Evaluation of calibration data in capillary electrophoresis using artificial neural networks to increase precision of analysis

An RP-HPLC study for the pKa determination of a series of basic compounds related to caproctamine, a dibenzylaminediamide reversible inhibitor of acetylcholinesterase, is reported. The 2-substituted analogues, bearing substituents with different electronegativity, were analysed by RP-HPLC by using C18 C4 stationary phases with a mobile phase consisting of mixture of acetonitrile and triethylamine phosphate buffer (pH range comprised between 4 and 10). Typical sigmoidal curves were obtained, showing the dependence of the capacity factors upon pH. In general, the retention of the investigated basic analytes increased with increasing of the pH. The inflection point of the pH sigmoidal dependence was used for the dissociation constant determination at a fixed acetonitrile percentage. When plotting pKa vs. percent of acetonitrile in the mobile phase for two representative compounds, linear regression were obtained: the y intercept gave the aqueous pKa(w). The pKa estimation by HPLC method was found to be useful to underline the difference of benzylamine basicity produced by the ortho aromatic substituents. The variation of pKa values (6.15-7.80) within the series of compounds was correlated with the electronic properties of the ortho-substituents through the Hammett sigma parameter, whereas the ability of substituents to accept H-bond was found to play a role in determining the conformational behavior of the molecules.     

Elliptic and hyperbolic inversions

Letx andy be orthogonal coordinates of a pointM(u=ax+iby orax+εby) of a plane whereasx′ andy′ are orthogonal coorditanes of a pointM′(v=ax′+iby′ orax′+εby′) inverse ofM in the elliptic or hyperbolic inversion $u\bar \upsilon = k$ (k positive) $\bar \upsilon $ designating the conjugate ofv whilei andε are Clifford numbers such thati ²=?1 andε ² = 1 (a andb are real)O is the origin of axises,Ox is the axis of the inversion.

1. Two inverse points are aligned withO.
2. The inverse of a conic having a centrec is a conic but this inverse is a straight line if the origin is on the conic.

There is a metric relation between sides and diagonals of a quadrilateral inscribed in an ellipse or in an hyperbola.     

Quantum Size Effects in the Size–Temperature Phase Diagram of Gallium: Structural Characterization of Shape‐Shifting Clusters

Finite temperature analysis of cluster structures is used to identify signatures of the low‐temperature polymorphs of gallium, based on the results of first‐principle Born–Oppenheimer molecular dynamics simulations. Pre‐melting structural transitions proceed from either the β‐ and/or the δ‐phase to the γ‐ or δ‐phase, with a size‐ dependent phase progression. We relate the stability of each isomer to the electronic structures of the different phases, giving new insight into the origin of polymorphism in this complicated element.     

A balanced procedure for the treatment of cluster–ligand interactions on gold phosphine systems in catalysis

Ligand‐protected metal clusters are difficult to describe within density functional theory due to the need to treat the electronic structure of the cluster, possible charge transfer between the ligands and the cluster, and weak ligand–ligand interactions in a balanced manner. We demonstrate the use of an appropriate, stepwise benchmarking process that accounts for the nonadditivity of these different contributions to stability and catalytic activity. We consider both open‐ and closed‐shell clusters, differently charged systems, and ligands of increasing complexity for gold phosphine systems. The use of a dispersion correction to density functional calculations was found to be crucial for both structure optimization and the calculation of binding energies. We find that PBE‐D3 performs well with a variation in energetics of 0.7–10.9 kcal/mol, PBE0‐D3 better with 0.0–3.3 kcal/mol, and B2PLYP‐D3 the best with 0.2–2.4 kcal/mol, when compared to the best available benchmark [CCSD(T) or SCS‐MP2]. Our systematic procedure clarifies that these functionals all give accurate results for certain cases, but for the total performance over a range of interactions, they perform in accordance with Jacob's ladder. © 2014 Wiley Periodicals, Inc.     

Pressure‐Induced Intersite BiM (M=Ru, Ir) Valence Transitions in Hexagonal Perovskites

Pressure‐induced charge transfer from Bi to Ir/Ru is observed in the hexagonal perovskites Ba_3+nBiM_2+nO_9+3n (n=0,1; M=Ir,Ru). These compounds show first‐order, circa 1 % volume contractions at room temperature above 5 GPa, which are due to the large reduction in the effective ionic radius of Bi when the 6s shell is emptied on oxidation, compared to the relatively negligible effect of reduction on the radii of Ir or Ru. They are the first such transitions involving 4d and 5d compounds, and they double the total number of cases known. Ab initio calculations suggest that magnetic interactions through very short (ca. 2.6 Å) M? M bonds contribute to the finely balanced nature of their electronic states.     

Zur Aufschliessung der Silicate

Ohne Zusammenfassung     

Differential operators and entire functions with simple real zeros

Let ? and f be functions in the Laguerre-Pólya class. Write ?(z)=e−αz²?₁(z) and f(z)=e−βz²f₁(z), where ?₁ and f₁ have genus 0 or 1 and α,β?0. If αβ<1/4 and ? has infinitely many zeros, then ?(D)f(z) has only simple real zeros, where D denotes differentiation.     

Proprietes electroniques et electrogalvaniques dutellurure d'argent β domaine d'existence

A study of the electronic and electrogalvanic properties of β silver telluride has been performed on samples whose non-stoichiometry has been determined by coulometric titration with the cell Ag/RbAg₄I₅/Ag₂Te/Pt. The data lead to the adoption of a model of Frenkel defects on the silver sublattice that are fully ionised. Their formation enthalpy is H_F′ = 0,70 eV. On the tellurium side this model is completed by the association V_AgV_Ag^x. Th homogeneity range is reported from ?10°C to 132°C: it extends essentially on the tellurium side of the stoichiometric composition.     

Wavelength-dependent reactivity of a quinolinone: toward a photochromic three-state system

The photochemical reactivity of the quinolinone 3 was investigated using NMR by monitoring its reactions under appropriate irradiation wavelengths. Besides the irreversible formation of degradation products which were structurally identified, the reversible formation of the enol 4 and cyclobutenol 5 was also observed. The enol and cyclobutenol can be switched or reversed back to the quinolinone 3, resulting in a photochromic three-state system in which the relative ratio of the three components largely depends on the irradiation wavelength used.