An efficient and robust integration scheme for the equations of motion of the multiconfiguration time-dependent Hartree (MCTDH) method

An efficient and robust integration scheme tailored to the equations of motion of the multiconfiguration time-dependent Hartree (MCTDH) method is presented. An error estimation allows the automatical adjustment of the step size and hence controls the integration error. The integration scheme decouples the MCTDH equations of motion into several disjoined subsystems, of which one determines the time evolution of the MCTDH-coefficients. While the conventional MCTDH equations are non-linear, the working equation for the MCTDH-coefficients becomes linear in the present integration scheme. To investigate the integrator’s performance it is applied to the photodissociation process of methyl iodide. The results of the novel integration scheme are in perfect agreement to those obtained by solving the MCTDH working equations conventionally. The computation time, however, is reduced by a factor of about ten when the new integration scheme is used to propagate large systems.     

Catalytic transesterification of dialkyl phosphates by a bioinspired dicopper(II) macrocyclic complex

For a number of phosphoryltransfer enzymes, including the exonuclease subunit of DNA polymerase I, a mechanism involving two-metal ions and double Lewis-acid activation of the substrate, combined with leaving group stabilization, has been proposed. Inspired by the active site structure of this enzyme, we have designed as a synthetic phosphoryl transfer catalyst the dicopper(II) macrocyclic complex LCu(2). Crystal structures of complexes [(L)Cu(2)(mu-NO(3))(NO(3))](NO(3))(2) (1), [(L)Cu(2)(mu-CO(3))(CH(3)OH)](BF(4))(2) (2), and [(L)Cu(2)(mu-O(2)P(OCH(3))(2))(NO(3))](NO(3))(2) (3) illustrate various possibilities for the interaction of oxoanions with the dicopper(II) site. 1 efficiently promotes the transesterification of dimethyl phosphate (DMP) in CD(3)OD, k(cat) = 2 x 10(-)(4) s(-)(1) at 55 degrees C. 1 is the only available catalyst for the smooth transesterification of highly inert simple dialkyl phosphates. From photometric titrations and the pH dependence of reactivity, we conclude that a complex [(L)Cu(2)(DMP)(OCH(3))](2+) is the reactive species. Steric bulk at the -OR substituents of phosphodiester substrates O(2)P(OR)(2)(-) drastically reduces the reactivity of 1. This is explained with -OR leaving group stabilization by Cu coordination, an interaction which is sensitive to steric crowding at the alpha-C-atom of substituent R. A proposed reaction mechanism related to that of the exonuclease unit of DNA polymerase I is supported by DFT calculations on reaction intermediates. The complex [(L)Cu(3)(mu(3)-OH)(mu-CH(3)O)(2)(CH(3)CN)(2)](ClO(4))(3) (4) incorporates a [Cu(OH)(OCH(3))(2)(CH(3)CN)(2)](-) complex anion, which might be considered as an analogue of the [PO(2)(OCH(3))(2)(OCD(3))](2)(-) transition state (or intermediate) of DMP transesterification catalyzed by LCu(2).     

Cu4O12-Baugruppen aus planaren CuO4-Polygonen im Barium-Vanadyl-Oxocuprat(II)-phosphat Ba(VO)Cu4(PO4)4

Cu₄O₁₂ Groups Built of Square Planar CuO₄ Polygones in the Barium Vanadyl Oxocuprate(II) Phosphate Ba(VO)Cu₄(PO₄)₄ Single crystals of Ba(VO)Cu₄(PO₄)₄ have been prepared by solid state reactions just below the melting points of the reaction mixtures of BaP₂O₆, Cu₃(PO₄)₂, CuO, V₂O₅ and V₂O₃ in evacuated closed quartz glas tubes. The compound crystallizes with tetragonal symmetry, Space group D? P42₁2, a = 9.560(2), c = 7.160(2) Å, Z = 2. Special and new features of the crystal structure are to each other isolated Cu₄O₁₂ and (VO)(PO₄)₄ groups. The crystal chemistry of the Cu₄O₁₂ groups is discussed with respect to other compounds containing out of plane connected square planar MO₄ polygones.     

Mitteilungen aus dem Institut für Radiumforschung

Zusammenfassung Es wurde mit Hilfe des schon früher beschriebenen Quarzapparates Thoriumbromid aus reinem Thoroxyd dargestellt, das nach zwei verschiedenen Methoden gereinigt war und auf Grund spektroskopischer Untersuchung als absolut rein und frei von seltenen Erden angesehen werden mu\te.Das geschmolzene Thorbromid wurde nach zwei Methoden analysiert und dabei die beiden VerhÄltnisse ThBr₄4 Ag und ThBr₄4 AgBr bestimmt.Zwei unabhÄngige Serien von 12, respektive 15 Analysen gaben die folgenden Resultate:Serie I. 54·45867g Thorbromid verbrauchten 42·58666g Silber und gaben 74·13448g Silberbromid, entsprechend einem Atomgewicht des Thoriums Th=232·15±0·016.Serie II. 74·30630g Thorbromid verbrauchten 58·11096g Silber und gaben 101·15848g Silberbromid, woraus sich das Atomgewicht Th=232·12±0·014 berechnet.Als Mittel dieser beiden Werte ergibt sich Th=232·135.Da aber die Analysenserie aus den oben besprochenen, uns triftig erscheinenden Gründen als die zuverlÄssigere angesehen werden mu\, glauben wir, da\ der aus ihr resultierende WertTh=232·12 als das derzeit wahrscheinlichste Atomgewicht des Thoriums anzusehen ist, wenn Ag=107·880 angenommen wird. Aus dem in 27 Bestimmungen gefundenen VerhÄltnis von angewandtem Silber zu gefundenem Silberbromid, AgAgBr= 0·574453, ergibt sich dann das Atomgewicht des Broms zu Br=79·916 in vollster übereinstimmung mit der von Baxter seinerzeit gefundenen Zahl.     

Synthese und Kristallstruktur von Hydronium-tris-ethylendiamin-cobalt(rhodium)-μ-trichloro-nonachlorotrirhenat(II)-chlorid,H3O[MEn3][Re3Cl12]Cl (M=Co,Rh)

Synthesis and Crystal Structure of Hydronium-tris-ethylenediamine-cobalt(rhodium)-μ-trichloro-nonachlorotrirhenate(III)-chloride, H₃O[MEn₃][Re₃Cl₁₂]Cl (M=Co, Rh) The chlorides H₃O[MEn₃][Re₃Cl₁₂]CI (M = Co, 1 ; Rh, 2 ) crystallize from hydrochloric acid solutions of ReCl₃ and MEn₃ · 3H₂O as deep red hexagonal columns. They are isotypic and crystallize with the hexagonal system (P6 , Z = 1; 1: a = 1010.87(3); c = 794.30(4) pm, R = 0.023, R_w = 0.016; 2: a = 1018.58(3); c = 794.74(4) pm, R = 0.026, R_w = 0.018). The anions [Re₃Cl₁₂]^3? are connected via H₃O₊ cation (C.N. 3). The large channels that run in the [001] direction contain, alternatively, the cations [MEn₃]³⁺ and the lonesome Cl^?-anions     

Molecular mechanics of organic halides. III. Fluorinated olefins

A molecular mechanical force field for fluorinated ethylenes and propylenes is described. The field computes geometries, dipole moments, and energy differences between isomers and rotamers. Component analysis indicates that “classical” strains alone (skeletal, nonbonded, electrostatic) cannot account for energy relationships. The discussion is supplemented by a semiempirical quantum chemical comparison of cis- and trans-FCH?CHF and of gauche- and anti-FCH₂CH₂F.     

Nondigestible oligosaccharides as dietary fiber

An overview is presented of the most important oligosaccharides that are classified as dietary fiber. Their occurrence and structures as well as their various physiological effects are described. The scientific evidence for health effects, associated with these physiological effects, along with the applications in the food industry, are also discussed.     

The thermodynamic properties of acetals+heptane mixtures at 298.15 K

Excess enthalpies and excess volumes were determined at 298.15 K for: dimethoxymethane+heptane, diethoxymethane+heptane, 1,1-dimethoxyethane+heptane, 1,1-diethoxyethane+heptane, 2,2-dimethoxypropane+heptane and 1,1-diethoxypropane+heptane.