Electrochemistry of ferric ruthenocyanide (Ruthenium Purple), and its electrocatalysis for proton reduction

Electrochemistry of ferric ruthenocyanide (Ruthenium Purple, RP) was studied in acidic solutions containing a sodium salt (NaH₂PO₄ or NaCl). Two kinds of redox peaks for the Fe^III/II couple were clearly seen in a Na⁺ solution, originating from a composite structure of both Fe₄^III[Ru^II(CN)₆]₃ (insoluble) and Fe^III[Ru^II(CN)₆]⁻ (soluble). In repeated CV scans in a NaCl solution, it was found that only the couple of the redox peak assigned to the insoluble form remains unchanged under the steady state. The ratio of the insoluble form was estimated by coulometry as ca. 40% of the initial coated unit cells of the RP. Efficient electrocatalytic H₂ formation was found to take place with the aid of the RP although this electrocatalysis was dependent on the type of sodium salt employed. In order to investigate the dominant factor affecting the overall kinetics in the H⁺ reduction catalysis, the dependences of both the catalytic activity and the electron transfer rate in the RP film were studied in a NaH₂PO₄ solution as a function of the coated amount. It was found that the overall kinetics are not dominated by electron transfer in the RP film.     

Dislocation of the <Superscript>137</Superscript>Cs and <Superscript>40</Superscript>K radionuclides in the podsol profiles of the Tatra Mountain soils (South Poland)

Summary The amount and dislocation of the gamma-radionuclides (artificial cesium and natural potassium) in the Haplic podsol profiles of the Tatra Mountains have been described. These soils belong to the group of penetrable formations what is a result of their texture. They provide a good example of percolation and sorption possibilities of the radionuclides within the soil profile. The highest concentration of radionuclides has been detected in raw humus and spodic (illuvial humus-iron) layers, at the surface.     

Iodination of aryl amines in a water-paste form via stable aryl diazonium tosylates

The diazotization of aryl amines at room temperature in paste form with NaNO₂, p-TsOH and a small amount of water, followed by treatment with KI provides a new, simple, and effective route for the preparation of various aryl iodides. The water-paste and strong acid-free reaction conditions are environmentally friendly and compatible with acid-sensitive functional groups.     

Fluorescent iminodiacetamide derivatives as potential ionophores for optical zinc ion-selective sensors.

Fluorescent sensor molecules were synthesized by conjugation of iminodiacetamide derivatives with fluorescent moieties of different structures and their UV-visible and fluorescent properties were characterized in acetonitrile solvent. The fluorescent measurements revealed that the N-(2-naphthyl) and N-phenyl derivatives exhibit a distinct zinc ion-selectivity over alkali and alkaline earth metal ions, while N-(anthrylmethyl) and N-(3-methoxyphenyl) derivatives do not possess any ion-selectivities. In contrast to the fluorescent measurements, all ligands show Zn(2+) selectivity over Ca(2+) and Mg(2+) ions in plasticized PVC membranes using potentiometric signal transduction. This observation found for N-(anthrylmethyl) and N-(3-methoxyphenyl) derivatives can be ascribed to the more hindered interaction between the signalling group of the ionophore and the central metal ion in PVC membranes than in acetonitrile solution upon complexation. From the fluorescent measurements it can also be concluded that the ligands with metal ions form complexes mainly with 2:1 stoichiometry (L(2)M). On complex formation a considerable decrease in the fluorescent intensity was observed for all ligands except the N-(anthrylmethyl) derivative, where a 25 - 30 fold fluorescence enhancement was found, which is explained by the photoinduced electron transfer (PET) mechanism. All ionophores exhibited serious hydrogen ion interference, therefore complexation-induced spectral changes were measured in aprotic acetonitrile solution.     

An Almost Optimal Heuristic for Preemptive C max Scheduling of Dependent Tasks on Parallel Identical Machines

We consider the problem of scheduling preemptable, dependent tasks on parallel, identical machines to minimize the makespan. The computational complexity of this problem remains open if the number of machines is fixed and larger than 2. The aim of this paper is to compare two heuristic algorithms on a basis of a computational experiment. The solutions generated by the heuristics are compared with optimal solutions obtained by a branch-and-bound algorithm. Computational results show that the heuristic based on node ordering finds optimal schedules for 99.9% of instances with the maximum relative deviation from optimum of 4.8%.     

Incommensurate antiferromagnetic structures in NdIn3

Among the AuCu₃-type RIn₃ series where R is a rare earth, the NdIn₃ compound presents a complex magnetic phase diagram. In this compound, which orders antiferromagnetically at T_N = 5.9 K, three magnetic phases are separated by two sharp first-order transitions. The phase diagrams, determined for the main crystallographic directions, by magnetization measurements in fields up to 7 T show a strong dependence of the transition temperatures. In order to determine the actual magnetic structures in NdIn₃, a neutron diffraction experiment has been performed on a single crystal under magnetic field. It shows that the magnetic structures are collinear (single q) with the magnetic moments aligned along the fourfold axis. They clearly evidence the existence of two incommensurate phases with q = (1/2, 1/2, τ): for T_N T 5.5 K, τ₁ ≈ 0.037 2π/a and the structure is sine-wave modulated, for 5.5 K > T > 4.7 K, τ₂ = 0.017 2π/a and the structure squares up. Below 4.7 K the q = (1/2, 1/2, 0) commensurate structure is stabilized.     

Well-positioned Closed Convex Sets and Well-positioned Closed Convex Functions

We characterize the class of those closed convex sets which have a barrier cone with a nonempty interior. As a consequence, we describe the set of those proper extended-real-valued functionals for which the domain of their Fenchel conjugate has a nonempty interior. As an application, we study the stability of the solution set of a semi-coercive variational inequality.     

Neutron activation analysis of some trace elements /selenium,chromium, cobalt and nickel/ in the blood of vitiligo patients

Samples of full blood of vitiligo patients and those of control persons were analyzed for Se, Cr, Co and Ni contents by neutron activation analysis. The concentrations are reported in ppm/dry weight. The results showed that the Se and Co levels were significantly higher in the blood of vitiligo patients while the increase of Cr and Ni was not significant as compared to the controls.     

The effect of water vapour on the cyclodextrin-solute interaction in gas-solid chromatography

The effect of water vapour on the interaction between the solutes and a cyclodextrin was studied chromatographically in a gas/solid system. It has been shown that all the sorbates capable of forming inclusion complexes with -CD are affected by the presence of water, in contrast to the sorbates that do not interact with -CD, which are unaffected. The measurements were carried out with the cyclodextrin deposited on a solid carrier (Chromosorb W) and with water vapour contained in the mobile phase. Some advantages of this system have been demonstrated for an analytical application.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.