Beitrag zur thermischen Analyse und zur Polymorphic optischer Antipoden: Pantolacton,Methadon und Usninsäure

Zusammenfassung Von den vier Enantiomerenpaaren Pantolacton, Methadonhydrochlorid, Methadon-Base und Usninsäure wurden die Phasendiagramme untersucht. Die DL-Form besteht bei Methadonhydrochlorid und Usninsäure aus einer Molekülverbindung (echtes Racemat), bei Methadon-Base aus einem Konglomerat und bei Pantolacton aus Mischkristallen. Besonders interessant ist das Pantolacton, da sowohl die optisch aktive als auch die inaktive Form enantiotrop ist. Die bei tiefer Temperatur stabilen Modifikationen sind anisotrop, während die Hochtemperaturformen Isotropie aufweisen. Der Umwandlungspunkt liegt für das D(-)-Pantolacton bei 66°, für DL-Pantolacton konnte er nicht bestimmt werden; die Umwandlung erfolgt im Temperaturanstieg spontan bei 30–40°. Zwischen den isotropen Kristallformen von D(-)- und DL-Pantolacton wird eine kontinuierliche Mischkristallreihe nach Typ. I (Roozeboom) gebildet.

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Contribution to thermal analysis and polymorphism of optic antipodes: Pantolactone, methadone and usnic acid

Summary The phase diagrams of the four enantiomer pairs pantolactone, methadone hydrochloride, methadone base and usnic acid were investigated. The DL form consists of a molecular compound (pure racemate) in the case of methadone hydrochloride and usnic acid, and of a conglomerate in the case of methadone base and of mixed crystals in the case of pantolactone. Pantolactone is especially interesting, since both the optically active and the optically inactive form is enantiotropic. The stable modifications at low temperature are anisotropic, whereas the high temperature forms display isotropism. The transformation point is at 66° for D(-)-pantoIactone; it could not be determined for DL-pantolactone; the transformation takes place spontaneously with rise in temperature between 30–40°. A continous mixed crystal series according to type I (Roozeboom) is formed between the isotropic crystal forms of D(-)- and DL-pantolactone.

     

Einfluß wasserlöslicher Polyelektrolyte aus 1,6-Hexamethylendiisocyanat und N-(2-Aminoethyl)-2-aminoethansulfonsaurem Natrium auf die Dispersionsbildung bei anionischen Polyurethanen

Zusammenfassung Polyelektrolyte wurden durch Umsetzung von 1,6-Hexamethylendiisocyanat und N-(2-Aminoethyl)-2-amino-ethansulfonsaurem Natrium hergestellt und als wäßrige Lösungen der acetonischen Lösung eines anionischen Polyurethans vor der Dispersionsbildung zugesetzt. Kontinuierliche Leitfähigkeitsmessungen während der Dispersionsbildung ergaben, daß oberhalb eines bestimmten Wassergehaltes die Leitfähigkeit mit steigender Polyelektrolytkonzentration abnimmt. Dies wird auf eine zum Teil reversible Partikelvereinigung zurückgeführt, bei der ein Einschluß von wäßriger Phase zwischen den geflockten Teilchen erfolgt. Der mittlere Partikeldurchmesser nimmt mit steigendem Polyelektrolytgehalt zu. Oberhalb einer kritischen Polyelektrolytkonzentration ist die Partikelvereinigung weitgehend irreversibel, wodurch die Bildung einer Dispersion verhindert wird.

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Summary Polyelektrolytes were prepared by reaction of 1,6-hexamethylene diisocyanate and the Na salt of N-(2-aminoethyl)-2-aminoethane sulfonic acid. Aqueous solutions of these polyelectrolytes were added to acetonic solutions of an anionic polyurethane before formation of the aqueous dispersion. Continuous conductivity measurements showed that above a certain water concentration the conductivity decreased with increasing amount of polyelectrolyte. This was attributed to an in part reversible association of particles with inclusion of water between the flocked particles leading to an increase of the mean particle diameter. Above a critical concentration of polyelectrolyte the association of particles becomes largely irreversible preventing the formation of stable dispersions.

     

An Implicit Function Theorem in Locally Convex Spaces

The notion of strict differentiability in BANACH spaces is generalized to locally convex spaces in such a way, that computations in the bornological operator ideal of bounded operators play the role of norm estimations. We get a remarkably rich theory including not only the easy formulas like the chain rule, but also the deep theorems like the implicit function theorem. The BANACH space proofs can be translated almost literally.     

Conical intersections and bound molecular states embedded in the continuum

Nuclear dynamics on coupled potential surfaces can lead to bound states embedded in the continuum. For one type of conical intersection situation, an explicit proof is presented that such states exist. Non-Born-Oppenheimer effects are responsible for the binding of these states. Once the Born-Oppenheimer approximation is introduced, these states at best become resonances which decay via potential tunneling. The tunneling is completely suppressed by the coupling between the electronic states. A numerical example is given.     

Non-fermi-liquid behavior of quasi-one-dimensional pseudogap materials

We study the spectral function of the pseudogap phase of quasi-one-dimensional charge density wave materials. Using a stochastic approach and emphasizing an exact treatment of non-Gaussian order parameter fluctuations we will go beyond a usual perturbative calculation. Our results give a good fit to angle-resolved photoemission spectroscopy data and explain the absence of the Fermi edge in charge density wave materials even above the Peierls transition, indicating non-Fermi-liquid behavior.     

ZnO nanowall networks grown on DiMPLA pre‐patterned thin gold films

ZnO nanowall networks grown by a high pressure pulsed laser deposition (PLD) technique on a pre‐patterned thin gold film are presented. The thin gold film on a c ‐plane oriented sapphire substrate was structured with diffraction mask projection laser ablation (DiMPLA). It is shown that only areas processed with the laser patterning technique reveal homogeneous growth of ZnO nanowall networks. Photoluminescence measurements prove the higher material quality of the pre‐patterned regions compared to the untreated ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and structural properties of MgZnO/ZnO hetero- and double heterostructures grown by pulsed laser deposition

MgZnO thin films, MgZnO/ZnO heterostructures (HS) and double heterostructures (DHS) have been prepared on a-plane sapphire substrates by means of pulsed laser deposition (PLD). A linear blueshift of the MgZnO emission with increasing Mg content is observed in photoluminescence spectroscopy (PL) at 2 K. Cathodoluminescence measurements verify the spatial homogeneity of the emission properties of the MgZnO films. The film roughness is evaluated from atomic force microscopy scans. In MgZnO/ZnO HS the ZnO grows on all appearing MgZnO facets. PL investigations of such PLD-grown heterostructures show the high optical quality of thin ZnO films (d≤100 nm) grown on MgZnO. Capping those structures with a thin MgZnO layer further improves their luminescence intensity and enhances the emission of free-exciton luminescence from the ZnO layers. MgZnO/ZnO/MgZnO DHS with nominal ZnO layer thicknesses of d_nom≤6 nm show a clear intensification of the ZnO PL. Temperature dependent PL and transmission measurements between 4.4 and 300 K prove the dominating emission to be due to the recombination of excitons localized in the ZnO. At 2 K, due to confinement effects, their emission energy is blueshifted up to 51 meV compared to free excitons in bulk ZnO. PACS 81.15.Fg; 78.66.Hf; 68.37.Ps     

Generation of shaped ultraviolet pulses at the third harmonic of titanium-sapphire femtosecond laser radiation

We experimentally demonstrate a method to generate shaped femtosecond laser pulses in the ultraviolet at a central wavelength of 267 nm, the third harmonic of conventional titanium-sapphire femtosecond laser systems. Employing a 128-pixel liquid-crystal spatial light modulator, we impose variable spectral phase modulations upon the near-infrared laser pulses. By this, complex laser pulses can be shaped whose overall spectrum is still conserved. Our experiments show that it is possible to easily transfer these pulses into the ultraviolet at 267 nm via sum-frequency mixing in nonlinear crystals and to predictably generate multistructured ultraviolet femtosecond laser pulses. We analyze the temporal and spectral composition of these pulses after frequency conversion into the ultraviolet using difference-frequency cross-correlation and XFROG (cross-correlation frequency-resolved optical gating) techniques with an unmodulated fundamental laser pulse. The method can be employed to facilitate adaptive quantum control experiments in the ultraviolet wavelength regime, where the major absorption bands of many organic molecular systems are located. PACS 42.65.Re; 42.72.Bj; 32.80.Qk