The chemistry of 1,3,5-triazacyclohexane complexes 5: cationic zinc(II) alkyl complexes of N-alkylated 1,3,5-triazacyclohexanes and 13-benzyl-1,5,9-triazatricyclo[7.3.1.0]-tridecane

Diethylzinc reacts with hydroperchlorates of N-alkylated 1,3,5-triazacyclohexanes (R₃TAC; R = methyl (Me), benzyl (Bz), isopropyl (ⁱPr)) and with the hydrotetrafluoroborate of 1,3,5-tris-(para-fluorobenzyl)-1,3,5-triazacyclohexane (FBz₃TAC) to give the corresponding cationic zinc ethyl complexes [(R₃TAC)Zn(Et)][X] (X = ClO₄⁻, BF₄⁻). Similar complexes were obtained from diethylzinc treated with [HNMe₂Ph][BF₄] or [HNMe₂Ph][B(C₆F₅)₄](Et₂O) in the presence of R₃TAC (R = Bz, FBz, s-1-phenylethyl (s-PhMeCH)). A product of decomposition of [(Bz₃TAC)Zn(Et)][ClO₄] was analyzed by X-ray diffraction. The structures of [({s-PhMeCH}₃TAC)Zn(Et)][BF₄] an [(FBz₃TAC)Zn(Et)][BF₄] were estimated using nuclear Overhauser enhancement spectroscopy. Protonolysis of diethylzinc with [HNMe₂Ph][BF₄] in the presence of 13-benzyl-1,5,9-triazatricyclo[7.3.1.0^5,13]-tridecane (BzTATC) yielded the complex [(BzTATC)Zn(Et)][BF₄].     

Zirconocene-mediated, high-yielding macrocyclizations of silyl-terminated diynes

A series of silyl-terminated diynes of varying lengths and substitution patterns have been prepared. These diynes undergo zirconocene coupling with selective formation of trimeric macrocycles from linear alkynes, while nonlinear diynes give cyclodimeric products. The length of the linear diynes can be increased for the preparation of macrocycles with large nanoscale cavities. Reaction of the zirconium-containing macrocycles with acid results in the synthesis of metal-free cyclophanes. All of these macrocycles were prepared in multigram quantities, in the absence of high-dilution conditions, to give products in > 75% yield that are easily purified as crystalline solids.     

Sub-nanogram per litre detection of the emerging contaminant progesterone with a fully automated immunosensor based on evanescent field techniques

Progesterone is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity in experimental animals and it can be found in various surface waters which are partly used as drinking water resources. Therefore, immunoanalytical methods at a very low limit of detection (LOD) and a low limit of quantification (LOQ) are becoming more and more important for environmental analysis and especially for monitoring drinking water quality. Biosensors have suitable characteristics such as efficiency in allowing very fast, sensitive, and cost-effective detection. Here we describe a fully automated immunoassay for progesterone with a LOD in the sub-nanogram per litre range and a LOQ in the lower nanogram per litre range. In contrast to common analytical methods such as GC-MS or HPLC-MS, the biosensor used requires no sample pre-treatment and no sample pre-concentration. The basis of our sensitive assay is the antibody with a high affinity constant towards progesterone and the robust biosensor setup used.     

SnCl4-catalyzed reaction of o-benzoquinones and aryl acetylenes: an unprecedented one-pot synthesis of tropone derivatives

Highly substituted tropone derivatives were obtained as a result of SnCl4-catalyzed cycloaddition of 3-methoxy-substituted o-benzoquinones with aryl acetylenes and subsequent rearrangement of the adducts with concomitant decarbonylation.     

Mise en evidence d''un intermediare cationique hydridoponte [1,5] lors de l''action du reactif de olah sur le phenyl-‘ aza-9 bicyclo [6.1.0.] nonane

The addition of hydrogen fluoride to 1-phenyl-9-azabicyclo [6.1.0] nonane gives two fluoroamines (52 %). The structures were established by n.m.r. techniques to be cis-2-fluoro-2-phenylcyclooctylamine and c-6-fluoro-c-2-phenylcyclooctyl-r-1-amine. A hydrido-bridged cation is likely the intermediate of the reaction.     

The determination of the nitrogen content and nitrogen-15 abundance by means of the nitrogen gas generated from inorganic and organic materials

A method is described for the determination of the total nitrogen content, after conversion to nitrogen gas, of various types of samples before the mass-spectrometric analysis of the ¹⁵N abundance. The sample is burned with a mixture of copper oxide, copper and lime in a closed tube under vacuum (modified Dumas method). The gas is released into an evacuated chamber of known volume and the nitrogen pressure is used to determine the nitrogen content of the sample. The gas is then admitted into a mass spectrometer. In order to obtain complete combustion of the material and to generate pure nitrogen gas, various combustion temperatures, combustion times and oxidizing agents were compared.     

Model Investigations of Controlled Release of Bioactive Compounds from Thin Metal Oxide Layers

Thin composite layers of silica with incorporated bioactive organic compounds (BOC) can be prepared by mixing metal oxide sols with dissolved BOC and coating with a conventional film coating machine. The release of antibacterial benzoic acid from the silica layers into a surrounding aqueous medium can be controlled by the mass ratio of silica to benzoic acid, by modification of the silica matrix and by addition of soluble or swelling penetration agents, respectively. Therefore, such composite materials are applicable for controlled release sytems in medicine and biology with excellent long-time effects.     

Asymptotic analysis of quasi-steady n-heptane droplet combustion supported by cool-flame chemistry

A skeletal chemical-kinetic mechanism for n-heptane cool flames is simplified to the maximum extent possible by introduction of steady-state approximations for intermediaries, following procedures employed previously in addressing two-stage ignition. A pair of ordinary differential equations in mixture-fraction space is thereby obtained, describing the quasi-steady structures of the temperature and heptylketohydroperoxide fields. Application of activation-energy asymptotics for the partial-burning regime to this pair of equations is shown to provide convenient expressions for flame structures and the extinction condition associated with maximally reduced chemistry. With the mixture-fraction co-ordinate related to radius, these results are used to address droplet-combustion experiments that have been performed in the International Space Station. Droplet diameters at extinction are predicted as functions of the oxygen concentration in the atmosphere and are compared with experiment. While the results are encouraging concerning qualitative predictions of dependences of extinction diameters on atmospheric conditions, there are noticeable quantitative differences that point to deficiencies in the analysis, likely resulting from a number of oversimplifications. Further investigation is therefore recommended.     

Synthesis of Diastereomeric 8-Fluoro-ABC-Steroid Building Blocks

An eight-step linear sequence for the preparation of two diastereomers of an 8-fluoro-ABC-steroid building block was developed. Key step was an intramolecular Diels–Alder reaction of an intermediate o-quinodimethane formed from a benzocyclobutene substituted with a 5-fluorohex-5-en-4-one chain. This side chain was prepared from 6-chlorohex-1-ene by bromofluorination, elimination of HBr, Finkelstein reaction and alkylation of a literature-known benzocyclobutene derivative with the thus-formed 6-iodo-2-fluorohex-1-ene. Allylic oxidation of side chain's fluorovinyl moiety to an α-fluoro-α,β-unsaturated ketone completed the preparation of the precursor for the [4+2]-cycloaddition.