Screening ofBothrops snake venoms forl-amino acid oxidase activity

Applied Biochemistry and Biotechnology - Toxins, enzymes, and biologically active peptides are the main components of snake venoms from the genusBothrops. Following the venom inoculation, the local...     

Enzymatic-spectrophotometric determination of sucrose in coffee beans

A spectrophotometric method for determining sucrose is proposed. Sucrose is hydrolyzed by invertase into glucose and fructose. Then, glucose is oxidized in presence of glucose oxidase and the produced hydrogen peroxide reacts with phenol-4-sulfonic acid sodium salt and 4-aminoantipyrine in presence of peroxidase, yielding a pink dye with an absorption maximum at 505 nm. This method was validated following the EURACHEM and VAM project guidelines for method validation. Trueness, precision, robustness, sensitivity and linearity were considered. The method was applied to the determination of sucrose in green and roasted coffee beans. A comparison with the HPLC method with pulsed amperometric detection was carried out.     

Synthesis of highly branched sulfur-nitrogen heterocycles by cascade cycloadditions of [1,2]dithiolo[1,4]thiazines and [1,2]dithiolopyrroles

We report the synthesis of some new polysulfur-nitrogen heterocycles by cascade cycloadditions to readily available polycyclic 1,2-dithiole-3-thiones. Thus, treatment of bis[1,2]dithiolopyrrole dithione 1 with dimethyl acetylenedicarboxylate (DMAD) or dibenzoylacetylene (DBA) gave the 1:4 adducts 2a,b and 3a. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine dithiones 4a-d with the same dipolarophiles gave the 1:2, 1:3, or 1:4 adducts 5a-c, 6a, 7a, 8a, 9a, and 10a,c,d selectively in fair to high yields. Reaction conditions were crucial for achievement of selectivity in thermal reactions. Catalysis by scandium triflate was used in the reaction of 4a and 2 equiv of DMAD. Treatment of the [1,2]dithiolo[1,4]thiazine dithione 11 with DBA gave the 1:2, 1:3 (two isomers), and 1:4 adducts 12-14 and 15a-d selectively. Cyclic voltammetry of selected examples showed irreversible processes that were not influenced by peripheral groups bonded to the heterocyclic system.     

Evaluation of a carbon paste electrode modified with organofunctionalized amorphous silica in the cadmium determination in a differential pulse anodic stripping voltammetric procedure

The determination of cadmium using a carbon paste electrode modified with organofunctionalized amorphous silica with 2-benzothiazolethiol was investigated. The Cd(II) oxidation peak was observed around −0.80 V (vs. SCE) in phosphate buffer (pH 4.0) in differential pulse anodic stripping voltammetry. The best results were obtained under the following optimized conditions: 1 min accumulation time, 50 mV pulse amplitude, 20 mV s⁻¹ scan rate in phosphate buffer pH 4.0. Using such parameters a linear dynamic range from 5.6×10⁻⁷ to 3.5×10⁻⁵ mol l⁻¹ Cd(II) was observed with a sensitivity of 2.83 μA mol⁻¹ l, limit of detection 1.0×10⁻⁷ mol l⁻¹. Cd(II) spiked in a natural water sample was determined with 99% mean recovery at 10⁻⁷ mol l⁻¹ level. Interference were also evaluated.     

Mass spectrometry on-line monitoring and MS2 product characterization of TiO2/UV photocatalytic degradation of chlorinated volatile organic compounds

On-line Mass Spectrometry and MS² are applied to monitor and identify the by-products and total mineralization products of TiO₂/UV photocatalytic degradation of four chlorinated volatile organic compounds (VOCs): trichloroethylene (TCE), tetrachloroethylene (TeCE), chloroform, and dichloromethane. Selected multiple ion mass spectrometry monitoring using characteristic 70 eV electron ionization ionic fragments monitors in real time the destruction of the starting VOC and the formation of by-products, i.e., the degrees of VOC mineralization, as a function of the flow and relative humidity of the carrier gas (synthetic air). Several by-products were detected: phosgene for TCE, TeCE, and chloroform; dichloroacetyl chloride for TCE; and trichloroacetyl chloride for TeCE. Cl₂ and CO₂ were also detected as final mineralization products of the four chlorinated VOCs. Structural characterization of by-products was accomplished via MS² collision-induced dissociation of molecular ions or characteristic ionic fragments.     

Complete assignment of 1H and 13C NMR data for three aryltetralin lignan lactones

We describe the complete 1H and 13C NMR analysis of three aryltetralin lignan lactones (polygamain, morelensin and 4,5-dimethoxymorelensin) using modern NMR techniques such as COSY, HMQC, HMBC, 2D-J-resolved and NOE experiments. The relative stereochemistry of these compounds, which is very important with regard to their biological activity, was completely determined.     

Thermal analysis applied in the osmotic tablets pre-formulation studies

Osmotically controlled and oral drug delivery systems utilize osmotic pressure for controlled delivery of active agent(s). Drug delivery from these systems, to a large extent, is independent of the physiological factors of the gastrointestinal tract and these systems can be utilized for systemic as well as targeted delivery of drugs. We apply the thermal methods and IR spectroscopy to study compatibility between atenolol and several excipients usually found in the osmotic systems formulations (Polyethylene oxide, MW 3350, 100000, 200000 and 5000000; HPMC K4000, magnesium stearate and cellulose acetate. Cellulose acetate, HPMC K4000 and magnesium stearate have essentially no interaction with atenolol otherwise all Polyethylene oxide excipients modifies significantly the drug melting point indicating some extend of interaction.     

The size exclusion chromatography calibration of ‘Mixed-A’ and ‘Mixed-D’ columns using various polymers and compounds: An application to coal-derived materials

This work attempts to obtain the calibration curves of two different size exclusion chromatography (SEC) columns operating with 1-methyl-2-pyrrolidinone (NMP) as eluent by using various standards. Polystyrene (PS) and polymethylmethacrylate (PMMA) standards were used for obtaining calibration curves, and checked against polysaccharide (PSAC) standards, some small aromatic polycyclic standards and miscellaneous polymers. Polystyrenes and polymethylmethacrylates gave identical calibrations while polysaccharides and miscellaneous polymers lay within 1 or 2 min of the polystyrene calibration. Small molecules of mass less than 1000 units lay on or near to the polystyrene calibration lines, with a shift to late elution for the smallest molecules. This shift may be caused by the interaction with the column packing. A sample has been examined by analytical size exclusion chromatography, which was calibrated using polystyrene and polymethylmethacrylate standards. Molecular mass (MM) distributions of the sample have been examined in terms of these calibrations.     

Reactions of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone: A convenient route to trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides

A new series of six 3-aryl-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides were synthesised in one-step in high yields by the reaction of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone in the presence of hydrochloric acid. The hydrochloride salts were easily converted to the respective new series of free trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazoles using triethylamine in anhydrous diethyl ether. X-ray structure and NMR data from the pyrazole hydrochlorides are reported.     

A molecular dynamics study on Rh3+ hydration: development and application of a first principles hydrated ion–water interaction potential

The Rh³⁺ aquaion exhibits one of the largest residence times of water molecules in the first hydration shell. The extreme stability of this hexahydrated ion in water solutions makes Rh³⁺ an extremely suitable candidate to be studied using the hydrated ion model. According to this approach, the representative cationic entity in aqueous solution is the ion plus its first hydration shell (i.e. the hydrated ion) and not the bare ion. Our group has successfully applied that concept in the framework of classical statistical simulations based on first principles ion–water interaction potentials. The methodology is now applied to the [Rh(H₂O)₆]³⁺ case based on a previous generalization in which some of the contributions were found to be transferable among the cases already studied (Cr³⁺, Al³⁺, Mg²⁺, Be²⁺). In this contribution a flexible hydrate model is presented, in which rigid first-shell water molecules have rotational and translational degrees of freedom, allowing for internal dynamics of the hydrated ion entity. The potential presented is thoroughly tested by means of a set of molecular dynamics simulations. Structural, dynamical, energetic and spectroscopic information is retrieved from the simulations, allowing the estimation of properties such as ion hydration energy, vibrational spectra of the intermolecular modes, cation mobility, rotational dynamics of the hydrated ion and first-shell water molecules and residence times of the second-shell water molecules. Extension of the Ewald sum to terms r^–4, r^–6 and r^–7 is presented and applied to systems of different size ([Rh(H₂O)₆]³⁺+(n–6)H₂O, n=50, 100, 200, 500, 1000 and 2500) and cutoff radii.Contribution to the Jacopo Tomasi Honorary Issue