Extracting Algorithms from Intuitionistic Proofs

This paper presents a new method - which does not rely on the cut-elimination theorem - for characterizing the provably total functions of certain intuitionistic subsystems of arithmetic. The new method hinges on a realizability argument within an infinitary language. We illustrate the method for the intuitionistic counterpart of Buss's theory S, and we briefly sketch it for the other levels of bounded arithmetic and for the theory IΣ₁.     

Quantitative evaluation of the catalytic activity of dendrimers with only one active center at the core: application to the nitroaldol (Henry) reaction

One reference tertiary amine and three families of structurally related trialkylamines and dendrimers have been synthesized, characterized, and studied by molecular dynamics simulations. The catalytic activity of these amines in the nitroaldol (Henry) reaction between 2-nitroethanol and benzaldehyde has been measured by FT-IR spectroscopy. It is found that, in this kind of molecule with only one catalytic center at the core, the efficiency of the catalytic process decreases with the size and/or the degree of ramification of the dendrimer. According to these results, there is a linear departure from the behavior predicted by the hard sphere collision theory (HSCT) as the size of the dendrimer increases. Therefore, the behavior of structurally related dendrimers can be quantified in terms of their molecular weight and reagent accessible surfaces.     

Fluorimetric enzymatic flow-injection determination of bile acids in human serum

Summary A fast, simple and convenient method for the individual and total determination of bile acids based on the enzymatic oxidation of the analytes and the fluorimetric measurement of a reaction product (the reduced form of the coenzyme, NADH) is proposed. The method allows the determination of the analytes (taurocholic, chenocholic, glycocholic and chenodesoxycholic acid) over the range of 0.3–10.0 g ml^–1, with an r.s.d. smaller than 3.0% in each case. It was applied to the determination of total bile acids in human serum. The simplicity of the method makes it useful for screening clinical samples in order to avoid implementing chromatographic processes on samples with analyte overall contents clearly below pathological limits.     

Transition structure in a diabatic surface formalism

The theory of an implementation of the diabatic surface model within the Heitler–London valence bond approach is described. It is shown that the HL –VB wave function can be obtained from a Van-Vleck transformation of an MC –SCF wave function which has been built from atom-localized orbitals. This wave function is built from a superposition of two diabatic components, reactantlike and productlike. The transition structure is then obtained as the minimum of the seam of intersection of the diabatic surfaces and the algorithm for performing this constrained optimization is described. Several areas of application are also discussed.     

Selective reduction of aromatic nitro compounds containing o- and n-benzyl groups with hydrazine and raney nickel

The selectiity in the catalytic reduction of aromatic nitro compounds containing O-benzyl, N-benzyl or chlorine with hydrazine and Raney nickel was studied.     

Atom-efficient assembly of 1,5-oxygen-bridged medium-sized carbocycles by sequential combination of a Ru-catalyzed alkyne-alkene coupling and a Prins-type cyclization

Ruthenium-catalyzed coupling of readily accessible 1-trimethylsilyl-1-alkyn-3-ols to allyl ethyl ether followed by in situ ketalization and Lewis-acid induced cyclization affords 1,5-oxygen-bridged eight- and nine-membered carbocycles, products which are difficult to construct with previously published strategies.     

Epidermal lignin deposition in quinoa cotyledons in response to UV-B radiations

UV-B radiation (280-320 nm) is harmful to living organisms and has detrimental effects on plant growth, development and physiology. In this work we examined some mechanisms involved in plant responses to UV-B radiation. Seedlings of quinoa (Chenopodium quinoa Willd.) were exposed to variable numbers of UV-B radiation doses, and the effect on cotyledons was studied. We analyzed (1) cotyledons anatomy and chloroplasts ultrastructure; (2) peroxidase activity involved in the lignification processes; and (3) content of photosynthetic pigments, phenolic compounds and carbohydrates. Exposure to two UV-B doses induced an increase in the wall thickness of epidermal cells, which was associated with lignin deposition and higher activity of the peroxidase. The chloroplast ultrastructure showed an appearance typical of plants under shade conditions, likely in response to reduced light penetration into the mesophyll cells due to the screening effect of epidermal lignin deposition. Exposure to UV-B radiation also led to (1) enhancement in the level of phenolics, which may serve a protective function; (2) strong increase in the fructose content, a fact that might be related to higher requirement of erythrose-4P as a substrate for the synthesis of lignin and phenolics; and (3) reduction in the chlorophyll concentration, evidencing alteration in the photosynthetic system. We propose that the observed lignin deposition in epidermal tissues of quinoa is a resistance mechanism against UV-B radiation, which allows growing of this species in Andean highlands.     

An effective one-pot synthesis of 5-substituted tetronic acids

An expeditious one-pot synthesis of 5-substituted tetronic acids from aldehydes and terminal conjugated alkyne as starting materials is described. The entire process embodies two consecutive chemical events: a catalytic domino reaction to build the 1,3-dioxolane scaffolds 5 and a two-step acid-catalyzed trans-acetalization-lactonization reaction to furnish the tetronic acid derivatives 6.     

Determination of Nickel in Fuel Ethanol Using a Carbon Paste Modified Electrode Containing Dimethylglyoxime

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol L⁻¹ was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 × 10⁻⁹ mol L⁻¹ and 5.2 × 10⁸ μA mol⁻¹ L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 × 10⁻⁸ to 6.9 × 10⁻⁸ mol L⁻¹. A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.     

Penning ionization of N2O molecules by He*(2(3,1)S) and Ne*(3P2,0) metastable atoms: a crossed beam study

The energetics of [Rg... N2O]* autoionizing collision complexes (where Rg=He or Ne) and their dynamical evolution have been studied in a crossed beam apparatus, respectively, by Penning ionization electron spectroscopy (PIES) and by mass spectrometry (MS) techniques in the thermal energy range. The PIES spectra, detected by an electron energy analyzer, were recorded for both complexes at four different collision energies. Such spectra allowed the determination of the energy shifts for Penning electron energy distributions, and the branching ratios for the population of different electronic states and for the vibrational population in the molecular nascent ions. For the [Ne...N2O]* collision complex it was found, by MS, that the autoionization leads to the formation of N2O+, NO+, O+, and NeN2O+ product ions whose total and partial cross sections were measured in the collision energy range between 0.03 and 0.2 eV. The results are analyzed exploiting current models for the Penning ionization process: the observed collision energy dependence in the PIES spectra as well as in the cross sections are correlated with the nature of the N2O molecule orbitals involved in the ionization and are discussed in term of the Rg-N2O interaction potentials, which are estimated by using a semiempirical method developed in our laboratory.