Diarylprolinol in an asymmetric aldol reaction of an α-alkyl-α-oxo aldehyde as an electrophile

The direct aldol reaction of an α-alkyl-α-oxo aldehyde was catalyzed by trifluoromethyl-substituted diarylprolinol 1 to afford a γ-oxo-β-hydroxy-α-substituted aldehyde in good yield with excellent anti-selectivity and excellent enantioselectivity.     

Kekuléan benzenoids

A Kekulé structure for a benzenoid or a fullerene $\Gamma $ is a set of edges $K$ such that each vertex of $\Gamma $ is incident with exactly one edge in $K$ , i.e. a perfect matching. All fullerenes admit a Kekulé structure; however, this is not true for benzenoids. In this paper, we develop methods for deciding whether or not a given benzenoid admits a Kekulé structure by constructing Kekulé structures that have a high density of benzene rings. The benzene rings of the Kekulé structure $K$ are the faces in $\Gamma $ that have exactly three edges in $K$ . The Fries number of $\Gamma $ is the maximum number of benzene rings over all possible Kekulé structures for $\Gamma $ and the set of benzene rings giving the Fries number is called a Fries set. The Clar number is the maximum number of independent benzene rings over all possible Kekulé structures for $\Gamma $ and the set of benzene rings giving the Clar number is called a Clar set. Our method of constructing Kekulé structures for benzenoids generally gives good estimates for the Clar and Fries numbers, often the exact values.     

Lithiumreaktionen anα-Picolinen

Ohne ZusammenfassungII. Mitteilung:W. Gruber undK. Schlögl, Mh. Chem.81, 83 (1950).     

Photoreduction of an α-Dichloroketone

We describe here a simple three step synthesis of B-santalene (1), one of the main hydrocarbons in East Indian Sandalwood oil,³ using the readily available camphene sultone (2) as a starting material. This synthesis, outlined in Figure 1, features the novel use of a sultone as a carbon activating group and involves a new desulfurization procechrre.     

Sauerstoffbestimmung an Silberoberfl?chen

Zusammenfassung Die Schwefelwasserstoffmethode zur Bestimmung von Sauerstoff in Zink, Cadmium und Blei ermöglicht die Bestimmung des Sauerstoffgehaltes an Silberoberflächen. Das auf der Oberfläche befindliche Oxyd wird nach Ag₂O + H₂S Ag₂S + H₂O umgesetzt und das gebildete Wasser mikrogravimetrisch bestimmt. Eine störende Diffusion von Sauerstoff aus dem Inneren des Metalles kann bei der Reaktionstemperatur von etwa 500° C nicht erfolgen. Gesamtsauerstoffbestimmungen wurden zur Kontrolle mit Hilfe der Wasserstoffreduktionsmethode durchgeführt.Bei einer spezifischen Oberfläche des untersuchten, drahtförmigen Silbers von 3,84 cm²/g ergab sich ein Oberflächen-Sauerstoffgehalt von 0,0013 g/m², der einer Ag₂O-Schichtdicke von 2,55 · 10^–6 mm entspricht.Herrn Prof. Dr. Justi bin ich für wertvolle Hinweise und anregende Diskussionen sowie für sein förderndes Interesse an der vorliegenden Arbeit zu großem Dank verpflichtet.     

Dielectric spectroscopy of an antiferroelectric liquid crystal showing an antiferroelectric–ferrielectric transition

We report the dielectric relaxation behaviour in the antiferroelectric SmC_A* and ferrielectric SmC_γ* phases of the antiferroelectric liquid crystal 4-[5-(4-octloxyphenyl)-2-pyrimidinyl]phenyl 4,4,4-trifluoro-3-(methoxyphenyl)butanoate which shows an antiferroelectric transition at around 88±0.1°C. In the SmC_A* phase, two dielectric relaxation modes have been found, namely the usual antiferroelectric Goldstone mode and another arising from molecular rotation around its short axis. In the SmC_γ* phase, one dielectric relaxation mode has been observed due to the ferrielectric Goldstone mode. Dielectric increments and relaxation frequencies of the antiferroelectric and ferrielectric phases are estimated from the fits of the Cole–Cole function of the dielectric spectrum. The dependence of the bias field in the ferrielectric phase is also discussed.     

Fiber-optic biosensors – an overview

This article reviews progress and developments during the past five years in the field of optical fiber biosensors. Because of the expense and time constraints associated with modern laboratory analysis, there is a growing need for real-time, low-cost technology that can be used industrially, environmentally, and clinically, and to monitor food processing. Miniaturization, integrated systems, and multianalyte determination have become key aspects of sensor development and efforts in this direction will also be discussed, with some pointers to likely directions of future research in the area. The review will provide information about the analytical characteristics and applications of fiber-optic biosensors classified depending on the biorecognition element employed - enzymes, whole cells, antibodies, nucleic acids, and biomimetic polymers.     

Sauerstoffbestimmung an Silberoberflächen

Analytical and Bioanalytical Chemistry - Die Schwefelwasserstoffmethode zur Bestimmung von Sauerstoff in Zink, Cadmium und Blei ermöglicht die Bestimmung des Sauerstoffgehaltes an...     

Röntgenuntersuchungen an Teflon

Ohne Zusammenfassung     

Synthesis of an Enkephalin Analogue Containing an α,α-Disubstituted Heterocyclic Aminophosphonic Acid

Abstract

Synthesis of a phosphonopentapeptide enkephalin analogue was achieved from heterocyclic aminophosphonates via the coupling of Boc-Tyr-Gly-Gly-OH with phosphonodipeptide. The latter was formed by coupling Boc-Phe-OH with N-terminal α,α-disubstituted heterocyclic α-aminophosphonates.

GRAPHICAL ABSTRACT      

Cellular uptake of an α-AApeptide

Some short and cationic peptides such as the Tat peptide can cross the cell membrane and function as vectors for intracellular delivery. Here we show that an α-AApeptide is able to penetrate the membranes of living cells from an extracellular environment and enter the endosome and cytoplasm of cells. The efficiency of the cellular uptake is comparable to a Tat peptide (48-57) of the same length and is unexpectedly superior to an α-peptide with identical functional groups. The mechanism of uptake is similar to that of the Tat peptide and is through endocytosis by an energy-dependent pathway. Due to the easy synthesis of the α-AApeptides, their resistance to proteolytic hydrolysis, and their low cytotoxicity, α-AApeptides represent a new class of transporters for the delivery of drugs.     

Dielektrische Messungen an Pigment-Leinöl-Suspensionen

Ohne Zusammenfassung D. 83. Die Arbeit wurde von A, Franceson zur Erlangung des Grades eines Dr.-Ing. eingereicht und von der Fakult?t für Allgemeine Wissenschaften an der Technischen Hochschule in Berlin genehmigt. Berichterstatter: Prof. Dr.-Ing. W. R?hrs. Mitberichter: Prof. Dr.-Ing. M. Volmer.     

Viskositätsmessung an sedimentierenden Suspensionen

Ohne Zusammenfassung Vortrag, gehalten auf der 1. Tagung der Deutschen Rheologen-Vereinigung e. V. am 16. Oktober 1954 in Stuttgart     

Reference materials – an industry perspective

Biotechnologically enhanced plants and products derived thereof continue to be the reason for much dispute. In order to address concerns raised by the public, several countries have imposed mandatory labeling schemes indicating the presence of products derived from modern biotechnology, while others rely on voluntary labeling codes. Mandatory labeling triggers the need for methods that can be used to check compliance with and enforcement of the corresponding labeling legislation. In order to ensure the proper validation and implementation of a detection method in a specific laboratory, reference materials play a crucial role.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Presented at the CCQM Workshop on Comparability and Traceability in Food Analysis, 18–19 November 2003, BIPM, Sèvre, France.