A New catalytic reaction for determination of nanogram amounts of copper

Summary A simple and very sensitive new catalytic method is proposed for determination of copper(II). The method is based on the oxidation of sulphanilic acid with H₂O₂ at pH 7 in the presence of pyridine as activator. The sensitivity of the method is 5 ng/ml. Cobalt(II) interferes at concentrations of the same order as copper(II). The method is suitable for determination of copper in biological materials.

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Zusammenfassung Eine einfache und sehr empfindliche katalytische Methode zur Bestimmung von Kupfer(II) wurde vorgeschlagen. Sie beruht auf der Oxydation von Sulfanilsäure mit Wasserstoffperoxid bei pH 7 in Gegenwart von Pyridin als Aktivator. Ihre Empfindlichkeit beträgt 5 ng/ml. Kobalt(II) stört in Konzentrationen der gleichen Größenordnung wie Kupfer(II). Das Verfahren eignet sich zur Kupferbestimmung in biologischem Material.

     

Synthesis and structural characterization of isomeric coumarino‐1,2‐oxaphosphole derivatives

The coumarino‐[3,4‐c]‐3H‐10‐methyl‐2‐oxo‐2‐phenyl‐1,2‐oxaphosphole was prepared by the addition of PhPCl₂ to 3‐acetylcoumarin in the presence of acetic anhydride. Its conversion to the isomeric coumarino‐[3,4‐c]‐9H‐9‐methyl‐2‐oxo‐2‐phenyl‐1,2‐oxaphosphole was studied in different reaction conditions. The structures of the two isomers were determined by X‐ray crystallography and by ab initio molecular orbital calculations.     

Electrochemical Vicinal Difluorination of Alkenes: Scalable and Amenable to Electron-Rich Substrates

Fluorinated alkyl groups are important motifs in bioactive compounds, positively influencing pharmacokinetics, potency and conformation. The oxidative difluorination of alkenes represents an important strategy for their preparation, yet current methods are limited in their alkene-types and tolerance of electron-rich, readily oxidized functionalities, as well as in their safety and scalability. Herein, we report a method for the difluorination of a number of unactivated alkene-types that is tolerant of electron-rich functionality, giving products that are otherwise unattainable. Key to success is the electrochemical generation of a hypervalent iodine mediator using an “ex-cell” approach, which avoids oxidative substrate decomposition. The more sustainable conditions give good to excellent yields in up to decagram scales.     

Electrochemical Vicinal Difluorination of Alkenes: Scalable and Amenable to Electron‐Rich Substrates

Fluorinated alkyl groups are important motifs in bioactive compounds, positively influencing pharmacokinetics, potency and conformation. The oxidative difluorination of alkenes represents an important strategy for their preparation, yet current methods are limited in their alkene‐types and tolerance of electron‐rich, readily oxidized functionalities, as well as in their safety and scalability. Herein, we report a method for the difluorination of a number of unactivated alkene‐types that is tolerant of electron‐rich functionality, giving products that are otherwise unattainable. Key to success is the electrochemical generation of a hypervalent iodine mediator using an “ex‐cell” approach, which avoids oxidative substrate decomposition. The more sustainable conditions give good to excellent yields in up to decagram scales.     

Hydrogen bond dynamics probed with ultrafast infrared heterodyne-detected multidimensional vibrational stimulated echoes

Hydrogen bond dynamics are explicated with exceptional detail using multidimensional infrared vibrational echo correlation spectroscopy with full phase information. Probing the hydroxyl stretch of methanol-OD oligomers in CCl4, the dynamics of the evolving hydrogen bonded network are measured with ultrashort (<50 fs) pulses. The data along with detailed model calculations demonstrate that vibrational relaxation leads to selective hydrogen bond breaking on the red side of the spectrum (strongest hydrogen bonds) and the production of singly hydrogen bonded photoproducts.     

Catalytic activity and complexation-iv 2,2'-Bipyridyl as activator for the catalytic ultramicro determination of silver

The activation of the catalytic persulphate oxidation of sulphanilic acid when the catalyst, silver(I), is suitably complexed, is discussed. 2,2'-Bipyridyl is proposed as activator as it accelerates the rate-determining step of the process-the oxidation of silver(I) to silver(II). The mechanism of activation is investigated and discussed in detail. On the basis of these investigations a catalytic method has been developed for the determination of silver(I), with a sensitivity of 4 x 10(-4)mug ml and +/-7.6% relative error.     

Picosecond multidimensional fluorescence spectroscopy: a tool to measure real-time protein dynamics during function

Advanced multidimensional time-correlated single photon counting (mdTCSPC) and picosecond time-resolved fluorescence in combination with site-directed fluorescence labeling are valuable tools to study the properties of membrane protein surface segments on the pico- to nanoseconds time scale. Time-resolved fluorescence anisotropy changes of protein bound fluorescent probes reveal changes in protein dynamics and steric restriction. In addition, the change in fluorescence lifetime and intensity of the covalently bound fluorescent dye is indicative of environmental changes at the protein surface. In this study, we have measured the changes in fluorescence lifetime traces of the fluorescent dye fluorescein covalently bound to the first cytoplasmic loop of bacteriorhodopsin (bR) after light activation of protein function. The fluorescence is excited by a picosecond laser pulse. The retinylidene chromophore of bR is light-activated by a 10 ns laser pulse, which in turn triggers recording of a sequence of fluorescence lifetime traces in the mdTCSPC-module. The fluorescence decay changes upon protein function occur predominantly in the 100 ps time range. The kinetics of these changes shows two transitions between three intermediate states in the second part of the bR photocycle. Correlation with photocycle kinetics allows for the determination of reaction intermediates at the proteins surface which are coupled to changes in the retinal binding pocket.     

Enhanced stability and bioconjugation of photo-cross-linked polystyrene-shell, Au-core nanoparticles

Encapsulating Au nanoparticles within a shell of photo-cross-linked block copolymer surfactant dramatically improves the physical and chemical stability of the nanoparticles, particularly when they are applied as bioconjugates. Photo-cross-linkable block copolymer amphiphiles [polystyrene-co-poly(4-vinyl benzophenone)]-block-poly(acrylic acid) [(PS-co-PVBP)-b-PAA] and [poly(styrene)-co-poly(4-vinyl benzophenone)]-block-poly(ethylene oxide) [(PS-co-PVBP)-b-PEO] were assembled around Au nanoparticles ranging from 12 to 108 nm in diameter. UV irradiation cross-linked the PVBP groups on the polymer to yield particles that withstood extremes of temperature, ionic strength, and chemical etching. Streptavidin was attached to [PS-co-PVBP]-b-PAA-coated particles using the same noncovalent and covalent conjugation protocols used to bind biomolecules to divinylbenzene-cross-linked PS microspheres. We expect that these particles will be useful as plasmonic, highly light-scattering and light-absorbing analogs to fluorescently labeled PS nanospheres.