Theoretical investigations on the solvation process

STO double-zeta SCF wavefunctions for various configurations of the H₅O ₂ ⁺ associate have been computed. Results are discussed and compared with other authors' similar calculations on gaussian bases.An electrostatic picture of the monosolvation of H₃O⁺ is proposed as a fairly satisfactory one.     

Quantum mechanical studies of environmental effects on biomolecules

Ab initia SCF calculations on the hydration of N-methylacetamide are reported and compared to the results previously obtained for formamide. The hydration energies are all slightly decreased. The angular positions of the two carbonyl sites are brought closer to the CO axis and the orientation of the water molecule on the NH site remains very flexible in spite of the a methyl group.     

Molecular structure of 9α-fluoro-11β-hydroxy-16β-propionyloxy-17-(2-ethyl-2-ethoxy-1,3-dioxan-5-one-6-yl)-pregna-1,4-dien-3-one

The title compound is orthorhombic, space groupP2₁2₁2₁,a=15.992(9),b=15.693(9),c=11.205(6) Å,Z=4. The structure was solved from diffractometer data by direct methods, and refined toR 0.085 for 1216 observed (of a total of 2421) reflections. Strain in the almost planar ringA is indicated by the endocyclic torsion angles, ringsB andC, which aretrans fused and chair-shaped, while ringD is intermediate between a 13-envelope and a 13, 14-half-chair conformation. RingE, a 2,5,6-trisubstituted 1,3-dioxane-like unit, adopts a highly distorted boat conformation. The bending of the skeleton is toward its side. TheA-ring carbonyl substituent accepts one hydrogen bond involving a symmetry-related 11-ol function [O(1)-O(2) 2.81, O(2)-H 1.0, H---O(1) 1.8 Å/ O(2)-H---O(1) 165°].We thank the Schering-Plough Research Division, Bloomfield, New Jersey, for the gift of the sample and the Istituto di Chimica e Tecnologia dei Radioelementi C.N.R., Padova, for equipment and computing facilities.     

Anodic ethylation of lead by cathodically produced diethylcadmium

o-, m- and p-Nitrophenyltrimethylsilanes and 2,4-dinitrophenyltrimethylsilane were conveniently prepared by the reactions of hexamethyldisilane with the corresponding nitrohalobenzenes catalyzed by tetrakis(triphenylphosphine)-palladium(O).     

A generalization of symplectic Pontrjagin classes to vector bundles with structure groupSp(n)·Sp(1)

Sunto Si considerano fibrati vettoriali reali con gruppo strutturale riducibile a Sp(n)· Sp(1)e a Sp(n)·tU(1)e si introducono classi caratteristiche relative a tali strutture mediante forme differenziali rappresentanti. Tali classi risultano generatori algebricamente indipenclenti dei quozienti modulo la 2-torsione degli anelli di coomologia intera dei rispettivi spazi classificanti, e si riducono mod. 2 a classi già introdotte. Si esamina in particolare il caso del fibrato tangente dello spazio proiettivo quaternionale.     

Sol-Gel Processed TiO2-Based Nano-Sized Powders for Use in Thick-Film Gas Sensors for Atmospheric Pollutant Monitoring

Sol-gel routes were used to prepare pure and 5 at% and 10 at% Ta- or Nb-dope TiO₂ nano-sized powders. The thermal decomposition behaviour of the precursors was studied using simultaneous thermogravimetric and differential thermal analysis (TG/DTA). X-ray diffraction (XRD) analysis showed that the powders heated to 400°C were crystalline in the anatase TiO₂ structure. The pure TiO₂ powder heated to 850°C showed the rutile structure. The addition of Ta and Nb inhibited the anatase-to-rutile phase transformation up to 950–1050°C. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired for 1 h at different temperatures in the 650–1050°C range. Scanning electron microscopy (SEM) observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO₂. The addition of Ta and Nb is effective to keep the TiO₂ grain size at a nanometric level even at 950°C, though grain growth was observed with increasing temperature. The gas-sensitive electrical response of the thick films were tested in laboratory, in environments with CO in dry and wet air. Conductance measurements showed a good gas response only for the nanostructured titania-based films. For field tests, the prototype sensors were placed beside a conventional station for atmospheric pollutant monitoring. The electrical response of the thick films was compared with the results of the analytical instruments. The same trend was observed for both systems, demonstrating the use of gas sensors for this aim.