Hydrophobic effect basic principles

The assembly of amphiphilic block copolymers to generate discrete nanoscale structures is primarily driven by the hydrophobic effect, with micelle size and shape governed by a set of basic principles rooted in surfactant phase-separation behavior [22-28]. Important parameters that control the size of micelles are the degree of polymerization of the polymer blocks and the Flory-Huggins interaction parameter [28]. 

Let us note here some of the basic principles underlying models, theories, and calculations of hydrophobic effects. The quantity of first interest is the free energy associated with the interaction of the solute with the aqueous environment. This is the chemical potential or partial molar Gibbs free energy of the solute. This quantity provides a driving force for rearranging molecules in thermodynamic systems and many quantities of interest are fundamentally connected to this free energy. Consider first an atomic solute of type A. For example, perhaps A = Ar. The chemical potential at extreme dilution may be expressed as... 

In principle, there are four basic strategies to compensate for the repulsive effects between the hydrophobic fullerene surface and water (a) encapsulation in the internal hydrophobic moiety of water-soluble hosts like cyclodextrins (Andersson et al., 1992 Murthy and Geckeler, 2001), calixarenes (Kunsagi-Mate et al., 2004) or cyclotriveratrylenes (Rio and Nierengarten, 2002) (b) supramolecular or covalent incorporation of fullerenes or derivatives into water-soluble polymers (Giacalone and Martin, 2006) or biomolecules like proteins (Pellarini et al., 2001 Yang et al., 2007) (c) suspension with the aid of appropriate surfactants and (d) direct exohe-dral functionalization in order to introduce hydrophilic moieties. 

The most important properties in respect to protein structures (Richardson and Richardson, 1989) are, however, not so much related to chemical reactivity. Even more important is the variation in water solubility (Hutchens, 1976) and hydrophobicity (Sueki et al., 1984) of proteins. Table 9.2.3 gives the usual assignments of acidic, basic, and hydrophobic amino acids. Solubility in water turns out to be unpredictable from first principles. Amino acids with charged side groups R are, for example, not always more soluble than those with electroneutral hydrocarbon substituents. On the contrary, by far the most soluble amino acid (1.5 kg/L ) is proline, with three CH2 groups in a pyrrolidine unit as the only substituent. Aspartic acid with an acetic acid side chain is less soluble by a factor of 250 (6g/L). Cationic amino acids are, in general, much more soluble than their anionic counterparts the effect of hydrophobic substituents (e.g., isobutyl, sec-butyl, phenyl, or indole) is not very pronounced (Table 9.2.3). 

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