Futtermittel

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Die Jods?urereaktion des Adrenalins

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Spin-flip processes and ultrafast magnetization dynamics in Co: Unifying the microscopic and macroscopic view of femtosecond magnetism

The femtosecond magnetization dynamics of a thin cobalt film excited with ultrashort laser pulses has been studied using two complementary pump-probe techniques, namely, spin-, energy-, and time-resolved photoemission and the time-resolved magneto-optical Kerr effect. Combining the two methods, it is possible to identify the microscopic electron spin-flip mechanisms responsible for the ultrafast macroscopic magnetization dynamics of the cobalt film. In particular, we show that electron-magnon excitation does not affect the overall magnetization even though it is an efficient spin-flip channel on the sub-200 fs time scale. Instead, we find experimental evidence for the relevance of Elliott-Yafet-type spin-flip processes for the ultrafast demagnetization taking place on a time scale of 300 fs.     

LC–high resolution MS in environmental analysis: from target screening to the identification of unknowns

This article provides an overview of the state-of-the-art and future trends of the application of LC–high resolution mass spectrometry to the environmental analysis of polar micropollutants. Highly resolved and accurate hybrid tandem mass spectrometry such as quadrupole/time-of-flight and linear ion trap/orbitrap technology allows for a more reliable target analysis with reference standards, a screening for suspected analytes without reference standards, and a screening for unknowns. A reliable identification requires both high resolving power and high mass spectral accuracy to increase selectivity against the matrix background and for a correct molecular formula assignment to unknown compounds. For the identification and structure elucidation of unknown compounds within a reasonable time frame and with a reasonable soundness, advanced automated software solutions as well as improved prediction systems for theoretical fragmentation patterns, retention times, and ionization behavior are needed.     

Integrated monolithic optical manipulation

We present a new approach to optical manipulation that integrates microfluidic channels directly onto semiconductor laser material creating a compact integrated optical trap that requires no alignment and is wholly portable.     

Fragmentation of trimethylsilyl derivatives of 2-alkoxyphenols: A further violation of the ‘even-electron rule’

The mass spectra of trimethylsilyl (TMS) ethers of 2-methoxyphenols show abundant [M–30]⁺˙ ions originating from consecutive loss of two methyl radicals. This is illustrated by comparison of the accurate mass-measured and linked-scan spectra of the TMS derivatives of 2-methoxyphenol (guaiacol), 4-hydroxy-3-methoxybenzaldehyde (vanillin) and 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid methyl ester (ferulic acid methyl ester) with those of the TMS derivatives of phenol, 4-hydroxybenzaldehyde, 3-(4-hydroxyphenyl)-2-propenoic acid methyl ester (p-coumaric acid methyl ester), 3-methoxyphenol and 4-methoxyphenol. This distinctive ortho effect is valuable in the identification of isomeric phenolic compounds. In the spectra of the TMS derivatives of 2-ethoxyphenol and 2-propoxyphenol the sequential loss of two radicals is less pronounced, because elimination of the side-chain and a methyl group with rearrangement and hydrogen migration is competitive.     

Oberflächenverbindungen von Übergangsmetallen. XVIII. Der Einfluß der Cr-Konzentration auf Oxydationszahl und „Qualität”︁ von Cr-Oberflächenverbindungen auf Silicagel

Surface Compounds of Transition Metals. XVIII. The Influence of Cr Concentration on Oxidation Number and “Quality” of Cr Surface Compounds on Silicagel Mean oxidation number (OZ ) and mean unsaturated character (q ) of reduced Cr surface compounds on silicagel depend on the concentration of Cr in the product. The first effect is caused by the decrease of thermally stable surface Cr^VI with increasing Cr concentration in the activated product, since surface Cr^VI is the only precursor of surface Cr^II (constant yield of reduction～90%); consequently OZ _red shifts to higher values with increasing concentration. — The measured decrease of q with increasing Cr content cannot be correlated with a possible coordination of neighbouring SiOH groups, as it was suggested for the influence of T_act and T_red; other explanations are proposed. For the analyzed product, the results support the postulated model of an ensemble of topologically different individual surface species of typical reactivity.