Particle shape in thixotropic aluminium and thorium molybdates gels

Summary Electron microscope examination of thixotropic aluminium and thorium molybdate gels shows that one hour after formation they are constituted by short fibrils of small axial ratio. The fibrils of the aluminium molybdate gels, with ageing at room temperature or with boiling, increase in diameter and length; the fibrous shape of the particles is maintained after two and a half years of ageing; all fibrils are crystalline by electron diffraction. The fibrils of the thorium molybdate gels, except in the gels containing hydrochloric acid, change with ageing at room temperature or with boiling, into plates of hexagonal, elliptical or rectangular profile; the fibrils and plates are crystalline and have the same electron diffraction pattern as the fibrils.This work was aided, in part, by grants from Conselho Nacional de Pesquisas and the Rockefeller Foundation.     

Effect of time on the interfacial and foaming properties of beta-lactoglobulin/acacia gum electrostatic complexes and coacervates at pH 4.2

The electrostatic complexation between beta-lactoglobulin and acacia gum was investigated at pH 4.2 and 25 degrees C. The binding isotherm revealed a spontaneous exothermic reaction, leading to a DeltaHobs = -2108 kJ mol(-1) and a saturation protein to polysaccharide weight mixing ratio of 2:1. Soluble electrostatic complexes formed in these conditions were characterized by a hydrodynamic diameter of 119 +/- 0.6 nm and a polydispersity index of 0.097. The effect of time on the interfacial and foaming properties of these soluble complexes was investigated at a concentration of 0.1 wt % at two different times after mixing (4 min, referred as t approximately 0 h and t = 24 h). At t approximately 0 h, the mixture is mainly made of aggregating soluble electrostatic complexes, whereas after 24 h these complexes have already insolubilize to form liquid coacervates. The surface elasticity, viscosity and phase angle obtained at low frequency (0.01 Hz) using oscillating bubble tensiometry revealed higher fluidity and less rigidity in the film formed at t approximately 0 h. This observation was confirmed by diminishing bubble experiments coupled with microscopy of the thin film. It was thicker, more homogeneous and contained more water at t approximately 0 h as compared to t = 24 h (thinner film, less water). This led to very different gas permeability's of Kt approximately 0 h = 0.021 cm s(-1) and Kt=24 h) = 0.449 cm s(-1), respectively. Aqueous foams produced with the beta-lactoglobulin/acacia gum electrostatic complexes or coacervates exhibited very different stability. The former (t approximately 0 h) had a stable volume, combining low drainage rate and mainly air bubble disproportionation as the destabilization mechanism. By contrast, using coacervates aged for 24 h, the foam was significantly less stable, combining fast liquid drainage and air bubble destabilization though fast gas diffusion followed by film rupture and bubble coalescence. The strong effect of time on the air/water interfacial properties of the beta-lactoglobulin/acacia gum electrostatic complexes can be understood by their reorganization at the interface to form a coacervate phase that is more fluid/viscous at t approximately 0 h vs rigid/elastic at t = 24 h.     

Racemization in stepwise solid-phase peptide synthesis at elevated temperatures

The present work is an attempt to assess racemization in stepwise solid-phase peptide synthesis at elevated temperatures (SPPS-ET), a high-speed approach in which peptide elongation occurs at 55-75 °C. This attempt was based on the notion that a high propensity for this side reaction would hamper employment of this alternative approach and would dampen interest in its further development. Simple peptide models were synthesized using customized protocols for classical SPPS or SPPS-ET. Systematic analyses of the resulting crude peptides by reversed-phase HPLC, ion-exchange HPLC, capillary electrophoresis and electrospray ionization mass spectrometry revealed low diastereomeric byproduct contents. These results indicate that, from the standpoint of racemization, classical SPPS and SPPS-ET protocols were equivalent. Therefore, further studies employing SPPS-ET protocols are justified.     

Phase separation of p53 precedes aggregation and is affected by oncogenic mutations and ligands

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF). The mechanism of the formation of the aggregates in the nucleus remains uncertain. The present study demonstrated that the DNA-binding domain of p53 (p53C) underwent phase separation (PS) on the pathway to aggregation under various conditions. p53C phase separated in the presence of the crowding agent polyethylene glycol (PEG). Similarly, mutant p53C (M237I and R249S) underwent PS; however, the process evolved to a solid-like phase transition faster than that in the case of wild-type p53C. The data obtained by microscopy of live cells indicated that transfection of mutant full-length p53 into the cells tended to result in PS and phase transition (PT) in the nuclear compartments, which are likely the cause of the GoF effects. Fluorescence recovery after photobleaching (FRAP) experiments revealed liquid characteristics of the condensates in the nucleus. Mutant p53 tended to undergo gel- and solid-like phase transitions in the nucleus and in nuclear bodies demonstrated by slow and incomplete recovery of fluorescence after photobleaching. Polyanions, such as heparin and RNA, were able to modulate PS and PT in vitro. Heparin apparently stabilized the condensates in a gel-like state, and RNA apparently induced a solid-like state of the protein even in the absence of PEG. Conditions that destabilize p53C into a molten globule conformation also produced liquid droplets in the absence of crowding. The disordered transactivation domain (TAD) modulated both phase separation and amyloid aggregation. In summary, our data provide mechanistic insight into the formation of p53 condensates and conditions that may result in the formation of aggregated structures, such as mutant amyloid oligomers, in cancer. The pathway of mutant p53 from liquid droplets to gel-like and solid-like (amyloid) species may be a suitable target for anticancer therapy.

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF).     

Influence of structure and solubility of chain transfer agents on the RAFT control of dispersion polymerisation in scCO2

Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerisation of methyl methacrylate (MMA) is performed in supercritical carbon dioxide (scCO₂) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. Kinetic studies of the polymerisation in scCO₂ also confirm these data. By contrast, only poor control of MMA polymerisation is obtained in toluene solution, as would be expected for this CTA which is better suited for acrylates. In this regard, we select a range of CTAs and use them to determine the parameters that must be considered for good control in dispersion polymerisation in scCO₂. A thorough investigation of the nucleation stage during the dispersion polymerisation reveals an unexpected “in situ two-stage” mechanism that strongly determines how the CTA works. Finally, using a novel computational solvation model, we identify a correlation between polymerisation control and degree of solubility of the CTAs. All of this ultimately gives rise to a simple, elegant and counterintuitive guideline to select the best CTA for RAFT dispersion polymerisation in scCO₂.

RAFT dispersion polymerisation of methyl methacrylate is performed in scCO₂ with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight.     

Synthesis of non-agglomerated Ba<Subscript>0.77</Subscript>Ca<Subscript>0.23</Subscript>TiO<Subscript>3</Subscript> nanopowders by a modified polymeric precursor method

In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba_0.77Ca_0.23TiO₃ nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis, morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy. In summary, Ba_0.77Ca_0.23TiO₃ nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution (30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the chelation in higher pHs.     

Perfluoropoly-ether/peroxide compounds: spectroscopic studies and quantum chemical calculations

Perfluoropolyethers (PFPEs) are a class of high performance materials used in a wide range of applications (refrigeration, lubrication, semiconductor industry, etc.). PFPEs containing peroxidic units are intermediate materials for the preparation of commercial end products. In this work we study the spectroscopic properties of ether and peroxides linkages in this class of compounds; nuclear magnetic resonance (NMR) spectra are discussed, FT-Raman data presented. Quantum chemical calculations on model molecules were used as a tool for the interpretation of the Raman experimental data and physical-chemical properties.     

Evaluation of isothermal kinetic of sweetener

Summary Sulfonylureas are widely used for the treatment of non-insulin dependent diabetes mellitus. Glibenclamide belongs to the group of substituted arylsulfonylureas. Many representative of this group shows polymorphism. The purpose of this work was to investigate the thermal behaviour and compatibility between glibenclamide and some excipients using thermoanalytical techniques (TG-DTG/DSC). The thermal and isothermal kinetics data showed incompatibility between glibenclamide and magnesium stearate.