Association hydrophobic

J. Bock and co-workers, "Hydrophobically Associating Polymers," ia G. A. Stahl and D. N. Schul2, eds., Water-Soluble Polymers for Petroleum Recorey, Plenum Press, New York, 1988, pp. 147—160. 

The theory of hydrophobic interaction [70-72] indicates that hydrophobic residues tend to associate with one another so as to minimize the surface area exposed to the aqueous phase and thereby to release a maximum number of structured water molecules. Therefore, the steric fit between the hydrophobic groups may be an important factor for the hydrophobic association. It is reasonable to consider that aromatic hydrophobic groups may undergo tighter hydrophobic self-association because planar aromatic rings would sterically fit with each other to favor the release of structured water. 

It is well known the tendency of polysaccharides to associate in aqueous solution. These molecular associations can deeply affect their function in a particular application due to their influence on molecular weight, shape and size, which determines how molecules interact with other molecules and water. There are several factors such as hydrogen bonding, hydrophobic association, an association mediated by ions, electrostatic interactions, which depend on the concentration and the presence of protein components that affect the ability to form supramolecular complexes. 

Rajagopal K, Ozbas B, Pochan DJ et al (2006) Probing the importance of lateral hydrophobic association in self-assembling peptide hydrogelators. Eur Biophys J Biophys Lett 35 162-169... 

A modified acrylamide polymer that is hydrophobically associating has remarkably improved the properties of salt resistance and temperature resistance, compared with high-molecular-weight polyacrylamide [1351]. 

There have been many studies of hydrophobic crosslinking. For example, Flynn40 produced a series of poly (acrylamides) (PAM) and recorded the low shear rate viscosity as a function of the chain overlap parameter. This was performed for a range of molecular weights and concentrations. This procedure was then repeated with the same polymer backbone but with the addition of differing concentrations of alkyl side chains which give rise to hydrophobic association (HPAM). A comparison between hydrophobe and non-hydrophobe polymers is shown in Figure 5.30. 

F. K. Ogasawara, Y. Wang, and D. R. Bobbitt, Dynamically modified, biospecific optical fiber sensor for riboflavin binding protein based on hydrophobically associated 3-octylriboflavin, Anal Chem. 

Funasaki, N., Hada, S., Neya, S., and Machida, K. Intramolecular hydrophobic association of two chains of oligoethyleneglycol diethers and diesters in water, J. Phys. Chem., 88(24) 5786-5790, 1984. 

Fig. 9. Schematic representation of hydrophobic association diagonal lines—water assembly stippling—van der Waals interaction cross-hatched lines—water assembly destroyed by the guest association.

Y. Feng, L. Billon, B. Grassl, A. Khoukh and J. Francois, Hydrophobically associating polyacrylamides and their partially hydrolyzed derivatives prepared by post-modification. 1. Synthesis and characterization, Polymer, 2002, 43, 2055-2064. 

With alkali halide-TBA-W or alkali halide-PD-W systems, the parameters Bne are negative for volumes and heat capacities (see Figures 1-5 and 10). This sign seems to be the one usually observed for the interaction of a hydrophobic with a hydrophilic solute (6). At intermediate cosolvent concentration, AYe°(W — W + TBA) and AYe°(W — W + PD) deviate in the direction we would expect for hydrophobic association the volume increases sharply, and the heat capacity decreases further. Inorganic electrolytes lower the critical micelle concentration of surfactants by salting out the monomers, thus favoring micellization (25) in a similar way, in the co-sphere of a hydrophilic ion, the hydrophobic bonding between the cosolvent molecules may be enhanced. 

The formation constant Kt for hydrophobic associations often increases with increasing temperature. This is in contrast to the behavior of Kt for many association reactions that involve polar molecules and for which AH0 is often strongly negative (heat is released). An example of the latter is the protonation of ammonia in an aqueous solution (Eq. 2-10). 

Molecules may interact with water in at least four main ways—hydrogen bonding, ionic bonding, hydrophobic association (nonpolar molecules placed in the polar environment of water), and l.ondon dispersion or van der Waals forces. 

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