Nonlinear Schrödinger equations with symmetric multi-polar potentials

This paper deals with a class of nonlinear elliptic equations involving a critical power-nonlinearity as well as a potential featuring multiple inverse square singularities. When the poles form a symmetric structure, it is natural we wonder how the symmetry affects such mutual interaction. The present paper means to study this aspect from the point of view of the existence of solutions inheriting the same symmetry properties as the set of singularities. Mathematics Subject Classification (2000) 35J60, 35J20, 35B33     

Laser properties of coactivated YAP: Nd free of colour centres

YAP:Nd, Cr grown under Ar-H₂ or Ar-He-H₂ atmosphere possesses good energy transfer from Cr³⁺ to Nd³⁺ but suffers from the colour centre formation. The centre formation was completely prevented using further admixture of Ce³⁺ and 10^–4–10^–3 wt. % Fe. Small luminescence quenching of Cr³⁺ or Nd³⁺ due to iron ions is negligible in the presence of Ce³⁺. The crystals may be also heavily doped with Nd³⁺ because the increased pumping efficiency compensates the shortening of the luminescence lifetime. YAP: Nd, Ce, Cr, Fe is advisible active laser material particularly for all the types of pulsed lasers.     

Structure and dynamics of the hydrogen-bond network around (R,R)-pterocarpans with biological activity in aqueous solution

Molecular dynamics simulations were carried out in the presence of 2380 water molecules (TIP3P) to explore the conformational preferences of 3,9-dimethoxy-4-prenylpterocarpan (bitucarpin A) and 3,9-dihydroxy-4,8-diprenylpterocarpan (erybraedin C) and the H-bond network around them, using the empirical general AMBER force field (GAFF). Specific angle and torsional parameters have been improved in order to match the geometries of the minimum energy structures obtained from an earlier DFT/ab initio study in vacuo, taking into account a few configurations [Alagona, G.; Ghio, C.; Monti, S. Phys. Chem. Chem. Phys. 2004, 6, 2849-2857]. RESP partial charges were assigned to reproduce the electrostatic potential determined at the HF/6-31G level of theory. The analysis of trajectories allowed the conformations of bitucarpin and erybraedin as well as the distribution of water molecules around them to be elucidated. During one of the simulations only, the scaffold of erybraedin undergoes interconversion from its most stable Ht conformation to the Ot one and vice versa. Radial distribution functions, coordination numbers, and angular distributions put forward the extent of solvent structure and the hydrogen bonding behavior of their various (methoxy, hydroxyl, or ethereal) oxygen atoms. The distribution of solvent molecules in the first and second solvation shells as well as the residence times for the different solute-solvent interacting sites have been considered.     

Mechanistic studies of the isomerization of peroxynitrite to nitrate catalyzed by distal histidine metmyoglobin mutants

Hemoproteins are known to react with the strong nitrating and oxidizing agent peroxynitrite according to different mechanisms. In this article, we show that the iron(iii) forms of the sperm whale myoglobin (sw Mb) mutants H64A, H64D, H64L, F43W/H64L, and H64Y/H93G catalyze the isomerization of peroxynitrite to nitrate. The two most efficient catalysts are H64A (k(cat) = (5.8 +/- 0.1) x 10(6) M(-1) s(-1), at pH 7.5 and 20 degrees C) and H64D metMb (k(cat) = (4.8 +/- 0.1) x 10(6) M(-1) s(-1), at pH 7.5 and 20 degrees C). The pH dependence of the values of k(cat) shows that HOONO is the species which reacts with the heme. In the presence of physiologically relevant concentrations of CO(2) (1.2 mM), the decay of peroxynitrite is accelerated by these metMb mutants via the concurring reaction of HOONO with their iron(iii) centers. Studies in the presence of free added tyrosine show that the metMb mutants prevent peroxynitrite-mediated nitration. The efficiency of the different sw metMb mutants correlates with the value of k(cat). Finally, we show that sw WT-metMb is nitrated to a larger extent than horse heart metMb, a result that suggests that the additional Tyr151 is a site of preferential nitration. Again, the extent of nitration of the tyrosine residues of the metMb mutants correlates with the values of k(cat).     

Coated-wire organic ion-selective electrodes in titrations based on ion-pair formation : Determination of arenediazonium salts with sodium tetraphenylborate

Titrimetric determinations of arenediazonium salts can be based on ion-pair formation between the diazonium cation and tetraphenylborate. Titrations are done under cooling with ice and are followed potentiometrically with organic ion-selective electrodes comprising PVC membranes plasticized with polar solvents and coated on aluminium wires. The method was tested in determinations of arenediazonium salts derived from 20 aromatic amines, including aniline, toluidines, naphthylamines and their derivatives. Except for compounds containing hydrophylic groups such as —COOH and —OH, the potentiometric titration curves have well defined end-points. The results are reproducible, with relative standard deviations in the range 0.4–1.4% at the millimolar level. The method can be used for reliable determinations of arenediazonium salts in analytical control of azo dyestuff production.     

α-Hydroxyalkylation of heteroaromatic bases by alcohols and hydroxylamine-O-sulphonic acid

The homolytic decomposition of hydroxylamine-O-sulphonic acid in alcoholic solvents was investigated in the presence or absence of protonated heteroaromatic bases and Fe(II) salt. The addition of the α-hydroxyalkyl radicals to the base and their oxidation by Fe(III) salt to the corresponding alkyl cyanide were competitive processes. A redox chain process involving the amino radical cation, NH₃^t., is suggested and the factors affecting the yields of the homolytic substitution are discussed.     

Determination of phosphate/arsenate by a modified molybdenum blue method and reduction of arsenate by S2O4

A modified molybdenum blue method for fast and accurate measurement of arsenate and phosphate in aqueous solution at concentrations below 10 μmol l⁻¹ is reported. The modification consists of optimizing the composition of the molybdenum-containing solution (potassium antimony tartrate, ammonium molybdate, sulfuric acid).Selective reduction of arsenate by sodium dithionite is used to determine phosphate concentrations, and for the speciation of arsenate and arsenite, in an aqueous mixture according to the scheme developed by Johnston and Pilson. Sodium dithionite is used for the first time to achieve complete, fast (<10 min), and selective reduction of arsenate in neutral solution.These two significant improvements afforded a colorimetric limit for As detection near 1 ppb, which easily meets the requirements imposed by the revised EPA threshold levels for As in drinking water.