Influence of the grain morphology of V2O5 on its reduction-reoxidation behaviour

The influence of the grain morphology of V₂O₅ on its reduction-reoxidation behaviour has been investigated by means of thermoanalytical methods. X-ray analysis and electron microscopy. Well-developed V₂O₅ platelets exposing predominantly the (010) face exhibited a significantly different reduction profile than poorly defined agglomerates of microcrystalline V₂O₅. Intermediate phases detected during reduction were V₆O₁₃ and VO₂ (rutile). The corresponding reoxidation profiles were found to be only weakly dependent on the grain morphology of V₂O₃. Electron microscopy showed that the original grain morphology of the V₂O₅ samples was not influenced markedly by the reduction-reoxidation cycle.     

Efficient S-alkylation of cysteine in the presence of 1,1,3,3-tetramethylguanidine

The synthesis of S-alkylated cysteine derivatives was carried out successfully in the presence of 1,1,3,3-tetramethylguanidine. Alkylation proceeded in high yields on unprotected amino acids and peptides containing a sulfhydryl group.     

Enol-keto tautomerism of aromatic photochromic Schiff base N,N'-bis(salicylidene)-p-phenylenediamine: ground state equilibrium and excited state deactivation studied by solvatochromic measurements on ultrafast time scale

A photochromic symmetric Schiff base, N,N'-bis(salicylidene)-p-phenylenediamine, is proposed as a probe for the study of solvent dependent enol-keto tautomerism in the ground and excited states. The ground state equilibrium between the enol-keto tautomers is found to depend mainly not on polarity but on the proton donating ability of the solvent. Upon selective excitation of each of these tautomers, the same excited state of a keto tautomer is created: in enol, after the ultrafast excited state intramolecular proton transfer (ESIPT), reaction, and in keto tautomer, directly. Then some part (<30%) of excited molecules are transferred to the photochromic form in its ground state. The evidence of another ultrafast deactivation channel in the excited enol tautomer competing with ESIPT has been found. The solvent does not influence the ESIPT dynamics nor the efficiency of the creation of the photochrome.     

Compounds of [btilde]-Cyclodextrin and Organosilicon Oligomers

Products of hydrolysis and condensation of organosilicon monomers in the presence of [btilde]-cyclodextrin (cycloheptaamylose [btilde]-CD) were studied by IR, NMR, MS, and x-ray methods. It was established that when an aqueous solution of [btilde]-CD is treated with dimethyldichlorosilane (DMDCS), diphenyldichlorosilane (DFDCS), methylphenyldichlorosilane (MFDCS), or with a mixture of the DMDCS and DFDCS, crystalline compounds of cyclodextrin with appropriate siloxane oligomers, are formed: /3-CD-MSO (69% yield by weight), [btilde] -CD-FSO (6.0% yield by weight), [btilde]-CD-MFSO (16%) yield by weight), [btilde]-CD-(MSO + FSO) (22–63% yield by weight). The content of the obtained products showed: [btilde]-CD:MSO = 1 mole of [btilde]-CD:2 (CH3)2SiO elements; [btilde]-CD:FSO = 1 mole of [btilde]-CD:0.57 mole of (C6H5)2SiO; [btilde]-CD:MFSO = 1 mole of [btilde]-CD:0.87 mole of (CH3) (C6H5)SiO. Contents of [btilde]-CD′ (MSO + FSO) depend on the starting monomer mixture. It is suggested that nonchemical bonds between [btilde]-CD molecules and siloxane elements occur. The topological structure of the obtained substances is analyzed. Analogous compounds are not formed with methyltrichlorosilane, triphenylchlorosilane, diethoxydichlorosilane, dimethyldimethoxysilane, dimethyl -diacetoxysilane, or silica tetrachloride. Compounds with [btilde]-cyclodextrin are not formed from already formed siloxane oligomers. In the processes described above, linear dextrins show a total lack of activity. Methylsiloxanes bound with [btilde]-CD have a cyclic structure, while phenyl ones probably have a linear structure.     

Preparation and characterisation of monolayers and Langmuir–Blodgett films of liquid crystal mixed with cubic silsesquioxanes

Polyhedral oligomeric silesquioxanes (POSS) with eight polyether substituents were mixed with the liquid crystal (LC) 4-octyloxy-4′-cyanobiphenyl and spread at the air/water interface. The surface pressure-area and surface potential-area isotherms were recorded for different weight ratios of both components. The obtained results showed that POSS molecules had beneficial influence on LC monolayer improving its stability and rigidity. Moreover, it was found that some LC–POSS mixtures collapse reversibly and form multilayer films on the top of LC monolayer. On the other hand, interfacial dilatational and shear rheology indicated decrease of elasticity of the films after mixing. Brewster angle microscopy revealed multilayer structure of the condensed film and formation of net-like structures in the expanded film. These films were successfully transferred on solid substrates using the Langmuir–Blodgett technique. The scanning electron microscopy images confirmed the film deposition and formation of networks by POSS–LC mixtures. These findings may be useful in the fabrication of electronic devices based on LCs.     

A quantitative approach to dynamic and isothermal curing of an epoxy resin modified with oligomeric siloxanes

Journal of Thermal Analysis and Calorimetry - The reactivity of a system comprising commercial epoxy resin Epidian® 6 (E6) and triethylenetetramine (Z-1) hardener was studied. The system was...     

Herstellung der Polydimethylsiloxane mit verschiedenen Molekulargewichtsverteilungen und ihre viskoelastischen Eigenschaften

Ohne Zusammenfassung     

Modeling of a vehicle seat suspension system with pneumatic spring and viscous dampers

The paper contains physical and mathematical model of the passive system of seat suspension, used in trucks and buses. Spring force in this system is performed by air spring, whereas damping force is generated by two viscous dampers. Based on the experimental research of characteristic parts of the suspension system, the parameters of mathematical model are determined. Both results of computer simulations and experiments are presented as power spectral density of acceleration courses, measured on seat, in comparison with courses measured on excitation platform in laboratory. Transmissibility of real system and its model are also presented in the paper. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Concepts of Trapping Topologically by Shell Molecules

Concepts of the synthesis of shell topological compounds, which consist of a guest molecule (or molecules) trapped by a host molecule with a spacial, egg shell-like structure are discussed. Generally, both constructing the shell molecule in the presence of a guest molecule and constructing the guest molecule in the presence of the shell (host) are ways to “shell” topological compounds. The preparation of shell molecules may consist of the completion of “preshell” molecules or of obtaining cascade branched oligomers and polymers. Cyclodextrins and substances like triquinance are considered to play a role in preshell molecules. Shell molecules may also be obtained by polyreaction of a monomer of the XRY_n type, which results in a cascade branched molecule of shell structure (spherical form). When the polyreaction is continued, the cascade branched molecule becomes a “cast” one. It is theoretically possible to enclose a guest molecule inside the shell during the cascade branching process if there is a good solvent (of high expansion coefficient value) in respect to the growing branches. A spacially developed molecule of both “empty” and “cast” structure may be obtained also by the known “step by step” cascade branching process which involves, for instance, a repeated cyanoethylation-reduction reaction.