Summary: Linear unsaturated nylons 6 u18 and 18 u18 have been made containing a double bond in the center of the diacid segment with potential for additional functionalization. Solution state NMR showed the presence of a small portion of cis amide units. Solid state NMR verified the presence of the double bond in the bulk, and that the polyamides were present in the α‐crystalline form. Thermal stability was comparable to linear saturated nylons, and the melting and crystallization temperatures of the unsaturated nylons were lower compared to the saturated analogs.
DSC heating and cooling thermograms for nylons 6 u18 and 18 u18. 相似文献
Chain anisotropic distribution in gelatin films has been obtained by uniaxial stretching at constant relative humidity, followed by air drying and successive cross-linking with glutaraldehyde. The drawn samples have been characterized by mechanical tests, differential scanning calorimetry and scanning electron microscopy. The Young’s modulus, E, and the stress at break, σb, increase linearly with the draw ratio and reach values which are about five times those characteristic of undrawn samples. Furthermore, on stretching the alignment of the gelatin strands along the direction of deformation increases while the thickness of the layers decreases significantly. The renaturation level, that is the fraction of gelatin in a collagen-like structure, has been calculated as the ratio between the melting enthalpy of gelatin samples and that of tendon collagen. The results indicate that the improvement of mechanical properties achieved by drawn gelatin is closely related to the renaturation level. The experimental approach utilized to induce segmental orientation in gelatin films, allows to obtain anisotropic materials with improved mechanical properties in the direction of deformation, and can be usefully applied in the preparation of biomaterials. 相似文献
The in situ thermal protein denaturation and its correlation with direct hyperthermic cell injury in Dunning AT-1 prostate tumor cells were investigated in this study. The in situ thermal protein denaturation was studied using both Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The FTIR spectra at different temperatures show changes in protein secondary structure (from alpha helix to extended beta sheet) during in situ thermal protein denaturation within AT-1 cells. Calorimetric studies using DSC show that endothermic heat release is associated with the in situ thermal protein denaturation. Furthermore, both the secondary structure changes detected by FTIR and the calorimetric changes detected by DSC were quantified and the kinetics of the overall in situ thermal protein denaturation was derived under different heating conditions. The onset temperature where the overall in situ thermal protein denaturation is first detectable was found to be scanning rate dependent (approximately 41 degrees C at 2 degrees C min(-1) and approximately 44 degrees C at 5 degrees C min(-1)). The kinetics of the overall in situ thermal protein denaturation was derived from both DSC and FTIR measurements and was fit using kinetic and statistical models. The kinetic data determined by FTIR and DSC under the same heating conditions match well with each other. The activation energy of the overall in situ thermal protein denaturation is found to be strongly dependent on the temperature range considered (the activation energy ranges from approximately 110 kJ mol(-1) between 44 and 90 degrees C to approximately 750 kJ mol(-1) between 44 and 50 degrees C). However, its dependence on heating rate is negligible. Several denaturation peaks, including a dominant one between approximately 62 and 65 degrees C, are identifiable from both the DSC and the FTIR results. To investigate directly the relationship between thermally induced cell injury and the in situ thermal protein denaturation, both acute (propidium iodide dye exclusion, assessed 3-h postthermal treatment) and chronic (clonogenics, assessed 7-day postthermal treatment) cell injury were quantified using AT-1 cells prepared under the same conditions as for the DSC protein studies. Comparisons of the results from the cell injury studies and the DSC protein denaturation studies show that the overall in situ thermal protein denaturation correlates well with both the acute and the chronic cell injury, which suggests that overall in situ thermal protein denaturation is an important mechanism of direct hyperthermic cell injury in AT-1 cells at the macromolecular level. 相似文献
Several syndiotactic polystyrene (sPS) samples have been synthesized by using different catalytic systems. Their stereochemistry has been determined by 13C NMR spectra in both the aliphatic CH2 and aromatic C1 resonance regions. The observed peaks have been unambiguously assigned to specific hexads and heptads, respectively, and their intensities have been used to draw the percent of defects (meso dyads) in the polymer chains. On the hypothesis that chain defects are at the origin of chain folding and thus determine the thickness of crystalline lamellae, we performed differential scanning calorimetry (DSC) analysis on the same samples, and their thermal parameters were measured. A model was developed to determine the amount of steric defects from the DSC melting‐peak profiles, and the results obtained were compared with the NMR results. A satisfactory agreement was found (correlation factor 0.96) in the explored range of defect concentrations (up to 2.5% of meso dyads). The possible influence of the extraction procedure of the amorphous fraction was found to be negligible. Thus, information on stereochemistry can be obtained from DSC experiments starting from as‐prepared (not extracted) samples.