Kernel energy method illustrated with peptides

We describe a kernel energy method (KEM) for applying quantum crystallography to large molecules, with an emphasis on the calculation of the molecular energy of peptides. The computational difficulty of representing the system increases only modestly with the number of atoms. The calculations are carried out on modern parallel supercomputers. By adopting the approximation that a full biological molecule can be represented by smaller “kernels” of atoms, the calculations are greatly simplified. Moreover, collections of kernels are, from a computational point of view, well suited for parallel computation. The result is a modest increase in computational time as the number of atoms increases, while retaining the ab initio character of the calculations. We describe a test of our method, and establish its accuracy using 15 different peptides of biological interest. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Influence de la structure cristalline sur la décomposition thermique des hydroxynitrates de métaux bivalents: Exemple des hydroxynitrates de cadmium

The solid solid equilibria in the binary system Ca₃(PO₄)₂-CaNaPO₄ have been studied. Different diagrams have been proposed for this system. The differences relate to the limits of the field of existence of a non-stoichiometric phase (phase A) stable at high temperature and undergoing eutectoid decomposition during cooling; they can be explained by the existence of two metastable equilibria diagrams which are superposed in the stable diagram. These metastabilities depend on both the cooling rates and the maximum temperatures reached before this cooling.

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Zusammenfassung Fest fest Gleichgewichte des binären Systems Ca₃(PO₄)₂-CaNaPO₄ wurden untersucht. Verschiedene Diagramme wurden für dieses System vorgeschlagen. Diese Unterschiede beziehen sich auf die Grenzen des Existenzbereiches einer nichtstöchiometrischen, hochtemperaturstabilen Phase (Phase A), die sich beim Abkühlen nach einer eutektoiden Reaktion zersetzt; sie können durch die Existenz von zwei dem stabilen Diagramm überlagerten metastabilen Gleichgewichtsdiagrammen erklärt werden. Diese metastabilen Zustände hängen sowohl von der Abkühlungsgeschwindigkeit als auch von den vor dem Abkühlen erreichten maximalen Temperaturen ab.

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Ca₃(PO₄)₂-CaNaPO₄ — . . / A/, , - , , . , , .

     

Etude thermodynamique de la décomposition thermique des hydroxynitrates de zinc

The reaction scheme of thermal decomposition for four zinc hydroxynitrates was investigated by means of differential scanning calorimetry, thermogravimetry, mass spectrometry, and radiocrystallography. The thermal transformation of Zn(OH)(NO₃) · H₂O and of Zn₃(OH)₄(NO₃)₂ involves the formation of gaseous water and nitric acid from an actual chemical reaction. This reaction is not observed for Zn₅(OH)₈(NO₃)₂ · 2H₂O and Zn₅(OH)₈(NO₃)₂. These results show that the formation of gaseous nitric acid molecules inside the solids is specific to hydroxynitrates of divalent metals M, whose lamellar crystalline structure is characterized by a stacking of hexagonal close-packed layers of formula MX_2+m, where m = 0 or 1 and X = OH^?, H₂O, or NO^?₃.     

catena‐Poly[[(2,2′‐bipyridyl)oxidovanadium]‐di‐μ2‐oxido‐[(2,2′‐bipyridyl)oxidovanadium]‐μ3‐selenito‐bis[(2,2′‐bipyridyl)dioxidovanadium]‐μ3‐selenito]

In the title compound, [V₄O₈(SeO₃)₂(C₁₀H₈N₂)₄], there are two distinct vanadium coordination environments. Alternating corner‐shared VO₄N₂ octahedra and SeO₃ pyramids result in eight‐membered centrosymmetric V₂Se₂O₄ rings. In addition, pairs of V centres form centrosymmetric V₂O₆N₄ clusters via edge‐sharing. These two kinds of secondary building units are linked in an ABABAB fashion to give an infinite chain whose nature is unprecedented in Se–V–O systems.     

Correlation of supercritical-fluid extraction recoveries with supercritical-fluid chromatographic retention data: A fundamental study

The possibility of using supercritical-fluid chromatographic retention data for examining the effects of operational parameters, such as pressure and flow rate, on the extraction characteristics in supercritical-fluid extraction (SFE) was investigated. A model was derived for calculating the extraction efficiency in SFE from retention data and peak shapes measured in supercritical-fluid chromatography (SFC). By performing the SFC experiments at the same pressure and temperature as the SFE extractions using the SFE extraction cell as the SFC column, an accurate prediction of extraction efficiencies could be made. Finally, the effects of matrix composition and analyte concentration on extraction efficiency were studied.     

Global well-posedness of the non-isentropic full compressible magnetohydrodynamic equations

In this paper, we are concerned with Cauchy problem for the multi-dimensional (N ≥ 3) non-isentropic full compressible magnetohydrodynamic equations. We prove the existence and uniqueness of a global strong solution to the system for the initial data close to a stable equilibrium state in critical Besov spaces. Our method is mainly based on the uniform estimates in Besov spaces for the proper linearized system with convective terms.