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Figure 23.6 Reduced set of data from Auton and Bolen (2004) demonstrating peptide backbone additivity and concentration scale independence of the peptide unit transferfree energy from water to 1 M TMAO, 1 M sarcosine, and 1 M urea. (A) Solubility of the linear N- acetyl glycinez amide peptides (open symbols) as a function of the number of internal peptide units (z — 0 to 4) and the cyclic glycylglycine (CGG) peptide (filled symbols) at 2 peptide units in molar (O), molal (◊), and mole fraction (□) concentration scales. (B) The constant increment method for determining the peptide unit transferfree energy from water to 1 MTMAO, 1 M sarcosine, and 1 Murea in which the intrinsic transfer-free energy on molar (O), molal (◊), and mole fraction (□) concentration scales is plotted as a function of the number of internal peptide units in the linear N-acetyl glycinez amide series of peptides. For z — 2, all scales coincide, and the slope of the constant increment represents the transfer-free energy of a single peptide unit (see right ordinate). (C) The intrinsic transfer-free energy of the peptide unit on molar (black), molal (gray), and mole fraction (white) concentration scales defined by dividing the intrinsic transfer-free energy of CGG by two.

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