Luminescence of porous silicon derived nanocrystals dispersed in water: dependence on initial porous silicon oxidation

Aqueous solutions of silicon nanocrystals have been obtained, by sonication, from porous Si (p-Si) aged in air for various times. The photoluminescence of these solutions changes with the aging time of p-Si. These changes correlate with nanocrystal core dimensions, i.e. with the oxidation of the nanocrystals. Infrared spectra show that the reaction with water depends on the age of the starting p-Si sample, since the native superficial oxide layer on p-Si inhibits these reactions.     

Zur Kenntnis cyclischer Acylale, 4. Mitt.: Über die Bildung von Cyclopropan-spiroderivaten

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(Phosphinomethylen)phosphane, 1,3,4,6-tetraphosphahexadiene-(1,5) und neue 1,3-diphosphetane aus R-N=CCl2 und PhPTms2

Interaction of different halogenated isocyanide dichlorides with phenylbis(trimethylsilyl)phosphine either yields 1,3,4,6-tetraphosphahexadienes-(1,5) via the (phosphinomethylene)phosphines or 1,3-diphosphetanes by way of the “monophosphacarbodiimides”.     

Spin echoes in the charge transport through phosphorus donors in silicon

The electrical detection of spin echoes via echo tomography is used to observe coherent processes associated with the electrical readout of the spin state of phosphorus donor electrons in silicon near a SiO2 interface. Using the Carr-Purcell pulse sequence, an echo decay with a time constant of 1.7+/-0.2 micros is observed and discussed in terms of decoherence and recombination times. Electrical spin echo tomography thus can be used to study the dynamics of the spin-dependent transport processes, e.g., in realistic spin qubit devices for quantum information processing.     

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Synthetische Polypeptide II

Zusammenfassung Durch Polymerisation von O-Acetyl-l-tyrosin-N-carbonsäureanhydrid wurde ein Poly-O-Acetyl-l-tyrosin vom mittleren Molgewicht 3800 erhalten, das somit etwa 18 bis 19 Amino-säurereste pro Peptidkette enthält. Alkalische Verseifung lieferte ein Poly-l-Tyrosin, das ausschließlich aus Tyrosinresten aufgebaut ist.Umsetzung dieses Poly-Tyrosins mit Dimethylsulfat, Dinitrofluorbenzol und Jod ergab ein Poly-O-Methyl-, Poly-O-DNP-und ein Poly-3,5-Dijod-l-tyrosin. Poly-O-DNP-Tyrosin konnte auch durch Polymerisation des entsprechenden N-Carbon-säureanhydrids gewonnen werden.Mit 2 AbbildungenI.:K. Schlögl, F. Wessely undG. Korger, Mh. Chem.83, 845 (1952).IX. Mittlg.:F. Wessely, K. Schlögl undE. Wawersich, Mh. Chem.84, 263 (1953).     

Fast and comprehensive analysis of secondary metabolites in cocoa products using ultra high‐performance liquid chromatography directly after pressurized liquid extraction

Fast methods for the extraction and analysis of various secondary metabolites from cocoa products were developed and optimized regarding speed and separation efficiency. Extraction by pressurized liquid extraction is automated and the extracts are analyzed by rapid reversed‐phase ultra high‐performance liquid chromatography and normal‐phase high‐performance liquid chromatography methods. After extraction, no further sample treatment is required before chromatographic analysis. The analytes comprise monomeric and oligomeric flavanols, flavonols, methylxanthins, N‐phenylpropenoyl amino acids, and phenolic acids. Polyphenols and N‐phenylpropenoyl amino acids are separated in a single run of 33 min, procyanidins are analyzed by normal‐phase high‐performance liquid chromatography within 16 min, and methylxanthins require only 6 min total run time. A fourth method is suitable for phenolic acids, but only protocatechuic acid was found in relevant quantities. The optimized methods were validated and applied to 27 dark chocolates, one milk chocolate, two cocoa powders and two food supplements based on cocoa extract.