Presence Of Multivalent Ions Research Articles

Effect of the counterions on the surface properties of surfactant solutions: kinetics of the surface tension and surface potential

The kinetics of adsorption from anionic surfactant solutions, containing counterions of different valence, is investigated by measuring the surface tension as a function of time and the surface potential. The surfactant used is sodium dodecyl polyoxiethylene-2 sulfate; the electrolytes are chlorides of sodium, calcium and aluminium at a constant total ionic strength of 0.024 M. A strong effect of the counterions on the adsorption kinetics is found. The increasing counterion valence leads to a faster relaxation of the surface tension toward its equilibrium value. A theoretical model for diffusion controlled adsorption of charged surface active ions in the presence of counterions is proposed. Asymptotic equations for the surface tension as a function of time are derived accounting for the contribution of micelles present in the solution. The theoretical predictions agree quantitatively with the experimental data. The calculated model parameters, characteristic diffusion and micellization time-constants are of reasonable magnitude. The results from surface tension experiments are in accordance with the surface potential measurements, which give an increase of the surfactant adsorption in the presence of multivalent ions.

Soil salts reduce hydration of polymeric gels and affect moisture characteristics of soil

Hydration of a hydrophilic crosslinked polystyrene (gel) in deionized water at 65 g of gel per g of soil was studied. Four different soil types were selected, three were light‐textured soils (loamy sand and sandy clay loam) and the other a clay. Container capacity, field capacity, permanent wilting point, and available water for these soils were measured for gel contents equal to 0,0.1, 0.2, and 0.3%. Absorption capacity of the gels when incorporated into the soil decreased considerably compared to its absorption in pure water. This was attributed to the increased ionic strength of soil moisture and the formation of additional ionic crosslinks in the gel network due to the presence of multivalent ions in the soils. It was found also that container capacity, field capacity, and available water capacity increased with the gel content in soil, whereas the permanent wilting point was not significantly affected.

Nodule DNA in the (GA)37.(CT)37 insert in superhelical plasmids.

Di- or trivalent metal ions stabilize a supercoil-dependent transition in pGA37, which contains the (GA)37.(CT)37 insert, at neutral and basic pH. The structure formed is different from the well known protonated triplexes (H-DNA) adopted at low pH by polypurine.polypyrimidine (Pur.Pyr) inserts in plasmids. DNA samples must be preincubated in the presence of multivalent ions at 50 degrees C for the new transition to occur. At neutral pH in the presence of Co hexamine, both strands of the insert have modification maxima situated at one-third of the distance from both ends. We propose the formation of a new structure called nodule DNA which consists of both Pyr.Pur.Pyr and Pur.Pur.Pyr triplexes and does not contain continuous single-stranded regions. At basic pH (greater than 8.5) in the presence of magnesium ions, the modification pattern corresponds to Pur.Pur.Pyr triplex formation in the whole insert. At neutral pH in the presence of magnesium, both nodule DNA and the Pur.Pur.Pyr triplex can be formed in the insert. We also observed a magnesium-dependent transition at neutral pH in the other Pur.Pyr insert containing plasmids. These data demonstrate that Pur.Pyr sequences can adopt several non-B conformations at close to in vivo conditions.

Swelling of anionic and cationic starch‐based superabsorbents in water and saline solution

AbstractStarch graft superabsorbents were prepared by graft copolymerization either with polyacrylonitrile (PAN) and saponification of the resulting copolymer or with trimethyl–aminoethylacrylate chloride (CMA) and methylene bisacrylamide as crosslinking agent. The influence of several structural parameters on the swelling properties of these absorbents have been studied: crosslink density, ionic content, and composition of the starch. As expected, the absorbency decreases with an increase of the crosslink density. It increases with the ionic content of the graft copolymer up to a maximum, an excess of charges leading to a swelling decrease. The PAN branch length depends on the origin of the starch. High molar weight PAN was grafted onto waxy corn, a starch with high amylopectin content. The swelling increases with increasing molar weight of PAN up to 5 × 105. In saline solution the absorbency of both ionic gels decreases significantly. However, in the presence of multivalent ions their behavior is different. For cationic absorbents the swelling depends on the ionic strength but not on the ion valency. On the other hand, anionic absorbents are significantly affected by multivalent cations.