Enantioselective behaviour of ethylated γ-cyclodextrins as GC stationary phases for chlorinated pesticides and phase characterisation by HPLC

Summary Small composition changes can influence the enantiomeric selectivity of alkylated cyclodextrins used as stationary phase in high resolution gas chromatography. A method is presented for the characterisation of such cyclodextrins using high performance liquid chromatography combined with evaporative light scattering and mass spectrometric detection (atmospheric pressure chemical ionisation in the positive ion mode). The method was applied to different batches of octakis (2,3,6-tri-O-ethyl)-γ-cyclodextrins (TEG-CD). Some showed a very good enantiomer selectivity for chlorinated pesticides. Separation evaluations were carried out with an improved test mixture containing selected, partly enantiomer enriched pesticides. Capillaries based on underethylated TEG-CD with up to 4 free OH groups dissolved in OV 1701-OH allowed the separation of α-HCH, o,p’-DDT, compounds of technical chlordane (cis-and trans-chlordane, U82, MC5, MC7, MC8) as well as chlordane metabolites (cis- and trans-heptachlor epoxide, oxychlordane) into enantiomers.     

Osmotic stress-dependent serine phosphorylation of the histidine kinase homologue DokA

Background  

Two-component systems consisting of histidine kinases and their corresponding receivers are widespread in bacterial signal transduction. In the past few years, genes coding for homologues of two-component systems were also discovered in eukaryotic organisms. DokA, a homologue of bacterial histidine kinases, is an element of the osmoregulatory pathway in the amoeba Dictyostelium. The work described here addresses the question whether DokA is phosphorylated in vivo in response to osmotic stress.     

The Synthesis and Dimerization of Transient 1-Silabutadienes

3-Methyl-1-tris(trimethylsilyl)silyl-2-butenol(1) ( 6 ) and (E)-3-Phenyl-1-tris(trimethylsilyl)silyl-2-propenol(1) ( 7 ) were prepared by the reaction of tris(trimethylsilyl)silyllithium ( 5 ) with 3,3-dimethylacrolein and (E)-cinnamaldehyde, resp. The alcohols 6 and 7 proved to be suitable precursors for the generation of the transient 1-silabutadienes (Me₃Si)₂Si = CHCH = CR¹R² 8 and 9 ( 8 : R¹ = R² = Me; 9 : R¹ = H, R² = Ph) following the principle of the modified Peterson reaction. Thus, 6 and 7 after deprotonation with excess MeLi in ether at low temperatures eliminated trimethylsilanolate and gave 8 and 9 , which were trapped by the excess organolithium reagent undergoing nucleophilic 1,2- or 1,4-addition reactions. In the absence of scavengers, e.g. when 8 and 9 were generated by treatment of 6 and 7 with stoichiometric quantities of MeLi in ether, the 1-silabutadienes dimerize in a [2 + 2] head-to-head fashion to give the 1,2-disilacyclobutanes 17 and 18 , resp., besides polymeric material. Treatment of the alcohol 6 with MeLi in tetrahydrofuran caused a 1,3-Si,O-trimethylsilyl shift affording the alkoxysilane (Me₃Si)₂SiH? CH(OSiMe₃)CH = CMe₂ 19 .     

The purification of water for inorganic ultratrace analysis

Various methods of preparing high-purity water are compared in terms of the cadmium, lead and copper contents of the product. The best system of those tested is the Millipore Milli-Q system, but it is strongly recommended that it should be fed with distilled (not demineralized) water.     

Neutraler Ionophor für Flüssigmembranelektroden mit hoher Selektivität für Natrium- gegenüber Kalium-Ionen

Neutral Ionophore for Liquid Membrane Electrodes of High Selectivity for Sodium Over Potassium Ions. The preparation of a neutral ion carrier suitable as a component for liquid membrane electrodes is described. These sensors may be used for the potentiometric determination of sodium ion activities with a discrimination of potassium ions by a factor of up to 250.     

Broken collinear SU(6) symmetries and the suppression of |ΔS| = 1 amplitudes

Within the framework of the general mapping between collinear SU(6) algebras in the current- and the constituent-quark picture, a unitary transformation involving the quark mass matrix M = λ₀ + cλ₈ is introduced. It results in a weight factor between ΔS = ± 1 and ΔS = 0 amplitudes. With a specific boundary condition, one obtains tg θ = cos(πc/2√2)θ = Cabibbo angle.     

Synthesis and structural characterization of novel silenes stabilized by intramolecular coordination of a dialkylamino group

Two intramolecularly donor-stabilized silenes, 1-(8-dimethylamino-1-naphthyl)-1,2,2-tris(trimethylsilyl)silene (6a) and 1-(2-dimethylaminomethylphenyl)-1,2,2-tris(trimethylsilyl)silene (6b), were synthesized according to a novel one-step process by the reaction of (dichloromethyl)tris(trimethylsilyl)silane (1) with a twofold molar excess of 8-dimethylamino-1-naphthyllithium or 2-(dimethylaminomethyl)phenyllithium, respectively. Compounds 6a and 6b are thermally stable compounds. X-ray structural analyses of both silenes revealed strong donor-acceptor interactions between the dialkylamino groups and the electrophilic silene silicon atoms (Si-N distances: 6a: 1.751(3) A; 6b: 1.749(3) A) that lead to pyramidalization at the silicon centers. In contrast, the configuration at the silene carbon atoms was found to be planar. The Si=C distances (6a: 1.751(3) A; 6b: 1.749(3) A) fit with literature data of comparable compounds. Addition of water or methanol to the Si=C bonds of 6a,b afforded the silanols 7a,b and the methoxysilanes 8a,b, respectively. The compound 1-(8-dimethylaminomethyl-1-naphthyl)-1,2,2-tris(trimethylsilyl)silene (6c), generated following the same procedure by the reaction of 1 with 8-(dimethylaminomethyl)-1-naphthyllithium (molar ratio 1:2) proved to be unstable at room temperature and underwent rapid insertion of the Si=C group into a methylene C-H bond of the dimethylaminomethylnaphthyl ligand to afford the 1-silaacenaphthene 9.