1,277 research outputs found
Rotational diffusion and segmental motions in solutions and melts of tetraoctylammonium perchlorate
No full textRelaxation times for the methylene carbon atoms in the aliphatic chains of tetraoctylammonium perchlorate have been measured in different solvents and in the melt. The results have then been interpreted on the basis of a theoretical model which considers the overall rotational diffusion and the internal conformational transitions in flexible chains attached to massive cores
Silver sheaves; gathered through clouds and sunshine. In two parts. Part 1st: Civil and military life of the author. Part 2d: Miscellaneous collection of prose and poetry.
No full text2d ed.2 p.l., [9]-360 p
Understanding the unusual transitional behaviour of liquid crystal dimers
No full textThe transitional properties of liquid crystal dimers within a homologous series differ significantly depending on whether the spacer joining the two mesogenic groups contains an even or an odd number of atoms. In order to obtain a physical understanding of this unusual behaviour we have developed a simple model in which the component molecules can adopt just two conformations, one linear and the other bent. An analysis of the model within the molecular field approximation reveals that it is able to provide us with a good understanding of the behaviour of liquid crystal dimers. In addition it predicts the existence of a nematic-nematic transition
Membrane contactor process to reduce ethanol in wine: volatile compounds and stable isotope ratios changes
No full textThe reduction of ethanol level in wine is nowadays a notable topic in wine production. There are many different reasons: climate change, health and social matters, wine quality. Many different techniques are available in wine industry to reduce high ethanol content in wine. Among theme contactor membranes, are certainly more efficient and common. We have studied the effect of this practice on the wine quality, aromas compounds and stable isotopes composition. A pilot and industrial plant equipped with the membrane contactor system were used in the study of several white and red wines dealcoholisation. In both scale experiments we have observed changes for several classes of aroma compounds, even if these changes are not in perfect correlation with sensorial evaluation carried out. In addition is observed a variability in aromas variations for each aroma compound and wine variety. We have in particularly studied the modifications on isotopes ratios. We have tested the process using waters with different δ18O ratios, or wines, in different osmotic conditions for both compartments. Modifications of up to 1‰ for 2 %v/v and of up to 4‰ for 8 %v/v ethanol removal were encountered. It is very important to note that the δ18O ratio changes are not only due by a water osmotic transfer through the membrane. The δ18O decrease, is even depending by the δ18O value of the extracting water solution. These variations must be taken into account when these parameters are evaluated to considered dealcoholised wine traceabilit
Steady-state kinetics of the tungsten containing aldehyde: Ferredoxin oxidoreductases from the hyperthermophilic archaeon Pyrococcus furiosus
No full textThe tungsten containing Aldehyde:ferredoxin oxidoreductases (AOR) offer interesting opportunities for biocatalytic approaches towards aldehyde oxidation and carboxylic acid reduction. The hyperthermophilic archaeon Pyrococcus furiosus encodes five different AOR family members: glyceraldehyde-3-phosphate oxidoreductase (GAPOR), aldehyde oxidoreductase (AOR), and formaldehyde oxidoreductase (FOR), WOR4 and WOR5. GAPOR functions as a glycolytic enzyme and is highly specific for the substrate glyceraldehyde-3-phosphate (GAP). AOR, FOR and WOR5 have a broad substrate spectrum, and for WOR4 no substrate has been identified to date. As ambiguous kinetic parameters have been reported for different AOR family enzymes the steady state kinetics under different physiologically relevant conditions was explored. The GAPOR substrate GAP was found to degrade at 60 °C by non-enzymatic elimination of the phosphate group to methylglyoxal with a half-life t1/2 = 6.5 min. Methylglyoxal is not a substrate or inhibitor of GAPOR. D-GAP was identified as the only substrate oxidized by GAPOR, and the kinetics of the enzyme was unaffected by the presence of L-GAP, which makes GAPOR the first enantioselective enzyme of the AOR family. The steady-state kinetics of GAPOR showed partial substrate inhibition, which assumes the GAP inhibited form of the enzyme retains some activity. This inhibition was found to be alleviated completely by a 1 M NaCl resulting in increased enzyme activity at high substrate concentrations. GAPOR activity was strongly pH dependent, with the optimum at pH 9. At pH 9, the substrate is a divalent anion and, therefore, positively charged amino acid residues are likely to be involved in the binding of the substrate. FOR exhibited a significant primary kinetic isotope effect of the apparent Vmax for the deuterated substrate, formaldehyde-d2, which shows that the rate-determining step involves a C[sbnd]H bond break from the aldehyde. The implications of these results for the reaction mechanism of tungsten-containing AORs, are discussed.Accepted Author ManuscriptBT/Biocatalysi
Una nuova classe di inibitori delle fosfodiesterasi IV: sintesi e valutazione biologica di derivati 1,8-naftiridinici.
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