Hydration of polar groups

Richards, N., Williams, P. B., and Tute, M. (1991) Empirical methods for computing molecular partition coefficients. I. Upon the need to model the specific hydration of polar groups in fragment based approaches. Int. J. Quant. Chem. 18, 299-316. 

The effect of low concentrations of urea (2M) on the large dihydroxy bile salt micelles is striking, while similar concentrations have no effect on the small trihydroxy or dihydroxy micelles. The effects of urea on micelle formation and aggregate size are undoubtedly complicated (10) and involve changes in solvent structure and thus hydrophobic bonding and hydration of polar groups. For large micelles of dihydroxy bile salt... 

Both hydrocolloids and emulsifiers increase the water-binding capacity in the mix (increased % of hydrogen atoms with low T2 and decreased T2 values). A synergistic effect is observed when both ingredients are present. From studies described earlier in this chapter, the effect of hydrocolloids is assumed to be due to simple water binding and increased thickness of protein layers around the fat globules, whereas the effect of emulsifiers may be due to the increased hydration of interfacially bound protein as well as increased hydration of polar groups of emulsifier at the oil-water interface. 

Hydration of polar groups in the interbands, accompanied by some... 

To summarize, three conclusions transpire from the nanoscale thermodynamics results (a) The interfacial tension between protein and water is patchy and the result of both nanoscale confinement of interfacial water and local redshifts in dielectric relaxation (b) the poor hydration of polar groups (a curvature-dependent phenomenon) generates interfacial tension, a property previously attributed only to hydrophobic patches and (c) because of its higher occurrence at protein-water interfaces, the poorly hydrated dehydrons become collectively bigger contributors to the interfacial tension than the rarer nonpolar patches on the protein surface. 

Later, after we have had a chance to examine in detail the properties of the molecules that make up living organisms, we shall see how intennolecular forces are extremely important in the functioning of cells. Hydrogen bond formation, the hydration of polar groups, and the tendency of nonpolar groups to avoid a polar environment all cause complex protein molecules... 

Peptide-CO Monomolecular hydration of polar groups Apolar side chains ... 

I. Upon the Need to Model the Specific Hydration of Polar Groups in Fragment-Based Approaches. 

Water binding varies with the number and type of polar groups (5 ). Other factors that affect the mechanism of protein-water interactions include protein conformation and environmental factors that affect protein polarity and/or conformation. Conformational changes in the protein molecules can affect the nature and availability of the hydration sites. Transition from globular to random coil conformation may expose previously buried amino acid side chains, thereby making them available to interact with aqueous medium. Consequently, an unfolded conformation may permit the protein to bind more water than was possible in the globular form ( ). 

To rationalize the effect of polar groups on and Sj, we can imagine that polar interactions with the water molecules around the solute cavity replace some of the hydrogen bonds between the water molecules. As indicated by the experimental data, this loss of water water interaction enthalpy seems to be compensated by the enthalpy gained from the organic solute water polar interactions. At this point it should also be mentioned that additional polarization effects could enhance the interaction between the organic solute and the water molecules in the hydration shell... 

The large water contents of the organic PIOP-w phases indicate that biopolymers may contain hydrates too. This possibility is neglected by some authors. The positions of polar groups of the solute in relation to the size of the non-polar group is a further parameter which induces the big scale of aqueous-mixtures properties. 

Hydration of polar side groups and peptide bonds. This must provide a large term in AG, including enthalpic and entropic contributions. It cannot be separated from the interactions mentioned in items 1 and 2. 

Fig. 33. Schematic representation of the effects of pressure on oligomeric proteins a) native dimeric protein with cavities/voids b) dissociation of the oligomer, hydration with electrostriction of polar/ionic groups, hydrophobic hydration of unpolar groups (-CR), release of void volume c) weakening of hydrophobic interactions provides pathways for water to penetrate into the interior of the protein, swelling of the core - molten-globule like state d) unfolding of subunits, disruption of the secondary/tertiary structure (hydration of residues not plotted here), loss of cavity volume within protein (adopted from ref. 139).

In Aqueous Solution. When the ionomer is placed in aqueous solution, water molecules diffuse into the ionomer and hydrate about polar groups. Depending on the history of the ionomeric material as well as... 

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