Mechanism of formation of unusual photodegradation products from friedelin

From the photolysate of friedelin1, 3,4-seco-3-nor-friedelan-2-al2 and 3,4-seco-3-nor-friedelan-2-oic acid3 were obtained in addition to the expected photoproducts. Evidence is provided that2 and3 are autoxidation products of the ketene13 produced by α-cleavage of1 followed by hydrogen transfer.     

Raman and luminescence processes under the resonant two-photon excitation of an excitonic molecule in CuCl

Emission spectra and its decay time under the resonant two-photon excitation of an excitonic molecule in CuCl were observed using a tunable dye laser. The Raman and luminescence processes were separated from their different decay times. The ratios of these two processes were estimated for the transverse and longitudinal excitons, respectively, at various band widths of the exciting laser.     

Magnetische Eigenschaften der Lanthanid-Nickel-Verbindungen LnNi5

Zusammenfassung Im Temperaturbereich 4–300° K werden Messungen der magnetischen Suszeptibilität in Abhängigkeit von der Temperatur an sechsLnNi₅-Verbindungen angegeben (Ln=Ce, Pr, Nd, Gd, Ho bzw. Tm). Die paramagnetischen Momente von Gd, Ho und Tm inLnNi₅-Verbindungen stimmen gut mit den für eine Anordnung aus freien dreifach positiven Ionen zu erwartenden Werten überein. TmNi₅ zeigt bei tiefen Temperaturen Tendenz zuVan Vleck-Paramagnetismus. Ferromagnetische Ordnungen treten bei GdNi₅, HoNi₅ und TmNi₅ im Temperaturbereich 22–33° K auf. Die Sättigungsmomente der Ho- und Tm-Verbindungen sind — vermutlich wegen der Kristallfeld-wechselwirkung — kleiner als gJ. Nickel scheint in PrNi₅ und NdNi₅ magnetisch zu sein.

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Magnetic characteristics of lanthanide-nickel (LnNi ₅) compounds

Magnetic susceptibility-temperature measurements are presented for sixLnNi₅ compounds, withLn=Ce, Pr, Nd, Gd, Ho and Tm, for the temperature range 4 to 300° K. Paramagnetic moments of the Gd, Ho and Tm in theLnNi₅ compounds are in good agreement with those expected for an assemblage of free tripositive ions. TmNi₅ exhibits a tendency towardVan Vleck paramagnetism at low temperatures. Ferromagnetic ordering is exhibited by GdNi₅, HoNi₅ and TmNi₅ at temperatures ranging from 22 to 33° K. The saturation moments of the Ho and Tm compounds are less than gJ presumably because of the crystal field interaction. Nickel appears to be magnetic in PrNi₅ and NdNi₅.

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Mit 4 Abbildungen

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Herrn Prof. Dr.H. Nowotny gewidmet

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Diese Arbeit wurde durch eine Stiftung des Army Research Office, Durham, gefördert     

Thermochromic properties of low-melting ionic uranyl isothiocyanate complexes

Temperature-dependent yellow-to-red colour changes of uranyl thiocyanate complexes with 1-alkyl-3-methylimidazolium cations have been studied by different spectroscopic methods and this phenomenon is attributed to changes in the local environment of the uranyl ion, including the coordination number, as well as to cation-anion interactions.     

Protective effect of small amounts of sodium dodecyl sulfate on the helical structure of bovine serum albumin in thermal denaturation

In the presence of sodium dodecyl sulfate (SDS), the secondary structure of bovine serum albumin (BSA) was almost protected against thermal denaturation above 50 degrees C, where the structural change became irreversible. Beyond 30 degrees C, the helicity (66%) of the protein sharply decreased with rise of temperature. In response to this, the proportions of beta-structure and random coil increased. The helicity and the beta-structural proportion were 44% and 13% at 65 degrees C, respectively. The protective effect was observed upon the coexistence of SDS of extremely low concentrations: the molar ratio of [SDS]/[BSA] of 15 was enough to induce the maximal protective effect on the helical structure of the protein. The maximal protected helicity was 58% at 65 degrees C, increasing to 64% upon cooling down to 25 degrees C. This protective effect became greater with an increase of chain length of alkyl sulfate ion. On the other hand, a cationic surfactant did not protect the BSA structure at all against the thermal denaturation. This protective effect was characterized by the specific amphiphilic nature of anionic surfactant. Such an anionic surfactant is considered to protect the protein structure by building bridges between particular nonpolar residues and particular positively charged residues located on different loops of the protein.     

Regioselective synthesis of polysubstituted pyridines via hetero-Diels-Alder reaction of isotellurazoles with acetylenic dienophiles

Treatment of substituted isotellurazoles or their Te-oxides with acetylenic dienophiles efficiently afforded polysubstituted pyridine derivatives through a pathway involving hetero-Diels-Alder reaction of isotellurazoles and the subsequent tellurium extrusion from the intermediary cycloadducts.     

Uniqueness and continuity of solution for the initial data in the scaling invariant class of the degenerate Keller�CSegel system

We consider the degenerate Keller–Segel system (KS) _m below. We find the functional space L^s(0,T;L^p(\mathbbR^N)){L^s(0,T;L^p(\mathbb{R}^{N}))} with some p,s for the uniqueness and continuity of weak solutions with respect to the initial data. Our space is discussed from a viewpoint of the scaling invariant class associated with (KS) _m for γ = 0. The technique is based on the L ¹-contraction principle for the porous medium equation.     

Correction for phase-shift deviation in a complex Fourier-transform integrated-optic spatial heterodyne spectrometer with an active phase-shift scheme

We report that a spectrum can be retrieved with a planar waveguide spatial heterodyne spectrometer (SHS) incorporating an active phase-shift scheme, where the phase shifts are distributed around π/2. This was confirmed experimentally with an SHS that had 32 interleaved Mach-Zehnder interferometers and whose free spectral range was 625 GHz. The phase shifts ranged from 0.71 to 2.2 rad against the target of π/2 rad.