Chemiluminescence of luminol induced by dissolution of oxide-covered aluminum in alkaline aqueous solution

One-electron reduction of oxygen, hydrogen peroxide, potassium peroxodisulphate and potassium peroxodiphosphate was studied during the dissolution of oxide-covered aluminum in alkaline aqueous solution. The production of free oxidizing radicals was monitored by luminol chemiluminescence (CL). It was observed superoxide, hydroxyl, sulphate and phosphate radicals can be generated by the present method. In addition, luminol can be detected below nanomolar level, the linear logarithmic calibration range covering several orders of magnitude of concentration. The metallic aluminum and low-valent aluminum ions are the primary reductants of the system. The electron transfer to the solution is proposed to occur by tunneling through a thin insulating aluminum oxide film at the solid/electrolyte interface in moderately alkaline solutions with simultaneous dissolution of the forming oxide film. In a highly alkaline solution, it is more probable that the oxidation of aluminum species occurs in direct contact of the metallic aluminum with the aqueous solution. In the latter case, short-lived solvated low-valent aluminum ions, hydrogen atom and its deprotonated form, the hydrated electron, can exist as reducing mediators in the chemical reactions in the close vicinity of the dissolving solid/electrolyte interface. Luminol was also observed to exhibit CL under purely reducing conditions produced by a presently unknown excitation pathway.     

Rigorous Scaling Law for the Heat Current in Disordered Harmonic Chain

We study the energy current in a model of heat conduction, first considered in detail by Casher and Lebowitz. The model consists of a one-dimensional disordered harmonic chain of n i.i.d. random masses, connected to their nearest neighbors via identical springs, and coupled at the boundaries to Langevin heat baths, with respective temperatures T ₁ and T _n . Let E J _n be the steady-state energy current across the chain, averaged over the masses. We prove that E J _n ~ (T ₁ − T _n )n ^−3/2 in the limit n → ∞, as has been conjectured by various authors over the time. The proof relies on a new explicit representation for the elements of the product of associated transfer matrices.     

Stable ammonium bisulfate clusters in the atmosphere

Liquid drop model based equilibrium thermodynamics predicts that in the presence of even small ammonia concentrations practically all the atmospheric sulfuric acid molecules are bound to tiny, stable ammonium-bisulfate clusters. Hitherto sulfuric acid has been believed to form hydrates with water. Thermodynamic theory predicts correctly the hydrate formation observed experimentally. Results from ab initio computer simulations contradict the thermodynamic results and also the experimental findings for cluster formation in both sulfuric acid-water and ammonia-sulfuric acid-water mixtures.     

Two-component heterogeneous nucleation kinetics and an application to Mars

We develop a two-component heterogeneous nucleation model that includes exact calculation of the Stauffer-type [D. Stauffer, J. Aerosol Sci. 7, 319 (1976)] steady-state kinetic prefactor using the correct heterogeneous Zeldovich factor for a heterogeneous two-component system. The model, and a simplified version of it, is tested by comparing its predictions to experimental data for water-n-propanol nucleating on silver particles. The model is then applied to water-carbon dioxide system in Martian conditions, which has not been modeled before. Using the ideal mixture assumption, the model shows theoretical possibilities for two-component nucleation adjacent to the initial stages of one-component water nucleation, especially with small water vapor amounts. The numbers of carbon dioxide molecules in the critical cluster are small in the case of large water amounts (up to 300 ppm) in the gas phase, but larger when there is very little water vapor (1 ppm).     

Rapid and practical synthesis of (-)-1-deoxyaltronojirimycin

Herein a practical and scalable route to 1-deoxyaltronojirimycin is presented. The target is achieved in 9 steps and 43% yield featuring only two chromatographic purifications.     

Hot electron-induced electrogenerated chemiluminescence of 1-aminonaphthalene-4-sulphonate at oxide-covered aluminium electrodes in aqueous solution

Electrogenerated chemiluminescence of 1-aminonaphthalene-4-sulphonate (ANS) provides a sensitive means for the detection of the ANS in aqueous solution when oxide-covered aluminium electrodes are used as tunnel emission electrodes and cathodic pulse polarisation is used for the excitation of the luminophore. During the pulse polarisation of insulating oxide film-coated aluminium cathodes, hot electrons are tunnel emitted from the aluminium to the aqueous electrolyte solution by direct field-assisted tunnelling (in the case of oxide films of thickness 2-6 nm) or by Fowler-Nordheim (FN) tunnelling in the cases of thicker oxide films. As a result of direct tunnel emission of these energetic electrons, the generation of hydrated electrons (e_aq⁻) becomes possible. These electrochemically generated, extremely strong reductants (dry hot or hydrated electrons) make the efficient excitation of various types of luminophores at thin insulating film-covered electrodes possible and provide a means for sensitive immunoassays and DNA-probing assays when these luminophores are used as label molecules.