM APFO at pH 8.5 as electrophoretic buffer. Satisfactory results were obtained in terms of linearity, precision (RSD from 3.4 to 5.1% for migration times and from 1.8 to 4.6% for corrected peak areas), accuracy, and LODs (3.1 × 10^?6 M and 3.7 × 10^?6 M for d and l enantiomers, respectively). The method was successfully applied to the determination of l ‐SeMet in food supplements.     

Photoprotective and Antigenotoxic Effects of the Flavonoids Apigenin,Naringenin and Pinocembrin

This work evaluated the photoprotective and antigenotoxic effects against ultraviolet B (UVB) radiation of flavonoid compounds apigenin, naringenin and pinocembrin. The photoprotective efficacy of these compounds was estimated using in vitro photoprotection indices, and the antigenotoxicity against UVB radiation was evaluated using the SOS chromotest and an enzymatic (proteinase K/T4 endonuclease V enzyme) comet assay in UV‐treated Escherichia coli and human (HEK‐293) cells, respectively. Naringenin and pinocembrin showed maximum UV‐absorption peak in UVC and UVB zones, while apigenin showed UV‐absorption capability from UVC to UVA range. These compounds acted as UV filters reducing UV‐induced genotoxicity, both in bacteria and in human cells. The enzymatic comet assay resulted highly sensitive for detection of UVB‐induced DNA damage in HEK‐293 cells. In this work, the photoprotective potential of these flavonoids was widely discussed.