Unprecedented cyclizations of calix[4]arenes with glycols under the Mitsunobu protocol, part 2.(1) O,O-and O,S-bridged calixarenes

[reaction: see text] Cycloalkylations of p-tert-butylcalix[4]arene (CA) and p-tert-butylthiacalix[4]arene (TCA) with various aliphatic glycols were performed under the Mitsunobu protocol using the DEAD/TPP system. CA gave 1,3-dialkylated diols, while C(2)-C(10) glycols gave 1,2- and 1,3-bridged calixarenes. The reaction of TCA with C(2) diols afforded sulfonium phenoxide betaines via O,S-cyclization, which is the first example for the alkylation of the sulfide bridge.     

Synthesis of Novel D-Seco-Pregnenes

A new synthetic route was developed for the preparation of trans-3-hydroxy-16,17-seco-pregna-5,17(20)-dien-16-al, using Grob fragmentation as the key step. This seco-steroid contains a formyl group and an unsaturated side-chain in a sterically favourable position, and is therefore a promising starting material for the synthesis of novel condensed steroid heterocycles.     

Synthesis,structural and spectral investigations of new types of dioxovanadium(V) complexes withS-methylthiosemicarbazones derived from salicyl and 2,4-dihydroxybenzaldehydes. X-ray structure of ammonium(salicylaldehydeS-methylthiosemicarbazonato) dioxovanadate(V) monohydrate

Summary The x-ray crystal structure of [VO₂(HL¹)] (where L¹ denotes the dianion of theS-methylthiosemicarbazone of salicylaldehyde) has been determined and refined to R=0.058 (R_w=0.063) for 3377 observed reflections.There are two symmetrically independent molecules in the asymmetric unit, showing no significant differences in their geometries. The vanadium atom is pentacoordinated in a distorted square-pyramidal arrangement.Absorption spectra of [VO₂(HL¹)] and [VO₂(HL²)], in the 10000–45000 cm^–1 range, were calculated from the measured reflectance spectra, applying Kubelka-Munk's theory. The extinction coefficients were determined from the absorption spectra of the solutions of these complexes in methanol. The observed maxima are interpreted on the basis of intraligand transition and charge-transfer spectra on the basis of the presence of approximate groupC _2v for both complexes.     

Extensions of real-valued difference posets

The difference poset of real-valued functions (fuzzy sets) is investigated. The difference posets on some subsets of the unit real interval [0, 1] are characterized. It is shown that although it is not always possible to represent the difference by some generator, for dense subsets such a representation exists and is unique.     

TG study on the chlorination of MoO2 by CCl4

Molybdenum-dioxide samples were produced by reduction of MoO₃ in flowing H₂. The chlorination kinetics of the pure crystalline MoO₂ and samples containing a mixture of Mo-oxides were studied by thermogravimetry, using gaseous CCl₄ as chlorinating agent. The initial samples and the chlorinated residues were investigated by XRD and BET methods, as well. The pure molybdenum-dioxide sample was remarkably less reactive than the partially reduced non-stoichiometric molybdenum-oxides or MoO₃. The characteristic sigmoid shape of the TG curves were explained by the difference in the reactivity of molybdenum-oxides and by the change of the specific surface area during chlorination. The observed reaction order ofn=0.5 suggests a fast, reversible dissociative adsorption of CCl₄ before the volatilization step. For samples of low specific surface area activation energies of 123 and 97 kJ·mol^?1 were obtained, and the kinetic curves could be well fitted by an Avrami-Erofeev equation. For sample of much higher specific surface area a diffusion controlled reaction (E _a=52 kJ·mol^?1) was supposed, and the kinetic model of contracting spheres could be applied.     

Curve fitting to asymmetrical chromatograms by the extended Kalman filter in frequency domain

An algorithm is presented to perform curve fitting on the basis of the Fourier transform of a signal. The curve fitting has been done with the exponentially modified Gaussian model, obtained when convolving a Gaussian distribution and an exponential decay function. The parameter estimation has been carried out by means of the two-dimensional extended Kalman filter. The goodness-of-fit has been characterized by the trace of the covariance matrix of the estimated parameters. The precision of the estimated parameters obtained by fitting either in time or frequency domain is compared.     

Spectrophotometric and thermoanalytical study of cypermethrin/cyclodextrin complexes

Cypermethrin/β-CD complexes were prepared at 1:2 cypermethrin/β-CD molar ratio by different complexation methods: conventional coprecipitation, suspension and kneading methods as well as “melting in solution” technique, which was developed in our laboratory. The complexes were investigated by UV-spectrophotometry and thermal analysis. It was found that complexes made by coprecipitation, suspension and kneading methods contained cypermethrin not only in complexed but also in uncomplexed form. The guest molecule in the complex prepared by “melting in solution” technique showed to be completely complexed, so it was the most effective complexation method studied.Investigating the solubility of cypermethrin with different cyclodextrins (CDs), it was established that the increase of solubility of cypermethrin was the highest in case of methylated cyclodextrins. The equilibrium constants were calculated from solubility isotherms. On the basis of these results, the heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) complex was the more stable. By UV-irradiation measurements it was found that the photodegradation of cypermethrin was inhibited by methylated β-CDs.     

Trace analysis of trichlorobenzenes in fish by microwave-assisted extraction and gas chromatography-electron-capture detection

An analytical method consisting of extraction, clean-up, and analysis by gas chromatography-electron-capture detection (GC-ECD) was developed for the determination of trichlorobenzenes (TCBs) in fish samples. Two extraction methods, saponification and liquid-liquid extraction (S-LLE), and microwave-assisted extraction (MAE), were evaluated. In both cases, n-pentane was used as the extraction solvent. For S-LLE, the recoveries ranged from 66.6+/-9.1% for 1-bromo-4-chlorobenzene (4-BCB) to 93.5+/-4.9% for 1,2,4-trichlorobenzene (1,2,4-TCB). The recoveries were significantly lower, between 31.0+/-3.9% for 1,2,3-trichlorobenzene (1,2,3-TCB) and 52.3+/-3.0% for 1,3,5-trichlorobenzene (1,3,5-TCB), in the absence of fish. Proteins and glycerides of the fish tissue seemed to compete with TCBs for the base, and hence decreased their decomposition rate. In the case of MAE, the recoveries were highly dependent on the pressure applied during extraction. At 5 bar, much higher recoveries were obtained, from 66.7+/-15.6% for 4-BCB to 79.9+/-13.6% for 1,2,4-TCB, than at 1 bar. Sulfur formation was, however, observed at 5 bar, and interfered with the GC-ECD analysis of TCBs. Sulfur was adequately removed by copper powder treatment, which was shown not to affect the recovery of analytes. The recoveries of target analytes by S-LLE and MAE did not differ statistically (t-test, alpha = 0.01). Both methods were appropriate for the detection of TCBs at concentration levels typically observed in marine biota, i.e. approximately 1 ng/g. S-LLE was, however, more time consuming, and required larger volumes of high-purity organic solvents than MAE.     

Effect of four bentonite samples on the rare earth element concentrations of selected Hungarian wine samples

Rare earth elements (REEs) were detected and determined (except Eu, and in some cases Gd, Tb and Tm) in three Hungarian wine samples - Királyleányka, Blauer Portugieser and Merlot (2004 vintage) - from the Eger viticulture area by double focusing inductively coupled plasma sector field mass spectrometry (ICP-SF-MS) in low resolution mode (R = 300). The REE average concentrations of the samples determined after microwave-assisted digestion were in the pg cm^− 3 concentration range. According to the results, among these grapes grown on volcanic slopes, the REEs uptake by the Királyleányka and Blauer Portugieser seemed to be more inhibited. Four, commercially available bentonite samples - fibrous (Gelbenton), protein containing (Evergel), and two Na bentonites (BW200 and Tükrös) - were used for wine clarifying. Gelbenton altered the less the REE concentrations of the wine samples. The lowest increase (1.1-1.5 times) was established for the Merlot red wine sample.