Hydrophobic effect origin

Water-soluble globular proteins usually have an interior composed almost entirely of non polar, hydrophobic amino acids such as phenylalanine, tryptophan, valine and leucine witl polar and charged amino acids such as lysine and arginine located on the surface of thi molecule. This packing of hydrophobic residues is a consequence of the hydrophobic effeci which is the most important factor that contributes to protein stability. The molecula basis for the hydrophobic effect continues to be the subject of some debate but is general considered to be entropic in origin. Moreover, it is the entropy change of the solvent that i... 

In the case of the retro Diels-Alder reaction, the nature of the activated complex plays a key role. In the activation process of this transformation, the reaction centre undergoes changes, mainly in the electron distributions, that cause a lowering of the chemical potential of the surrounding water molecules. Most likely, the latter is a consequence of an increased interaction between the reaction centre and the water molecules. Since the enforced hydrophobic effect is entropic in origin, this implies that the orientational constraints of the water molecules in the hydrophobic hydration shell are relieved in the activation process. Hence, it almost seems as if in the activated complex, the hydrocarbon part of the reaction centre is involved in hydrogen bonding interactions. Note that the... 

Hydrophobic interactions of this kind have been assumed to originate because the attempt to dissolve the hydrocarbon component causes the development of cage structures of hydrogen-bonded water molecules around the non-polar solute. This increase in the regularity of the solvent would result in an overall reduction in entropy of the system, and therefore is not favoured. Hydrophobic effects of this kind are significant in solutions of all water-soluble polymers except poly(acrylic acid) and poly(acrylamide), where large heats of solution of the polar groups swamp the effect. 

The origins of experimentally observed slow mode need to be explored in terms of hydrophobic effects arising from the intrinsic chemical properties of polymer molecules. 

Peppas et al. divided the free energy change, g23, into three components originating from (i) dispersive forces (g23), (ii) the acid-base interactions (g23) and (iii) the hydrophobic effect (g23). 

The substrate specificities for these enzyme reactions were originally based only on electronic effects of substituents 12,13) the chemical mechanism of action depending on the electron-withdrawing ability of aromatic substituents has been postulated as being expressible by biphasic Hammett plots such as Fig. 1 for the reactions of Eq. 12. Eq. 9 and 10 clearly indicate the significance not only of electronic but also of steric and hydrophobic effects. 

Hydrophobic binding. The hydrophobic effect can have both enthalpic and entropic components, although the classical hydrophobic effect is entropic in origin (Section 1.9.1). Studies on the associations between planar aromatic molecules show an approximately linear relationship between the interaction energy and their mutual contact surface area with slope 64 dyn cm-1, very close to the macroscopic surface tension of water (72 dyn cm-1). Hence, in the absence of specific host or guest interactions with the solvent the hydrophobic effect can be calculated solely from the energy required to create a free surface of 1 A2 which amounts to 7.2 X 10 12 J or 0.43 kjA 2 mol. ... 

An intruding hydrocarbon must compete with the tendency of water to re-form the original structure and is squeezed out of solution [23]. This hydrophobic effect is attributed to the high cohesive energy density of water because the interactions of water with a nonpolar solute are weaker than the interactions of water with itself [24]. Leo [22] notes that part of the energy cost of creating the cavity in each solvent is paid back when the solvent interacts favorably with parts of the solute surface. ... 

In principle, two different mechanisms have been proposed on how the ions influence protein stability. Firstly, it has been suggested that a modification of water s structure is the origin of the Hofmeister sequence (130). It has been hypothesized that some ions kosmotropes enhance the structure that surrounds the ions, which leads to a strengthening of the hydrophobic effect and thereby stabilizes the proteins (131). However, the ions that break the stmcture that surrounds the ions ( chaotropes )... 

The hydrophobic effect on a woven cotton fabric can be obtained by surface treatment. Plasma treatment with acid as a component of original gas will result in a hydrophilic surface [66]. 

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