Effects of Redox Couple on the Response of Polypyrrole‐Based Electrochemical DNA Sensors

Much research‐to‐date exists to create sensitive and selective DNA sensors. A variety of approaches are adopted, including those involving polypyrrole and electrical impedance spectroscopy. Combined these are able to sense as well as aptly transduce signals. Many such sensors employ ferri/ferrocyanide to exhibit surface hybridization. This redox reporter, though with merits, can prove disadvantageous. To this end, a comparative study was performed with the redox reporter hydroquinone. For comparison purposes ferri/ferrocyanide indicated greater sensitivity, suggested to arise from inherent charge. Conversely, with hydroquinone steric hindrance is the main influencing factor. Such a study aims to guide design of analogous sensors.     

Comparative analysis of lipophilic compounds in eggs of organically raised ISA Brown and Araucana hens

Hens?? eggs represent a rich source of important nutrients, including lipids and carotenoids. The lipid composition of hens?? eggs is influenced by genetic factors, age, and diet. The aim of this study was to compare the fatty acids, cholesterol, and carotenoids content of the egg yolk of ISA Brown and Araucana hens grown in free-range housing systems. Fatty acids and cholesterol were analysed by GC-FID and GC-MS and carotenoids were quantified by RP-HPLC-PDA. The Araucana egg yolk has a higher lipid content and higher egg-to-albumen ratio than the ISA Brown yolk, while the total cholesterol, carotenoids content and profile are not significantly different. The lipids of the Araucana egg yolk have a higher content of mono-unsaturated fatty acids (MUFAs), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) and a better n-6/n-3 ratio than the ISA Brown egg yolk lipids. The major carotenoids were lutein and zeaxanthin, which account for more than 83 % in egg yolk. Eggs of both breeds, when raised organically, represent very good sources of highly bio-available lutein and zeaxanthin, pigments which are related to lower risk of age-related macular degeneration. We report for the first time on the fatty acids composition in lipid fractions and the profile and content of carotenoids of the Araucana egg yolk.     

Surface‐enhanced Raman spectroscopy of DNA from leaves of in vitro grown apple plants

Ultrasensitive Raman measurements of nucleic acids are possible by exploiting the effect of surface‐enhanced Raman scattering (SERS). In this work, the vibrational spectra of eight genomic DNAs from in vitro grown apple leaf tissues (Malus domestica Borkh., Fam Rosaceae, cvs. Florina, Idared, Rebra, Goldrush, Romus 3, Romus 4 and the rootstocks M9 and M26) were analyzed using surface‐enhanced Raman spectroscopy, in the wavenumber range 200–1800 cm⁻¹. SERS signatures, spectroscopic band assignments and structural interpretations of these plant genomic DNAs are reported. Strong dependences of the SERS spectra on genomic DNA amount in the measured sample volume and on time were observed. Similarities of the SERS signals of DNAs from Rebra and Romus 3 leaves were detected. To our knowledge, this is the first SERS study on genomic DNA from leaf tissues. The present work provides a basis for future use of surface‐enhanced Raman spectroscopy to analyze specific plant DNA–ligand interactions or DNA structural changes induced by plants' stress conditions associated with their natural environment. Besides, this study will generate information that is valuable in the development of low‐level plant DNA‐based analytical sensors. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochemical Deposition of CdTe Layers. Their Structure and Electrical Properties

CdTe layers have been deposited catodically on nickel substrates from an aqueous solution of CdSO₄ and TeO₂. The degree of erystallinity increases with increasing temperature and decreasing deposition potential. The structure of the layers is cubic with 〈111〉 or 〈110〉 texture which is determined by TeO₂ concentration predominantly. Amorphous phase is found in deposits prepared at higher deposition potential or at lower temperatures of bath (60 °C). After annealing at 200 °C the amorphous deposits crystallized and pure tellurium appeared in diffraction spectra. The resistivity of the films was determined by means of I—V characteristics. Films with deposition potentials (−500 to −400) mV vs SCE are p-type conductivity whereas at lower potentials (down to − 700 mV vs. SCE) the n-type material is formed.     

Six-membered tetracarbonylmanganese(I) and -rhenium(I) metalacycles containing the [Ph2P(Se)NP(Se)Ph2] ligand: solution and solid state characterization

The halocarbonyls BrM(CO)₅, M = Mn and Re, were reacted with the KN(SePPh₂)₂ salt in equimolar amounts; the reactions were thermally carried out and resulted in the generation of the hexacoordinated isostructural complexes [M(CO)₄{Ph₂P(Se)NP(Se)Ph₂-Se,Se′}] with a twist MSePNPSe ring conformation. Complexes’ characterizations were achieved by IR, mass, NMR (¹H, ¹³C, ³¹P, ⁷⁷Se) spectroscopies, and by single-crystal X-ray diffraction.     

Preconcentration and voltammetric determination of the herbicide metamitron with a silica-modified carbon paste electrode

A carbon paste electrode incorporating silica (Si-MCPE) was fabricated to accumulate Metamitron at the electrode surface. Several electroanalytical techniques were used to explore its reductive behaviour. The results indicate that the system is irreversible and fundamentally controlled by adsorption. The adsorptive stripping response has been evaluated with respect to accumulation time, deposition potential, scan rate, pH and other variables, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. In both cases a voltammetric peak is obtained, at –0.542 V (DPV) and –0.421 V (SWV) in Britton-Robinson buffer (pH 1.9). The detection limits were 3.66 × 10^–1 M and 4.22 × 10^–9 M for AdS-DPV and AdS-SWV, respectively. Under optimum conditions the Metamitron reduction peak gave two linear regions in the range from 4.0 × 10^–9 M to 8.0 × 10^–8 M by means of AdS-DPV, with a coefficient of variation of 2.19% (n = 10) for 1 × 10^–8 M herbicide solution. A method was developed for determination of Metamitron in soils, with a recovery of 98.8% and a coefficient of variation of 5.26% (0.01 g/g of soil).     

Sample pre-treatment methods for the trace elements determination in seafood products by atomic absorption spectrometry

Different sample pre-treatments for seafood products have been compared with determine trace elements (As, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn) by flame atomic absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAAS). Classic pre-treatments as microwave assisted-acid digestion and the slurry sampling technique were compared with new procedures such as microwave energy or ultrasound energy assisted-acid leaching process and enzymatic hydrolysis methodologies based on the use of pronase E. The methods were applied to DORM-1 and DOLT-1 reference materials with certified contents for the studied elements. The Student-Newman-Keuls (SNK) method was used to compare with element concentration means obtained with each sample pre-treatment and also the certified concentration means in both reference materials. Multivariate techniques such as principal components analysis (PCA) was also applied to comparative purposes.     

The biosynthesis of cyclitols

Information has recently been obtained, mainly with the aid of radioactive compounds, about the biosynthesis of various cyclitols. It was found that the most widely occurring cyclitol, meso-inositol, is biosynthesized by a pathway probably common to all organisms, in which the cyclohexane ring is formed by ring closure between the two terminal carbon atoms of D -glucose. Cell-free extracts or enzyme systems that catalyse the conversion of D -glucose into meso-inositol can be prepared from various biological materials. The biosynthesis of the other hexahydroxycyclohexanes (inositols) involves meso-inositol as an intermediate. A few steps in the conversion of meso-inositol into other inositols have been studied.     

Selenium speciation in cow milk obtained after supplementation with different selenium forms to the cow feed using liquid chromatography coupled with hydride generation-atomic fluorescence spectrometry

The purpose of this paper is to develop an easy and quick on-line selenium speciation method (LC-UV-HG-AFS) in cow milk obtained after different supplementation to cow feed. This study focuses on selenium speciation in cow milk after the use of different selenium species (organic selenium as selenised yeast and inorganic selenium as sodium selenite) in the supplementation of forages. Separation was carried out on a μBondapack C₁₈ column with the positively charged ion-pairing agent tetraethylammonium chloride in the mobile phase. The optimization of pre-reduction conditions was carried out; this step was done with UV irradiation and a heating block to improve the reduction of the different Se-compounds. Variables such as exposure time, hydrochloric acid concentration and temperature were studied. The detection limits for SeCyst₂, Se(IV), SeMet and Se(VI) were 0.4, 0.5, 0.9 and 1.0 μg l⁻¹, respectively. The proposed method was applied to cow milk samples. The milk samples obtained after an organic supplementation of feeding as selenised yeast present three species of selenium, SeCyst2, Se(IV) and SeMet, while only SeCyst2 and Se(IV) are present in milk samples obtained after an inorganic supplementation of feeding.     

New hypoxia-selective cytotoxines derived from quinoxaline 1,4-dioxides

A new series of quinoxaline 1,4-dioxides, structurally related to the benzotriazine tirapazamine 1 have been prepared starting from 5,6-dichlorobenzofuroxane 2 . The Beirut reaction between 2 and alkyl or aryl thiopropanones afforded the 2-methyl-3-alkyl(aryl)thioquinoxaline 1,4-dioxides 3a-3e . Selective oxidation of 3 with m-chloroperbenzoic acid yielded the sulphinyl 4a-4c and sulphonyl 5a-5b derivatives. Replacement of the sulphonyl group of 5a by chlorine or bromine gave 6 or 7 , while nucleophilic displacement by 3-(N,N-dimethylamino)propylamine afforded 8 . A dimer 9 was prepared from 5a and hydrazine hydrate. The methylthio group of 3a was replaced by using formamidine acetate giving the amino compound 10 . Bromination of the methyl group of 3b afforded 11 , which reacted with 2-aminoethanol giving 12 . Compounds were tested as cytotoxic agents both in oxic and in hypoxic cells.