Influence Of Multivalent Cations Research Articles

Multiscale modelling of nucleosome core particle aggregation

The nucleosome core particle (NCP) is the basic building block of chromatin. Under the influence of multivalent cations, isolated mononucleosomes exhibit a rich phase behaviour forming various columnar phases with characteristic NCP–NCP stacking. NCP stacking is also a regular element of chromatin structure in vivo. Understanding the mechanism of nucleosome stacking and the conditions leading to self-assembly of NCPs is still incomplete. Due to the complexity of the system and the need to describe electrostatics properly by including the explicit mobile ions, novel modelling approaches based on coarse-grained (CG) methods at the multiscale level becomes a necessity. In this work we present a multiscale CG computer simulation approach to modelling interactions and self-assembly of solutions of NCPs induced by the presence of multivalent cations. Starting from continuum simulations including explicit three-valent cobalt(III)hexammine (CoHex3+) counterions and 20 NCPs, based on a previously developed advanced CG NCP model with one bead per amino acid and five beads per two DNA base pair unit (Fan et al 2013 PLoS One 8 e54228), we use the inverse Monte Carlo method to calculate effective interaction potentials for a ‘super-CG’ NCP model consisting of seven beads for each NCP. These interaction potentials are used in large-scale simulations of up to 5000 NCPs, modelling self-assembly induced by CoHex3+. The systems of ‘super-CG’ NCPs form a single large cluster of stacked NCPs without long-range order in agreement with experimental data for NCPs precipitated by the three-valent polyamine, spermidine3+.

The influence of multivalent cations on the flocculation of activated sludge with different sludge retention times

The mechanism governing the flocculation of activated sludge (AS) with different sludge retention times (SRTs) was studied in this paper. AS samples were cultivated in 8 lab-scale reactors with SRTs of 5 d, 7.5 d, 10 d, 12.5 d, 15 d, 20 d, 30 d, and 40 d. The bulk solution, loosely bound extracellular polymeric substances (LB-EPS), tightly bound EPS (TB-EPS), and pellet were extracted for all 8 AS samples. There was a clear trend that the effluent turbidity decreased as the SRT increased, and we deduced that this is because AS samples with longer SRTs have lower interaction energy barriers and lower LB-EPS content. Furthermore, the concentrations of multivalent cations (especially trivalent cations) in the pellets were found to be closely correlated to the AS flocculability, total interaction energy (Wtot), and LB-EPS content. The multivalent (especially trivalent) cations possess greater binding ability, and this ability to bind tightly to AS in large quantities is responsible for the superior flocculability of AS samples with longer SRTs. Hence, the concentrations of multivalent cations in the pellets are an important indicator of AS flocculability. We deduced that variations in the quantities of multivalent cations that tightly bind with the AS rather than remaining in the influent are the core reason behind observed fluctuations in the AS flocculability with different SRTs.

Formation, Stability, and Rheology of Particle Stabilized Emulsions: Influence of Multivalent Cations

Recently, it has been shown that hydrophilic colloidal silica particles (Ludox) can be rendered sufficiently hydrophobic to stabilize oil in water (O/W) emulsions simply by changing the pH of the suspending medium to ∼2, and such emulsions have been shown to display novel rheology (shear thickening) compared to conventional emulsions (Wolf et al. J. Rheol., 2007, 51, 465). However, while lowering pH can render nanosized silica (∼10 nm) sufficiently hydrophobic so as to stabilize O/W emulsions, this method does not appear to generalize to larger silica particles (∼200 nm). In this present study, we explore a different approach, which employs hydrophilic, (i.e., not surface modified) colloidal silica particles to stabilize O/W emulsions in the presence of a range of cations. It appears that certain cations at high pH (in particular La3+) will render various inorganic oxide surfaces more hydrophobic. As such this makes the combination of silica particles with appropriate concentrations of Lanthanum cations a...

The influence of multivalent cations on negative thixotropy in aqueous glycerol solutions of partially hydrolyzed polyacrylamide

AbstractNegative thixotropic behavior in aqueous glycerol solutions of partially hydrolyzed polyacrylamide was studied at various concentrations of Na+, Ca2+ and Al3+ chlorides. A decrease in critical shear stresses and more intensive negative thixotropic behavior observed in the presence of multivalent cations were explained in terms of their stronger charge screening effect. This effect suppresses intermolecular electrostatic repulsions, which act against association of polymer molecules and, thus, against the occurrence of negative thixotropy.

Influence of secondary and tertiary amines on the stability of stearic acid monolayers

Acid-base interactions and the influence of multivalent cations on the stability of stearic acid monolayers were studied by means of the Langmuir technique. The surface activity of secondary and tertiary amines increases with increasing size of the hydrocarbon moiety. The Langmuir study revealed that the dibutylamine-stearic acid complex is water-soluble, whereas the complexes formed when stearic acid interacts with tributylamine, dihexylamine, trihexylamine or trioctylamine are not sufficiently polar to be water-soluble. The presence of Ca 2+ ions in the subphase results in a reduced penetration of the monolayer. Relaxation measurements show that salt in the bulk solution stabilizes the monolayer.

Flotation properties of silicon carbide: II. On the influence of multivalent cations on the flotation of silicon carbide with sodium oleate

This article presents the results of investigations concerning the influence of multivalent cations on the flotation of silicon carbide with sodium oleate as a collector. These results show that there is great similarity of the effect of multivalent cations on the flotation of, respectively, silicon carbide and quartz, some oxides and silicates. The influence of multivalent cations on the flotation of SiC with sodium oleate is manifested by the maxima recoveries observed at specific pH values for the different cations tested: Fe +3, Al +3, Cu +2, Mn +2. In order to interpret the mechanism of their activity, both measurements of adsorption and of electrokinetic potential were carried out. The maxima recoveries observed are due to the presence of hydroxy complexes of the type MeOH +, MeOH +2, which were adsorbed on the negatively charged surface of the silicon carbide, as a result of which the adsorption of the anionic collector became possible. The flotation maxima occured in those pH ranges in which the hydroxy complexes reach the highest concentration in solution. This mechanism is similar to that explaining the phenomena observed in the case of quartz and some oxides and silicates.