Minimum dissipative relaxed states in toroidal plasmas

Relaxation of toroidal discharges is described by the principle of minimum energy dissipation together with the constraint of conserved global helicity. The resulting Euler-Lagrange equation is solved in toroidal coordinates for an axisymmetric torus by expressing the solutions in terms of Chandrasekhar-Kendall (C-K) eigenfunctions analytically continued in the complex domain. The C-K eigenfunctions are obtained as hypergeometric functions that are solutions of scalar Helmholtz equation in toroidal coordinates in the large aspect-ratio approximation. Equilibria are constructed by assuming the current to vanish at the edge of plasma. For the m=0, n=0 (m and n are the poloidal and toroidal mode numbers respectively) relaxed states, the magnetic field, current, q (safety factor) and pressure profiles are calculated for a given value of aspect-ratio of the torus and for different values of the eigenvalue λ _{r 0}. The new feature of the present model is that solutions allow for both tokamak as well as RFP-like behaviour with increase in the values of λ _{r 0}, which is related directly to volt-sec in the experiment.     

Sequential and simultaneous determination of bromate and chlorite (DBPs) by flow techniques: kinetic differentiation

3-3′-Dimethoxybenzidine (o-dianisidine, ODA) is oxidised by Br₂, among other oxidants, generating a compound that absorbs at 450 nm, while the non-oxidised reagent absorbs in the UV region. This reaction has been used previously as the basis of a continuous-flow method for the determination of bromate in ozonised water, with a detection limit lower than the maximum permitted for drinking water (10 μg L⁻¹). The only interference observed in the method was that due to the chlorite ion (ClO₂⁻), which generated the same ODA bromation product. Thus, in systems in which O₃ is employed as a disinfectant and disinfection is later enhanced with ClO⁻ and ClO₂, there exists the possibility of finding BrO₃⁻ and ClO₂⁻, oxoanions generated as subproducts. The kinetic behaviour of the reaction between bromate and chlorite with bromine in acidic medium is different, allowing the proposal of a continuous-flow method for the simultaneous or sequential determination of both subproducts in water purification systems. None of the other subproducts interfered in the reaction. Kinetic differentiation was achieved by combining the temperature of the reaction and the length of the coils, after which it was possible to determine both analytes sequentially within a concentration range of 6–160 μg L⁻¹.     

Metal-sensitive and thermostable trypsin from the crevalle jack (<Emphasis Type="Italic">Caranx hippos</Emphasis>) pyloric caeca: purification and characterization

Background

Over the past decades, the economic development and world population growth has led to increased for food demand. Increasing the fish production is considered one of the alternatives to meet the increased food demand, but the processing of fish leads to by-products such as skin, bones and viscera, a source of environmental contamination. Fish viscera have been reported as an important source of digestive proteases with interesting characteristics for biotechnological processes. Thus, the aim of this study was to purify and to characterize a trypsin from the processing by-products of crevalle jack (Caranx hippos) fish.

Results

A 27.5 kDa trypsin with N-terminal amino acid sequence IVGGFECTPHVFAYQ was easily purified from the pyloric caeca of the crevalle jack. Its physicochemical and kinetic properties were evaluated using N-α-benzoyl-_DL-arginine-p-nitroanilide (BApNA) as substrate. In addition, the effects of various metal ions and specific protease inhibitors on trypsin activity were determined. Optimum pH and temperature were 8.0 and 50°C, respectively. After incubation at 50°C for 30 min the enzyme lost only 20% of its activity. K _m , k_cat, and k _cat /K _m values using BApNA as substrate were 0.689 mM, 6.9 s^-1, and 10 s^-1 mM^-1, respectively. High inhibition of trypsin activity was observed after incubation with Cd²⁺, Al³⁺, Zn²⁺, Cu²⁺, Pb²⁺, and Hg²⁺ at 1 mM, revealing high sensitivity of the enzyme to metal ions.

Conclusions

Extraction of a thermostable trypsin from by-products of the fishery industry confirms the potential of these materials as an alternative source of these biomolecules. Furthermore, the results suggest that this trypsin-like enzyme presents interesting biotechnological properties for industrial applications.

     

An efficient method for the N-arylation of phenylurea via copper catalyzed amidation

The coupling reaction of phenylurea with different functionalized aryl halides in the presence of air stable CuI,N,N-dimethylethylenediamine as a ligand,and K₃PO₄ as a base gives symmetrical and unsymmetrical diarylureas in relatively high yields.This method is milder than the palladium catalyzed arylation and avoids the use of toxic phosphine ligands.     

Online Monitoring of Bromate in Ozonized Water Without a Previous Separation Process

The use of ozonation for the purification of drinking water can lead to the formation of bromate. The US Environmental Protection Agency and the European Directive for human drinking water has lowered the regulatory level for bromate down to 10 μg l⁻¹, such that methods must be developed for monitoring the formation of bromate, particularly in on-site situations. In the present work we report a fluorometric method for the determination of bromate based on the reaction with carbostyril-124, a compound that shows florescence mainly at pH values above 4 and, when bromated, generates a non-fluorescent product. The reaction can thus be used as an indirect method for determination of the ion. The proposed method, which uses the flow injection (FI) technique, allows online application and kinetic control of the variables affecting the process, together with shorter reaction times, and it provides maximum sensitivity and selectivity. Under optimum conditions, it is possible to determine the analyte within the 4–200 μg l⁻¹ range, with a limit of detection of 0.9 μg l⁻¹ and a relative standard deviation (n = 12, [] = 5 and 30 μg l⁻¹) of 3.2% and 2.6% respectively. The determination rate was ten samples per hour.