Thermodynamic stability and retinol binding property of β-lactoglobulin in the presence of cationic surfactants

In this work the stability parameters of bovine β-lactoglobulin, variant A (BLG-A), with regard to their transition curves induced by dodecyltrimethylammonium bromide (C₁₂TAB), tetradecyltrimethylammonium bromide (C₁₄TAB) and hexadecyltrimethylammonium bromide (C₁₆TAB) as cationic surfactants, were determined at 298 K. For each transition curve, the conventional method of analysis which assumes a linear concentration dependence of the pre- and post-transition base lines, gave the most realistic values for ΔG_D(H₂O). The results represent the increase in the denaturating power of surfactants with an increase in hydrocarbon chain length. The value of about 22.27 kJ · mol^?1 was obtained for ΔG_D(H₂O) from transition curves. Subsequently, the retinol binding property of BLG as its functional indicator was investigated in the presence of these surfactants using the spectrofluorimeter titration method. The results represent the substantial enhancement of retinol binding affinity of BLG in the presence of these surfactants.     

Fibrillation of β-lactoglobulin at low pH in the presence of a complexing anionic polysaccharide

The influence of electrostatic complexation with κ-carrageenan was tested on the fibrillation process of β-lactoglobulin at pH 2.0. Morphology and structural development were monitored through cross correlation dynamic light scattering, transmission electron microscopy, and atomic force microscopy. Scattering indicated that noncomplexed β-lactoglobulin monomers aggregated to form fibrils after 15-90 min of heating at 90 °C. However, electrostatic protein-carrageenan complexes found in the unheated system were unchanged by the thermal process. Images and scattering results showed that carrageenan complexes slowed fibrillation kinetics, possibly through reduction in available monomer concentration. Complexes adhered to fibrils at ends and junctions in TEM images, indicating interactive affinity with the fibers, presumably as heterogeneous nucleation sites.     

Comparison of the results of thermal denaturation of β-lactoglobulin obtained by DSC and UV-spectroscopy

The thermal denaturation of β-lactoglobulin in the presence of urea and alkylurea solutions were measured. In the presence of a high concentration of urea this protein shows not only heat but also cold denaturation. For studying the effect of temperature two methods were used, differential scanning calorimetry (DSC) and UV-spectroscopy. DSC provides direct model-independent determination of the transition enthalpy in comparison with UV-spectroscopy, which gives only apparent or van't Hoff enthalpy of transition. The UV-melting curves were analyzed on the basis of a two-state approximation. The apparent standard enthalpies of thermal denaturation, ΔH _app. ^o , were compared with calorimetric ones.     

DSC study of cold and heat denaturation processes of β-lactoglobulin A with guanidine hydrochloride

The cold and heat denaturations of bovine β-lactoglobuhn A (β-lg A) has been studied in solutions of guanidine hydrochloride (GuHCl) by differential scanning calorimelry (DSC) The experimental results are presented and discussed.It is shown that the number of protons bound by the monomeric molecules of β-lg A was unchanged before and after its heat denaturation below pH 3,and that the activation energy of the heat denaturation was depressed owing to the presence of GuHCl.In the solutions with 2.50 and 3.06 mol/L of GuHCl,both the cold and heat denat-urations of β-lg A were observed.In comparison with the heat denaturation,the activation energy of cold denaturation was far lower and the number of GuHCl molecules bound by the unfolded polypeptide chains after cold denaturation increased a lot.The absolute value of the enthalpy of cold denaturation was larger than that of heat denaturation It was found by the analysis that the contribution to the total denaturational enthalpy of conformational change i     

Crystallization of post-consumer polypropylene in the presence of β-nucleating agent

Journal of Thermal Analysis and Calorimetry - In this paper, the heat transfer characteristics of the nanofluid through a parallel plate soft nanochannel are investigated under the fully developed...     

Kinetics of peroxidase-catalyzed oxidation of quercetin in the presence of β-cyclodextrin

It is established that the rate of peroxidase-catalyzed oxidation of flavonoid quercetin is increased by 20% in the presence of macrocyclic complexing agent β-cyclodextrin. The comparison of the kinetic parameters of the indicated reaction in the presence and in the absence of β-cyclodextrin shows that its introduction does not significantly influence the specificity of the enzyme with respect to the reducing substrate (characterized as k _cat/K _M ratio), while the increase in the reaction rate does not depend on the duration of the incubation of quercetin with β-cyclodextrin. It is assumed that the increase of the reaction rate is associated with nonspecific interaction between β-cyclodextrin and quercetin oxidation product.     

Spectrofluorimetric study and determination of desipramine in the presence of β-cyclodextrin

The native fluorescence intensity of desipramine was enhanced in the presence of β-cyclodextrin in aqueous solution. The inclusion complex formation between these compounds was studied by spectrofluorimetry. A stable complex with a 2: 1 stoichiometry of β-cyclodextrin to desipramine was formed (logβ₂ = 9.29 ± 0.01). In the presence of an optimum concentration of β-cyclodextrin, the fluorescence intensity was linearly proportional to desipramine concentration in the range of 0.1–100 μg/mL (7.2 × 10^?7?1.0 × 10^?4 M) with a limit of detection of 7 × 10^?8 M. The method was successfully applied to the detection of desipramine in its tablets.     

Synthesis of SAPO-34 using metakaolin in the presence of β-cyclodextrin

SAPO-34 molecular sieves were synthesized by the addition of β-cyclodextrin(β-CD) as crystal growth inhibitor using metakaolin as silicon and aluminum sources. Properties of the obtained samples were characterized by XRD,SEM,N2adsorption–desorption,FTIR,XRF,EDX,NH293-TPD andSi MAS NMR. When β-CD was added,crystal size of the SAPO-34 crystals decreased. Variation of Si content from the crystal center to surface decreased while total Si content hardly changed.29 Si MAS NMR results showed that β-CD contributed to better Si dispersion and decreased the size of Si(4Si) patches. Moreover,the MTO(methanol-to-olefin) process was conducted to investigate the influence of β-CD on catalytic performance. The synthesized sample with molar ratio of β-CD/Al2O3 equaling 0.055 remained active for 610 min while the sample synthesized without β-CD for only 280 min,which indicates that the lifetime of catalyst synthesized with β-CD is greatly prolonged.     

Hydrogenation of β-N-substituted enaminoesters in the presence of ruthenium catalysts

β-Aminoesters were prepared in two simple steps from β-ketoesters derivatives and primary amines under mild conditions. Their hydrogenation was performed at 50 °C in the presence of several organometallic catalysts under acidic conditions. The new β-N-substituted aminoesters were isolated in moderate to good yields.     

Unfolding and refolding details of lysozyme in the presence of β-casein micelles

In this work, we selected a small globular protein, lysozyme, to study how it unfolds and refolds in the presence of micelles composed of the unstructured β-casein proteins by using microcalorimetry and circular dichroism spectroscopy. It was found that a partially unfolded structure of lysozyme starts to form when the β-casein/lysozyme molar ratio is above 0.7, and the structure forms exclusively when the β-casein/lysozyme molar ratio is above 1.6. This partially unfolded state of lysozyme loses most of its tertiary structure and after heating, the denatured lysozyme molecules are trapped in the charged coatings of β-casein micelles and cannot refold upon cooling. The thus obtained protein complex can be viewed as a kind of special polyelectrolyte complex micelle. The net charge ratios of the two proteins and the ionic strength of the dispersions can significantly modulate the electrostatic and hydrophobic interactions between the two proteins. Our present work may have implications for the nanoparticle protein engineering therapy in the biomedicine field and may provide a better understanding of the principles governing the protein-protein interactions. Besides, the heating-cooling-reheating procedure employed in this work can also be used to study the unfolding and refolding details of the target protein in other protein-protein, protein-polymer and protein-small solute systems.     

Liquid—liquid equilibria in water—aliphatic alcohol systems in the presence of sodium chloride

Liquid—liquid equilibria in mixtures of water, propyl or butyl alcohol isomers and sodium chloride have been studied experimentally at 25 °C The solvent behaviour of the various alcohols is discussed. Setschenow constants, calculated from the measured data, are compared with the results of the scaled particle theory.     

Reaction of 4,4′-dimethyldiphenyl ether with phosphorus trichloride in the presence of anhydrous aluminum chloride

The reaction of 4,4-dimethyldiphenyl ether with phosphorus trichloride in the presence of anhydrous aluminum chloride was studied. This reaction affords 2,8-dimethyl-10H-10⁵-phenoxaphosphine 10-oxide as virtually the only product. In air, the latter in an alkaline solution is quantitatively transformed into 10-hydroxy-2,8-dimethyl-10H-10⁵-phenoxaphosphine 10-oxide.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2762–2765, December, 2004.     

Isolation of ovine β-lactoglobulin genetic variants by chromatofocusing: Heterogeneity of β-lactoglobulin A

Summary Chromatofocusing was applied to the isolation of ovine -Lactoglubulin (-Lg) genetic variants. Ovine -Lg A and B, which are known to differ only by a single amino-acid substitution, were separated. Moreover, one component differing from A variant in isoelectric point and relative molecular mass has been isolated in samples containing ovine -Lg A. Although elution of -Lgs occurred far from their normal isoelectric points, chromatofocusing is a powerful technique effective for both analytical and preparative scale.     

Oxidation of β-dicarbonyl compounds with tert-butyl hydroperoxide in the presence of vanadyl acetylacetonate

Oxidation of β-dicarbonyl compounds with tert-butyl hydroperoxide in the presence of vanadyl acetylacetonate (benzene, 20°C) involves the activated methylene group with intermediate formation of trioxo derivatives and is accompanied by decomposition of carbon skeleton. The oxidation products are carbon dioxide, carboxylic acids, and tert-butyl and peroxy esters derived from the latter.     

Improved thermal oxidation stability of polypropylene films in the presence of β-nucleating agent

Thermal oxidation behavior of isotactic polypropylene (PP) films with and without nucleating agent was investigated at 100 °C in air. The crystal form of PP was modified with a specific aryl amide derivative as β-nucleating agent (β-NA). Fourier transform infrared spectroscopy (FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and tensile tests were performed to determine the extent of chemical degradation and the variations of microstructure of the two kinds of PP films during thermal oxidation. It was found that the mechanism of thermal oxidation of PP films was not changed in the presence of β-NA, but the time to initiation and the rate of oxidation both declined. Moreover, during the thermal oxidation aging, the melting temperature of neat PP significantly decreased while only a slight decrease of the melting temperature occurred for β-PP. Overall, the investigation indicated that the thermal oxidative stability of β-PP was higher than that of neat PP. The underlying mechanism was further analyzed by considering the change in the physical structure, especially the crystalline and the amorphous structure, of PP in the presence of β-NA.     

β-Casein aids in the formation of a sodium caprate-induced β-lactoglobulin B gel

The effects of sodium caprate on the gelation of β-lactoglobulin B and a β-lactoglobulin B/β-casein mixture at ambient temperature were investigated using ultrasonic spectroscopy and rheology. A 12% β-lactoglobulin B solution gelled in the presence of 3.6% sodium caprate. Conversely, sodium caprate did not induce the formation of a gel when β-casein was in isolation, regardless of the protein concentration. Although a 6% β-lactoglobulin B/1.8% sodium caprate solution did not form a gel, a gel was formed when 6% β-casein was added to a mixture containing 6% β-lactoglobulin B and 3.6% sodium caprate. This gel showed comparable rheological properties to that of a gel containing 12% β-lactoglobulin B. The results clearly indicated that β-casein aids in the gelation of a β-lactoglobulin B/sodium caprate mixture, when the concentration of β-lactoglobulin B is insufficient to allow for gelation. It appears that β-casein self-aggregation is also inhibited. Therefore, it could be concluded that β-casein can be used as a texture modifier for β-lactoglobulin gelation induced by sodium caprate.     

Thermodynamic Determination of the Most Probable Route of High-Temperature Formation of β-Spodumene in Lithium-Alumina-Silica Mixtures

The equilibrium composition of -spodumene formed in high-temperature synthesis from lithium carbonate, metakaolinite, and silica was calculated thermodynamically. The extents of the thermodynamically possible reactions were determined in the range 400-1600K.     

Electrochemical production of novel products from 2,3-dimethylhydroquinone in the presence of some β-diketones

Abstract  Electrochemical oxidation of 2,3-dimethylhydroquinone has been studied in the presence of β-diketones as nucleophiles in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the derivatives of 2,3-dimethylhydroquinone participate in a Michael addition reaction to form the corresponding benzofuran derivatives. The electrochemical synthesis has been successfully performed at pH 7.0 and E = 0.1 V versus an Ag|AgCl|KCl (3 M) in an undivided cell in good yield and purity. Graphical Abstract        

Electrochemical production of novel products from 2,3-dimethylhydroquinone in the presence of some β-diketones

Abstract  

Electrochemical oxidation of 2,3-dimethylhydroquinone has been studied in the presence of β-diketones as nucleophiles in aqueous solution using cyclic voltammetry and controlled-potential coulometry. The results indicate that the derivatives of 2,3-dimethylhydroquinone participate in a Michael addition reaction to form the corresponding benzofuran derivatives. The electrochemical synthesis has been successfully performed at pH 7.0 and E = 0.1 V versus an Ag|AgCl|KCl (3 M) in an undivided cell in good yield and purity.