The effects of substituents at C5, C6 and C7 on the solvolysis rates of 2-norbornyl p-toluene sulfonates confirm that through space induction is directional and depends on distance and bridging strain. 相似文献
Local density and generalized gradient approximation time-dependent density functional methods have been used for calculation of the singlet and triplet excited states of nickel-porphine, Ni-tetraphenyloporphine, and Ni-octaethyloporphyrine. Special attention is paid to metal-ligand transitions and d-d transitions. It is shown that the lowest exited singlet states of the three compounds can be described as a transfer of an electron from the porphine ring to the d(x2-y2) orbital of the nickel atom. On the other hand, the lowest excited triplet state arises from promotion of an electron between two nickel d orbitals, an occupied d(z2) and an empty d(x2-y2). It is proposed that a rapid quenching of the excited singlet states is due to an ultrafast intersystem crossing between 1Eg)and 3Eg or 3B1g states. 相似文献
The sorption of hydrogen between the layers of the multilayered wall of nanotubular TiO2 was studied in the temperature range of -195 to 200 degrees C and at pressures of 0 to 6 bar. Hydrogen can intercalate between layers in the walls of TiO2 nanotubes forming host-guest compounds TiO2 x xH2, where x < or = 1.5 and decreases at higher temperatures. The rate of hydrogen incorporation increases with temperature and the characteristic time for hydrogen sorption in TiO2 nanotubes is several hours at 100 degrees C. The rate of intercalate formation is limited by the diffusion of molecular hydrogen inside the multilayered walls of the TiO2 nanotube. 1H NMR-MAS and XRD data confirm the incorporation of hydrogen between the layers in the walls of TiO2 nanotubes. The nature and possible applications of the observed intercalates are considered. 相似文献
Non-linear effects were observed in acyclic amino acid-catalyzed direct asymmetric intermolecular aldol reactions. The non-linear effects are due to the equilibrium solid-liquid phase behavior of amino acids. The results suggest that the phase behavior of amino acids linked to asymmetric catalysis may have implications to the evolution of homochirality. 相似文献
We propose a novel composite organic-inorganic coating in the form of a redox polymer film for protection of stainless steel against general corrosion in strong acid medium (2 M H2SO4). We utilize an anion exchange polymer, protonated poly(4-vinylpyridine), into which hexacyanoferrate anions have been introduced. Owing to the presence of Fe(CN)63–/4– at the interface formed by the film and the steel, a sparingly soluble metal hexacyanoferrate (mostly Prussian blue, PB) is formed as an overcoating on the steels surface, presumably on the passive (metal oxide) layer. The redox polymer film on the steel seems to act as a composite three-dimensional bilayer-type coating in which hexacyanoferrate(III,II) anions (that are capable of effective charge storage) exist in the outer portions of the film, whereas the inner PB layer improves the systems overall adherence and stability. By analogy to a conducting polymer (e.g. polyaniline, polypyrrole), introduction of the redox polymer composite film leads to stabilization of the steel substrates potential within the passive range.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003) 相似文献
Electrochemistry and biomembranes are interface science in that both are concerned with the phenomena at, as well as across, the interfaces. Membrane electrochemistry may be defined as the application of electrochemistry to biomembrane studies. Additionally, transport processes within the membrane are involved in biomembranes. Since biomembranes are diverse and are usually not amenable to probing by electrochemicophysical techniques, model membrane systems have been developed for their investigation.
The introduction of experimental bilayer lipid membranes (BLM) technique and its modifications have been instrumental in the development and testing of membrane transport concepts (carriers vs channels) and electronic processes in membranes. Instead merely viewing a biomembrane as a physical barrier containing carriers or channels to carry out ionic processes, an ultrathin lipid or biological membrane can also be considered as a complete ‘electrochemical cell’ with one membrane/solution interface reducing (as a cathode) and the other membrane/solution interface oxidizing (as an anode). It is now possible to understand energy transduction (charge generation, separation, and redox reactions) in terms of ultrathin lipid membranes separating two aqueous solutions.
In this paper, we shall discuss the basic principles of electrochemistry as they are applied to membrane studies. Emphasis will be on experimental bilayer lipid membranes (BLM) which have been extensively investigated as models of biomembranes. 相似文献
The effect of the bifunctional crosslinking reagent glutaraldehyde on the activity of the restriction enzymes Bam HI,Hind III, EcoRI, and Tthlll I was investigated. The four enzymes exhibited differential sensitivity to inactivation. Tthlll I
was the most sensitive, with activity losses occurring at levels of 0.0025% and above.Hind III was the most stable of the four and remained fully active at concentrations as high as 0.075%. Addition of BSA to incubation
mixtures generally had a stabilizing effect. Implications of these results for the design of glutaraldehyde-based methods
for the immobilization of restriction endonucleases are discussed. 相似文献
Zusammenfassung Ein zweites spektrochemisches Verfahren zur Bestimmung von Silber, Blei, Zinn, Wismut, Tellur, Arsen und Antimon in Eisen und Stahl wurde entwickelt. Auch hier wird die spektrographische Analyse nach Auflösen der Probe in Salpetersäure und Eindampfen der Lösung zur Trockne durchgeführt. Die leichtflüchtigen Elemente werden ohne Puffer durch Anwendung eines inhomogenen Magnetfeldes und einer zweckmäßigen Elektrodenform störungsfrei und mit guter Reproduzierbarkeit bestimmt. Dabei sind die unteren Bestünmungsgrenzen gleich oder niedriger als die anderer spektrochemischer Methoden, die bisher beschrieben wurden. Das Verfahren zeichnet sich durch Schnelligkeit und Einfachheit aus.
Spectrochemical determination of trace elements in iron and steelPart II. determination of Ag, Pb, Sn, Bi, Te, As and Sb by using an inhomogeneous magnetic field
A second spectrochemical method for the determination of silver, lead, tin, bismuth, tellurium, arsenic and antimony in iron and steel has been developed. Here also the spectrographic analysis is to be carried out after dissolution of the sample in nitric acid and evaporation of the solution to dryness. Without buffer, the easily volatile elements are determined free of interferences and with good reproducibility by using an inhomogeneous magnetic field and electrodes of an appropriate form. The lower limits of determination are the same or lower than those obtained by any other spectrochemical method described. The method is characterised by rapidity and simplicity of procedure.