On the convergence rate of a cusp-corrected damped multipole expansion for the second-order H-H+ induction energy

The improvement in the convergence rate of the damped multipole expansion for the second order H-H⁺ induction energy due to the inclusion into the first-order function of a term satisfying the electron-proton cusp condition is quantitatively investigated. Following a technique suggested by Schwartz, the multipole contributions to the energy are put in the form of series ordered by inverse powers of the quantum number l. It is shown that, for high values of l, the dependence of the leading terms is raised from l ^-4 to l ^-6 by the cusp correction.     

Methylene blue as an electrochemical indicator for DF508 cystic fibrosis mutation detection

Cystic fibrosis is one of the most common life-shortening, childhood-onset inherited diseases. Among the 1,000 known cystic fibrosis-related mutations, DF508 is the most common, with a frequency varying between 50% and 70% according to geographical areas and population typology. In this work, we report the use of methylene blue as an electrochemical reporting agent in the discrimination of synthetic PCR analogue of the DF508 cystic fibrosis mutation (Mut) from the wild type (Wt). At optimum experimental condition, a discrimination factor between mutant and wild type of approximately 1.5-fold was found. The proposed assay was quantitative and linear in the range of 10–100 nM, exhibiting a limit of detection of 2.64 nM. Electrochemical studies at variable ionic strength conditions allowed further elucidation of the mechanism of the methylene blue (MB)–DNA interaction. To the best of our knowledge, this is the first report of detection of hybridisation solely via guanine-specific MB–DNA interaction simultaneously in MB solution, independent of electrostatic interaction as demonstrated in the ionic strength study. The introduction of formamide in the hybridization buffer, to improve discrimination, was also investigated. Finally, mutant wild type discrimination was demonstrated, at 10 nM concentration, with the use of a multi-sensor setup.     

Reduced dipole pseudospectra for the accurate tabulation of C6 dispersion coefficients

The possibility of tabulating accurate reduced dipole pseudospectra of single molecules is of great importance for obtaining reliable dipole dispersion constants from which C₆ dispersion coefficients can be derived for all possible interacting pairs. Use of an efficient interpolation procedure allows to obtain dispersion constants from analytical integration of the Casimir–Polder integral over the product of frequency-dependent polarizabilities (FDPs) at imaginary frequencies. FDP calculations can then be done at a few selected frequencies, so overcoming at a time the difficulties arising from numerical quadratures and sensibly reducing the computational demand. In the static case, appropriately reduced n-term pseudospectra are obtained by forcing in an optimal way large N-term extended pseudospectra to be converted to FDPs using the same interpolation technique. Calculations performed at the eight frequencies arising by choosing n = 4 (four-term approximation) in the optimized interpolation procedure, give reduced dipole pseudospectra from which isotropic C₆ dispersion coefficients and γ₆ anisotropy coefficients are obtained in almost perfect agreement with the result of the most accurate data available from the literature and of recently proposed variational techniques.     

Computer modelling of BaY2F8: defect structure, rare earth doping and optical behaviour

BaY₂F₈, when doped with rare earth elements, is a material of interest in the development of solid-state laser systems, especially for use in the infrared region. This paper presents the application of a computational technique, which combines atomistic modelling and crystal field calculations, in a study of rare earth doping of the material. Atomistic modelling is used to calculate the intrinsic defect structure and the symmetry and detailed geometry of the dopant ion-host lattice system, and this information is then used to calculate the crystal field parameters, which are an important indicator in assessing the optical behaviour of the dopant-crystal system. Energy levels are then calculated for the Dy³⁺-substituted material, and comparisons with the results of recent experimental work are made. PACS 61.50.Ah; 61.72.Bb; 78.20.Bh     

A simple model of short-range interactions

The short-range interaction between any two molecular fragments can be split into coulombic and penetration components, the last part being dominant in neutral systems. A simple theoretical model is developed to describe the penetration part of the short-range interaction between two localized electron pairs. The main body of the interaction is seen to take place through the overlap arising between nonorthogonal electron groups. For closed-shell fragments the interaction can be visualized in terms of a distortion of the electron density resulting in a decrease of charge in the overlap region and in an increase of charge in the region of the component groups.Zusammenfassung Die Wechselwirkung kurzer Reichweiten zwischen zwei Molekülteilen kann in Coulomb- und Durchdringungsanteile aufgeteilt werden, von denen der letztere in neutralen Systemen dominiert. Ein einfaches Modell wird entwickelt, das den gesamten Durchdringungsanteil der Wechselwirkung zweier lokalisierter Elektronenpaare kurzer Reichweite beschreibt. Der Hauptanteil der Wechselwirkung kommt durch die Überlappung zwischen nichtorthogonalen Elektronengruppen zustande. Für Bruchstücke mit abgeschlossenen Schalen kann man sich die Wechselwirkung mit Hilfe einer Verlagerung der Elektronendichte vorstellen, die zu einer Verminderung der Ladung in der Überlappungsregion and einer Vermehrung der Ladung im Gebiet der beiden Gruppen führt.Resumé L'interaction à courte distance entre deux fragments moléculaires quelconques peut être decomposée dans une composante coulombienne et une composante pénétrative, cette dernière étant dominante dans le cas de systèmes neutres. Un modèle théorique simple a été developé pour décrire la composante pénétrative de l'interaction à courte distance entre deux paires localisées d'électrons. La partie la plus importante de l'interaction a lieu via le recouvrement entre groupes nonorthogonales d'électrons. Pour des fragments moléculaires correspondants à des couches complètes l'interaction peut être visualisée dans une distortion de la densité electronique aboutissante à une diminution de charge dans la région de recouvrement et à une augmentation de charge dans la région des groupes composants.     

“One pot” synthesis of 2,9-disubstituted 8-azaadenines (3,5-disubstituted 7-amino-3H-1,2,3-triazolo[4,5-d]pyrimidines)

A new simple method for the synthesis of title compounds is described starting from malononitrile, benzyl-azide and an aliphatic or aromatic nitrile.     

Aqua bridged Cu2 dimer of a heptadentate N4O3 coordinating ligand: Synthesis,structure and magnetic properties

The N₄O₃ coordinating heptadentate imidazolidinyl phenolate ligand, H₃L (2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) forms with Cu(II) a rare aqua bridged complex [{Cu₂(μ-L)(μ-H₂O)}₂](ClO₄)₂ · 4.5H₂O (1 · 4.5H₂O). Complex 1 · 4.5H₂O contains two crystallographically different but chemically equivalent dinuclear [Cu₂(μ-L)(μ-H₂O)]⁺ cationic units in the asymmetric unit. The copper atoms of each dinuclear unit are in a distorted square-pyramidal environment and are held together by phenolate, imidazolidinyl and aqua bridges with a Cu···Cu separation of av. 3.34 Å. The compound exhibits a very weak antiferromagnetic exchange interaction (J = −0.77 cm⁻¹, ? = −2 J?₁?₂) between the two copper(II) (S = 1/2) ions. The ¹H NMR spectrum of the complex shows a total of 17 hyperfine shifted peaks, as expected from the idealized C_s symmetry of the compound, spread over a very large window of chemical shift, spanning about 250 ppm. The complex, having an appropriate intermetallic separation for catechol binding, shows catecholase like activity in MeCN at 25 °C, with the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ).