Insolubility hydrophobic domain

In adapting water-insoluble catalysts for use in biological systems it is necessary to introduce the catalyst into the membrane using a solvent vector. Solvents such as tetrahydrofuran and dimethyl sulfoxide have been found to be useful. The introduction of catalyst in a minimum amount of solvent, which is miscible with water, causes the insoluble complex to partition into the hydrophobic domain created by the lipid substrate. The catalyst obviously cannot be removed subsequently from the substrate without destroying the integrity of the membrane. It is also important to verify that the solvent used to introduce the catalyst does not perturb the stability of the membrane. 

We Now Know What Controls Insolubility and Solubility of Hydrophobic Domains... 

Whether a particular hydrophobic region or domain of a model protein or of a natural protein associates with a second hydrophobic domain in the same molecule or a separate molecule, the same process of loss of solubility occurs. If the two hydrophobic domains can associate and if together they have so much hydrophobic hydration that their T, is below the temperature of the environment, they associate they are insoluble AG(solubility) is positive. 

Hydrophobic Hydration Disappears When a Pair of Hydrophobic Domains Associate, That Is, When the Pair of Domains Becomes Insoluble... 

The hydrophobically associated state represents the insolubility side of the T,-(solubility/insolubility)divide. As discussed in Chapter 5, contraction of the model elastic-contractile model proteins capable of inverse temperature transitions arises due to hydrophobic association. Hydrophobic association occurs, most fundamentally, on raising the temperature, on adding acid (H" ) to protonate and neutralize carboxylates (-COO ), and on adding calcium ion to bind to and neutralize carboxylates. Most dramatically, hydrophobic association occurs on dephosphorylation of (i.e., phosphate release from) protein, and it commonly occurs with formation of ion pairs or salt bridges between associated hydrophobic domains. 

The phenomena that drive muscle contraction—thermal activation, pH activation, calcium ion activation, stretch activation in insect flight muscle, and dephosphorylation itself—have all been shown to drive contraction by hydrophobic association in the elastic-contractile model proteins discussed in Chapter 5. As concerns a pair of hydrophobic domains, all of these processes surmount the T,-divide (the cusp of insolubility in Figure 7.1) to go from a soluble state to an insoluble state either by raising the... 

The phenomenon of hydrophobic association on raising the temperature, as noted above and treated in detail in Chapter 5, derives from the thermodynamics of structured water surrounding hydrophobic moieties. Hydrophobic hydration disappears, due to an unfavorable Gibbs free energy for solubility, as the temperature is raised from below to above the transition temperature that reaehes the cusp of insolubility represented in Figure 7.1. This causes the hydrophobic domains to separate from water by means of intra- and intermolecular hydrophobic association. 

Phosphate attached to a model protein is three to four times more effective on a mole fraction basis than carboxylate in raising the T,-divide for hydrophobic association, which we have shown is due to a decrease in hydrophobic hydration (see Figures 5.25 and 5.27). Dephosphorylation, therefore, would re-establish hydrophobic hydration and dramatically lower the Trdivide, which is to lower the temperature range of the cusp of insolubility to below physiological temperature. The result would be an insolubilization of hydrophobic domains (a hydrophobic association) that we consider to be the power stroke of muscle contraction. 

A modest increase in temperature moves the hemoglobin tetramer across the T,-divide, surmounting the cusp of insolubility, to arrive at the more insoluble side wherein pairs of hydrophobic domains have moved from having greater exposure to water to exhibiting more... 

Micelles are composed of amphiphilic block copolymers that self-assemble into spherical shapes of nanometer diameter due to energy minimization with the surrounding solvent. When exposed to a hydrophilic solvent the hydrophilic domains orient toward the solvent, while the hydrophobic domains orient toward the core and form a clump away from the solvent. In a similar manner, when amphiphilic molecules are exposed to a hydrophobic solvent they form micelles with a hydrophobic block on the surface and a hydrophilic block in the core. Micelles thus have a unique core-shell architecture composed of either hydrophobic or hydrophilic blocks depending on the chemical structures and the medium. The hydrophobic or hydrophilic core provides a reservoir for water-soluble or insoluble drugs and protects them from decomposition in order to maintain activity and stability. Stearic acid (SA)-grafted chitosan oligosaccharide (CSO-SA) formed... 

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