Phase behavior of crystalline blends of poly(tetrafluoroethylene) and of random fluorinated copolymers of tetrafluoroethylene

In the present article, we investigate by differential scanning calorimetry (DSC) the thermal behavior (melting, crystallization, and crystal–crystal transitions) far from equilibrium of blends constituted of two crystalline polymers. In particular, the following blends are examined: PTFE–PFMVE, PTFE–FEP, and FEP–PFMVE where PTFE is poly(tetrafluoroethylene), PFMVE is poly(tetrafluoroethylene‐co‐perfluoromethylvinylether), and FEP is poly(tetrafluoroethylene‐co‐hexafluoropropylene). The two last ones are random tetrafluoroethylene copolymers with small amounts of comonomer. Our results indicate that, under the experimental investigated conditions, the blends containing PTFE do not give cocrystallization on cooling from the melt, although under very rapid crystallization conditions, quenching, the presence of the copolymer would seem to slightly influence PTFE crystallization (lower peak temperatures are observed for the crystalline transitions and the melting with respect to those of the neat homopolymer). The behavior of the FEP–PFMVE blend is completely different; in fact, our results indicate the occurrence of cocrystallization, then miscibility in the crystalline phase, for almost all compositions and all investigated experimental conditions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 679–689, 1999     

Effect of thermal history on the melting behavior and the crystal-crystal transitions of tetrafluoroethylene-perfluoroalkylvinylether copolymers

By differential scanning calorimetry (DSC), the effect of thermal treatments on the melting of tetrafluoroethylene-perfluoroalkylvinylether copolymers (PFA) with different contents of perfluoromethylvinylether as a comonomer has been investigated. Two melting peaks can be identified for all copolymers, whose presence, value, and extent depend upon the thermal treatments. The higher temperature one, scarcely influenced by the crystallization conditions (i.e., cooling rate and annealing), can be attributed to more perfect crystals present in the original samples. The lower temperature one is produced only by annealing (annealing peak) and can be interpreted as resulting from much poorer crystals grown among the larger ones. For the copolymer with the lowest content of comonomer, the effect of thermal treatments on the low-temperature (crystal-crystal) transitions has also been studied. The rejection of the counits from the crystals, at least in equilibrium conditions, is confirmed. © 1996 John Wiley & Sons, Inc.     

Palytoxin in seafood by liquid chromatography tandem mass spectrometry: investigation of extraction efficiency and matrix effect

Blooms of Ostreopsis spp. have been recently reported along the Mediterranean coasts of Spain, France, Italy, and Greece posing serious risks to human health. Occurrence of Ostreopsis spp. may result in palytoxin contamination of seafood and, in order to prevent sanitary risks, the need exists to develop efficient extraction procedures to be coupled to rapid and sensitive monitoring methods of palytoxin-like compounds in seafood. In the present study, the best conditions for both extraction of palytoxin from seafood and palytoxin quantification by using liquid chromatography tandem mass spectrometry (LC-MS/MS) were investigated. Three seafood matrices (mussels, sea-urchins, and anchovies) were selected and five different extraction systems were tested, namely: the official protocol for extraction of lipophilic toxins and various aqueous methanol or acetonitrile solutions (MeOH/H₂O 1:1, MeOH/H₂O 8:2, MeCN/H₂O 8:2 and MeOH 100%). Extraction with MeOH/H₂O 8:2 provided the best results in terms of accuracy and matrix interference on LC-MS/MS detection of palytoxin. Accuracy and intra-day reproducibility (n = 3) were evaluated for all the selected matrices but only for mussels at three spiking concentration levels, including the provisional limit proposed by the Community Reference Laboratory for marine biotoxins (250 μg kg⁻¹). Limits of quantitation of palytoxin in mussels, sea-urchins and anchovies tissues were calculated using matrix-matched standards; taking into account extraction efficiency of MeOH/H₂O 8:2, they resulted to be 228, 343, and 500 μg kg⁻¹, respectively.     

On uniqueness in the inverse problem for transversely isotropic elastic media with a disjoint wave mode

We study general anisotropic elastic media that have a disjoint wave mode, that is, elastic media with the property that one sheet of the slowness surface never intersects the others. We extend results from microlocal analysis to describe the propagation of singularities for the disjoint mode. Applying these results to the study of the dynamic inverse problem, we show that displacement–traction surface measurements uniquely determine the travel time between boundary points for the disjoint mode. We conclude that two of the five elastic parameters describing transversely isotropic elastodynamics with ellipsoidal slowness surfaces and a disjoint mode are partially determined by surface measurements. Our approach is well suited to inhomogeneous materials and applying microlocal analysis to the inverse problem.     

Switching the N-Capping Region from all-L to all-D Amino Acids in a VEGF Mimetic Helical Peptide

The N-capping region of an α-helix is a short N-terminal amino acid stretch that contributes to nucleate and stabilize the helical structure. In the VEGF mimetic helical peptide QK, the N-capping region was previously demonstrated to be a key factor of QK helical folding. In this paper, we explored the effect of the chiral inversion of the N-capping sequence on QK folding, performing conformational analysis in solution by circular dichroism and NMR spectroscopy. The effect of such a modification on QK stability in serum and the proliferative effect were also evaluated.     

A Quantitative Relaxometric Version of the ELISA Test for the Measurement of Cell Surface Biomarkers

Quantitative measurement of marker expression in diseased cells is still a topic of considerable interest and different methodologies are currently under intense scrutiny. This work aims at developing an in vitro diagnostic method based on the release of paramagnetic species from relaxometrically “silent” liposomes operated by the action of a phospholipase A₂ (PLA₂) previously targeted to the epitope of interest. The released paramagnetic species causes an increase of the longitudinal water proton relaxation rate proportional to the number of PLA₂ bound to the cell outer surface. The sensitivity of the herein proposed method, named R‐ELISA, was attempted in the detection of folate receptor expression on human ovarian cancer cells by functionalizing PLA₂ with folic acid. Receptor/cell number of 8.3×10⁵ has been measured on IGROV‐1 cells. The R‐ELISA assay can detect nanomolar cell suspension receptor concentrations and has been validated by well‐established spectrofluorimetric procedures.     

Synthesis of new polyazines by 1,4 photochemical or anionic polymerization of 1,2-diaza-1,3-butadienes

Photochemical and anionic polymerizations of 1,2-diaza-1,3-butadienes are described. Photochemical polymerization was smoothly performed by irradiation of some 1-aminocarbonyl-1,2-diaza-1,3-butadienes with high pressure mercury arc (λ = 300 nm) in the presence of allyltributylstannane. Molecular weights (M_w) in the range 14.6-559 × 10² g/mol were obtained. The TGA curve revealed a first weight loss starting at about 200 °C of some 85%, and a second starting at about 300 °C. The DSC showed the glass transition (T_g) at about −34 °C. Anionic polymerization was performed by treatment of some 1-alkoxycarbonyl-1,2-diaza-1,3-butadienes with n-butyllithium. Molecular weights (M_w) in the range 8.44-242 × 10² g/mol were obtained.     

Bifunctional ligands based on the DOTA-monoamide cage

Efficient routes to DOTA-monoamide ligands bearing amino, hydroxyl, aldehyde and maleimido groups are described. These functional groups, which can be spaced at will from the coordination cage, will readily react with suitable groups of targeting moieties. Bioconjugates obtained in this way can be used for diagnostic imaging and therapeutic applications.     

Thermal characterization of tetrafluoroethylene-perfluoroalkylvinylether copolymers: Melting behavior and low-temperature transitions

Differential scanning calorimetry has been used to study the melting and the low-temperature transitions of tetrafluoroethylene-perfluoroalkylvinylether copolymers (PFA). Melting is similar to that of PTFE in that it is subject to superheating, moreover the melt-crystallized samples show temperatures and heats of fusion lower than the native ones. At temperatures lower than room temperature, crystal-crystal transitions are observed for copolymers containing 2 mol % of perfluoromethyl-, perfluoroethyl-, and perfluoro-n-propylvinylether. In the case of perfluoromethylvinylether as a comonomer, low-temperature transitions are present only up to a content of 4 mol %. The effect on melting and low-temperature transitions of both the comonomer content and of the type of side groups has been investigated. The temperatures and heats of transitions show the expected dependence as a function of the comonomer concentration and have been found to be independent on the chemical nature of the side group. © 1994 John Wiley & Sons, Inc.