Carbonates in zeolites: Formation,properties, reactivity

Two possible schemes of carbonate formation (with and without water participation) in cationic form zeolites are considered. Activation energy for the formation of hydrogen carbonate in NaX zeolite from water and carbon dioxide is calculated at the DFT level with periodic boundary conditions, while the problems of modeling the formation of symmetric carbonate in the same zeolite are discussed. The formation of copper carbonate is studied using binuclear CuOCu clusters from CO₂ where the influence of water on the barrier is discussed. The questions related to DFT application to binuclear copper clusters are also considered by comparison with the data obtained at the MP2 level. The reactivity of copper carbonate is tested in the reaction with methanol. © 2015 Wiley Periodicals, Inc.     

The mass spectrum of 1:12, 2:3, 4:5, 6:7, 8:9, 10:11-hexabenzocoronene

The mass-spectra of 1:12, 2:3, 4:5, 6:7, 8:9, 10:11-hexabenzocoronene and the isomer 1:2, 3:4, 5:6, 7:8, 9:10, 11:12-hexabenzocoronene have been examined. The former is typically that of an aromatic conjugated hydrocarbon and is sparse, the latter is more intense. It is conjectured that the former may be found in interstellar space.     

Lipophilicity in PK design: methyl, ethyl, futile

Lipophilicity, often expressed as distribution coefficients (log D) in octanol/water, is an important physicochemical parameter influencing processes such as oral absorption, brain uptake and various pharmacokinetic (PK) properties. Increasing log D values increases oral absorption, plasma protein binding and volume of distribution. However, more lipophilic compounds also become more vulnerable to P450 metabolism, leading to higher clearance. Molecular size and hydrogen bonding capacity are two other properties often considered as important for membrane permeation and pharmacokinetics. Interrelationships among these physicochemical properties are discussed. Increasing size (molecular weight) often gives higher potency, but inevitably also leads to either higher lipophilicity, and hence poorer dissolution/solubility, or to more hydrogen bonding capacity, which limits oral absorption. Differences in optimal properties between gastrointestinal absorption and uptake into the brain are addressed. Special attention is given to the desired lipophilicity of CNS drugs. In examples using -blockers, Ca channel antagonists and peptidic renin inhibitors we will demonstrate how potency and pharmacokinetic properties need to be balanced.     

Multi-pumping in flow analysis: concepts, instrumentation, potentialities

A novel strategy for the implementation of flow-based analytical procedures using several micropumps is proposed. The pumps are switched individually or in combination, in order to create a pulsed flowing stream through the analytical path, and are the only active devices acting simultaneously as liquid propelling units, sample insertion ports and commuting elements. Configuration and control of the flow system are then greatly simplified. The micropumps produce distinct stroke volumes at distinct pulse frequencies with high reproducibility ensuring the attainment of very stable flow rates. This leads to an enhanced versatility that enables the utilisation of different approaches for sample management including step-wise variable sample volume, binary sampling and merging zones without reconfiguration of the system hardware. In contrast to the typical flow systems, the proposed one is characterised by a pulsed flow ensuring a fast sample/reagent mixing that contributes to improve the reaction development—thus sensitivity—even in situations of limited dispersion. The basic features and the performance of the proposed strategy are evaluated in the spectrophotometric determination of Cr(VI) in natural waters with 1,5-diphenylcarbazide.     

Phytochromes, cryptochromes, phototropin: photoreceptor interactions in plants

In higher plants, natural radiation simultaneously activates more than one photoreceptor. Five phytochromes (phyA through phyD), two cryptochromes (cry1, cry2) and phototropin have been identified in the model species Arabidopsis thaliana. There is light-dependent epistasis among certain photoreceptor genes because the action of one pigment can be affected by the activity of others. Under red light, phyA and phyB are antagonistic, but under far-red light, followed by brief red light, phyA and phyB are synergistic in the control of seedling morphology and the expression of some genes during de-etiolation. Under short photoperiods of red and blue light, cry1 and phyB are synergistic, but under continuous exposure to the same light field the actions of phyB and cry1 become independent and additive. Phototropic bending of the shoot toward unilateral blue light is mediated by phototropin, but cry1, cry2, phyA and phyB positively regulate the response. Finally, cry2 and phyB are antagonistic in the induction of flowering. At least some of these interactions are likely to result from cross talk of the photoreceptor signaling pathways and uncover new avenues to approach signal transduction. Experiments under natural radiation are beginning to show that the interactions create a phototransduction network with emergent properties. This provides a more robust system for light perception in plants.     

Chemie in der Freskomalerei: Kunst,Computer, Chemie

Prehistoric cave paintings have been conserved for about 15000 to 20000 thousand years. As modern investigations have shown the applied pigments are covered with a surface film of crystallized lime.This is the principle used when fresco‐painting. The pigments are painted on freshly applied, wet lime‐water walls or ceilings. During the process of ripening carbon dioxide is absorbed from atmosphere. Lime mortar is hardening, the pigments dry with the plaster to become a permanent part of brickwork. Though fresco buono (= true fresco)is the most durable technique it depends sensitively on processes of acid‐base‐equilibria. Thus, fresco‐paintings are „in dialogue”︁ with environmental conditions for all times. The physico‐chemical principles of fresco‐painting are discussed and demonstrated.     

Tetrahydrogestrinone: discovery, synthesis, and detection in urine

Tetrahydrogestrinone (18a-homo-pregna-4,9,11-trien-17beta-ol-3-one or THG) was identified in the residue of a spent syringe that had allegedly contained an anabolic steroid undetectable by sport doping control urine tests. THG was synthesized by hydrogenation of gestrinone and characterized by mass spectrometry and NMR spectroscopy. We developed and evaluated sensitive and specific methods for rapid screening of urine samples by liquid chromatography/tandem mass spectrometry (LC/MS/MS) of underivatized THG (using transitions m/z 313 to 241 and 313 to 159) and gas chromatography/high-resolution mass spectrometry (GC/HRMS) analysis of the combination trimethylsilyl ether-oxime derivative of THG (using fragments m/z 240.14, 254.15, 267.16, and 294.19). A baboon administration study showed that THG is excreted in urine.     

Lithium bromide in acetonitrile: Thermodynamics,theory, and simulation

A variety of methods has been used for the study of lithium bromide solutions in acetonitrile yielding by their combination reliable information on different levels of approximation. Osmotic coefficients based on precise vapor pressure measurements are reproduced by CM (chemical model) and HNC (hypernetted chain) calculations and by BD (brownian dynamics) simulations. The results of neutron scattering experiments are treated with the help of HNC and BD methods. Hartree-Fock calculations on isolated LiBr pairs and solvated lithium ions yield reliable particle distances and reveal the geometry of the lithium solvation sphere.     

Recent Advances in Polyallenes: Preparation,Self-Assembly,and Stimuli-Responsiveness

Polyallenes, as a typical type of reactive polymers, are of great significance and have aroused widespread interest because they contain double bonds that can be post-modified into other functionalities to afford varieties of functional materials. This Minireview firstly highlights the recent advances in the preparation of polyallenes, including preparation of helical polyallenes through directly polymerization of chiral allene monomers or helix-sense-selective polymerization (HSSP) of achiral allene monomers, synthesis of 1,2-regulated polyallenes and 2,3-regulated polyallenes via selective polymerization of allene monomers, polymerization of allene monomers catalyzed by Ni(II)-terminated poly(3-hexylthiophene) (P3HT), and so on. Then, latest progress on the self-assembly and stimuli-responses of polyallene-based diblock, ABA and ABC triblock copolymers is summarized. We hope this Minireview will inspire more interest in developing polyallenes and encourage further advances in functional materials.     

Polymer chemistry in flow: New polymers,beads, capsules,and fibers

The union between polymer science and microfluidics is reviewed. Fluids in microreactors allow the synthesis of a wide range of polymeric materials with unique properties. We begin by discussing the important fluid dynamics that dominate the behavior of fluids on the micrometer scale. We then progress through a comprehensive analysis of the polymeric materials synthesized to date. This highlight concludes with an overview of the methods used to make microreactors. We enthusiastically endorse microreactors as a powerful approach to making materials with controlled properties, although we have tried to provide a critical eye to help the nonexpert enter the field. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6505–6533, 2006     

ChemInform Abstract: Syntheses,Structures, Physical Properties,and Electronic Structures of Ba2MLnTe5 (M: Ga and Ln: Sm,Gd, Dy,Er, Y; M: In and Ln: Ce,Nd, Sm,Gd, Dy,Er, Y).

The title compounds are synthesized by solid state reactions of BaTe, Ga₂Te₃ or In₂Te₃, Ln, and Te (1273—1323 K, 20—48 h) and characterized by single crystal XRD, diffuse reflectance spectroscopy, magnetic susceptibility measurements, second harmonic generation measurements, and DFT electronic structure calculations.     

Chiral metallacyclophanes: self-assembly, characterization, and application in asymmetric catalysis

[structure: see text] A family of chiral metallacyclophanes has been readily assembled based on robust Pt-acetylide linkage and characterized by a variety of spectroscopic techniques and X-ray crystallography. The steric congestion around the chiral dihydroxy groups in rigid metallacyclophane 4 prevents their reactions with Ti(O(i)()Pr)(4) to form active catalysts for enantioselective diethylzinc additions to aromatic aldehydes. In contrast, chiral dihydroxy groups in more flexible unclosed metallacyclophane 5 are effective ligands for enantioselective catalytic diethylzinc additions to aromatic aldehydes.