Chemiluminescent reaction of lucigenin with reducing sugars.
The chemiluminescent reaction, in alkaline solution, of lucigenin with the reducing sugars sorbose, fructose, lactose, glucose, xylose, galactose, arabinose and mannose has been studied. There is a linear relationship (correlation coefficient = 0.996) between the emission intensity and the second-order rate constant for the alkaline oxidation of these sugars. The emission intensity is linearly related to the sugar concentration; at high sugar concentrations (5mM) it is independent of the lucigenin concentration, but at low concentrations (<0.05mM) is linearly related to the lucigenin concentration. These facts support the view that the rate-limiting step is the tautomerization of the sugars to the 1,2-enediol form; the enediol then undergoes reaction with lucigenin.
LIGHT PRODUCTION IN ALKALINE MIXTURES OF REDUCING AGENTS AND DIMETHYLBIACRIDYLIUM NITRATE *
Abstract— Kinetic studies were made of light production and 02 absorption elicited by treatment of dimethylbiacridylium hydroxide [D(OH)2] with reducing agents in alkaline aqueous solutions. D(OH)2 addition stimulated O2 uptake which proceeded with zero‐order kinetics until nearly all of the O2 or of the D(OH)2 was converted to end products. At the termination of the reactions with fructose as reductant the D(OH)2 was converted to methylacridone and to dimethylbiacridene each compound accounting for approximately one‐half the D(OH)2 consumed. O2 was reduced to H2O2. With hydroxylamine as the reducing agent the emitted light intensity was related to the first power of the D(OH)2 concentration and the rate of O2 uptake to the square root of the D(OH)2. The disappearance of D(OH)2 in these circumstances was by a first order or pseudo‐first order rate. Fructose as a reducing agent by contrast resulted in an O2 uptake nearly independent of D(OH)2 concentration over a range from 1 × 10‐5M‐1 × 10‐4M, while the light intensity and disappearance of D(OH)2 followed a one‐half order rate. O2 uptake was by zero order kinetics and the oxidation of fructose proceeded at the same rate as was found with ferricyanide as oxidant. The kinetics, quantum yields and temperature dependence of the fructose reactions were compared with similar reactions employing H2O2 as the light eliciting reagent. The results are interpreted as indicating that D(OH)2 acts as a chain initiator in a manner analogous to better known, radical producing compounds found to accelerate hydrocarbon autooxidations.
High‐precision U‐Pb zircon age calibration of the global Carboniferous time scale and Milankovitch band cyclicity in the Donets Basin, eastern Ukraine
High‐precision ID‐TIMS U‐Pb zircon ages for 12 interstratified tuffs and tonsteins are used to radiometrically calibrate the detailed lithostratigraphic, cyclostratigraphic, and biostratigraphic framework of the Carboniferous Donets Basin of eastern Europe. Chemical abrasion of zircons, use of the internationally calibrated EARTHTIME mixed U‐Pb isotope dilution tracer, and improved mass spectrometry guided by detailed error analysis have resulted in an age resolution of <0.05%, or ∼100 ka, for these Carboniferous volcanics. This precision allows the resolution of time in the Milankovitch band and confirms the long‐standing hypothesis that individual high‐frequency Pennsylvanian cyclothems and bundles of cyclothems into fourth‐order sequences are the eustatic response to orbital eccentricity (∼100 and 400 ka) forcing. Tuning of the fourth‐order sequences in the Donets Basin to the long‐period eccentricity cycle results in a continuous age model for the Middle to Late Pennsylvanian (Moscovian‐Kasimovian‐Ghzelian) strata of the basin and their record of biological and climatic changes through the latter portion of the late Paleozoic Ice Age. Detailed fusulinid and conodont zonations allow the export of this age model to sections throughout Euramerica. Additional ages for Mississippian strata provide among the first robust radiometric calibration points within this subperiod and result in variable lowering of the base ages of its constituent stages compared to recent global time scale compilations.