Zur maßanalytischen Bestimmung von lllangan,Chrom und Nickel in legierten Stählen aus einer Einwage

Analytical and Bioanalytical Chemistry -     

Growth and decrescence of two-dimensional crystals: A Markov rate process

A Markov rate process whose transitions are captures and escapes of single atoms from the edge of a two-dimensional crystal is introduced. The stochastic equilibrium states of this process describe steady crystal growth, crystal-fluid equilibrium, and steady crystal decrescence. Exact and asymptotic growth rates are found. This extends recent results which dealt only with capture events. One application is to the growth of lamellar crystals from polymers.     

Supersymmetric matter gravitino multiplets

We construct all on-shell, massless, supersymmetric multiplets with maximum field spin three-halves. The supergeometry of these theories is developed. We study the off-shell N = 1 matter gravitino multiplet and exhibit the supergeometries of the known theories. Explicit superfield constructions for two new off-shell theories are presented.     

Scanning kinetic spectroscopy (SKS): A new method for investigation of surface reaction processes

Multiple reaction pathways are available to a polyatomic molecule interacting with a solid surface. Delineation of exact temperature regions in which the various pathways are either active or inactive is accomplished using a new method, Scanning Kinetic Spectroscopy (SKS). SKS uses a calibrated and collimated beam of reactant molecules incident upon a clean single crystal surface in UHV. A multiplexed quadrupole mass spectrometer (QMS) is enclosed inside a differentially pumped random flux shield, in line of sight to the crystal surface. The crystal temperature is programmed with a linear ramp (dT/dt = 2K/s.) and reactant consumption, product evolution, and desorption of stable surface species are simultaneously measured in one experiment. SKS data are presented here which characterize the reactions of methanol with the single crystal surfaces Ni(111), Cu(111), and Cu(111) plus preadsorbed oxygen. Application of the SKS method as an efficient probe of surface reaction pathways is illustrated by the contrasting chemistry of these surfaces. The methanol plus Ni(111) system is examined in detail in order to relate the observed SKS features to specific molecular reaction pathways on the Ni(111) surface.     

Photochemical electron transfer reactions of tirapazamine

The absorption and fluorescence spectra of 3-aminobenzo-1,2,4-triazine di-N-oxide (tirapazamine) have been recorded and exhibit a dependence on solvent that correlates with the Dimroth ET30 parameter. Time-dependent density functional theory calculations reveal that the transition of tirapazamine in the visible region is pi-->pi* in nature. The fluorescence lifetime is 98+/-2 ps in water. The fluorescence quantum yield is approximately 0.002 in water. The fluorescence of tirapazamine is efficiently quenched by electron donors via an electron-transfer process. Linear Stern-Volmer fluorescence quenching plots are observed with sodium azide, potassium thiocyanate, guanosine monophosphate and tryptophan (Trp) methyl ester hydrochloride. Guanosine monophosphate, tyrosine (Tyr) methyl ester hydrochloride and Trp methyl ester hydrochloride appear to quench the fluorescence at a rate greater than diffusion control implying that these substrates complex with tirapazamine in its ground state. This complexation was detected by absorption spectroscopy.