Formation Of Hydration Layer Research Articles

Anodic reaction characteristics of tungsten in basic phosphate solutions

DC polarization and electrochemical impedance spectroscopy techniques were used to investigate the pH dependent anodic behaviour of tungsten in basic solutions. Anodic currents of W were pH independent between pH 8 and 11. Above pH 12 as pH increased the anodic currents of W also increased. The diffusion control in pH independent regime was observed to arise from slow diffusion of the solubilized species. At higher pH levels, however, OH − ion diffusion from bulk of solution was observed to control the anodic process. Hydrate layer formation, which was observed with low frequency capacitive loop formation, accelerated with increase in pH.

Thermodynamic Correlation Analysis: Hydration and Perturbation Sensitivity of RNA Secondary Structures

The thermodynamic parameters DeltaH, DeltaS, T(m), and DeltaG of a total of 36 RNA strands, 22 tetralooped 22mers, and 14 heptalooped 25mers (same stem sequence) were analyzed with respect to enthalpy-entropy compensation (EEC). The EEC plots [DeltaH, DeltaS] were compared with collected literature data from protein and nucleic acid unfolding studies (3224 and 241 datapoints, respectively) which all proved to be remarkably linear. The similarity of the compensation slopes and intercepts for all compounds indicate that, irrespective of the chemical nature and stability of the folding solutes, the exothermicity DeltaH and entropic penalty T x DeltaS of folding are strongly dominated by the rearrangement and formation of hydration layers around the solutes, while it is well-known that the stability of folding results only from the difference (DeltaG) and ratio (T(m)) of both parameters. EEC plots [DeltaH, DeltaS] are presented in an extended context, as 3D plots [DeltaH, DeltaS, T(m)] allowing for a correct analytical description of the enthalpy-entropy relationship and for more practical interpretations of large amounts of thermodynamic data when replotted as [DeltaH, T(m)] or [DeltaG(T), T(m)]. The introduction of a variety of mismatches into nucleic acids, or limited irreguliarities into any supramolecular complex, and the analysis of the involved thermodynamics as shown in this study-i.e., scanning the "enthalpy-entropy space" of whole macromolecular subgroups-should permit to extract and quantify more "hidden information", such as hydration extent and sensitivity of macromolecular frameworks toward desolvation and structural perturbation, from thermodynamic analyses of large sample sizes.

Internally mismatched RNA: pH and solvent dependence of the thermal unfolding of tRNA(Ala) acceptor stem microhairpins.

The thermal unfolding of two RNA hairpin systems derived from the aminoacyl accepting arm of Escherichia coli tRNA(Ala) that included all possible single internal mismatches mostly in the third base pair position was measured spectroscopically in 0.1 M NaCl at pH 7.5 and, in part, 5.5. The thermodynamic parameters DeltaH(o), DeltaS(o), DeltaG(o), and T(m) of a total of 36 RNA strands were determined through nonlinear curve fitting of the melting profiles (22 tetralooped 22mers and 14 heptalooped 25mers, same stem sequence). Only three of the 22mers, the A.C-containing variants, were shown to be significantly more stable at pH 5.5. A number of remarkable differences-most likely of more general relevance-between the thermodynamics of certain structurally very similar hairpin variants (e.g., G.C versus A.U, G.U versus I.U) at pH 7.5 are discussed with respect to two possible ways of helix stabilization: pronounced hydration versus low entropic penalty. Four selected 22mers were additionally analyzed in 1 M NaCl and in solvent mixtures containing ethanol, ethylene glycol, and dimethylformamide. The wealth of thermodynamic data suggest that the exothermicity DeltaH(o) and entropic penalty T x DeltaS(o) of folding are strongly dominated by the rearrangement and formation of hydration layers around the solutes, while it is well-known that the stability of folding results only from the difference (DeltaG(o)) and ratio of both parameters (T(m) = DeltaH (o)/DeltaS(o)).

Hydrated Layer Formation on Tricalcium and Dicalcium Silicate Surfaces: Experimental Study and Numerical Simulations

In this paper, an original approach is used to study the calcium silicate hydrate (C−S−H) layer formation on the surface of grains of anhydrous silicate during tricalcium and dicalcium silicate hydration from the variation of the rate of hydration with lime concentration. The effects of C−S−H nucleation and growth on the curves for the degree of reaction against time have been separated in both experimental study of the rate of hydration in controlled conditions and numerical simulation of the growth of C−S−H on a surface from a particle aggregation model. The influence of the number of nuclei and of the different growth modes has been quantified.

Emulsifying Potency of New Amino Acid-Type Surfactant. (1). O/W Emulsions.

Oil-in-water (O/W) emulsions were prepared using a new amino acid-type emulsifier (surfactant), N-[3-lauryloxy-2-hydroxypropyl]-L-arginine L-glutamate (C12HEA-Glu), and the emulsifying potency of C12HEA-Glu was examined in terms of dispersibility, droplet size, interfacial tension, viscosity and hydrophilic microenvironment of droplet surface, whose emulsifying potency was compared with that of general amphoteric and nonionic surfactants. The effects of the constituent oils on the stability of emulsions were also examined. The emulsifying potency of C12HEA-Glu was greater than that of amphoteric N-lauryl-N, N-dimethyl-α-betaine and nonionic polyoxyethylene(10) laurylether, especially, the stability of emulsions containing oleic acid (OA), (C12HEA-Glu/OA/water system), was greatest, while the stability of emulsions containing octane (OC), (C12HEA-Glu/OC/water system), was inferior. OA possesses a hydrophilic carboxyl group and the viscosity of OA is higher than that of OC. The higher visco-elasticity of OA droplet surface and the formation of hydration layer on the droplet contributed to the greater stability of OA emulsions, thereby raising the stability of emulsions for the system C12HEA-Glu/OA/water in spite of the small | zeta-potential | (insufficiently electrostatic repulsion) of droplets.