Search results for "Stability"
showing 10 items of 3085 documents
Nonenzymatic glycation reaction of folate with reducing sugars: A case study on [6S]-5-methyltetrahydrofolate and fructose
2006
In the Maillard reaction, free amino groups react with reducing sugars to form nonenzymatic glycation products. It has recently been shown that in the presence of reducing sugars (i.e. fructose) folic acid is subjected to a non-enzymatic glycation reaction, which may represent an important pathway of folate degradation besides the established oxidative degradation pathways. In the current study, the thermal stability of [6S]-5-methyltetrahydrofolic acid ([6S]-5-CH3H4PteGlu, 0.4µM), the predominant naturally occuring folate derivate, was investigated on a qualitative and kinetic basis in the presence of different fructose concentrations (0-3M) in milliQ water (8.11ppm O2). Samples were isoth…
Calculation of chromatographic parameters by molecular topology: sulphamides
1994
This investigation was undertaken to test the ability of the molecular connectivity model to predict RF values in thin-layer chromatography (TLC) for a group of sulphamides using multi-variable regression equations with multiple correlation coefficients, standard error of estimate, F-Snedecor function values and Student's t-test as criteria of fit. Regression analyses showed that the molecular connectivity model predicts the values for this property in different silica gel stationary phases and different polar mobile phases. Corresponding stability and random studies were made on the selected prediction models which confirmed their goodness of fit. The results also demonstrated that differe…
Rayleigh and Brillouin scattering in a lysozyme–water mixture: An unusual behavior around 343K
2011
Abstract This article describes Rayleigh and Brillouin light scattering studies on a lysozyme–water mixture from 293 K to 355 K. The scattering intensities from this system are compared with those from a sodium acetate buffer used to dissolve the lysozyme. It is found that in the vicinity of 343 K the lysozyme–water mixture becomes opalescent, and the intensity of the Brillouin peaks decreases and almost vanishes, to be restored at temperatures above 343 K. Around the same temperature the intensity of the central, unshifted Rayleigh peak, however, increases strongly. No such behavior was observed for the sodium acetate buffer. The analysis of the experimental data indicates an irreversible …
Perspective: The Asakura Oosawa model: A colloid prototype for bulk and interfacial phase behavior
2014
In many colloidal suspensions, the micrometer-sized particles behave like hard spheres, but when non-adsorbing polymers are added to the solution a depletion attraction (of entropic origin) is created. Since 60 years the Asakura-Oosawa model, which simply describes the polymers as ideal soft spheres, is an archetypical description for the statistical thermodynamics of such systems, accounting for many features of real colloid-polymer mixtures very well. While the fugacity of the polymers (which controls their concentration in the solution) plays a role like inverse temperature, the size ratio of polymer versus colloid radii acts as a control parameter to modify the phase diagram: when this …
Evaluation of molecular mass and tacticity of polyvinyl alcohol by non-equilibrium capillary electrophoresis of equilibrium mixtures of a polymer and…
2011
Non-equilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) has been used to characterize polyvinyl alcohol (PVA). Commercial PVA samples with different molecular masses, from M(w)=15 up to 205 kDa, were used. According to the (13)C NMR spectra, the samples also differed in tacticity (stereoregularity). Mixtures of PVA and the anionic azo-dye Congo Red (CR) were injected in the presence of a borate buffer. The electropherograms gave a band and a peak due to the residual PVA-CR complex and the excess dye, respectively, plus a superimposed exponential decay due to the partial dissociation of the complex during migration. The stoichiometry of the PVA-CR complex, q=[monomer]/[dye…
Hidden and self-excited attractors in radiophysical and biophysical models
2017
One of the central tasks of investigation of dynamical systems is the problem of analysis of the steady (limiting) behavior of the system after the completion of transient processes, i.e., the problem of localization and analysis of attractors (bounded sets of states of the system to which the system tends after transient processes from close initial states). Transition of the system with initial conditions from the vicinity of stationary state to an attractor corresponds to the case of a self-excited attractor. However, there exist attractors of another type: hidden attractors are attractors with the basin of attraction which does not have intersection with a small neighborhoods of any equ…
Chemical and dimensional evolution of cationic ions exchange resins in cement pastes
2013
Ion exchange resins (IERs) are widely used by the nuclear industry to decontaminate radioactive effluents. After use they are usually encapsulated in cementitious materials. However, the solidified waste forms can exhibit a strong expansion, possibly leading to cracking. Its origin is not well understood as well as the conditions when it occurs.In this work, the interactions between cationic resins in the Na+ or Ca2+ form and tricalcium silicate (C3S), Portland cement (CEM I) or Blastfurnace slag cement (CEM III/C) are investigated at an early age in order to gain a better understanding of the expansion process.The results show that during the hydration of a paste of C3S or CEM I containing…
Production of spray-dried proanthocyanidin-rich cinnamon (Cinnamomum zeylanicum) extract as a potential functional ingredient: Improvement of stabili…
2018
International audience; Cinnamon proanthocyanidins present important biological properties. However, these molecules are unstable and possess an astringent taste, which can make their ingestion difficult. In this context, entrapment by spray-drying technology may be used to produce a concentrated extract with improved stability and reduced astringency. Thus, this work aimed to prepare spray-dried microparticles loaded with a proanthocyanidin-rich cinnamon (Cinnamomum zeylanicum) extract (PRCE), immobilized in a maltodextrin matrix. Freeze-dried samples of the extract (without the carrier) were also prepared for comparison. The particles were characterized for moisture content, water activit…
Entrapment of A Beta 1-40 peptide in unstructured aggregates
2012
Recognizing the complexity of the fibrillogenesis process provides a solid ground for the development of therapeutic strategies aimed at preventing or inhibiting protein-protein aggregation. Under this perspective, it is meaningful to identify the possible aggregation pathways and their relative products. We found that Aβ-peptide dissolved in a pH 7.4 solution at small peptide concentration and low ionic strength forms globular aggregates without typical amyloid β-conformation. ThT binding kinetics was used to monitor aggregate formation. Circular dichroism spectroscopy, AFM imaging, static and dynamic light scattering were used for structural and morphological characterization of the aggre…
Glucagon fibril polymorphism reflects differences in protofilament backbone structure
2010
Amyloid fibrils formed by the 29-residue peptide hormone glucagon at different concentrations have strikingly different morphologies when observed by transmission electron microscopy. Fibrils formed at low concentration (0.25 mg/mL) consist of two or more protofilaments with a regular twist, while fibrils at high concentration (8 mg/mL) consist of two straight protofilaments. Here, we explore the structural differences underlying glucagon polymorphism using proteolytic degradation, linear and circular dichroism, Fourier transform infrared spectroscopy (FTIR), and X-ray fiber diffraction. Morphological differences are perpetuated at all structural levels, indicating that the two fibril class…