Bimetallic Alkoxides of Barium and Zirconium: Preparation of BaZrO3 Powder

Complex formation in solutions of barium and zirconium alkoxides in ROH (R=i-Pr, Et) was studied. A number of bimetallic complexes were isolated, and their structure and properties were studied. The sol-gel method yields a single-phase BaZrO₃ powder only wheni-PrOH solutions of the alkoxides are used. In this case, the oxocomplex, BaZrO(OPr-i)₄.(1–2)i-PrOH, is the precursor of the mixed oxide.     

Experimental (NMR) and Computational (MD) Studies on the Inclusion Complexes of 1-Bromoadamantane with alpha-, beta-, and gamma-Cyclodextrin

The inclusion complexes between the most commonly used cyclodextrins (alpha-, beta-, and gamma-CD) and 1-bromoadamantane were prepared and studied experimentally by NMR methods and by molecular dynamics simulations (AMBER force field) with solvation. The NMR results suggest host/guest ratios of 2:1, 1:1, and 1:1 for the complexes with alpha-, beta-, and gamma-cyclodextrin, respectively, as well as defined geometries for the complexes. Averaged geometrical data from the molecular dynamics simulations agree with the complexation geometries deduced experimentally.     

Synthetic analogs of natural flavolignans. IV. Synthesis of benzodioxocane analogs of silandrin and hydnocarpin

1,6-Benzodioxocane analogs of chalcones have been synthesized. From them have been obtained benzodioxocane analogs of silandrin and hydnocarpin. The PMR spectra of the substances synthesized are given and are discussed.Taras Shevchenko Kiev University, Ukraine. KIEN, Karakalpak Division, Academy of Sciences of the Republic of Uzbekistan, Nukus. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 490–493, July–August, 1994.     

Unique structural properties of the Mg-Al hydrotalcite solid base catalyst: an in situ study using Mg and Al K-edge XAFS during calcination and rehydration

The changes in the layered structure of Mg-Al hydrotalcite (Mg/ Al = 2) during heat treatment have been investigated by using in situ XAFS simultaneously at the Mg and Al K-edges. The development of unique in situ instrumentation allowed the coordination environments at both the Mg and Al centers to be monitored as a function of the temperature and heat treatment. The results of this study show that the hydrotalcite structure is highly flexible, and should lead to the further development of hydrotalcites as new solid basic catalysts. Moreover, the Mg and Al cations in the cation layers show different behavior as a function of temperature. The coordination of some octahedral Al ions decreases already at a temperature of 425 K, whereas the coordination about Mg does not show any modification at this temperature. However, hydrotalcite treated at 425 K, followed by cooling down to room temperature resulted in a complete reversal to the original octahedral Al coordination. It is proposed that Al-OH bond breakage occurs at 425 K, without the evolution of H2O. This bond is restored after cooling to room temperature. The actual dehydroxylation of hydrotalcite commences between 425 and 475 K, as indicated by a change in coordination of both the Mg and Al centers. This is accompanied by the evolution of H2O molecules and the changes are hence irreversible without the presence of excess water. Heat treatment at 725 K leads to the development of an MgO-like phase (octahedral Mg) and a mixed octahedral/tetrahedral Al phase. A subsequent rehydration at room temperature entirely restores the original coordination about the Al and Mg centers of hydrotalcite to a distance of 15 A, to which XAFS spectroscopy is sensitive.     

Synthesis and study of tautomeric properties of 2-(5-R-2-furyl)thiazolin-4-ones

Compounds were synthesized by reaction of 5-R-2-cyanofurans with thioglycolic acid, which, according to IR, PMR, and mass spectrometric data, exist in the form of two tautomers, 4-hydroxythiazole and thiazolin-4-one.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 404–409, March, 1987.     

Analysis of primary aliphatic short-chain monoamines by LC in water samples

Several derivatization procedures with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) were compared for a rapid analysis of primary aliphatic short-chain monoamines in water samples by HPLC using a LiChorospher analytical separation column (100RP₁₈ mm i.d., 5 μm). Both the solution and the solid-support assisted off-line derivatization on C₁₈ SPE cartridges were inadequate options because of beginning degradation processes of the instable isoindol derivatives during their transfer to the analytical column. This problem was precluded with the on-column or solid-support assisted on-line derivatization. In the last mentioned procedure, the derivatization took place in a Hypersil C₁₈ precolumn ( mm i.d., 30 μm) connected with an additional preconcentration step resulting in better detection limits (0.002-0.040 μg ml⁻¹ requiring only 150 μl of water sample) than in the on-column procedure (0.08-0.16 μg ml⁻¹). The improved sample handling, the better control of parameters affecting reaction rates, the fully automation of this method with only 10 min analysis time for each sample are further advantageous. The potential of the solid-support assisted on-line derivatization was outlined and applied to water samples from several sources. Recovery values near 100% were obtained.     

Determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples using hollow fiber-protected liquid-phase microextraction and high performance liquid chromatography

A new method based on hollow fiber-protected liquid-phase microextraction (LPME) was developed for the simultaneous determination of atrazine, desethyl atrazine and desisopropyl atrazine in environmental water samples. In LPME, analytes were extracted into 1-octanol immobilized in the micropores of a poly(vinylidene fluoride) porous hollow fiber membrane, and back extracted into the acceptor (4 M HCl) filled in the lumen of the hollow fiber. After LPME, the analytes trapped in the acceptor were analyzed with high-performance liquid chromatography after neutralization. The effect of extraction factors such as sample pH, acceptor pH, salinity, extraction time, stirring rate, and humic acid were studied. Under the optimized conditions, the limits of detection and relative standard deviations were respectively in the range of 0.5–1.0 μg L⁻¹ and 3.9–4.7% (n = 5). The proposed method was applied to determine atrazine, desethyl atrazine and desisopropyl atrazine in wastewater and groundwater samples. The three analytes were below the limits of detection, but good relative spiked recoveries over 90.1 ± 5.9% at 5 μg L⁻¹ spiked level were obtained.     

Experimental and computational studies of intracomplex reactions in Mg+(primary, secondary alkylamine) complexes induced by photoexcitation of Mg+

We report herein a comprehensive study of photoinduced reactions in complexes of Mg+ with primary (n-propyl- and isopropylamine) and secondary amines (dipropyl- and diisopropylamine) in the spectral range of 230-440 nm. Similar to the methyl- and ethylamine complexes studied previously, N-H bond activation of these complexes is very unfavorable. Instead, the C(alpha)-C, C-N, and C(alpha)-H bond-cleavage photoproducts are observed after photoexcitation of the Mg+ complexes (3(2)P<--3(2)S). For Mg+(primary amine) complexes, for example, Mg+-NH2CH2CH2CH3, and Mg+-NH2CH(CH3)2, the photoproducts resulting from C(alpha)--C rupture prevail after P(z) and charge-transfer excitations, whereas the Mg+ photofragment is predominant upon P(x,y) excitation. However, with further N-alkyl substitution, as in Mg+(secondary amine) complexes, for example, Mg+-NH(CH2CH2CH3)2 and Mg+-NH[CH(CH3)2]2, a novel intracomplex C-C coupling photoreaction dominates on P(x,y) excitation of Mg+, which is believed to arise from Mg+* insertion into the C-N bond. With P(z) and charge-transfer excitation, the Mg-R elimination photoproducts, arising from C(alpha)-C bond cleavage, predominate. The energetics and possible mechanisms of the intracomplex photoreactions are analyzed in detail with the help of extensive quantum mechanics calculations.     

Degradation of ²-O-4 lignin model and related compounds by the ascomyceteChrysonilia sitophila (TFB 27441 strain)

Growth of the ascomyceteChrysonilia sitophila during degradation of lignin model dimers and monomers was compared to a glucose control. An inhibition of growth by Cα-carbonyl monomers and stimulation by β-O-4 lignin model and vanillyl alcohol were observed. A comparison of the degradation by this ascomycete with the basidiomycetePhanerochaete chrysosoporium showed similarities in relation to the type of degradation caused.     

Doppler-free laserspectroscopic investigations of hyperfine structure in the atomic cobalt spectrum

Performing Doppler-free laserspectroscopic investigations in the red wavelength region (640–670 nm) we were able to determine 10A-factors and 9B-factors of atomic cobalt levels. Now precise values of 18A-factors and 16B-factors of levels belonging to the configurations (3d+4s)⁹ are known. Fitting of the one-electron radial parameters to introduce agreement between experimental and theoretical hfs constants allows the prediction of hfs constants of not yet investigated fine structure levels. Values of the electric quadrupole moment of the Co⁵⁹ nucleus are determined in two electron configurations. The resulting mean value of the spectroscopic quadrupole moment isQ=0.35(3) barn.