Diterpenes from the Brown Alga Dictyota crenulata

The crude extract of the Brazilian brown alga Dictyota crenulata was analyzed by NMR spectroscopy and HRGC-MS techniques. Seven diterpenes were identified: pachydictyol A, dictyodial, 4beta-hydroxydictyodial A, 4beta-acetoxydictyodial A, isopachydictyol A, dictyol C and dictyotadiol. Xeniane diterpenes have previously been found in D. crenulata from the Pacific Ocean. The results characterize D. crenulata as a species that provides prenylated guaiane (group I) and xeniane diterpenes (group III), thus making it a new source of potential antiviral products.     

Isotachophoretic determination of hydrosulfite and metabisulfite in technical samples

A method for determination of metabisulfite and hydrosulfite in poultice and decolorant by isotachophoresis was developed. Metabisulfite and hydrosulfite are ionizable oxoanions of sulfur of similar character that can easily be oxidized to sulfates. To protect the analytes from oxidation the solid samples were dissolved in a 1% (w/v) solution of formaldehyde. Hydrosulfite and metabisulfite present in the samples were transformed by the reaction with formaldehyde to stable compounds, hydroxymethanesulfinate and hydroxymethanesulfonate that were determined isotachophoretically without any pretreatment except for sample filtering and degassing. A capillary of 0.4 mm i.d. and 100 mm effective length made of fluorinated ethylene-propylene copolymer was filled with an electrolyte system consisting of 10 mmol L⁻¹ HCl + 11 mmol L⁻¹ imidazole, 0.15% (w/v) hydroxyethylcellulose, pH 6.0 (leading electrolyte) and 5 mmol L⁻¹ benzoic acid + 6 mmol L⁻¹ imidazole, pH 6.5 (terminating electrolyte). Separation was performed at a driving current of 80 μA and for detection current was decreased to 30 μA. Using contactless conductivity detection, the calibration curves in the tested concentration range up to 2.5 mmol L⁻¹ were linear for both metabisulfite and hydrosulfite complexes. The concentration detection limits for metabisulfite and hydrosulfite were 2.9 and 3.4 μmol L⁻¹, respectively. For 1 mmol L⁻¹ concentration, values of R.S.D. (n = 6) were 2.6% for hydrosulfite and 0.8% for metabisulfite. Isotachophoretic determination took about 20 min. The elaborated isotachophoretic procedure is simple to perform, sufficiently sensitive and accurate. In addition to this, low cost of analyses makes the method an alternative procedure to methods used so far for the determination of oxoanions of sulfur.     

Solvent Mixture Optimization in the Extraction of Bioactive Compounds and Antioxidant Activities from Garlic (Allium sativum L.)

Garlic is a health promoter that has important bioactive compounds. The bioactive extraction is an important step in the analysis of constituents present in plant preparations. The purpose of this study is to optimize the extraction with the best proportion of solvents to obtain total phenolic compounds (TPC) and thiosulfinates (TS) from dried garlic powder, and evaluate the antioxidant activities of the optimized extracts. A statistical mixture simplex axial design was used to evaluate the effect of solvents (water, ethanol, and acetone), as well as mixtures of these solvents, after two ultrasound extraction cycles of 15 min. Results showed that solvent mixtures with a high portion of water and pure water were efficient for TPC and TS recovery through this extraction procedure. According to the regression model computed, the most significant solvent mixtures to obtain high TPC and TS recovery from dried garlic powder are, respectively, the binary mixture with 75% water and 25% acetone and pure water. These optimized extracts presented oxygen radical absorbance capacity. Pure water was better for total antioxidant capacity, and the binary mixture of water–acetone (75:25) was better for DPPH scavenging activity. These optimized extracts can be used for industrial and research applications.     

Effect of the carbon filler on the curing kinetics of epoxycyanate cooligomer

The influence of carbon fibre on the curing kinetics of the prepolymer based on bisphenol A cyanurate and epoxy resin has been studied using infra‐red spectroscopy. It was found that curing process of prepolymer is very complicated. It is shown that in curing the prepolymer a number of the sequential transformations of ones cycle structure into others occurs. An introduction of the carbon fiber (CF) of two types, original CF and modified CF (MCF) containing phosphate groups, affect strongly the prepolymer curing. Both CF and MCF accelerate the conversion rate of epoxy groups. In the case of cyanate groups, the former does not practically affect their conversion whereas the latter decelerates strongly this process. In the paper the influence mechanism of CF is considered.     

The layered structure of poly­[[di‐μ‐chloro‐bis­[chloro(2‐ethyl­tetrazole‐κN4)copper(II)]]‐di‐μ‐2‐ethyl­tetrazole‐κ2N1:N4]

In the polymeric title complex, [CuCl₂(C₃H₆N₄)₂]_n, there are two ligands in the asymmetric unit. The Cu atom adopts an elongated octahedral geometry, with two 2‐ethyl­tetrazole ligands [Cu—N = 2.0037 (16) and 2.0136 (16) Å] and two Cl atoms [Cu—Cl = 2.2595 (6) and 2.2796 (6) Å] in equatorial positions. A Cl atom and a symmetry‐related 2‐ethyl­tetrazole mol­ecule [Cu—Cl = 2.8845 (8) Å and Cu—N = 2.851 (2) Å] lie in the axial positions of the octahedron. One of the two 2‐­ethyltetrazole ligands of the asymmetric unit exhibits bidentate binding to two Cu atoms through two N atoms of the tetrazole ring, whereas the other ligand is coordinated in a monodentate fashion via one tetrazole N atom. The Cu‐atom octahedra form dimer entities by sharing edges with equatorial and axial Cl atoms. The dimers are linked together through the 2‐ethyl­tetrazole ligands to form one‐dimensional polymeric zigzag chains extending along the b axis. The chains are connected into infinite layers parallel to the (10) plane via the 2‐ethyl­tetrazole ligands.     

2‐Nitr­imino‐1‐nitro­imidazolidine

The mol­ecule of the title compound, C₃H₅N₅O₄, has a planar geometry. Due to the presence of a second nitro group, the lengths of the two conjugated C—N bonds are different. Nevertheless, the conjugation of the nitr­imine group spreads to the nitr­amine group. Intermolecular N—H...O bonds connect mol­ecules into dimers in the crystal structure.     

1,2‐Dinitroguanidine

The title compound, CH₃N₅O₄, is almost planar, and the conformation is fixed by two intramolecular N—H⋯O hydrogen bonds. Owing to the delocalization of π‐electron density over the whole mol­ecule, there is through‐conjugation, with the C—N, N—N and N—O bond lengths having values intermediate between those typical for the corresponding single and double bonds.     

TNT-Based condensation monomers and polymers

New aromatic diamines were obtained on the basis of available and inexpensive 2, 4, 6-trinitrotoluene (trotyl, TNT). Monomers obtained were used for the preparation of the new organo-soluble polyimides containing thiophenoxy and phenoxy side groups.