The thermal study of oxyfluoride glass with strontium fluoride

A thulium (Tm 3+) doped oxyfluoride glass ceramic containing SrF2 nanocrystals has been presented. Transparent glass ceramic was obtained by heat treating the glass from the SiO2-Al2O3-ZnO-SrF2 system at the first crystallization temperature. Cerammization of glass was studied by DTA/DSC, XRD and SEM methods. It has been found that nanocrystallization of SrF2 strongly depends on the ratio between the components and amount of SrF2. Moreover the rare earth dopant Tm3+ influenced on the thermal properties of glass. The formation of SrF2 nanocrystals in glass ceramic was confirmed by X-ray diffraction. X-ray diffraction analysis of the transparent glass ceramic revealed that the SrF2 nanocrystals are precipitated in the glass matrix. Analysis of the local atomic interactions in the structure of oxyfluoride glass has been used to explain the course of the crystallization.     

Determination of the association constant of NaS2O 3 − with the sodium-selective electrode and UV spectrophotometry

The association constant of NaS₂O ₃ ^? complex in a medium of μ=1.0M at 25.0±0.1°C was determined by two techniques: sodium-selective electrode (β₁ = 1.48 ± 0.13) and UV spectrophotometry (β₁ = 1.25 ± 0.10). There is no evidence, under our experimental conditions, of the existence of the binuclear complex Na₂S₂O₃, which might exist at the very low value of the ratio \(C_{Na_2 s_2 o_3 } /C_{Na} +\) used in our experiments.     

An isotopic dilution approach for 1,3-butadiene tailpipe emissions and ambient air monitoring

An isotopic dilution approach for 1,3-butadiene analysis in gaseous samples is presented. The methodology is based on active sampling on sorbent tubes and subsequent analysis by thermal desorption into a gas chromatography/mass spectrometry system. By adding a perdeuterated internal standard onto the sorbent tubes before sampling, and using mass spectrometric detection, the methodology gives high accuracy for this unstable analyte. The method has been used to monitor 1,3-butadiene ambient air concentrations in a residential area in proximity to a heavy-traffic roadway over a one-week period, for comparison with other traffic-related pollutants analysed by standard procedures. It has also been used to determine tailpipe emissions of two vehicles by standard emission testing procedures in a dynamometer. These vehicles were chosen as examples of low- and high-end emission rate vehicles, i.e., an old no-catalytic converter Otto engine and a new direct-injection diesel engine with catalytic converter. Exhaust gas emissions were 0.052 and 35.85 mg/km, reflecting differences in fuel, engine design, age, and presence (or not) of a catalytic abatement system. The ambient air results showed a weekly average concentration of 1,3-butadiene of 0.53 microg/m(3).     

Solid-phase synthesis of conformationally constrained peptidomimetics based on a 3,6-disubstituted-1,4-diazepan-2,5-dione core

Starting from a Cl-trytyl linked hydroxylamine, a hydroxamic dipeptide having serine in the second position was prepared by using DMTMM as the coupling agent. Mitsunobu cyclization carried out under microwave heating gave very good yields of a 3,6-disubstituted-perhydro-diazepin-2,5-dione. This heterocycle can be used as a new platform for combinatorial chemistry or as a constraint to rigidify a small peptide.     

A germanium zeotype with a three-dimensional net of interconnected 14-, 12- and 12-ring channels. Ge13O26(OH)4[C6N2H16]2(H2O)1.5

Ge(13)O(26)(OH)(4)[C(6)N(2)H(16)](2)(H(2)O)(1.5) is a novel germanium zeotype built up from a new type of SBU; the SBU-13 is formed from polyhedra distributed in three shells. Its open 3D framework has a three-dimensional system of intersecting channels, where the 14-ring channels are lined with OH(-) anions.     

From an inactive prokaryotic SOD homologue to an active protein through site-directed mutagenesis

It is known that several prokaryotic protein sequences, characterized by high homology with the eukaryotic Cu,ZnSODs, lack some of the metal ligands. In the present work, we have stepwise reintroduced the two missing copper ligands in the SOD-like protein of Bacillus subtilis, through site-directed mutagenesis. The mutant with three out of the four His that bind copper is not active, whereas the fully reconstituted mutant displays an activity of about 10% that of human Cu,ZnSOD. The mutated proteins have been characterized in solution and in the solid state. In solution, the proteins experience conformational disorder, which is believed to be partly responsible for the decreased enzymatic activity and sheds light on the tendency of several human SOD mutants to introduce mobility in the protein frame. In the crystal, on the contrary, the protein has a well-defined conformation, giving rise to dimers through the coordination of an exogenous zinc ion. The catalytic properties of the double mutant, which might be regarded as a step in an artificial evolution from a nonactive SOD to a fully functioning enzyme, are discussed on the basis of the structural and dynamical properties.     

Synthesis of tricyanovinyl-substituted thienylpyrroles and characterization of the solvatochromic, electrochemical and non-linear optical properties

Tricyanovinyl-substituted 1-(alkyl)aryl-2-(2′-thienyl)pyrroles 1 have been synthesized by direct tricyanovinylation reaction of 1-(alkyl)aryl-2-(2′-thienyl)pyrroles 2 using TCNE. The tricyanovinyl-derivatives 1 display dramatic reductions in both their optical and electrochemical band gaps relative to thienylpyrrole precursors 2. The solvatochromic behavior of compounds 1 was investigated in a variety of solvents. Hyper-Rayleigh scattering was used to measure the first hyperpolarizabilities β of the mentioned compounds. The β values show that the new compounds prepared could be used on the manufacture of materials with good non-linear (NLO) properties.