Tuning of photo- and electroluminescence of new soluble, PPV-analogous short-chain compounds with naphthalene moieties

A series of oligomers analogous to poly(p-phenylenevinylene) (PPV), combining naphthalene and benzene as aromatic units, have been synthesized by a Knoevenagel reaction. By measuring UV/Vis spectra, photoluminescence (PL) and electroluminescence (EL), we studied the influence of the position of the naphthalene unit as well as the steric and electronic influences of cyano and alkyloxy substituents on the luminescent properties of these compounds.

New donor-acceptor pair for fluorescent immunoassays by energy transfer

A novel Förster donor-acceptor dye pair for an immunoassay based on resonance energy transfer (RET) is characterized with respect to its photophysical properties. As donor and acceptor, we chose the long-wavelength excitable cyanine dyes Cy5 and Cy5.5, respectively. Due to the perfect spectral overlap, an exceptionally high R(0) value of 68.7 A is obtained in solution. For biochemical applications, antibodies (IgG) are labeled with Cy5, while a tracer for competitive binding is synthesized by labeling bovine serum albumin (BSA) with an analyte derivative and Cy5.5. Binding the dyes to proteins at a low dye/protein ratio increases the fluorescence lifetimes and quantum yields, leading to an enhanced R(0) value of 85.2 A. At higher dye/protein ratios, the formation of nonfluorescent dimeric species causes a decrease in the fluorescence lifetime and quantum yield due to RET from monomeric dyes to dimers within one protein molecule. The Förster distances could be calculated using the dimer absorption spectra to 83.9 and 83.6 A for Cy5 and Cy5.5, respectively. Upon binding of the Cy5-labeled IgG to the tracer, efficient quenching of Cy5 fluorescence is observed. Steady-state and time-resolved measurements reveal that approximately 50% of the quenching results in Förster-type RET, while the residual quenching effect is caused by static quenching processes. The applicability of this dye pair is demonstrated in a homogeneous competitive immunoassay for the pesticide simazine.

Surface acidity of solid pharmaceutical excipients III. Excipients for solid dosage forms

The surface acidities of pharmaceutical excipients are detected by color changes of acid-base indicators on the substrate's surface. To quantify the indicator's transition interval on the surface of hydrophilic excipients, as an organic solvent methanol is introduced for the preparation of indicator-excipient mixtures. The influence of the particle size on the determination of the surface acidity is investigated and particle size did not influence the determination within the particle size range investigated. Surface acidities of common excipients used in preparation of solid dosage forms are presented.

Comparative luminescence of rat liver Cu-thionein and its chemically synthesized alpha-domain

A peptide corresponding to the alpha-domain of rat liver metallothionein-2 was chemically synthesized employing the solid phase peptide synthesis technique. Its luminescence properties that depend on the coordinated Cu(I) have been studied using luminescence spectrometric titration in the presence of Cu(I). Unlike the intact metallothionein which has been converted into the Cu species, the emission and excitation spectra of the Cu-alpha-fragment showed a red shift by 20 nm and 65 nm, respectively, suggesting a more compact and stable luminophore in the alpha-domain. Saturation of Cu(I) coordination was reached in the presence of 6.5 mol eq Cu(I) when the alpha-fragment was used and 12 mol eq Cu(I) were specifically bound by the intact metallothionein. The emission bands were homogeneous and no decline of the cluster structure was observed when excessive Cu(I) was added after saturation. A rearrangement of the Cu-cluster in metallothionein during its formation seems to be plausible.

Über den Streukoeffizienten der Kubelka-Munk-Theorie

Der in der Theorie von Kubelka und Munk auftretende Streukoeffizient wurde als Funktion von Wellenlänge und Korngröße untersucht. Dazu wurden neben dem Reflexionsvermögen bei „unendlicher“ Schichtdicke auch die Reflexion oder die Durchlässigkeit einer sehr dünnen Pulverschicht bestimmt und daraus nach den aus der Theorie abgeleiteten Gleichungen der Streukoeffizient berechnet. Das Verfahren führt nur bei relativ schwach absorbierenden Pulvern zum Ziel, es ist deshalb vor allem zur Messung des Streukoeffizienten von Adsorbentien geeignet, wenn man die Reflexionsspektren adsorbierter Stoffe untersuchen will. Das Streuvermögen wird durch letztere praktisch nicht geändert. Entgegen bisher gemachten Annahmen ist die Wellenlängenabhängigkeit des Streukoeffizienten nicht zu vernachlässigen, wenn die Korngröße der Pulver merklich unterhalb λ sinkt. Wie im Falle der Einfachstreuung ist die Abhängigkeit bei sehr kleinen Teilchen etwa proportional zu λ-4 (Rayleigh-Streuung); erst bei sehr großen Teilchen - verglichen mit der Lichtwellenlänge - konnte keine Wellenlängenabhängigkeit mehr gefunden werden. Die durch die λ.-Abhängigkeit des Streukoeffizienten bedingte Verschiebung von Absorptionsmaxima wurde berechnet.