Hydrogen Radical Additions to Unsaturated Hydrocarbons and the Reverse β‐Scission Reactions: Modeling of Activation Energies and Pre‐Exponential Factors

The group additivity method for Arrhenius parameters is applied to hydrogen addition to alkenes and alkynes and the reverse β‐scission reactions, an important family of reactions in thermal processes based on radical chemistry. A consistent set of group additive values for 33 groups is derived to calculate the activation energy and pre‐exponential factor for a broad range of hydrogen addition reactions. The group additive values are determined from CBS‐QB3 ab‐initio‐calculated rate coefficients. A mean factor of deviation of only two between CBS‐QB3 and experimental rate coefficients for seven reactions in the range 300–1000 K is found. Tunneling coefficients for these reactions were found to be significant below 400 K and a correlation accounting for tunneling is presented. Application of the obtained group additive values to predict the kinetics for a set of 11 additions and β‐scissions yields rate coefficients within a factor of 3.5 of the CBS‐QB3 results except for two β‐scissions with severe steric effects. The mean factor of deviation with respect to experimental rate coefficients of 2.0 shows that the group additive method with tunneling corrections can accurately predict the kinetics and is at least as accurate as the most commonly used density functional methods. The constructed group additive model can hence be applied to predict the kinetics of hydrogen radical additions for a broad range of unsaturated compounds.     

Control of Relative Direction and Amplitude in Extension/Contraction Motions of Molecular Strands Induced by Ion Binding

The shape of ligand strands composed of six‐membered aza‐heterocycles (het) connected at the α and α′ positions by hydrazone (hyz) units is determined in a predictable fashion by the nature of the heterocyclic groups (pyridine, pyrimidine, pyrazine etc.), and covers the range from extended linear to compact helical structures. The binding of metal ions to the coordination subunits, defined by the het‐hyz sequences, leads to marked shape changes by inter‐converting bent and linear conformations of the subunits, thus inducing relative motions of strand domains either in the same (con‐sense, “twirling”) or in opposite (dis‐sense, “flapping”) directions. The amplitude of the motion induced by metal‐ion binding and release and the relative directions of the formal motions can be controlled by the nature of the heterocyclic units. Thus, motions around a central 4,6‐disubstituted pyrimidine are dis‐sense motions, whereas there are con‐sense motions around a central 2,5‐disubstituted pyrazine unit, as illustrated by model ligands 1 and 2 , respectively. The more extended helical 3 and undulating (zigzag shape) 4 ligands undergo larger‐amplitude motions combining the relative displacements displayed by 1 and 2 . Ligands 3 and 4 form linear tetranuclear Pb^II and Zn^II complexes, thus producing an extension motion. The same holds for [Ru( 4 )(terpy)₄](PF₆)₈ (terpy=terpyridine). Reversible acid–base‐triggered molecular motions have been generated with [Zn₄( 4 )(OTf)₈] (TfOH=triflic acid).     

Metabolic stability and determination of cytochrome P450 isoenzymes' contribution to the metabolism of medetomidine in dog liver microsomes

Medetomidine is a potent and selective α2‐adrenergic agonist. The activation of α2‐adrenergic receptor mediates a variety of effects including sedation, analgesia, relief of anxiety, vasoconstriction and bradycardia. However, our main interest is the sedative effects of medetomidine when used as a premedicant prior surgery in companion animals, especially in dogs. Recently, data suggested that following intravenous infusion at six dosing regiments non‐linear pharmacokinetics was observed. Major causes of non‐linear pharmacokinetics are the elimination of the drug not following a simple first‐order kinetics and/or the elimination half‐life changing due to saturation of an enzyme system. The goal of this study was to establish the metabolic stability and determine the metabolic pathway of medetomidine in dog liver microsomes. Consequently, Michaelis–Menten parameters (V_max, K_m), T_1/2 and CL_i were determined. The incubations were performed in a microcentrifuge tube and containing various concentrations of medetomidine (10–5000 nm ), 1 mg/mL of microsomal proteins suspended in 0.1 m phosphate buffer, pH 7.4. Microsomal suspensions were preincubated with NADPH (1 mm ) for 5 min at 37°C prior to fortification with medetomidine. Samples were taken at various time points for kinetic information and the initial velocity (v_i) was determined after 10 min incubation. The reaction was stopped by the addition of an internal standard solution (100 ng/mL of dextrometorphan in acetone). Medetomidine concentrations were determined using a selective and sensitive HPLC‐ESI/MS/MS method. Using non‐linear regression, we determined a K_m value of 577 nm , indicating relatively low threshold enzyme saturation consistent with previous in vivo observation. The metabolic stability was determined at a concentration of 100 nm (?K_m) and the observed T_1/2 was 90 min with a CL_i of 0.008 mL/min indicating moderately low clearance in dog liver microsomes, also consistent with previous in vivo data. Moreover, results suggest that principally medetomidine is metabolized by the CYP3A with a small contribution from CYP2D and CYP2E. The participation of CYP3A is an important discovery since medetomidine is used as a premedicant in combination with fentanyl, ketamine and/or midazolam. These findings combined with a low K_m value may indicate that medetomidine can competitively inhibit the metabolism of these drugs and consequently significantly impair metabolic clearance. Copyright © 2009 John Wiley & Sons, Ltd.     

Pulsed laser deposition of ZnO in N2O atmosphere

The contribution deals with ZnO thin layers doped by nitrogen which were prepared by pulsed laser deposition in N₂O ambient atmosphere. Our approach is based on ablation of undoped ZnO target in active atmosphere containing N₂O gas without any supporting excitation equipment in parallel. Ablation of ZnO target was performed at different pressures (1–32 Pa) of N₂O ambient atmosphere by pulsed Nd:YAG laser (at 355 nm). Layers of ZnO were grown on different substrates (Si, sapphire, fused silica) and their properties were investigated by various analytical methods: scanning electron microscopy (SEM), secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD), and optical transmission spectroscopy. The results confirmed incorporation of nitrogen into ZnO layers and its concentration was pressure dependent. According to SIMS analysis, there is a certain pressure level (above 10 Pa) when the presence of N becomes negligible. Transmittance spectra showed increasing of the optical band gap (E _g) according to the pressure of N₂O.     

Teachers' Conceptions of Integrated Mathematics Curricula

In this qualitative research study, we sought to understand teachers' conceptions of integrated mathematics. The participants were teachers in the first year of implementation of a state‐mandated, high school integrated mathematics curriculum. The primary data sources for this study included focus group and individual interviews. Through our analysis, we found that the teachers had varied conceptions of what the term integrated meant in reference to mathematics curricula. These varied conceptions led to the development of the Conceptions of Integrated Mathematics Curricula Framework describing the different conceptions of integrated mathematics held by the teachers. The four conceptions—integration by strands, integration by topics, interdisciplinary integration, and contextual integration—refer to the different ideas teachers connect as well as the time frame over which these connections are emphasized. The results indicate that even when teachers use the same integrated mathematics curriculum, they may have varying conceptions of which ideas they are supposed to connect and how these connections can be emphasized. These varied conceptions of integration among teachers may lead students to experience the same adopted curriculum in very different ways.     

17O NMR gives unprecedented insights into the structure of supported catalysts and their interaction with the silica carrier

Flame silica was surface-labeled with (17)O, through isotopic enrichment of both siloxanes and silanols. After heat treatment at 200 and 700 °C under vacuum, the resulting partially dehydroxylated silica materials were investigated by high-field solid-state (1)H and (17)O NMR. More specifically, MQ MAS and HMQC sequences were used to probe the (17)O local environment. In a further step, these (17)O-tagged supports were used for the preparation of supported catalysts by reaction with perhydrocarbyl transition metal derivatives (zirconium tetraalkyl, tantalum trisalkyl-alkylidene, and tungsten trisalkyl-alkylidyne complexes). Detailed (17)O 1D and 2D MQ and HMQC MAS NMR studies demonstrate that signals in the Si-OH, Si-O-Si, and Si-O-metal regions are highly sensitive to local structural modifications, thanks to (17)O wide chemical shift and quadrupolar constant ranges. Experimental results were supported by DFT calculations. From the selective surface labeling, unprecedented information on interactions between supported catalysts and their inorganic carrier has been extracted.     

Synthesis and characterization of a neutral titanium tris(iminosemiquinone) complex featuring redox-active ligands

The neutral tris(semiquinonate) complex [Ti(dmp-BIAN(isq))(3)] [dmp-BIAN(isq) = N,N'-bis(3,5-dimethylphenylimino)acenaphthenesemiquinonate] was structurally, spectroscopically, and electrochemically characterized. Solid-state magnetism experiments reveal field-quenchable, enhanced temperature-independent paramagnetism (TIP). Density functional theory calculations employing the experimental geometry predicts a strong antiferromagnetic coupling, leading to an S = 0 ground state, but they also hint at spin frustration and concomitant close-lying, excited states, which cause the observed large TIP by admixture into the ground state. The dmp-BIAN(isq) ligand, which facilitates intramolecular electron transfer, was shown to undergo four quasi-reversible redox processes, demonstrating the ability of the ligand to act as an electron reservoir in complexes of early metals.     

Novel tailormade Bi4MO4(PO4)2 structural type (M = Mg, Zn)

In the Bi(2)O(3)-MO-P(2)O(5) ternary system, the commonly observed sizable 1D ribbon-like units have been extended to their 2D infinite end member, leading to the novel tailormade Bi(4)MO(4)(PO(4))(2) compounds. It contains planar [Bi(2)O(2)](2+) derivatives, separated by two slabs of PO(4), which create channels hosting the M(2+) cations (M = Mg, Zn). For both compounds, supercell orderings occur comparatively to the predicted ideal crystal structure (V(Mg) = 2V(ideal) and V(Zn) = 8V(ideal)). In the Mg case a transition into the ideal lattice occurs above 450 °C. In spite of the conceptual assembly of 2D motifs, the final architecture is three-dimensional due to strong interbonds. Thus, our work gives new insights on the possibility for versatile organization of original secondary building units (SBUs) able to self-assemble into predicted structural edifices. Single-crystal and powder XRD versus temperature, high-temperature (31)P NMR, as well as transmission electron microscopy were used for structural characterization. Preliminary electric characterization is also reported.     

A Copper(II) Thiolate from Reductive Cleavage of an S-Nitrosothiol

S-Nitrosothiols RSNO represent circulating reservoirs of nitric oxide activity in the plasma and play intricate roles in protein function control in health and disease. While nitric oxide has been shown to reductively nitrosylate copper(II) centers to form copper(I) complexes and ENO species (E = R(2)N, RO), well-characterized examples of the reverse reaction are rare. Employing the copper(I) β-diketiminate [Me(2)NN]Cu, we illustrate a clear example in which an RS-NO bond is cleaved to release NO(gas) with formation of a discrete copper(II) thiolate. The addition of Ph(3)CSNO to [Me(2)NN]Cu generates the three-coordinate copper(II) thiolate [Me(2)NN]CuSCPh(3), which is unstable toward free NO.     

Preparation and characterization of aluminum phthalocyanine acetate, propionate, and benzoate

Aluminum phthalocyanine acetate, propionate and benzoate were prepared by the reaction of hydroxy aluminum phthalocyanine and the corresponding acetic, propionic, and benzoic anhydrides. The reaction products were characterized by ¹H and ¹³C NMR spectroscopy and mass spectrometry. The thermal behavior of the products was determined by thermal analysis of particular samples.