Monitoring of liquid-phase organic reactions by photoelectron spectroscopy

There are strings attached: after linking the reacting groups to head groups of ionic liquids to drastically lower the vapour pressures of the reactants, ordinary liquid-phase organic reactions can be monitored by in situ X-ray photoelectron spectroscopy. This approach is demonstrated for the nucleophilic substitution of an alkyl amine and an alkyl chloride moiety, which are attached to the cation and anion of ionic liquids, respectively.     

Parallel solution-phase synthesis of a 2-aminothiazole library including fully automated work-up

A straightforward and effective procedure for the solution phase preparation of a 2-aminothiazole combinatorial library is described. Reaction, work-up and isolation of the title compounds as free bases was accomplished in a fully automated fashion using the Chemspeed ASW 2000 automated synthesizer. The compounds were obtained in good yields and excellent purities without any further purification procedure.     

Direct Correlation of Surface Tension and Surface Composition of Ionic Liquid Mixtures—A Combined Vacuum Pendant Drop and Angle-Resolved X-ray Photoelectron Spectroscopy Study

We investigated the surface tension and surface composition of various mixtures of the two ionic liquids (ILs) 1-methyl-3-octyl-imidazolium hexafluorophosphate [C₈C₁Im][PF₆] and 1,3-bis(polyethylene glycol)imidazolium iodide [(mPEG₂)₂Im]I in the temperature range from 230 to 370 K under ultraclean vacuum conditions. The surface tension was measured using a newly developed apparatus, and the surface composition was determined by angle-resolved X-ray photoelectron spectroscopy (ARXPS). In the pure ILs, the alkyl chains of [C₈C₁Im][PF₆] and the PEG chains of [(mPEG₂)₂Im]I are enriched at the IL/vacuum interface. In the mixtures, a strong selective surface enrichment of the alkyl chains occurs, which is most pronounced at low [C₈C₁Im][PF₆] contents. For the surface tension, strong deviations from an ideal mixing behaviour take place. By applying a simple approach based on the surface composition of the mixtures as deduced from ARXPS, we are able to predict and reproduce the experimentally measured temperature-dependent surface tension values with astonishingly high accuracy.     

Hydrated Cs+-exchanged MFI zeolites: location and population of Cs+ cations and water molecules in hydrated Cs6.6MFI from in and ex situ powder X-ray diffraction data as a function of temperature and other experimental conditions

Extending our previous investigation of dehydrated, Cs-exchanged MFI zeolites (J. Phys. Chem. B 2006, 110, 97-106) to hydrated analogues, we have determined the crystal structures of members of the Cs(6.6)H(0.3)MFI.xH(2)O series, for 0 < x < 28, from synchrotron-radiation powder diffraction data. In the fully hydrated phase, three independent Cs(+) cations and six water molecules are identified in difference Fourier maps. The populations of the cations amount to 2.79/3.40/0.41 Cs/unit cell (uc) for the Cs1/Cs2/Cs3 sites, respectively, and those of the water molecules to 4/4/4/4/8/4 H(2)O/uc for the Ow1/Ow2/Ow3/Ow4/Ow5/Ow6 sites, respectively. Close to water saturation, the Cs3 and Ow6 sites are near each other (approximately 1.44 A) and are not occupied simultaneously. At saturation, Cs cations and water molecules form three interconnected Cs(H(2)O)(n) clusters and one (H(2)O)(4) cluster in the MFI channel system: Cs2(H(2)O)(5) centered at x/y/z approximately -0.018/0.146/0.546 (midway between the intersection and the straight channels), Cs1(H(2)O)(4) centered at approximately 0.056/0.240/0.889 (the zigzag channel openings), Cs3(H(2)O)(2) centered at approximately 0.228/0.25/0.899 (in the zigzag channel), and the (H(2)O)(4) cluster (in the zigzag channel) bonded to Cs1 and Ow1. (H(2)O)(4) and Cs3(H(2)O)(2) exclude each other. The Cs2(H(2)O)(5) clusters are connected through weak Ow5...Ow5' hydrogen bonds (2.88 A) and form polymeric chains in the straight channel direction (010). During progressive hydration this Cs2 cation enlarges its hydration shell, stepwise, from Cs2(H(2)O)(2) to Cs2(H(2)O)(3), to Cs2(H(2)O)(4), and finally to a Cs2(H(2)O)(5) cluster. During the dehydration process, these extraframework species migrate, and it is shown that for varying total H(2)O/uc loadings the individual populations of the Cs(+) cations and H(2)O molecules strongly depend on experimental and measurement (in situ vs ex situ) conditions. The shapes of the channels change also; except for T > 150 degrees C, in all the Cs(6.6)H(0.3)MFI.xH(2)O phases, the straight channel D10R (double 10-ring) pore openings (1.16 < epsilon < 1.23) become strongly elliptical. The framework structure of all the investigated phases conforms to orthorhombic Pnma space group symmetry. Hydration and dehydration in Cs(6.6)MFI are fully reversible processes. From a knowledge of the Cs(+) locations, we are able to estimate, by computer simulations, the positions of H(2)O molecules in Cs(6.6)H(0.3)MFI.28H(2)O. The maximum theoretically possible water loading in an hypothetical and idealized cationless [Cs(6.6)H(0.3)]MFI structure amounts to 48 H(2)O/uc (nine independent water species), which is in fair agreement with existing high-pressure data (47 H(2)O/uc). This value is to be compared with the water saturation capacity obtained in a structural refinement of sealed-tube diffraction data of a proton-exchanged H(6.9)MFI.38H(2)O (seven independent water molecules). In the crystal structure of this H-ZSM-5 phase, the straight channel openings are almost circular (epsilon = 1.08). From this we conclude that the main factor responsible for the flexibility of the MFI framework is the presence of the Cs(H(2)O)(n)() clusters residing in, or close to, the straight channel double 10-rings.     

Hausdorff Dimension of Operator Stable Sample Paths

The Hausdorff dimension of the sample paths of a stochastic process with stationary independent operator stable increments is computed. With probability one, every sample path has the same dimension, depending on the real parts of the eigenvalues of the operator stable exponent.     

Exact results for the persistent current in an aharonov-bohm ring with a quantum impurity

We consider the problem of a persistent current in a one-dimensional mesoscopic ring with the electrons coupled by a spin exchange to a magnetic impurity. We show that this problem can be mapped onto an integrable model with a quadratic dispersion (with the latter property allowing for an unambiguous definition of the persistent current). We have solved the model exactly by a Bethe ansatz and found that the current is insensitive to the presence of the impurity. We conjecture that this result holds for any integrable quantum impurity model with an electronic dispersionε(k) that is an even function ofk.     

Generatrices of rational curves

We investigate the one-parametric set of projective subspaces that is generated by a set of rational curves in projective relation. The main theorem connects the algebraic degree of , the number of degenerate subspaces in and the dimension of the variety of all rational curves that can be used to generate . It generalizes classical results and is related to recent investigations on projective motions with trajectories in proper subspaces of the fixed space. Received 9 May 2001.     

Transitivity is neither hereditary nor finitely productive

We construct a transitive space that is the union of two subspaces homeomorphic to the (non-transitive) Kofner plane. Moreover, we show that the product of two transitive spaces need not be transitive. Finally, we observe that results of E.K. van Douwen establish that, under b = c, there exists a locally countable locally compact non-transitive zero-dimensional space. It follows that under b = c neither a locally transitive nor a compact space need be transitive.     

Rationale Tschebyscheff-Approximation über unbeschränkten Intervallen

Summary We consider rational best approximations to functions real-valued and continuous on closed unbounded intervals of the extended real numbers. The error of the best approximation is characterized by an alternant, whose length may be different from the well-known number for a bounded interval. Besides some exceptional cases the best approximation is unique.