Effect of Ultrasonic Field on the State of Starch Hydrogels

Some fundamental aspects of how the primary structure of starch hydrogels with concentration of 1 to 8 wt % disintegrates in an ultrasonic field are discussed. The effect of ultrasonic vibrations on the basic characteristics of starch hydrogels: degree of grain cleavage, viscosity, transparence, and phase composition, is analyzed.     

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 structure of copper(II) complexes with diaminodioxime (H<Subscript>2</Subscript>L), a derivative of the monoterpenoid (+)-3-carene

Copper(II) compounds with the optically active diaminodioxime (H₂L) derived from the monoterpenoid (+)-3-carene, Cu(H₂L)(NO₃)₂ H₂O (I), Cu(H₂L)(ClO₄)₂ H₂O (II), Cu(H₂L)Br₂ H₂O (III), and Cu(H₂L)SO₄0.5H₂O (IV) with µ_eff equal to 1.81, 1.79, 1.71, and 1.8 µ_B, respectively, were prepared. Studies of the complexes by IR and EPR spectroscopy showed that I and II are mononuclear ionic complexes. Compound III apparently has polymeric structure (the CuN₄Br₂ coordination unit). According to EPR data, the Cu²⁺ ions in polycrystalline compounds III and IV undergo exchange interactions.Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 897–900.Original Russian Text Copyright © 2004 by Larionov, Myachina, Sheludyakova, Boguslavskii, Tkachev, Bizyaev.     

Thermodynamic parameters for the molecular inclusion reaction of dulcin with beta-cyclodextrin. spectrofluorimetric determination of dulcin

The inclusion of dulcin in alpha- and beta-cyclodextrin has been studied by fluorescence spectroscopy. To quantitatively describe complex formation between the beta-cyclodextrin and dulcin, an association constant of 290 M(-1) at 21 degrees was obtained. The thermodynamics associated with the complex formation between dulcin and beta-cyclodextrin in aqueous solution has been studied. The obtained value of DeltaG(0) = -13.7 kJ/mole at 21 degrees , together with DeltaH(0) = -33.6 +/- 2.3 kJ/mole and DeltaS(0) = -67.2 +/-8.3 Jmole(-1) K(-1) indicate that dulcin has a very marked tendency to associate with beta-cyclodextrin in water. The inclusion complex of dulcin in beta-cyclodextrin has been used to determine dulein in the range 0.13-5 mug/ml the method has been applied to determine dulcin in soft drinks.     

Evaluation of the thermochemical changes in agricultural by-products and in the carbon adsorbents obtained from them

The thermochemical decomposition of waste products from a coconut (Cocos nucifera L.), a nut (Juglans regia L.) an apricot (Armeniaca vulgaris L.), an almond (Amygdalus communis L.var amara DC.), a grape (Vitis vinifera L.) and a cherry (Prunus avium L.), as raw materials for producing carbon adsorbents, was investigated by DTA and TG. The thermo-oxidative and decomposition processes resulting in increased number of oxygen-containing functional groups of phenolic and carbonyl type are responsible for the high adsorption capacities of the carbon adsorbents. The thermochemical changes in adsorbents based on agricultural wastes are similar to those in commercial activated carbons. The adsorbents derived from apricot stones have the highest overall thermal stability.     

Stereoisomerism of N-(1-Propenyl)thiobenzamide

A prototropic rearrangement of N-prop-2-enylbenzocarbothioamide afforded two stereoisomeric N-prop-1-enylbenzocarbothioamides (IIa, b) isolated as individual compounds. The stereoisomerism is due to hindered rotation around thioamide bond C(S)-N and also to -diastereoisomerism. The configuration of the isolated isomers was investigated by IR spectroscopy, AM1 and PM3 methods. In the molecules occurs the p,-conjugation with participation of nitrogen atom and multiple bonds resulting in formation of a united delocalized MO in the planar fragment C(S)-NC = C.     

Infrared spectra of negative ions with a strong,symmetric hydrogen bond (HO...H...OH)− and (H3CO...H...OCH3)−

From the multiple attenuated total internal reflection (MATIR) infrared spectrum of an aqueous KOH solution, the spectrum of the (HO)₂H^– ion, formed by a strong, symmetric H-bond, has been segregated. The spectrum of the analogous ion (CH₃O)₂H^– has been segregated from the MATIR infrared spectrum of a solution of KOCH₃ in methanol. The segregated spectra contain large numbers of individual bands that are not present in the spectra of the original components of the solution. This may be a consequence of strong interaction of vibrations of the proton in the central strong, symmetric hydrogen bond with vibrations of other groups in the ion.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1363–1366, June, 1991.     

HPLC Determination of some antibilharzial antimonials by extraction of antimony

The antimonial drug (antimony potassium tartrate, antimony piperazine tartrate or antimony lithium thiomaleate) in aqueous solution or biological fluid is treated with sodium diethyldithiocarbamate in the presence of a suitable masking reagent, the pH is adjusted to 9 +/- 0.5. and the antimony complex extracted with n-hexane and determined by reversed-phase HPLC with an ODS column and detection at 254 nm. The limits of detection are 20 ng (for antimony potassium tartrate and antimony lithium thiomaleate) and 16 ng (for antimony piperazine tartrate).     

Meroterpenoids—III : Psoralea corylifolia linn.—3. Synthesis of (±)-bakuchiol methyl ether

A synthesis of (±)-bakuchiol methyl ether, involving Claisen rearrangement of geranyl vinyl ether as the key step, is described. Further thermal reorganisation of the intermediate 3-vinyl-citronellal is discussed.     

Selective complexometric determination of palladium, with thiourea as masking agent

A method is proposed for selective complexometric determination of palladium, thiourea being used as masking agent. An excess of EDTA is added and the surplus EDTA is back-titrated at pH 5-5.5 with lead nitrate, with Xylenol Orange as indicator. Thiourea is then added to decompose the palladium-EDTA complex and the liberated EDTA is again back-titrated with lead nitrate. The interference of various cations has been studied.