Water structure enhancement

The properties of ions in the aqueous mixtures, x2 < 0-64 show no extrema comparable to those observed in TA mixtures, compensation effects also being absent (Moreau and Douheret, 1974). These observations are consistent with the lack of any water-structure enhancement by this co-solvent. 

Marcus Y (2010) Cohesive energy of molten salts and its density. J Chem Thermodyn 42 60-64 Marcus Y (2011) Water structure enhancement in water-rich binary solvent mixtures. J Mol Liq 158 23-26... 

Marcus Y (2011a) Water structure enhancement in water-rich binary solvent mixtures. J Mol Liq... 

Proton exchange rates in aqueous solutions are enhanced by small amounts (0.5% V/V) of hydrophobic substances (e.g., methanol, dioxane) because of a consequent increase in H-bonded water structure in the hydration shells through which the proton transfer is mediated (9). 

The underlying metal lattice structure also has a significant effect on the water structure. As pointed out by Spohr," although the Pt-Pt nearest-neighbor distance is ao/ Jl = 0.277 nm, which is very close to the 0-0 distance in ice, the cubic symmetry of the 100 surface is incompatible with the hexagonal symmetry of the ice lattice. As a result, the water molecules cannot form a uniform monolayer and occupy all adsorption sites. On the other hand, Berkowitz and co-workers showed that the hexagonal Pt (111) surface is able to support a more complete layer of adsorbed water molecules, and one can identify patches of an icelike structure in the first layer. This freezing is further enhanced by an external electric field, as will be discussed later. 

In the Frank and Evans iceberg model, ice-like structures form around hydrophobic entities, such as methane. In this model, the hydrophobic molecules enhance the local water structure (greater tetrahedral order) compared with pure water. Ordering of the water hydration shell around hydrophobic molecules has been attributed to clathrate-like behavior, in which the water hydration shell is dominated by pentagons compared to bulk liquid water (Franks and Reid, 1973). 

In addition, the effect of water, and universal and phosphate buffer, on the degree of hydrolysis was investigated (Tables 3 and 4). It can be observed that it was necessary to use both pretreatments (conditions 1, 2, and 3) to obtain higher amounts of xylose. Probably, this could be ascribed to the fact that these pretreatments had opened up the pores of the cell wall structure, enhancing the enzyme s access to the substrate... 

The tendency for Ato increase with the increase in the size of the solute indicates that the extent of structure forming action also increases. The positive value of ACp is attributed to the need to melt off this enhanced water structure as the temperature is raised. The two quantities, AH° and AS , are much more dependent on... 

The actual organization of water molecules around an apolar solute and the mechanism of structure enhancement are not clear cut. Nemethy and Scheraga (1962b) suggested that a solute molecule stabilizes water molecules having four hydrogen bonds by means of dispersion interactions between the solute and water. Regions of... 

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