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241.
The low-temperature endotherm in poly(ethylene terephthalate): partial melting and rigid amorphous fraction mobilization 总被引:1,自引:0,他引:1
Righetti MC Lorenzo ML Tombari E Angiuli M 《The journal of physical chemistry. B》2008,112(14):4233-4241
A detailed investigation of the low-temperature endotherm of poly(ethylene terephthalate) (PET) performed by temperature-modulated differential scanning calorimetry is presented. The origin of the small endotherm, generally observed a few degrees above the crystallization temperature in PET and in many other polymers, is a widely discussed matter. The most frequent interpretation considers it the result of partial fusion with superposition of a recrystallization process even if it has also been proposed that it can originate from enthalpic recovery connected to mobilization of the rigid amorphous fraction. In an attempt to resolve the question, a new method for the interpretation of the modulated heat-flow-rate curve resulting from a temperature modulation program is proposed. The procedure consists of the analysis of the initial points of the steady-state heat-flow-rate signals in the heating and cooling semiperiods with the temperature modulation being performed with a sawtooth profile. The study conducted in parallel on the reversing specific heat capacity and the heat-flow-rate curves, observed on heating after isothermal crystallization at various temperatures, showed that multiple processes, involving both the crystalline and the rigid amorphous fraction, overlap in the temperature range in which the low-temperature endotherm is observed. The origin of the endotherm under investigation is therefore connected with both partial fusion of the crystalline portions and enthalpy recovery subsequent to structural relaxation of the rigid amorphous fraction. An estimation of the relative percentages of the two different processes is presented and discussed. 相似文献
242.
Marengo E Robotti E Bobba M Milli A Campostrini N Righetti SC Cecconi D Righetti PG 《Analytical and bioanalytical chemistry》2008,390(5):1327-1342
2D gel electrophoresis is a tool for measuring protein regulation, involving image analysis by dedicated software (PDQuest,
Melanie, etc.). Here, partial least squares discriminant analysis was applied to improve the results obtained by classic image
analysis and to identify the significant spots responsible for the differences between two datasets. A human colon cancer
HCT116 cell line was analyzed, treated and not treated with a new histone deacetylase inhibitor, RC307. The proteins regulated
by RC307 were detected by analyzing the total lysates and nuclear proteome profiles. Some of the regulated spots were identified
by tandem mass spectrometry. The preliminary data are encouraging and the protein modulation reported is consistent with the
antitumoral effect of RC307 on the HCT116 cell line. Partial least squares discriminant analysis coupled with backward elimination
variable selection allowed the identification of a larger number of spots than classic PDQuest analysis. Moreover, it allows
the achievement of the best performances of the model in terms of prediction and provides therefore more robust and reliable
results. From this point of view, the multivariate procedure applied can be considered a good alternative to standard differential
analysis, also taking into account the interdependencies existing among the variables. 相似文献
243.
Marengo E Robotti E Bobba M Liparota MC Rustichelli C Zamò A Chilosi M Righetti PG 《Electrophoresis》2006,27(2):484-494
Mantle cell lymphoma (MCL) cell lines have been difficult to generate, since only few have been described so far and even fewer have been thoroughly characterized. Among them, there is only one cell line, called GRANTA-519, which is well established and universally adopted for most lymphoma studies. We succeeded in establishing a new MCL cell line, called MAVER-1, from a leukemic MCL, and performed a thorough phenotypical, cytogenetical and molecular characterization of the cell line. In the present report, the phenotypic expression of GRANTA-519 and MAVER-1 cell lines has been compared and evaluated by a proteomic approach, exploiting 2-D map analysis. By univariate statistical analysis (Student's t-test, as commonly used in most commercial software packages), most of the protein spots were found to be identical between the two cell lines. Thirty spots were found to be unique for the GRANTA-519, whereas another 11 polypeptides appeared to be expressed only by the MAVER-1 cell line. A number of these spots could be identified by MS. These data were confirmed and expanded by multivariate statistical tools (principal component analysis and soft-independent model of class analogy) that allowed identification of a larger number of differently expressed spots. Multivariate statistical tools have the advantage of reducing the risk of false positives and of identifying spots that are significantly altered in terms of correlated expression rather than absolute expression values. It is thus suggested that, in future work in differential proteomic profiling, both univariate and multivariate statistical tools should be adopted. 相似文献
244.
A. Fontana M. Montagna L. Righetti F. Rossi G. Cicognani A. J. Dianoux F. Terki 《Journal of Non》2001,280(1-3):217-221
New coherent inelastic neutron scattering measurements on silica xerogels in the 300–1000 K temperature range are presented and compared with those obtained in vitreous silica (heralux). The spectra show the presence of the Boson peak, at temperatures, where the quasi-elastic contribution due to absorbed water is negligible. The Boson peak in silica xerogels is at a frequency of around 5 meV (40 cm−1) and has a shape similar to that of melted silica, even in the smaller density xerogels. This important result seems to indicate that the disorder introduced by the presence of pores does not affect the density of states in frequency region. This evidence is also confirmed by changes in the inelastic structure factor S(Q,ω), measured at the frequencies of the Boson peak as a function of the exchanged Q. 相似文献
245.
Gianfranco Cainelli Paola Galletti Daria Giacomini Paolo Orioli MarioA. Polidoro MariaCristina Righetti 《Helvetica chimica acta》2000,83(8):1951-1961
Temperature‐dependent selectivity in nucleophilic additions is affected by the solvent. In this context, we investigated the effect on diastereoselectivity of solvent mixtures with respect to pure solvents. Binary systems of THF/hexane and of four different hydrocarbon mixtures were employed in BuLi addition to 2‐phenylpropanal, (2S)‐2‐[(tert‐butyl)dimethylsilyloxy]‐2‐phenylethanal, and (2S)‐2‐[(tert‐butyl)dimethylsilyloxy]‐N‐(trimethylsilyl)propan‐1‐imine. A 5‐mol‐% of THF in hexane affects the isomer ratio by reducing both ΔΔH≠ and ΔΔS≠ contributions, and suppresses Tinv. On the contrary, in hydrocarbon binary mixtures, the Tinv is still observed and occurs at a higher temperature than in pure solvents. Studying the dependence of Tinv on the hexane/decane mixture composition, we propose the formation of a peculiar solvation cluster that is unaffected by the composition of the bulk reaction solvent. 相似文献