Composition and thermal stability of SiO2-based hybrid materials TEOS-MTEOS system

Hybrid materials with different amounts of organics permanently bound on the inorganic network obtained in the TEOS-MTEOS (tetraethoxysilan-methyltriethoxysilan) system are used for obtaining coatings with different optical and mechanical properties. To study the thermal stability of the mentioned materials, compositions with different molar ratios of the precursors were prepared. The influence of the solvent and water amounts on the gelation process was also investigated. The gels obtained were characterised by IR spectrometry and their decomposition temperatures were determined by DTA/TG. Thermal stability of the gels is rather influenced by their composition than the conditions of the gelation process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radiation dose contribution from coal-slags used as structural building material

A significant dose contribution on the population could be derived from coal slags used as isolation material. Extremely high natural activities are measured in the coal slag, derived from the region of the settlement Ajka, Hungary. In some buildings monitored, the elevated -doses were nearly 5–10 times higher than the world average ones. The annual average indoor radon concentrations from the slag exceeded 400 Bq/m³ and in some cases up to 1200 Bq/m³. Due to the elevated exposure and the radon concentrations in the dwellings the annual dose was estimated to 8–24 mSv/y more than 5–10 times of the world average one.     

CIRCULAR DICHROISM SPECTRA OF SYSTEM I PARTICLES FROM NORMAL CHLOROPLASTS AND CAROTENOID-DEFICIENT MUTANTS OF MAIZE

Abstract— Circular dichroism (CD) spectra were studied in System I particles prepared by digitonin fragmentation of chloroplasts of normal maize and carotenoid-deficient mutants. CD bands of pigment molecules were found to be higher in particles than in solutions. This phenomenon was most pronounced for the particles containing the carotenoid composition of normal chloroplast lamellae. The CD signal of chlorophylls bound to particles of carotenoid-deficient chloroplasts was closer to that found in solutions. This indicates that aggregation and/or binding of chlorophylls in carotenoid-deficient mutants may be less extensive than in normal chloroplasts.     

A DFT investigation of the addition reaction of monomeric lithium enolate derived from propiophenone to propene oxide: examination of the possible transition structures

The addition reaction of monomeric lithium enolate (Z)-1, derived from propiophenone, to propene oxide 2, was examined to clarify the exact geometry of the transition state (TS) involved in this type of reaction. The eight possible TSs and the corresponding pathways, four leading to syn gamma-hydroxy ketone (gamma-HK) 3 and four leading to anti gamma-HK 4, were compared, using the B3LYP/6-31+G(d)//B3LYP/6-31+G(d) theory level in vacuo and in the presence of the reaction solvent (toluene/hexane). In every case, the favored pathway involves a TS where the enolate C=C and the epoxide C-C are in a gauche relationship and where the Li(+) is stabilized by some C-C and C-H sigma bonds of epoxide 2.     

Polarizability effects and dispersion interactions in alkene-Br2 pi-complexes

Weakly bound molecular complexes play an important role in chemistry, physics, and biodisciplines. The preequilibrium pi-complexes of various alkenes with bromine have been examined quantitatively, and a direct relationship between association constants (KF) of these pi-complexes and polarizability of the olefins was found. The stability of the Br2-olefin pi complexes is affected by both the donor ionization potential and the polarizability of the olefin, and an equation able to take into account both effects is proposed.     

Differentiable Distance Spaces

The distance function \({\varrho(p, q) ({\rm or} d(p, q))}\) of a distance space (general metric space) is not differentiable in general. We investigate such distance spaces over \({\mathbb{R}^n}\), whose distance functions are differentiable like in case of Finsler spaces. These spaces have several good properties, yet they are not Finsler spaces (which are special distance spaces). They are situated between general metric spaces (distance spaces) and Finsler spaces. We will investigate such curves of differentiable distance spaces, which possess the same properties as geodesics do in Finsler spaces. So these curves can be considered as forerunners of Finsler geodesics. They are in greater plenitude than Finsler geodesics, but they become geodesics in a Finsler space. We show some properties of these curves, as well as some relations between differentiable distance spaces and Finsler spaces. We arrive to these curves and to our results by using distance spheres, and using no variational calculus. We often apply direct geometric considerations.     

Influence of the interaction between hydrogen sulfide and ionic liquids on solubility: experimental and theoretical investigation

The solubility of H(2)S in a series of 1-butyl-3-methylimidazolium ([bmim](+)) based ionic liquids (ILs) with different anions, chloride, tetrafluoroborate ([BF(4)](-)), hexafluorophosphate ([PF(6)](-)), triflate ([TfO](-)), and bis(trifluoromethyl)sulfonylimide ([Tf(2)N]-), and in a series of [Tf(2)N] ILs with different cations, i.e., N-alkyl-N'-methylimidazolium, 2-methyl-N-methyl-N'-alkyimidazolium, N-alkylpyridinium, N-butyl-N-methylpyrrolidinium, and N-alkyl-N,N-dimethyl-N-(2-hydroxyethyl)ammonium has been determined using medium-pressure NMR spectroscopy. The observed solubilities are significantly higher than those reported for many other gases in ILs, suggesting the occurrence of specific interactions between H2S and the examined ILs. Quantum chemical calculations have been used to investigate at a molecular level the interaction between H2S and the [bmim](+)-based ILs.     

Theoretical conformational study of six-membered cyclic allyl epoxides

Accurate “ab initio” calculations (MP2 method) were performed to outline the conformational profile of a number of six-membered cyclic allyl epoxides differing either in the nature of the cycle fragment (Y) bound to the unsaturation, or in the substitution at the endocyclic carbon bound to the epoxy ring and bridging the epoxy ring with the Y fragment. In particular, we calculated structures 4 (Y=CH₂), 5 (Y=O), 6 (Y=NH), 7 (Y=S), 8 (Y=CF₂), 9 (Y=NH₂ ⁺), 10 (Y=CO), 11 (Y=BH) and 12 (Y=NCOOH), where the fragment of the endocyclic carbon bridging “Y” and the epoxy fragment is either non-substituted (4a – 12a) or bears a methyl side chain trans (4b–12b) or cis (4c–12c) to the epoxidic oxygen. Saturated analogs (Y=O and Y=CH₂) were also computed to test the method and to evaluate the conformational profile in the absence of the unsaturation. Minimum energy conformations were found which differ in the relative position of the Y group and the epoxy oxygen, with respect to a plane containing the epoxy ring carbons and the adjacent saturated endocyclic carbon: they may be on the same side (conformer A) or on opposite sides (conformer B). Conformers A are generally more stable. The conjugation effect of Y with the double bond lowers the barrier between the two conformers to the extent that in a few cases only conformer A is associated with a minimum of energy. On the basis of the elongation of the allylic oxirane C–O bond, we postulated the order of reactivity of epoxides 4–12 in the oxirane ring-opening process, and a mechanism based on the more reactive conformer A. A comparison was also made between MP2 and DFT calculation methods.