Hydrophobic domain repulsion

III PEG MPD Steric exclusion Repulsion from charges To hydrophobic regions Good precipitants stabilizers of native structure at low temp., unfolded structure at high temp. stabilizers and solubilizers of hydrophobic domains in proteins... 

Due to the strong hydrophobicity of the blocks B, the interface between the collapsed hydrophobic domain and the surrounding aqueous environment is narrow compared to the size of the core. Therefore, the coronal blocks A can be envisioned as tethered to the interface to form a polymer brush [33, 39, 40]. The hydration of the corona and the repulsion between different coronae ensure the solubility (aggregative stability) of the micelles in water. 

Derivation of Equation (5.21) considers hydrophobic-induced pK shifts and hydrophobic-induced increases in positive cooperativity. In Figure 5.30, however, there is experimental delineation between the hydrophobic domain where the above considerations dominate and the electrostatic domain where charge-charge repulsion dominates with a negative cooperativity. Thus we require an expression that would properly include both effects. 

Specific effects described below are known for shifting the equilibrium in the direction of either the T or the R state. These effects are explicable in terms of the AT -mechanism for moving the T,-divide and the approximately equivalent Gibbs free energy of hydrophobic association, AGha, and its component the apolar-polar repulsive free energy of hydration, AGap. In all cases ion-pair formation associated with hydrophobic domains drives hydrophobic association. 

The 14 subunits arrange as two heptameric rings, that is, with 7 units having a C7 symmetry axis, related to the second 7 units by a twofold dyad axis. This results in two water-filled cavities of 85,000 each. Each of the 14 subunits consists of three domains—an equatorial domain, an intermediate domain, and an apical domain. Seven ATP molecules bind to the 7 equatorial domains at a position near the intermediate domain and, in our view by means of AG,p, propagate dissociations of hydrophobic domains (including their intrinsic ion pairs) and domain rotations in the intermediate and apical domains due to apolar-polar repulsions. The result is a water-filled cavity with its size doubled to 175,000 A . ... 

Repulsion Between Bound ATP and the Hydrophobic Domain Responsible for Positive Cooperativity and for Apical Domain Rotation... 

TTie association of hydrophobic domains between the y-rotor and the p-empty subunit in Figure 8.34A profoundly dominates the structural view of the EG interaction. Also striking is the seeming repulsion between the y-rotor(G) and the a-ATP(C) subunit seen as an aqueous cleft between the G and C chains. The symmetry is partially restored when the diametrically opposed subunits contain P-ADP and a-ATP, as shown in Figure 8.34B. The... 

Expectation 2 That the ADP plus Pi state at the cross-bridge active site effects a repulsive AGap force for dissociation of hydrophobic domains within the cross-bridge. Relevance of the hydrophobic consilient mechanism to the motion of contraction requires that formation of the most polar state, ADP " Mg + HPO/", effects hydrophobic dissociation within the cross-bridge. This sets the stage for the loss of Pi, that is, of HPO/", that drives the hydrophobic association required by the hydrophobic consilient mechanism as... 

Poly(N,N-dimethylacrylamide) (PDMA) star polymers with 2, 3, and 4 arms and with dodecyl chains as hydrophobic end-caps were obtained in high yield with narrow polydis-persities by means of the RAFT technique. At sufficiently high concentration they form interconnected hydrophobic domains, i.e., a transient network. SANS experiments show that these hydrophobic domains contain about 20 dodecyl chains and they interact repulsively due to the PDMA chains that separate them. While the static structure is only very little affected by the number of arms this applies not at all to the dynamic properties as observed by DLS and rheology. Here one observes in DLS a complex, trimodal relaxation process, where the slower modes become more pronounced with increasing munber of arms. The fast mode corresponds to the diffusion of the hydrophobic domains while the second mode shows no q-dependence and corresponds in its values to the time deduced from the cross-over of G and G" in the oscillatory rheological experiments. Finally the slowest motion shows a rather pronounced q-dependence and is pre-stunably linked to a more complex relaxation mechanism of... 

Pratt and co-workers have proposed a quasichemical theory [118-122] in which the solvent is partitioned into inner-shell and outer-shell domains with the outer shell treated by a continuum electrostatic method. The cluster-continuum model, mixed discrete-continuum models, and the quasichemical theory are essentially three different names for the same approach to the problem [123], The quasichemical theory, the cluster-continuum model, other mixed discrete-continuum approaches, and the use of geometry-dependent atomic surface tensions provide different ways to account for the fact that the solvent does not retain its bulk properties right up to the solute-solvent boundary. Experience has shown that deviations from bulk behavior are mainly localized in the first solvation shell. Although these first-solvation-shell effects are sometimes classified into cavitation energy, dispersion, hydrophobic effects, hydrogen bonding, repulsion, and so forth, they clearly must also include the fact that the local dielectric constant (to the extent that such a quantity may even be defined) of the solvent is different near the solute than in the bulk (or near a different kind of solute or near a different part of the same solute). Furthermore... 

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