Mono- and diboronates derived from tridentate ONO ligands and arylboronic acids

The syntheses of eight [4.3.0] heterobicyclic boronates containing a N → B coordinative bond are described. The monomeric compounds were prepared by reaction of arylboronic acids with a tridentate ligand having the ONO donor set of atoms. It was shown that substituents at the para-position of the B-phenyl moiety transmit electronic effects to the CN bond which in turn is polarized by formation of the N → B coordination bond. At the same time, related tridentate ligands were also reacted with 1,4-benzenediboronic acid in order to prepare benzene diboron complexes. The structure of this type of compounds was confirmed by X-ray analysis for one of the derivatives.     

Construction of Rank 2 Semistable Torsion Free Sheaves Which Are Not Limit of Vector Bundles

We show the following theorem of compensated compactness type: Ifu _n ⇁u weakly in the spaceH ^1,p (Ω, ℝ ^k ) and if also in the sense of distributions then ∂_α(∣∇u∣ ^p-2∂_α u)=0. This result has applications in the partial regularity theory ofp-stationary mappings Ω→S ^k −1.     

Derivatization procedures for the detection of beta(2)-agonists by gas chromatographic/mass spectrometric analysis

An evaluation of derivatization procedures for the detection of beta(2)-agonists is presented. The study was performed with the beta(2)-agonists bambuterol, clenbuterol, fenoterol, formoterol, salbutamol, salmeterol and terbutaline. Different derivatizating agents were employed, aiming to obtain derivatives with high selectivity to be used in the gas chromatographic/mass spectrometric analysis of beta(2)-agonists in biological samples. Trimethylsilylation was compared with different agents and the role of some catalysts was evaluated. Acylation, combined trimethylsilylation and acylation, and the formation of cyclic methylboronates were also studied. Sterical hindrance caused by different substituents at the nitrogen atom of the beta-ethanolamine lateral chain of beta(2)-agonist molecules is mainly responsible for differences in the abundances of the derivatives obtained. The use of catalysts produces an increase in the derivatization yield, especially for compounds with low steric hindrance (substituents with primary and secondary carbon atoms). The formation of trimethylsilyl (TMS) ethers is not influenced by structural molecular differences when only hydroxy groups are involved in derivatization. Combined trimethylsilylation and acylation showed that compounds with a secondary carbon atom linked to the nitrogen atom form mainly N-TFA-O-TMS derivatives, with a small amount of N-TMS-O-TMS derivatives. Compounds with tert-butyl substituents at the amino group (bambuterol, salbutamol and terbutaline) formed O-TMS derivatives as the main products, although a limited amount of trifluoroacylation at the nitrogen atom also occurred. Cyclic methylboronates were formed with bambuterol, clenbuterol, formoterol, salbutamol and salmeterol. Owing to hydroxy substituents in unsuitable positions for ring formation, this procedure was not effective for fenoterol and terbutaline. Mass spectra of different derivatives and tentative fragmentation profiles are also shown. For screening purpose (e.g. sports drug testing), derivatization with MSTFA or BSTFA alone is recommended as a comprehensive derivatization technique for beta(2)-agonists owing to minimal by-product formation; formation of cyclic methylboronates can be useful for confirmation purposes. Detection limits were obtained for the TMS and cyclic methylboronate derivatives using the derivatizing reagents MSTFA and trimethylboroxine, respectively. For most of the compounds, lower detection limits were found for the TMS derivatives.     

A density functional theory study on the electrocyclization of 1,2,4,6-heptatetraene analogues: converting a pericyclic to a pseudopericyclic reaction

A comprehensive B3LYP/6-31+G* study on the electrocyclization of 1,2,4,6-heptatetraene analogues was conducted. Starting from the cyclization of (2Z)-2,4,5-hexatrienal, a pericyclic disrotatory process favored by the assistance of a electron lone pair, we incorporated small modifications in its molecular structure to obtain a truly pseudopericyclic process. To this purpose electronegative atoms (fluorine and nitrogen) were added to give a more electrophilic character on the carbon atom which is attacked by the electron lone pair of the oxygen atom. The complete pathway for each reaction was determined, and changes in magnetic properties were monitored with a view to estimating the aromatization associated with each process. This information, together with the energetic and structural results, allowed us to classify the reactions as pseudopericyclic or pericyclic. Among all studied reactions only one was a truly pseudopericyclic process and another was a borderline case. The features of this unequivocally pseudopericyclic case were analyzed in depth.     

Purification of human leucocyte pyruvate kinase

The M2 form of pyruvate kinase (M2-PK) was purified from human leucocytes by a new method involving a succession of two different Dyematrex agarose chromatographies. The main step consisted of an orange dye affinity column with elution by fructose-1,6-diphosphate. This purification procedure allowed us to obtain M2-PK with a specific activity of 433 I.U./mg of protein, i.e. a 188-fold purification with an overall yield of 33%. The homogeneity of this preparation was verified by sodium dodecyl sulphate polyacrylamide gel electrophoresis and double immunodiffusion in Ouchterlony plates. Anti-M2-PK antibodies obtained from rabbit neutralized the enzyme activity. Their specificity with regard to other types of PK showed that anti-M2-PK also reacted with M1-PK but not with R-PK.     

Water adsorption on and desorption from crystalline copolymers of vinylidene fluoride with trifluoroethylene

Water adsorption and absorption on crystalline polyvinylidene fluoride with 30% trifluoroethylene, P(VDF-TrFE, 70:30), was examined by thermal desorption spectroscopy. Two distinctly different water adsorption sites are identified: one adsorbed species that resembles ice and another species that interacts more strongly with the polymer thin film. The existence of the latter species is consistent with X-ray diffraction studies of water absorbed into the bulk of copolymers of polyvinylidene fluoride with trifluoroethylene crystalline thin films. There are strong steric effects observed in the angle-resolved thermal desorption that may be a result of the large polymer thin film surface dipoles.     

Coffee Chlorogenic Acids Incorporation for Bioactivity Enhancement of Foods: A Review

The demand of foods with high antioxidant capacity have increased and research on these foods continues to grow. This review is focused on chlorogenic acids (CGAs) from green coffee, which is the most abundant source. The main CGA in coffee is 5-O-caffeoylquinic acid (5-CQA). Coffee extracts are currently the most widely used source to enhance the antioxidant activity of foods. Due to the solubility of CGAs, their extraction is mainly performed with organic solvents. CGAs have been associated with health benefits, such as antioxidant, antiviral, antibacterial, anticancer, and anti-inflammatory activity, and others that reduce the risk of cardiovascular diseases, type 2 diabetes, and Alzheimer’s disease. However, the biological activities depend on the stability of CGAs, which are sensitive to pH, temperature, and light. The anti-inflammatory activity of 5-CQA is attributed to reducing the proinflammatory activity of cytokines. 5-CQA can negatively affect colon microbiota. An increase in anthocyanins and antioxidant activity was observed when CGAs extracts were added to different food matrices such as dairy products, coffee drinks, chocolate, and bakery products. The fortification of foods with coffee CGAs has the potential to improve the functionality of foods.     

Effect of Biodegradable Coatings on the Growth of Aspergillus flavus In Vitro,on Maize Grains,and on the Quality of Tortillas during Storage

The fungus Aspergillus flavus causes serious damage to maize grains and its by-products, such as tortilla. Currently, animal and plant derivatives, such as chitosan and propolis, and plant extract residues, respectively, are employed as alternatives of synthetic fungicides. The objective of this research was to evaluate the efficacy of several formulations based on propolis-chitosan-pine resin extract on the in vitro growth of A. flavus, the growth of maize grain plantlets and the quality of stored tortillas at 4 and 28 °C. The most outstanding formulation was that based on 59.7% chitosan + 20% propolis nanoparticles + 20% pine resin extract nanoparticles; since the in vitro conidia germination of A. flavus did not occur, disease incidence on grains was 25–30% and in tortillas, 0% infection was recorded, along with low aflatoxin production (1.0 ppb). The grain germination and seedling growth were markedly reduced by the nanocoating application. The percentage weight loss and color of tortillas were more affected by this coating compared to the control, and the rollability fell within the scale of non-ruptured at 4 °C and partially ruptured at 28 °C. The next step is to evaluate the toxicity of this formulation.