Metallo‐supramolecular block copolymer micelles: Improved preparation and characterization

Micelles prepared from amphiphilic block copolymers in which a poly(styrene) segment is connected to a poly(ethylene oxide) block via a bis‐(2,2′:6′,2″‐terpyridine‐ruthenium) complex have been intensely studied. In most cases, the micelle populations were found to be strongly heterogeneous in size because of massive micelle/micelle aggregation. In the study reported in this article we tried to improve the homogeneity of the micelle population. The variant preparation procedure developed, which is described here, was used to prepare two “protomer”‐type micelles: PS₂₀‐[Ru]‐PEO₇₀ and PS₂₀‐[Ru]‐PEO₃₇₅. The dropwise addition of water to a solution of the compounds in dimethylformamide was replaced by the controlled addition of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equilibrium analyses in an analytical ultracentrifuge and by transmission electron microscopy of negatively stained samples. Sedimentation analysis showed virtually unimodal size distributions, in contrast to the findings on micelles prepared previously. PS₂₀‐[Ru]‐PEO₇₀ micelles were found to have an average molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle preparation by the standard method) and an average hydrodynamic diameter (d_h) of 18 nm. For PS₂₀‐[Ru]‐PEO₃₇₅ micelles, the corresponding values were M = 603,000 g/mol (31 protomers per micelle) and d_h = 34 nm. The latter particles were found to be identical to the “equilibrium” micelles prepared in pure water. Both micelle types had a very narrow molar mass distribution but a much broader distribution of s values and thus of hydrodynamic diameters. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity analysis. The findings from electron microscopy were in disagreement with those from the sedimentation analysis both in average micelle diameter and in the width of the distributions, apparently because of imperfections in the staining procedure. The preparation procedure described also may be useful in micelle formation from other types of protomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4458–4465, 2004     

Metallo‐supramolecular micelles: Studies by analytical ultracentrifugation and electron microscopy

In aqueous solutions, amphiphilic block copolymers in which a polystyrene (PS) segment is connected to a poly(ethylene oxide) (PEO) block via a bis(2,2′:6′,2″‐ terpyridine ruthenium) complex can form micelles. Such micelles of the protomer type PS₂₀‐[Ru]‐PEO₇₀, according to the preparation procedure representing frozen micelles, were studied by sedimentation velocity and sedimentation equilibrium analysis in an analytical ultracentrifuge and by transmission electron microscopy, with different techniques applied for the sample preparation. The particles obtained were surprisingly multifarious in size. In ultracentrifugation experiments performed at relatively low salt concentrations, the distributions of the sedimentation coefficient s_20,w showed a pronounced peak at 9.6 S and a broad, only partly separated second peak around 14 S. The molar mass of the particles at the peak was around 430,000 g/mol, corresponding to an aggregation number of approximately 85. The average hydrodynamic diameter of the particles in the peak fraction was approximately 13 nm. In electron micrographs of negatively stained samples, spheres of diameters between 10 and 25 nm were the most abundant particles, but larger ones with a wide size range were also visible. The latter particles apparently were composed of smaller ones. The data from both sedimentation analysis and electron microscopy showed that (1) the studied compound formed primary micelles of diameters around 20 nm and (2) the primary micelles had a tendency toward aggregation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3159–3168, 2003     

Chemical studies of marine invertebrates—XXVIII: Diterpenes from clavularia inflata (coelenterata,octocorallia, stolonifera)

The presence of terpenoids in the order Stolonifera has been established by the isolation of three novel diterpenes, 1α,4β-dihydroxyclavular-17-ene (1), 4β-hydroxyclavulara-1(15),17-diene (2) and 3α.4β-dihydroxyclavulara-1(15), 17-diene (3) from Clavularia infiata. The structure of 1 has been determined by X-ray diffraction analysis and those of 2 and 3 by chemical intercorrelation with 1.     

Die Verfeinerung der Kristallstruktur eines metamorphen Orthopyroxens

The atomic coordinates, the isotropic temperature factors and the site-occupancy factors of a metamorphic orthopyroxene Mg_1,56Fe_0,39Ca_0,05Si₂O₆ have been refined by the least-squares method using 1373 crystallographically independent reflections. Three-dimensional intensity data have been determined by integrated Weissenberg photographs. The final residual is 0.11. The site-occupancy factors M 1 = Mg_0,968 + Fe_0,032 and M 2 = Mg_0,589 + Fe_0,361 + Ca_0,050 reflect a high degree of order in the intracrystalline Mg, Fe distribution. The M 1, M 2 octahedra, the Si tetrahedra and the dependence of the means interatomic distances M  O on the Mg. Fe site occupancy are the subject of discussions.     

Die Anwendung des Quantimet zur Ätzgrubendichtebestimmung an Silizium-Einkristallen

A quantitative estimation of the structure of etched silicon crystals is possible with the microscope Quantimet by a fast counting the number of particles, i.e. etch pits on {111}-planes. Boundary conditions of the measuring technique are the requisite size of the etch pits of from > 3 … 5 μm, a plane specimen surface, the correct optical magnification, threshold and acceptance width. Sources of errors due to the structure result from the overlap of etch pits at dislocation densities > 10⁴ cm⁻² which leads to an underestimation of the number of etch pits because of the reduced signal output. An overestimation is most caused by an unwished contrast in the surface which yields additional signal outputs. The errors will be eliminated by using a calibration curved. Due to the short time which is necessary for counting, the Quantimet is well suitable for routine testings and for quantitative evaluation of the structure defects (etch pit density) in silicon, including consideration of possible errors.     

Broadband excitation pulses for high‐field solid‐state nuclear magnetic resonance spectroscopy

In nuclear magnetic resonance spectroscopy, experimental limits due to the radiofrequency transmitter and/or coil means that conventional radiofrequency pulses (“hard pulses”) are sometimes not sufficiently powerful to excite magnetization uniformly over a desired range of frequencies. Effects due to nonuniform excitation are most frequently encountered at high magnetic fields for nuclei with a large range of chemical shifts. Using optimal control theory, we have designed broadband excitation pulses that are suitable for solid‐state samples under magic‐angle‐spinning conditions. These pulses are easy to implement, robust to spinning frequency variations, and radiofrequency inhomogeneities, and only four times as long as a corresponding hard pulse. The utility of these pulses for uniformly exciting ¹³C nuclei is demonstrated on a 900 MHz (21.1 T) spectrometer. Copyright © 2012 John Wiley & Sons, Ltd.