QUENCHING OF OXONINE EXCITED STATES BY EDTA VIA ELECTRON TRANSFER AND DEACTIVATION PROCESSES. A COMPARATIVE STUDY OF EXCITED SINGLET AND TRIPLET STATE REACTIVITY

The quenching of excited singlet oxonine by EDTA in aqueous solution leads mainly to deactivation of the dye to the ground state and, to a lesser extent, to electron abstraction. The rate constants for these processes have been measured and compared to those for the same reactions involving the oxonine triplet state. The rate constant of electron abstraction is about ten times greater via the singlet state than via the triplet state. However, the rate constant of deactivation to the ground state is 10³-10⁴ times greater for the excited singlet state than for the triplet state, so that the efficiency of electron transfer is much smaller for the singlet state.     

Neuere Entwicklungen der flammenphotometrischen Analysenverfahren

Zusammenfassung Es wird gezeigt, daß man durch Einsatz von reduzierenden Flammen, durch Einsatz von Chemiluminescenzvorgängen in Flammen, durch Atomabsorptionsverfahren, durch Modulations- und Differentiations-operationen eine Reihe von weiteren Elementen mit den schnellen und spezifischen Flammenmethoden analytisch gut erfassen kann. Hierbei wird insbesondere auf die Bestimmung von Spurenelementen in Mikroproben mit möglichst einfachen Mitteln eingegangen.

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Summary It is demonstrated that one can grasp analytically well a series of further elements with the quick and specific flame methods by use of chemiluminescence processes in flames, by atomic absorption methods, by operations of modulation and differentiation. Hereby the determination of trace elements is specifically treated in microprobes with the most possible simple means.

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Unterstützt mit Mitteln der Deutschen Forschungsgemeinschaft.

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Herrn Prof. Dr. Bohnstedt zum 65. Geburtstag gewidmet.

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Meinen Mitarbeitern, insbesondere Herrn Dipl. Phys. W. Lang und Frau B. Gutsche, die an den zuletzt besprochenen Ergebnissen einen maßgeblichen Anteil hatten, als auch der Deutschen Forschungsgemeinschaft sei an dieser Stelle herzlichst gedankt.     

Extraction du titane(IV) d'une phase aqueuse chlorhydrique par des mélanges de thénoyltrifluoroacétone—tri-n-butylphosphate et d'oxyde de tri-n-butylphosphine en solution dans le 1,2-dichloroethane

The extraction of titanium(IV) from hydrochloric acid solutions by thenoyltrifluoroacetone (HTTA) in the presence of tributylphosphate (TBP) or tri-n-butylphosphine oxide (TBPO) was studied in 1,2 dichloroethane. It is shown that there is a synergic effect because of the formation of a 1:1:1 HTTA—TBP (or TBPO)—Ti(IV) complex. The apparent stability constants of these complexes increase with the acidity of the aqueous phase.     

Branched Star-Type Polysilyllithium Compounds: The Effects of beta-Silyl Substitution and of Complexation on Their Molecular Structure

No Abstract     

Comment on: "Disentangling density and temperature effects in the viscous slowing down of glass forming liquids" [J. Chem. Phys. 120, 6135 (2004)

Recently, Tarjus et al. [G. Tarjus, D. Kivelson, S. Mossa, and C. Alba-Simionesco, J. Chem. Phys. 120, 6135 (2004)] concluded from a review of data for a variety of glass formers that the supercooled dynamics are almost invariably dominated by temperature T, rather than by density rho. By including additional published data into such a compilation, we show that for van der Waals molecular liquids, the dynamics near T(g) are in fact governed as much by density as by temperature. Moreover, relaxation times measured at various temperatures and pressures can be superimposed by plotting as a function rho(gamma)/T. This scaling form can arise from an assumed inverse power law for the intermolecular repulsive potential, with gamma a material constant. (c) 2004 American Institute of Physics.     

An improved synthesis of 3-deazaeytosine, 3-deazauracil, 3-deazacytidine,and 3-deazauridine

3-Dcazacytosine (4-amino-2-pyridone, 3 ), 3-doazauracil (4-hydroxy-2-pyridone, 5 ), 3-deaza-cytidine (4-amino-1-β-D-ribofuranosyl-2-pyridonc, 9 ), and 3-deazauridine (4-hydroxy-1-β-D-ribo-furanosyl-2-pyridone, 11 ) were prepared in high overall yields from 1-methoxy-1-buten-3-yne ( 1 ). Ethyl 3,5,5-triethoxy-3-pentenoate ( 2 ), obtained from acylatioti of 1 with diethyl carbonate and subsequent in situ conjugate addition of ethoxide, was cyelized with ammonia to provide 3 . Diazotization of 3 and subsequent in situ hydroxydediazotization afforded 5 . Nucleoside 9 was obtained from the stannic chloride-catalyzed condensation of bis-trimethylsilylated 3 and 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose ( 7 ), followed by ammonolysis of the blocking groups. Diazotization of 9 and subsequent in situ hydroxydediazotization afforded nucleosidc 11 .     

Synthesis of unsymmetrical 2,4-dialkylpyrazolo[1,5-a]-1,3,5-triazines

The reaction of 3-aminopyrazole with imidate esters such as ethyl acetimidate, gave N-(pyrazol-3-yl)acetamidine (1) rather than the isomeric 2-acetamidoyl-3-aminopyrazole. Ring closure of 1 with orthoesters such as ethyl propionimidate, afforded unsymmetrically substituted 2.4-dialkylpyrazolo[1,5-a]-1,3,5-triazines such as 4-ethyl-2-methylpyrazolo[1,5-a]-1,3,5-triazine (3). The structure of 1 was confirmed by several alternate syntheses. The unique feature of this two-step synthetic approach to the synthesis of pyrazolo[1,5-a]-1,3,5-triazines is that it is a convenient method of preparing fused triazines based on available pyrazoles rather than the less accessible dialkyltriazines.