Synthesis and ion sensing properties of new colorimetric and fluorimetric chemosensors based on bithienyl-imidazo-anthraquinone chromophores

Novel colorimetric receptors for fluoride ion sensing containing anthraquinone as a chromogenic signaling unit and imidazo-2,2'-bithiophene binding sites are reported. Well-defined color change was observed upon addition of fluoride ions to acetonitrile solutions of receptors 2. Compounds 2a-c, deprotonated after fluoride ion addition, were studied as metal ion chemosensors in the presence of Zn(II), Hg(II), and Cu(II) in acetonitrile solutions, especially compound 2a which displayed a marked change from pink to yellow-gold colors upon complexation.     

Spectral and photophysical characterization of donor-pi-acceptor arylthienyl- and bithienyl-benzothiazole derivatives in solution and solid state

A comprehensive study has been made in solution at room temperature (293 K), low temperature (77 K), and in thin films (Zeonex matrixes) of the spectral and photophysical properties of six arylthienyl- and bithienyl-benzothiazole derivatives functionalized with different donor groups. Similar experiments have been carried out with two related precursors (containing the arylthienyl and aryl-bithienyl conjugated systems), and results are compared. Singlet-singlet and triplet-triplet absorption spectra, emission spectra together with lifetimes and quantum yields have been obtained, and from these data the rates for all the radiative and nonradiative processes determined, providing information on the dominant decay processes. The arylthienyl-benzothiazole derivatives show high fluorescence quantum yields (phi(F)) with negligible internal conversion (phi(IC)), whereas the bithienyl-benzothiazoles display lower but still significant phi(F) values, but now radiationless processes (phi(IC) and phi(ISC)) are competitive. A comparison with the analogous oligothiophenes is made. Singlet oxygen yields were also determined and the triplet energy transfer to (3)O2 to produce (1)O2 was found to be highly efficient with values of S(Delta)(= phi(Delta)/phi(T)) varying from 0.4 to 1.     

Boron nitride nanotubes as templates for half-metal nanowires

We investigate by means of a GGA + U implementation of density functional theory the electronic and structural properties of magnetic nanotubes composed of an iron oxide monolayer and (n,0) boron nitride (BN) nanotubes, with n ranging from 6 to 14. The formation energy per FeO molecule of FeO covered tubes is smaller than the formation energy of small FeO nanoparticles, which suggests that the FeO molecules may cover the BN nanotubes rather than aggregating locally. Both GGA (PBE) and Van der Waals functionals predict an optimal FeO-BN interlayer distance of 2.94 ?. Depending on the diameter of the tube, novel electronic properties for the FeO covered BN nanotubes were found. They can be semiconductors, intrinsic half-metals or semi-half-metals that can become half-metals if charged with either electrons or holes. Such results are important in the spintronics context.     

[13C]Dynamic NMR and Molecular Modeling of 2,4-Bis(N-Pyrrolidinyl)-6-chloro-s-triazine

The room temperature [¹³C]NMR spectrum of 2,4-bis(N-pyrrolidinyl)-6-chloro-s-triazine shows doubled signals for the pyrrolidine rings, which suggests restricted rotation about the Ar-C—N bond. The rotational barrier around this bond was determined by [¹³C]dynamic NMR (DNMR) spectra run at different increasing temperatures and also by the PM3 Hamiltonian contained in the MOPAC package. The values thus obtained, 16.6 and 13.6 kcal mol^–1, respectively, are in good agreement.     

Vegetable proteins and milk puddings

In recent years, interest in animal free foods has increased tremendously due to factors like BSE crisis, rise of nutritionally dependent illnesses, like diabetes type II, cardiovascular and digestive diseases, along with ethic orientations of denying animal intakes of any kind. The use of proteins from leguminous seeds as an alternative to the animal proteins in dairy desserts was studied. Lupin, pea and soya protein isolates were used in combination with κ-carrageenan, gellan and xanthan gum, in order to obtain a synergistic effect. Milk puddings were also produced for comparison. Texture studies suggested that mixed protein–polysaccharide systems, with vegetable proteins and κ-carrageenan or gellan gum, would be good systems to develop vegetable gelled desserts. Rheological oscillatory measurements were carried out to clarify the kinetics of gelation and characterise the microstructure of the best performing products. Results from time sweep tests showed that formulations with gellan gum present an industrial advantage over formulations with κ-carrageenan, since the maturation time for gellan gels is of the order of 5–10 h compared with 4–6 days in the case of κ-carrageenan. All the mixed gels presented the typical weak gel structure; therefore, it was possible to perform steady-state measurements, which allowed the observation of a shear-thinning behaviour for all gels.     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Fractionation of Protein Hydrolysates of Fish and Chicken Using Membrane Ultrafiltration: Investigation of Antioxidant Activity

In this work, chicken and fish peptides were obtained using the proteolytic enzymes α-Chymotrypsin and Flavourzyme. The muscle was hydrolyzed for 4 h, and the resulting peptides were evaluated. Hydrolysates were produced from Argentine croaker (Umbrina canosai) with a degree of hydrolysis (DH) of 25.9 and 27.6 % and from chicken (Gallus domesticus) with DH of 17.8 and 20.6 % for Flavourzyme and α-Chymotrypsin, respectively. Membrane ultrafiltration was used to separate fish and chicken hydrolysates from Flavourzyme and α-Chymotrypsin based on molecular weight cutoff of >1,000, <1,000 and >500, and <500 Da, to produce fractions (F1,000, F1,000–500, and F500) with antioxidant activity. Fish hydrolysates produced with Flavourzyme (FHF) and α-Chymotrypsin showed 60.8 and 50.9 % of peptides with a molecular weight of <3 kDa in its composition, respectively. To chicken hydrolysates produced with Flavourzyme and α-Chymotrypsin (CHC) was observed 83 and 92.4 % of peptides with a molecular weight of <3 kDa. The fraction that showed, in general, higher antioxidant potential was F1,000 from FHF. When added 40 mg/mL of FHF and CHC, 93 and 80 % of lipid oxidation in ground beef homogenates was inhibited, respectively. The composition of amino acids indicated higher amino acids hydrophobic content and amino acids containing sulfuric residues for FHF, which showed antioxidant potential.     

Simultaneous determination of Cd, Cu, Mn, Ni, Pb and Zn in nail samples by inductively coupled plasma mass spectrometry (ICP-MS) after tetramethylammonium hydroxide solubilization at room temperature: comparison with ETAAS

A simple method is described for the determination of Cd, Cu, Mn, Ni, Pb and Zn in nails by using inductively coupled plasma mass spectrometry (ICP-MS) or electrothermal atomic absorption spectrometry (ETAAS). Prior to analysis, 10-20 mg of nail samples were accurately weighed into (15 mL) conical tubes. Then, 1 mL of 25% (w/v) tetramethylammonium hydroxide (TMAH) solution was added to the samples, incubated at room temperature overnight and then further diluted to 10 mL with 1% (v/v) HNO(3). After that, samples were directly analyzed. Rhodium was used as internal standard for ICP-MS analysis. Method detection limits (3 s, n=20) were 0.1, 3.0, 1.0, 4.5, 1.5, 5.0 ng g(-1) for Cd, Cu, Mn, Ni, Pb and Zn, respectively for ICP-MS, and 24, 26, 30, 143, 130 and 1000 ng g(-1), respectively for ETAAS. The key issue addressed here is the elimination of the acid digestion prior to analysis. Moreover, with the use of the proposed method there is a considerable improvement in the sample throughput comparing to the traditional methods using microwave-assisted acid sample digestion prior to analysis. For validation purposes, six ordinary nail samples were solubilized and then directly analyzed by ICP-MS and ETAAS, with no statistical difference between the two techniques at 95% level on applying the t-test.