An investigation of the triplet state dynamics of zinc chlorophyll b by microwave-induced changes in the intensity of fluorescence and singlet-singlet absorption

Optical detection of magnetic resonance experiments on the triplet state of zinc-substitution chlorophyll b has provided the zero-field splitting and depopulation rate constants for the individual triplet spin sublevels. The zero field triplet state EPR transitions could be observed at 890 MHz and 1085 MHz as either microwave-induced changes in the fluorescence intensity or in the intensity of S₀ → S_n absorption. The dynamics experiments show that intersystem crossing from the Zn chlorophyll b triplet state into the ground state occurs primarily through the out-of-plane (lowest energy) spin sublevel.     

Determination of fluoride by analate additions potentiometry

Summary A novel direct potentiometric technique called analate additions potentiometry has been applied to the determination of fluoride using a fluoride ion selective indicator electrode. As expected, the analytical results are comparable to those obtained by the standard additions technique. An error of less than 1 part in 1000 and a precision of about 0.5% was achieved. The technique should be most useful in the determination of small sample volumes which cannot be done by the standard additions method without prior dilution.

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Zusammenfassung Ein neues, direktes potentiometrisches Verfahren wurde für die Fluoridbestimmung angewendet, wobei eine für Fluoridionen selektive Indikatorelektrode verwendet wurde. Wie erwartet sind die Ergebnisse dieses Probenzusatzverfahrens mit denen der Standardzusatzmethode vergleichbar. Der Fehler ist kleiner als l, die Genauigkeit beträgt etwa 0,5%. Das angegebene Verfahren eignet sich vor allem zur Analyse kleiner Probevolumina, die ohne vorherige Verdünnung mit der Standardzusatzmethode nicht analysiert werden können.

     

Solution-based assembly of conductive gold film on flexible polymer substrates

Conductive films of gold were assembled on flexible polymer substrates such as Kapton and polyethylene using a solution-based process. The polymer substrates were modified by using argon plasma and subsequent coupling of silanes with amino- or mercapto- terminal groups. These modified surfaces were examined by X-ray photoelectron spectroscopy and contact angle measurements. Colloidal gold was assembled onto the silane-modified surface from solution. The gold particles are attached to the surface by covalent interactions with the thiol or amine group. Formation of a conductive film is achieved by increasing the coverage of gold by using a "seeding" method to increase the size of the attached gold particles. Field emission scanning electron microscopy was used to follow the growth of the film. The surface resistance of the films, measured using a four-point probe, was about 1 Omega/sq.     

Mechanism for collision-induced transitions between Λ-doublets in 1Π molecules: Reduction to a single scattering potential

The theory is presented for rotational excitation of ¹Π molecules by collisions with rare gas atoms. It is shown that collision dynamics are described by the two electronic potential energy surfaces which correlate with the electronically degenerate Λ components (doublets) in the diatomic molecule. Because the ±Λ degeneracy can alternatively be described as being in the rotational rather than in the electronic degree of freedom, one can reformulate the collision dynamics in terms of a single effective electronic potential which then depends on Φ, the angle of rotation about the diatomic axis. The form of this Φ dependence is found to be identical to that postulated to explain experimental data for collisional transfer of laser-induced fluorescence.     

Simple instrument for titrimetry without visual indicators. gasometric titrations: Cerimetry,chlorometry, nitrate,nitrite, hydroxide and carbonate determination

It was shown in previous papers, that many titrimetric problems can be solved by observing the pressure change of a closed system above the solution titrated at the equivalence point. This principle was made the basis of a gasometric titration method in which the end-point is found graphically. The titrant is added to the sample solution in measured increments at fixed intervals of time and the corresponding gas pressure or volume of the system is recorded and then plotted against the volume of added titrant. Half a dozen readings are sufficient to establish the end-point of a titration, which is found at the intersection of two straight lines. This graphical method was applied to cerimetry and chlorometry, as well as to some other analytical reactions (determination of nitrite, nitrate, hydroxide and carbonate) already described in previous papers on the gas pressure end-point technique. The results are comparable in precision and accuracy to the values obtained by the conventional visual end-point titrations. A gasometric titration takes about 10 minutes. The presence of other substances in the sample capable of reacting with the titrant does not necessarily cause interference.     

Beta galactosidase enzyme fragment complementation as a novel technology for high throughput screening

In this review, the applications of beta galactosidase complementation are described. alpha Complementation is a naturally occurring process in bacteria and in engineered cells, and can also occur in eukaryotic cells. Two forms of alpha complementation have been used in high throughput screening (HTS), in which interacting fragments complement with either low or high affinity. Low affinity complementation is used to monitor protein protein interactions, such as those occurring in homodimerization of the epidermal growth factor receptor (EGFR), and provides a robust screen for detection of EGFR inhibitors. High affinity complementation provides the basis for several HTS assays, in which analytes, such as cAMP or IP(3), are detected in crude cell lysates. A development of the latter approach is protein labeling, providing for measurement of cell protein expression and trafficking. Collectively, the use of beta galactosidase complementation provides a novel and flexible technology for highly sensitive, homogeneous HTS assay development.     

Structure‐Dependent Photoinduced Electron Transfer in Fullerodendrimers with Light‐Harvesting Oligophenylenevinylene Terminals

Oligophenylenevinylene (OPV)‐terminated phenylenevinylene dendrons G1 – G4 with one, two, four, and eight “side‐arms”, respectively, were prepared and attached to C₆₀ by a 1,3‐dipolar cycloaddition of azomethine ylides generated in situ from dendritic aldehydes and N‐methylglycine. The relative electronic absorption of the OPV moiety increases progressively along the fullerodendrimer family C₆₀G1 – C₆₀G4 , reaching a 99:1 ratio for C₆₀G4 (antenna effect). UV/Vis and near‐IR luminescence and transient absorption spectroscopy was used to elucidate photoinduced energy and electron transfer in C₆₀G1 – C₆₀G4 as a function of OPV moiety size and solvent polarity (toluene, dichloromethane, benzonitrile), taking into account the fact that the free‐energy change for electron transfer is the same along the series owing to the invariability of the donor–acceptor couple. Regardless of solvent, all the fullerodendrimers exhibit ultrafast OPV→C₆₀ singlet energy transfer. In CH₂Cl₂, the OPV→C₆₀ electron transfer from the lowest fullerene singlet level (¹C₆₀*) is slightly exergonic (ΔG_CS≈0.07 eV), but is observed, to an increasing extent, only in the largest systems C₆₀G2 – C₆₀G4 with lower activation barriers for electron transfer. This effect has been related to a decrease of the reorganization energy upon enlargement of the molecular architecture. Structural factors are also at the origin of an unprecedented OPV→C₆₀ electron transfer observed for C₆₀G3 and C₆₀G4 in apolar toluene, whereas in benzonitrile, electron transfer occurs in all cases. Monitoring of the lowest fullerene triplet state by sensitized singlet oxygen luminescence and transient absorption spectroscopy shows that this level is populated through intersystem crossing and is not involved in photoinduced electron transfer.     

Stability of tin etiopurpurin

Formulations of the tin etiopurpurin (SnET2) have been observed to undergo a spectral change on storage in dimethylformamide solution. This results in an alteration in the action spectrum, with enhanced photodynamic activity at lower wavelengths and decreased activity at 660 nm. On the basis of structural considerations, a reduced analog of SnET2 was prepared with an absorbance maximum at 640 nm. Formation of this product, termed SnET2H(2) relieves steric strain inherent in the parent molecule. Nuclear magnetic resonance, spectral and photodynamic data are consistent with the formation of SnET2H(2) during SnET2 storage. Slight modifications in the original synthesis are also reported, resulting in improved yields of intermediate products.     

Empfindliche Methode zur Bestimmung geringer Schwefelgehalte in Wolframoxiden und Wolframpulvern

Zusammenfassung Der Schwefel in Wolframoxiden und Wolframpulvern wird im Wasserstoffstrom bei 800°C in H₂S übergeführt, der in Cadmium-Zinkacetat-Lösung absorbiert und anschließend jodometrisch titriert wird. Die Anwesenheit von WO₃ ermöglicht eine quantitative Umwandlung von Sulfatschwefel in H₂S. Die Standardabweichung beträgt für ein Wolframoxid mit 310 ppm S±13 ppmS und für ein Wolfram-Metallpulver mit 45 ppm S±1 ppm S.

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Sulfur is converted into hydrogen sulphide by hydrogenation at 800°C. This H₂S is absorbed in a cadmium-zinc acetate solution and titrated iodometrically. The presence of WO₃ makes possible a quantitative conversion of sulphate sulphur into H₂S. The standard deviation is ±13 ppm S for WO₃ containing 310 ppm S, and ±1 ppm S for metallic tungsten powder containing 45 ppm S.

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Herrn Prof. Dr.E. Hayek zum 60. Geburtstag gewidmet.