Über Laplace-Ketten mit Kongruenzen von Goursat

Ohne Zusammenfassung     

Über die Reaktionen von monosubstituierten Guanidinen mit α,β-ungesättigten Ketonen

Action of methyl-, benzyl- and phenylguanidine on mesityloxide yields the 2-R ³-imino-4,4,6-trimethyl-1,2,3,4-tetrahydropyrimidines resp. 2-R³-aminopyrimidines8 b, c ande, cyclohexylidenacetone reacts with benzylguanidine to give the 2-benzylimino-4-methyl-1,3-diazaspiro[5.5]undeca-4-en resp. the benzylaminodiazaspiroundecadien (8 d). The isomeric 1- and 3-R³-pyrimidinimines (resp.-amines)9 b-e and10 b-e are not formed in the reaction. The structures were proved by spectroscopical and chemical methods.

Herrn Prof. Dr.G. Zigeuner zum 60. Geburtstag gewidmet.     

Electrochemical determination of mesoscopic phenomena, defect states in CdSe nanocrystals and charge carrier manipulability

The review gives an overview of cyclic voltammetry measurements performed on CdSe nanocrystals (so called Quantum Dots). Data of relevant publications is gathered and newly interpreted to give complete insights in charge transfer processes at QD surfaces. In specific, it is focused on the size-dependent electronic properties (Quantum-Size-Effect), the characterisation of surface defects, and the characterisation of hybrid nanocrystal/conducting polymer composites. First two authors contribute equally to this work Correspondence: Thomas Nann, School of Chemical Sciences and Pharmacy, University of East Anglia (UEA), Norwich NR4 7TJ, U.K.     

Organometallic synthesis and electrophoretic characterization of high-quality ZnS:Mn/ZnS core/shell nanoparticles for bioanalytical applications

A novel and facile preparation method for colloidal ZnS nanoparticles doped with Mn²⁺ is introduced, using a simple one pot heating process followed by a capping procedure for saturation of the surface bound doping atoms to increase the nanoparticles’ stability and photoluminescence quantum yield. The particles were transferred into water with a standard ligand exchange method and investigated by means of laser Doppler electrophoresis, agarose gel electrophoresis, and isotachophoresis. Correspondence: Alexey Merkulov, Freiburg Materials Research Centre (FMF), University of Freiburg, Stefan-Meier-Strasse 21, D-79104 Freiburg, Germany     

Nanoparticles as Semi‐Heterogeneous Catalyst Supports

Nanoparticles can serve as semi‐heterogeneous supports since they readily disperse in common solvents and combine high surface area with excellent accessibility. Reversible agglomeration through solvent changes and magnetic separation provide technically attractive alternatives to classical catalyst filtration. This account places emphasis on recent developments in this emerging area.     

Physical defect formation in few layer graphene-like carbon on metals: influence of temperature, acidity, and chemical functionalization

A systematical examination of the chemical stability of cobalt metal nanomagnets with a graphene-like carbon coating is used to study the otherwise rather elusive formation of nanometer-sized physical defects in few layer graphene as a result of acid treatments. We therefore first exposed the core-shell nanomaterial to well-controlled solutions of altering acidity and temperature. The release of cobalt into these solutions over time offered a simple tool to monitor the progress of particle degradation. The results suggested that the oxidative damage of the graphene-like coatings was the rate-limiting step during particle degradation since only fully intact or entirely emptied carbon shells were found after the experiments. If ionic noble metal species were additionally present in the acidic solutions, the noble metal was found to reduce on the surface of specific, defective particles. The altered electrochemical gradients across the carbon shells were however not found to lead to a faster release of cobalt from the particles. The suggested mechanistic insight was further confirmed by the covalent chemical functionalization of the particle surface with chemically inert aryl species, which leads to an additional thickening of the shells. This leads to reduced cobalt release rates as well as slower noble metal reduction rates depending on the augmentation of the shell thickness.     

Electrophoretic properties of BSA-coated quantum dots

Low toxic InP/ZnS quantum dots (QDs), ZnS:Mn²⁺/ZnS nanocrystals and CdSe/ZnS nanoparticles were rendered water-dispersible by different ligand-exchange methods. Eventually, they were coated with bovine serum albumin (BSA) as a model protein. All particles were characterised by isotachophoresis (ITP), laser Doppler velocimetry (LDV) and agarose gel electrophoresis. It was found that the electrophoretic mobility and colloidal stability of ZnS:Mn²⁺/ZnS and CdSe/ZnS nanoparticles, which bore short-chain surface ligands, was primarily governed by charges on the nanoparticles, whereas InP/ZnS nanocrystals were not charged per se. BSA-coated nanoparticles showed lower electrophoretic mobility, which was attributed to their larger size and smaller overall charge. However, these particles were colloidally stable. This stability was probably caused by steric stabilisation of the BSA coating.     

Mussel-inspired load bearing metal-polymer glues

A mussel-inspired synthetic adhesive based on dopamine containing methacrylate copolymers was developed to bond polymers to metal surfaces at an adhesion strength of up to 20 MPa for bulk samples.     

Special reactions of α,β-unsaturated ketones: Part II. Structure and stereochemistry of perhydro-5a,11a-epoxydibenz[b,f]oxepin-4a-ol,a bridged Diels–Alder dimer of 2-methylenecyclohexanone

The paper deals with the structure elucidation of (4aRS,5aRS,9aRS,11aRS)-perhydro-5a,11a-epoxydibenz[b,f]oxepin-4a-ol ( 6 ), which is unexpectedly formed from 2-dimethylaminomethylcyclohexanone hydrochloride ( 1 ·HCl) in the presence of phenylguanidine in boiling ethanol. In detail, two molecules of 2-methylenecyclohexanone (generated from 1 by elimination of dimethylamine) afforded via Diels–Alder reaction, subsequent addition of water and ring closure a product C₁₄H₂₂O₃, which finally proved to be the title compound. The structure of the tetracyclic hemiacetal 6 was deduced from one- and two-dimensional NMR experiments (1D TOCSY, DEPT-135, ¹H,¹H-COSY, gs-HSQC, gs-HMBC, gs-HSQC-TOCSY). In particular, the one-dimensional selective TOCSY and the gradient-selected HSQC-TOCSY, performed as a pseudo-3D experiment without the evolution period in the TOCSY part, proved to be very helpful for the unambiguous assignment of signals in overcrowded regions. NOE data confirmed the stereochemistry of epoxydibenzoxepinol 6 . Copyright © 2001 John Wiley & Sons, Ltd.