Die Anwendung der Pyrogallolcarbons?ure als komplexometrischem Indicator

Zusammenfassung PyrogallolcarbonsÄure kann mit Vorteil als Indicator bei der direkten Titration von Calciumsalzlösungen mit 0,1 m Komplexon(III)-lösung benutzt werden. Es ergibt sich ein scharfer Farbumschlag von Violettrot nach Gelb; die Titrationsergebnisse stimmen auch in Anwesenheit von Magnesiumsalz sowohl untereinander als auch mit den Sollwerten sehr befriedigend überein.Die direkte Titration von Barium- oder Strontium-Ionen ist wegen des in diesen FÄllen undeutlichen Farbumschlages nicht zu empfehlen. Dagegen sind beide Metall-Ionen (und auch Ca-Ion) gut zu bestimmen, wenn man mit einem gemessenen Komplexonüberschu\ versetzt und den unverbrauchten Rest mit 0,1 m Bariumchloridlösung zurücktitriert. Der Farbumschlag des PyrogallolcarbonsÄure-Indicators von Gelb nach Violettrot ist scharf.Das gleiche indirekte Bestimmungsverfahren (Rücktitration mit 0,1 m BaCl₂-Lösung) eignet sich auch zur Bestimmung von Blei-, Cadmium-, Aluminium- und Zink-Ionen.     

Synthesis of high purity single-walled carbon nanotubes in high yield

A simple method for the synthesis of high purity single wall carbon nanotubes has been developed by using nickel formate as a precursor for the formation of nearly mono-dispersed nickel seed-nanoparticles as catalysts in the CVD growth process.     

Entirely circular quartics in the pseudo-Euclidean plane

A curve in the pseudo-Euclidean plane is circular if it passes through at least one of the absolute points. If it does not share any point with the absolute line except the absolute points, it is said to be entirely circular.     

Flavin–cyclodextrin conjugates: effect of the structure on the catalytic activity in enantioselective sulfoxidations

A series of flavin–cyclodextrin conjugates has been prepared and tested in the enantioselective oxidations of prochiral aromatic and aliphatic sulfides with hydrogen peroxide. The newly prepared conjugates contain isoalloxazinium or alloxazinium moieties attached to the primary rim of α- and β-cyclodextrins at the C-6 positions. In addition, flavinium units were attached to the secondary rim of the β-cyclodextrin macrocycle. The relationship between the structural features and the catalytic performance of the conjugates, including those recently reported by us, was analyzed. The rate and enantioselectivity of the sulfoxidations catalyzed by flavin–cyclodextrin conjugates are influenced mainly by the size of the cyclodextrin cavity, the type of flavin unit (alloxazine or isoalloxazine), and by the relative orientation of the flavin and cyclodextrin moieties.     

Maximal chains of isomorphic subgraphs of the Rado graph

The partial order 〈E(R)∪{?},?〉, where E(R) is the set of isomorphic subgraphs of the Rado graph R, is investigated. The order types of maximal chains in this poset are characterized as the order types of compact sets of reals having the minimum non-isolated.     

Acid-Catalyzed RNA-Oligomerization from 3’,5’-cGMP

The assembly of ancient informational polymers from nucleotide precursors is the central challenge of life's origin on our planet. Among the possible solutions, dry polymerization of 3’,5’-cyclic guanosine monophosphate (3’,5’-cGMP) has been proposed as a candidate to create oligonucleotides of 15–20 units in length. However, the reported sensitivity of the reaction to the presence of cations raised questions of whether this chemistry could be relevant in a geological context. The experiments in this study show that the presence of cations is not restrictive as long as the reaction is conducted in an acidic environment, in contrast to previous reports that suggested optimal conditions at pH 9.