Influence of temperature and solubility on substrate-specific peptide adsorption

2 Influence of temperature and solubility on substrate-specific peptide adsorption 

The probability for a macrostate with substrate and hh hydrophobic contacts is given by PT,sins, hh) hh) exp(—Assuming that the minimum of the free-energy 

The map of all possible free-energy minima in the range of external parameters T [0,10] andi 6 [—2,10] is shown in Fig, 14,2 for the peptide in the vicinity of a substrate that is equally attractive for both hydrophobic and polar monomers. Solid lines visualize paths through the free-energy landscape when changing temperature under constant solvent (i = const) conditions. Let us follow the exemplified trajectory for 5 = 2.5. 

Starting at very low temperatures, we know from the pseudophase diagram in Fig. 14.1(a) that the system resides in pseudophase ACT This means that the macrostate of the peptide is dominated by the class of compact, filmlike single-layer conformations. The system obviously prefers surface contacts at the expense of hydrophobic contacts. Nonetheless, the formation of compact hydrophobic domains in the two-dimensional topology is energetically favored, but maximal compactness is hindered by the steric influence of the substrate-binding polar residues. 

Increasing the temperature, the system experiences close to 7 035 a sharp first-order-like conformational transition, and a second layer forms (AC2). This is a mainly entropy-driven transition as the extension into the third dimension perpendicular to the substrate surface increases the number of possible peptide conformations. Furthermore, the loss of energetically favored substrate contacts of polar monomers is partly compensated by the energetic gain due to the more compact hydrophobic domains. Increasing the temperature further, the density of the hydrophobic domains reduces and overall compact conformations dominate in the globular pseudophase AG, Reaching AE, the number of 

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