Flow equations for the spin-boson problem

Using continuous unitary transformations recently introduced by Wegner [1], we obtain flow equations for the parameters of the spin-boson Hamiltonian. Interactions not contained in the original Hamiltonian are generated by this unitary transformation. Within an approximation that neglects additional interactions quadratic in the bath operators, we can close the flow equations. Applying this formalism to the case of Ohmic dissipation at zero temperature, we calculate the renormalized tunneling frequency. We find a transition from an untrapped to trapped state at the critical coupling constant α _c =1. We also obtain the static susceptibility via the equilibrium spin correlation function. Our results are both consistent with results known from the Kondo problem and those obtained from mode-coupling theories. Using this formalism at finite temperature, we find a transition from coherent to incoherent tunneling atT ₂ ^* ≈2T ₁ ^* , whereT ₁ ^* is the crossover temperature of the dynamics known from the NIBA.     

Hollow polymer shells from biological templates: fabrication and potential applications

Three-dimensional ultrathin polymer shells have been produced by a combination of step-by-step adsorption of polyelectrolytes on glutaraldehyde-treated human erythrocytes and subsequent solubilization of the cytoplasmatic constituents by means of a deproteinizing agent. The obtained hollow films preserve both the size and shape of the templating cells. This opens a pathway for the fabrication of polymeric capsules within a wide range of size and shape by using various biological templates. They may have exciting potential applications, such as templates for nanocomposites, as containers for a large class of materials, or as cages for chemical reactions. The thickness of the films can be adjusted over a large range: from a few nm up to several tens of nm. The polymer shells are permeable to small molecules and ions but not to macromolecules. An increase in the ionic strength of the solution up to 100 mmol make the capsules permeable for proteins. Permeability and conductivity studies have provided evidence that the adsorption of lipids on polyelectrolyte layers is a means of producing capsules with controlled permeability properties. 6-Carboxyfluorescein and Rhodamin 6G were precipitated within the capsules.     

EDTA and mixed-ligand complexes of tetravalent and trivalent plutonium

EDTA forms stable complexes with plutonium that are integral to nuclear material processing, radionuclide decontamination, and the potentially enhanced transport of environmental contamination. To characterize the aqueous Pu(4+/3+)EDTA species formed under the wide range of conditions of these processes, potentiometry, spectrophotometry, and cyclic voltammetry were used to measure solution equilibria. The results reveal new EDTA and mixed-ligand complexes and provide more accurate stability constants for previously identified species. In acidic solution (pH < 4) and at 1:1 ligand to metal ratio, PuY (where Y4- is the tetra-anion of EDTA) is the predominant species, with an overall formation constant of log beta110 = 26.44. At higher pH, the hydrolysis species, PuY(OH)- and PuY(OH)(2)2-, form with the corresponding overall stability constants log beta(11 - 1) = 21.95 and log beta(11 - 2) = 15.29. The redox potential of the complex PuY at pH = 2.3 was determined to be E(1/2) = 342 mV. The correlation between redox potential, pH, and the protonation state of PuY- was derived to estimate the redox potential of the Pu(4+/3+)Y complex as a function of pH. Under conditions of neutral pH and excess EDTA relative to Pu4+, PuY(2)4- forms with an overall formation constant of log beta120 = 35.39. In the presence of ancillary ligands, mixed-ligand complexes form, as exemplified by the citrate and carbonate complexes PuY(citrate)3- (log beta1101 = 33.45) and PuY(carbonate)2- (log beta1101 = 35.51). Cyclic voltammetry shows irreversible electrochemical behavior for these coordinatively saturated Pu4+ complexes: The reduction wave is shifted approximately -400 mV from the reduction wave of the complex PuY, while the oxidation wave is invariant.     

Nachweisgrenzen der Flavone mit Tetraphenyl-diboroxyd und langkettigen quartären Ammoniumverbindungen durch die Tüpfelreaktion nach F. Feigl

Zusammenfassung Die Nachweisgrenze in Mikrogramm von 20 Hydroxyderivaten der Phenyl-benzo--pyrone und ihren Glykosiden auf Grund der Farbe der Tüpfel auf Filterpapier im Tages- und UV-Licht, die Änderung der Farbe und Nachweisgrenze durch Tetraphenyl-diboroxyd und durch Tetraphenyl-diboroxyd und langkettige quartäre Ammoniumverbindungen wird mit dem Tüpfeltest bestimmt. Die Flavonderivate zeigen charakteristische Farbreaktionen, die eine Abhängigkeit der entstehenden Farbe von der Stellung und Anzahl der Hydroxylgruppen erkennen lassen und dadurch konstitutionelle Hinweise geben. Einige Flavone zeigen im UV-Licht charakteristische Fluoreszenzen. Durch die beiden Reagenzien lassen sich die Nachweisgrenzen der Flavone erheblich herabsetzen. Isomere Flavone unterscheiden sich durch die auftretenden Farben und durch Ausbleiben oder Auftreten der Fluoreszenz.Der Tüpfeltest mit Tetraphenyldiboroxyd in der beschriebenen Ausführung ermöglicht die Erkennung geringerer Mengen, als sie papierchromatographisch bestimmt werden können.Für einige Hydroxyphenyl-benzo--pyron-Derivate werden die Absorptionsmaxima und -minima nach der Umsetzung mit Tetraphenyldiboroxyd und Dimethyl-dodecyl-3,4-diehlorbenzyl-ammoniumchlorid bestimmt und auf deren Auswertung zur Konstitutionsermittlung hingewiesen.

---

Summary The detection limit (in micrograms) of 20 hydroxy derivatives of phenylbenzo--pyrones and their glucosides was determined with the spot test on the basis of the color of the stain on filter paper in daylight and ultraviolet light, along with the change of the color and the detection limits by means of tetraphenyl-diboron oxide and by means of tetraphenyl-diboron oxide and long chain quaternary ammonium compounds. The flavone derivatives exhibit characteristic color reactions, which reveal a dependence of the colors obtained on the position and number of the hydroxyl groups, and thus yield clues to the structural constitution. Several flavones show characteristic fluorescences in ultraviolet light. The detection limits of the flavones can be distincly lowered through use of the two reagents. Isomeric flavones differ in the colors they produce and through the absence or occurrence of fluorescence.The spot test with tetraphenyl diboron oxide using the procedure described here permits the detection of smaller quantities than can be determined paper chromatographically.The absorption maxima and minima were determined for several hydroxyphenyl-benzo--pyrone derivatives after the reaction with tetraphenyl diboron oxide and dimethyl-dodecyl-3,4-dichlorobenzyl ammonium chloride, and their use in determining structures is pointed out.

---

Résumé Détermination, par essais à la touche, des limites d'identification, en microgrammes, de vingt dérivés hydroxylés de la phényl-benzo--pyrone et de ses glucosides sur la base de la couleur de la touche sur papier filtre dans les lumières du jour et ultra-violette, du changement de couleur et des limites d'identification par addition, soit de tétraphényl-diboroxyde, soit de tétraphényl-diboroxyde et de combinaisons ammonium quaternaire à longue chaîne. Les dérivés de la flavone présentent des réactions colorées caractéristiques pour lesquelles la couleur développée dépend de la position et du nombre des groupements oxhydryle fournissant ainsi des indications sur la constitution. Quelques flavones présentent des fluorescences caractéristiques en lumière ultra-violette. L'emploi des deux réactifs permet d'abaisser considérablement les limites d'identification des flavones. Les flavones isomères se différencient par les couleurs développées et par l'inexistence ou l'existence de la fluorescence.L'essai à la touche à l'aide du tétraphényl-diboroxyde d'après le mode opératoire décrit, permet d'identifier des quantités inférieures à celles que l'on peut déterminer par chromatographie sur papier.On a déterminé les maximum et minimum d'absorption pour quelques dérivés de l'hydroxyphényl-benzo--pyrone après traitement par le réactif tétraphényl-diboroxyde et le chlorure de diméthyl-dodecyle-dichlorobenzyle-3–4-ammonium et on a indiqué la possibilité de leur emploi pour l'étude des constitutions.

---

---

XII. Mitt. über aromatische Borverbindungen; XI. Mitt.²⁹