Surface Properties of Aqueous Dispersions of Bovine Serum Albumin Fibrils

The surface properties of aqueous dispersions of worm-like fibril aggregates of bovine serum albumin (BSA) differ from those of the adsorption layers of the native protein. The dispersions of BSA fibrils are characterized by slower changes of the surface tension and dynamic surface elasticity and also have different steady-state values of the surface properties. The fourfold compression of the adsorption layer of BSA fibrils leads to noticeably higher surface pressures than those of a compressed layer of the native protein, indicating the formation of a more rigid layer structure in the former case. The spreading of BSA fibrils onto a liquid surface from a concentrated dispersion reduces the effect of surface-active admixtures on the layer properties. The dependencies of the dynamic surface elasticity on surface pressure almost coincide for the spread layers of fibrils and the native protein in the range of low surface pressures, but only the spreading of the native protein can lead to surface pressures higher than 4 mN/m. This distinction is presumably caused by the formation of stable clusters of BSA fibrils at the interface and their slow propagation along the liquid surface

DNA Penetration into a Lysozyme Layer at the Surface of Aqueous Solutions

The interactions of DNA with lysozyme in the surface layer were studied by performing infrared reflection–absorption spectroscopy (IRRAS), ellipsometry, surface tensiometry, surface dilational rheology, and atomic force microscopy (AFM). A concentrated DNA solution was injected into an aqueous subphase underneath a spread lysozyme layer. While the optical properties of the surface layer changed fast after DNA injection, the dynamic dilational surface elasticity almost did not change, thereby indicating no continuous network formation of DNA/lysozyme complexes, unlike the case of DNA interactions with a monolayer of a cationic synthetic polyelectrolyte. A relatively fast increase in optical signals after a DNA injection under a lysozyme layer indicates that DNA penetration is controlled by diffusion. At low surface pressures, the AFM images show the formation of long strands in the surface layer. Increased surface compression does not lead to the formation of a network of DNA/lysozyme aggregates as in the case of a mixed layer of DNA and synthetic polyelectrolytes, but to the appearance of some folds and ridges in the layer. The formation of more disordered aggregates is presumably a consequence of weaker interactions of lysozyme with duplex DNA and the stabilization, at the same time, of loops of unpaired nucleotides at high local lysozyme concentrations in the surface layer

Spread Layers of Lysozyme Microgel at Liquid Surface

The spread layers of lysozyme (LYS) microgel particles were studied by surface dilational rheology, infrared reflection–absorption spectra, Brewster angle microscopy, atomic force microscopy, and scanning electron microscopy. It is shown that the properties of LYS microgel layers differ significantly from those of ß-lactoglobulin (BLG) microgel layers. In the latter case, the spread protein layer is mainly a monolayer, and the interactions between particles lead to the increase in the dynamic surface elasticity by up to 140 mN/m. In contrast, the dynamic elasticity of the LYS microgel layer does not exceed the values for pure protein layers. The compression isotherms also do not exhibit specific features of the layer collapse that are characteristic for the layers of BLG aggregates. LYS aggregates form trough three-dimensional clusters directly during the spreading process, and protein spherulites do not spread further along the interface. As a result, the liquid surface contains large, almost empty regions and some patches of high local concentration of the microgel particles

Solubilities of 3-acetylpyridine in supercritical carbon dioxide at several temperatures and pressures: Experimental and modeling

3-Acetylpyridine(methyl 3-pyridyl ketone)is one of the important compounds to impart flavor and fragrance in various food products. In this work,the solubility data of 3-acetylpyridine in supercritical carbon dioxide (SC-CO 2)were experimentally measured at several temperatures (313.15 K, 323.15 K, 333.15 K, and 343.15 K) and pressures from 10 MPa to 26 MPa under static mode. The experimental solubilities over the measurement range were correlated using Chrastil and Del Valle and Aguilera density-dependent models while phase equilibrium behavior of the studied system was interpreted by Peng–Robinson equa-tion of state (PR-EoS) incorporated with quadratic and Stryjek–Vera mixing rules. The agreement between the model predictions and experimental solubilities was assessed in respect to root-mean-square deviation (RMSD) and consistency of physical meaning of model parameters. Concerning phase equilibria of the studied supercritical system, PR-EoS incorporated with quadratic mixing rule was superior to PR-EoS incorporated with Stryjek–Vera mixing rule and capable to describe the dependency of adjustable binary interaction parameters with temperature

Production of gamma-valerolactone from sugarcane bagasse over TiO2-supported platinum and acid-activated bentonite as a co-catalyst

Nowadays, biomass utilization has become the center of attention for researchers worldwide and is driven by the depletion of global petroleum supplies for the production of energy and valuable chemicals while easing the atmospheric CO 2 burden. We propose here a green strategy for transforming sugarcane bagasse into gamma-valerolactone (GVL), an attractive platform molecule that can be further converted into a variety of chemical derivatives for wide use in industrial applications. Our recent strategy involves the solid acid-catalyzed hydrothermal conversion of cellulose and hemicellulose derived from biomass to give an aqueous solution comprising levulinic acid (LA), followed by catalytic hydrogenation of LA to GVL. Native and acid-activated bentonites were used as solid acid catalysts to promote hydrothermal conversion of cellulose and hemicellulose. The maximum achievable yield of LA was 159.17 mg per gram of oven-dried biomass for 60 min reaction at 473.2 K in the presence of a 2% acid-activated bentonite catalyst. Catalytic hydrogenation reactions of LA to GVL over 1% Pt@TiO 2 and acid-activated bentonite as a co-catalyst were performed at temperatures of 393.2 – 473.2 K and residence times of 120 – 360 min. The combined solid catalyst gave an attractive performance with respect to LA conversion ( 100%) and GVL selectivity (95%) under milder reaction conditions in comparison to 1% Pt@TiO 2 without an acid co- catalyst. The spent catalyst could be reused for fi ve consecutive hydrogenation cycles with a marginal decrease in the catalytic activity and GVL selectivity. Coke formation was believed to be the main cause of catalyst poisoning and calcination of the spent catalyst under a stream of pure oxygen at 723.2 K was applied for removing coke deposits from the active catalyst sites, thus restoring the catalytic performanc