Vibrational spectra and rotational barriers of methyl titanium halides CH3TiX3 and CD3TiX3 (X = Cl,Br, I)

The IR and Raman spectra of gaseous and solid CH₃TiX₃ and CD₃TiX₃ species (X = Cl, Br, I) are reported. The gas phase spectra have been recorded between 4000 and 20 cm^?1 at pressures of 1 atm and 4 atm at 350 K and the Raman spectra of the solid phase recorded at 4.2 K. Internal rotation barriers and thermodynamic functions have been calculated.     

Hydrophobic effect in aqueous solutions of nonelectrolytes. II. Cross-interactions of alkylureas

The heats of mixing of the aqueous solutions of monomethylurea, monoethylurea, 1,3-dimethylurea, 1,3-diethylurea were determined at 25°C. The excess enthalpies obtained are expressed in virial form, in terms of pair and triplet interaction coefficients. A method previously discussed for predicting the excess enthalpies and the interaction coefficients of ternary solutions has been applied to the alkylureas. The large deviations between the experimental and calculated values, led to the modification of that method, which better accounts for the marked mixed character of these substances.     

Infrared spectra of matrix-isolated gaseous ternary oxides: Part V. The sodium—phosphorus—oxygen system

The IR spectra of vapour from a Na₃PO₄, Na₅P₃O₁₀ and Na₂O-P₂O₅, mixture have been obtained in solid nitrogen at 12 K. The results suggest that it is possible to isolate both NaPO₃ and NaPO₂ when sodium tripolyphosphate and the Na₂O-P₂O₅ mixture are vaporized. There was no evidence of the NaPO molecule, reported to be one of the most abundant vapour species in mass-spectrometric work on the vaporization of Na₅P₃O₁₀.     

Thermoanalytical and phytochemical study of the cupuassu (Theobroma grandiflorum Schum.) seed by-product in different processing stages

Journal of Thermal Analysis and Calorimetry - Cupuassu (Theobroma grandiflorum Schum.) is a typical Amazonian fruit, whose seed is used as raw material to produce cupulate. The by-product of its...     

On a question of Mauldin and Ulam concerning homeomorphisms

In this paper we solve a question of Mauldin and Ulam about transformations preserving homeomorphic pairs.     

Improved CO oxidation activity in the presence and absence of hydrogen over cluster-derived PtFe/SiO2 catalysts

The catalytic performance of cluster-derived PtFe/SiO(2) bimetallic catalysts for the oxidation of CO has been examined in the absence and presence of H(2) (PROX) and compared to that of Pt/SiO(2). PtFe(2)/SiO(2) and Pt(5)Fe(2)/SiO(2) samples were prepared from PtFe(2)(COD)(CO)(8) and Pt(5)Fe(2)(COD)(2)(CO)(12) organometallic cluster precursors, respectively. FTIR data indicate that both clusters can be deposited intact on the SiO(2) support. The clusters remained weakly bonded to the SiO(2) surface and could be extracted with CH(2)Cl(2) without any significant changes in their structure. Subsequent heating in H(2) led to complete decarbonylation of the supported clusters at approximately 350 degrees C and the formation of Pt-Fe nanoparticles with sizes in the 1-2 nm range, as indicated by HRTEM imaging. A few larger nanoparticles enriched in Pt were also observed, indicating that a small fraction of the deposited clusters were segregated to the individual components following the hydrogen treatment. A higher degree of metal dispersion and more homogeneous mixing of the two metals were observed during HRTEM/XEDS analysis with the cluster-derived samples, as compared to a PtFe/SiO(2) catalyst prepared through a conventional impregnation route. Furthermore, the cluster-derived PtFe(2)/SiO(2) and Pt(5)Fe(2)/SiO(2) samples were more active than Pt/SiO(2) and the conventionally prepared PtFe/SiO(2) sample for the oxidation of CO in air. However, substantial deactivation was also observed, indicating that the properties of the Pt-Fe bimetallic sites in the cluster-derived samples were altered by exposure to the reactants. The Pt(5)Fe(2)/SiO(2) sample was also more active than Pt/SiO(2) for PROX with a selectivity of approximately 92% at 50 degrees C. In this case, the deactivation with time on stream was substantially slower, indicating that the highly reducing environment under the PROX conditions helps maintain the properties of the active Pt-Fe bimetallic sites.     

Scaling of a collapsed polymer globule in two dimensions

Extensive Monte Carlo data analysis gives clear evidence that collapsed linear polymers in two dimensions fall in the universality class of athermal, dense self-avoiding walks, as conjectured by Duplantier [Phys. Rev. Lett. 71, 4274 (1993)].10.1103/PhysRevLett.71.4274 However, the boundary of the globule has self-affine roughness and does not determine the anticipated nonzero topological boundary contribution to entropic exponents. Scaling corrections are due to subleading contributions to the partition function corresponding to polymer configurations with one end located on the globule-solvent interface.     

Production and Stability of Protease from <Emphasis Type="Italic">Candida buinensis</Emphasis>

Cow raw milk from dairy cooperatives was examined for its microbial composition. Among the isolates identified, 17.6% were yeasts. The most frequent genus was Candida, although members belonging to the genera Brettanomyces, Dekkera, and Geotricum were also identified. Although qualitative and quantitative tests for extracellular proteolytic activity were positive for all the species isolated, Candida buinensis showed the highest response (23.5 U/mg); therefore, it was selected for subsequent investigation. The results of fermentations carried out at variable temperature, pH, and soybean flour concentration, according to a 2³ full factorial design, demonstrated that this yeast ensured the highest production of extracellular proteases (573 U/mL) when cultivated at 35 °C, pH 6.5, and using soybean flour concentrations in the range 0.1–0.5% (w/v). The cell-free supernatants showed the highest activity at 25 °C and pH 7.0, and satisfactory stability in the ranges 25–30 °C and pH 7–9. The first-order rate constants of protease inactivation in the cell-free supernatants were calculated at different temperatures from semi-log plots of the residual activity versus time and then used in Arrhenius and Eyring plots to estimate the main thermodynamic parameters of thermoinactivation (E* = 40.0 kJ/mol; ΔH* = 37.3 kJ/mol; ΔS* = −197.5 J/mol K; ΔG* = 101 kJ/mol).     

A Perturbation Method for Nonlinear Two-Dimensional Maps

A new perturbation method for a weakly nonlinear two-dimensional discrete-time dynamical system is presented. The proposed technique generalizes the asymptotic perturbation method that is valid for continuous-time systems and detects periodic or almost-periodic orbits and their stability. Two equations for the amplitude and the phase of solutions are derived and their fixed points correspond to limit cycles for the starting nonlinear map. The method is applied to various nonlinear (autonomous or not) two-dimensional maps. For the autonomous maps we derive the conditions for the appearance of a supercritical Hopf bifurcation and predict the characteristics of the corresponding limit cycle. For the nonautonomous maps we show amplitude-response and frequency-response curves. Under appropriate conditions, we demonstrate the occurrence of saddle-node bifurcations of cycles and of jumps and hysteresis effects in the system response (cusp catastrophe). Modulated motion can be observed for very low values of the external excitation and an infinite-period bifurcation occurs if the external excitation increases. Analytic approximate solutions are in good agreement with numerically obtained solutions.     

A new deuterated alkylating agent for quantitative proteomics

Weakly basic molecules containing a double bond, such as 2- and 4-vinylpyridine, are able to react and selectively alkylate -SH groups in proteins, thus preventing their re-oxidation to disulphide bridges. In contrast to conventional alkylating agents such as iodoacetamide and non-charged acrylamide derivatives, such molecules achieve 100% alkylation of all -SH residues, even in complex proteins, without reacting with other functional groups. Their use is particularly effective in proteome analysis and more generally for analyzing proteins in which the -SH groups should be blocked. Additionally, the use of vinylpyridines, partially or totally deuterated and thus with a mass difference compared with their non-deuterated counterparts of 4-7 Da, allows studies of induction/repression of protein synthesis (quantitative proteomics).