Demulsification mechanism of asphaltene-stabilized water-in-oil emulsions by a polymeric ethylene oxide-propylene oxide demulsifier

The demulsification mechanism of asphaltene-stabilized water-in-toluene emulsions by an ethylene-oxide-propylene oxide (EO-PO) based polymeric demulsifier was studied. Demulsification efficiency was determined by bottle tests and correlated to the physicochemical properties of asphaltene interfacial films after demulsifier addition. From bottle tests and droplet coalescence experiments, the demulsifier showed an optimal performance at 2.3 ppm (mass basis) in toluene. At high concentrations, the demulsification performance deteriorated due to the intrinsic stabilizing capacity of the demulsifier, which was attributed to steric repulsion between water droplets. Addition of demulsifier was shown to soften the asphaltene film (i.e., reduce the viscoelastic moduli of asphaltene films) under both shear and compressional interfacial deformations. Study of the macrostructures and the chemical composition of asphaltene film at the toluene-water interface after demulsifier addition demonstrated gradual penetration of the demulsifier into the asphaltene film. Demulsifier penetration in the asphaltene film changed the asphaltene interfacial mobility and morphology, as probed with Brewster angle and atomic force microscopy

Design of a VLP-nanovehicle for CYP450 enzymatic activity delivery

Background: The intracellular delivery of enzymes for therapeutic use has a promising future for the treatment of several diseases such as genetic disorders and cancer. Virus-like particles offer an interesting platform for enzymatic delivery to targeted cells because of their great cargo capacity and the enhancement of the biocatalyst stability towards several factors important in the practical application of these nanoparticles. Results: We have designed a nano-bioreactor based on the encapsulation of a cytochrome P450 (CYP) inside the capsid derived from the bacteriophage P22. An enhanced peroxigenase, CYPBM3, was selected as a model enzyme because of its potential in enzyme prodrug therapy. A total of 109 enzymes per capsid were encapsulated with a 70% retention of activity for cytochromes with the correct incorporation of the heme cofactor. Upon encapsulation, the stability of the enzyme towards protease degradation and acidic pH was increased. Cytochrome P450 activity was delivered into Human cervix carcinoma cells via transfecting P22-CYP nanoparticles with lipofectamine. Conclusion: This work provides a clear demonstration of the potential of biocatalytic virus-like particles as medical relevant enzymatic delivery vehicles for clinical applications

Growth Kinetics of Gold Nanorods Synthesized by a Seed-Mediated Method Under pH Acidic Conditions

A systematic study of the effect of ascorbic acid concentration on the growth kinetics of gold nanorods under pH acidic conditions was done. We employed the seed-mediated approach at pH 1.25 using different ascorbic acid/Au+3 molar ratios. We monitored the gold nanorods growth using UV-Vis spectroscopy and the apparent growth rates were determined fitting the experimental data with a theoretical non-linear Boltzmann function. We found that, under the conditions proven, an increase of the ascorbic acid/Au+3 molar ratio induces a red-shift in the longitudinal surface plasmon resonance, as well as the formation of undesirable by-products. The apparent growth rates show a linear dependence with the increment of ascorbic acid concentration. We determined a range of growth rates from 0.034 to 0.078 min(-1), from the lowest to the highest molar ratio used, respectively; which corresponds to deposition rates from 0.128 to 0.235 atoms per second. A low pH in the growth solution promotes a slower growth nanorods rate, which prevents the drastic blue-shift observed in the synthesis at higher pH and provides an aspect ratio tuning.CONACYT (Mexico) 236185 CONACYT/CONICYT (Mexico) 204393 CONICYT/CONACYT (Chile) 130048 FONDECYT (Chile) 3140487 UNISON-PTC-197 DSA/103.5/14/10

Electrophoretic Mobilities of a Viral Capsid, Its Capsid Protein, and Their Relation to Viral Assembly

The self-assembly of many viral capsids is dominated by protein–protein electrostatic interactions. To have a better understanding of this process, it is important to know how the protein and the capsid surface charges vary as a function of the pH and ionic strength. In this work, using phase analysis light scattering, we measured the electrophoretic mobility (EM) of the cowpea chlorotic mottle virus (CCMV), its capsid protein (CP), and a cleaved CP that lacks its basic terminus, as a function of pH and ionic strength. The EM measurements of the CP are difficult to carry out due to its tendency to self-assemble into capsids; we show how to circumvent this problem by appropriately changing the CP concentration. We found that the isoelectric points (pIs) of the virion and of the CP are insensitive to ionic strength. The onset of multishell structures in the phase diagram of the CCMV CP as a function of ionic strength and pH (and its absence in the brome mosaic virus (BMV) CP phase diagram) can be related to the pI of the capsid. We propose that the transition from multiwall shells to nanotube structures is due to a change in the spontaneous curvature of the CP at its pI. A nonzero limit of the EM at high ionic strength is characteristic of a <i>soft colloid</i>, but a near identity of the EMs of empty capsids and those containing RNA indicates that the EM reflects only the charge distribution in the CP. The Henry equation has been used to provide approximate values of the capsid surface charge as a function of pH and <i>I</i>