Encapsulation complexes permit the observation of molecules under conditions of limited motion. Inside capsules, molecular encounters are prolonged, prearranged, and protected from the medium, in contrast to the short‐lived and random encounters that occur in bulk solution. Herein, the interaction of α‐, β‐, and γ‐picolines in a cylindrical capsule is described. Two picolines were taken up, and NMR spectra indicated dynamic combinations of various social isomers. The stabilities of the complexes are interpreted through computational methods. The shape of the space in the capsule allowed the alignment of molecules and revealed delicate, atom‐to‐atom interactions and attractive forces that elude observation in dilute solution. These weak forces were amplified in the isolated small space of the capsule. 相似文献
Abstract The effect of mono-, di- and trivalent metal salts on the maximum aqueous solubility of β-cyclodextrin (β-CD) has been investigated. The results show the solubility to be highly dependent on the cation charge: M+ < M2+ < M3+. For chloride as the anion, the solubility increases down Group II for a given salt concentration: Mg2+ < Ca2+ < Sr2+ < Ba2+. However for nitrate as the anion, solubility is largely cation-independent. The increased solubility allows mediumfield NMR (200 MHz) to be used in the study of the β-CD-thymol inclusion complex. 相似文献
2-Organylseleno(telluro)ethyl phosphines and 4-organylthio(seleno (telluro))butyl phosphines were prepared by reduction of diethyl 2-organylseleno(telluro)ethyl phosphonates and diethyl 4-organylthio(seleno(telluro)) butyl phosphonates with lithium aluminium hydride in diethyl ether. 1H and 31P NMR spectra as well as mass spectra of the resulting phosphines were considered. Their stability in regard to the oxidation by oxygen was discussed. 相似文献
Quantitative HPLC and colorimetry are used to study color variations in dyeings with indigo, 6-bromoindigo, and 6,6′-dibromoindigo, the main components of the historic dye Tyrian purple. For the first time, visible light is identified conclusively as a cause of debromination of the leuco form of 6-bromoindigo. A dyeing run using 6-bromoindigo alone is found to yield a dyed fabric containing large amounts of indigo, when the vat is exposed to visible light. The extent of debromination is dependent upon the pH of the dye bath and also the source of the visible light. This information allowed development of a dyeing procedure which is demonstrated to give consistent colors through two passes. Quantitative HPLC analysis of extracts from the dyed fabrics indicates that the leuco form of 6-bromoindigo vs. the leuco forms of indigo and 6,6′-dibromoindigo has the strongest affinity for wool fabric. This is postulated to be due to attractive electrostatic interactions between the leuco form of 6-bromoindigo and wool.
The linear spatial stability of the incompressible corner flow under pressure gradient has been studied. A self-similar form has been used for the mean flow, which reduces the related problem to the solution of a two-dimensional problem. The stability problem was formulated using the parabolised stability equations (PSE) and results were obtained for the viscous modes at medium and high frequencies. The related N-factors indicate that the flow is stable at these frequencies, but probably unstable for small frequencies. Furthermore the inviscid mode for each mean flow was obtained and the results indicate that its importance increases considerably with an increase in the adverse pressure gradient. Finally the dependence of the stability characteristics on the extent of the domain is also considered. 相似文献
We study the complex symplectic geometry of the space QF(S) of quasi-Fuchsian structures of a compact orientable surface S of genus g > 1. We prove that QF(S) is a complex symplectic manifold. The complex symplectic structure is the complexification of the Weil–Petersson symplectic structure of Teichmüller space and is described in terms which look natural from the point of view of hyperbolic geometry. 相似文献
We provide semilocal convergence theorems for Newton’s method in Banach space using outer or generalized inverses. In contrast
to earlier results we use hypotheses on the second instead of the first Fréchet-derivative. This way our Newton-Kantorovich
hypotheses differ from earlier ones. Our results can be used to solve undetermined systems, nonlinear least squares problems
and ill-posed nonlinear operator equations. We complete our study with some very simple examples to show that our results
apply, where others fail.
(Received 26 April 2000; in final form 17 November 2000) 相似文献