Solubility of peptides and proteins

The relative hydrophilicities of the side-chains of the amino acids correlate well with 

Side hain Amino acid Hydrophobic LogPt 

High positive values indicate very hydrophobic amino acids, and negative values indicate amino acids with hydi ophilic character. From reference 3. 

The phase behaviour of protein solutions is affected by pH, ionic strength and temperature. 

Protein-water solutions sometimes exhibit critical solution temperatures (see Chapter 5 for a discussion of phase separation). Phase transitions are important not only in manufacture and formulation, but also because they 

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It is well known that conformational stability, and frequently the solubility, of peptides and proteins can be manipulated by exposure to different salts, organic solvents, organic polymers, and pH changes particularly near the isoelectric point or alternatively to aqueous-aqueous or aqueous-nonaqueous two- or multiphase liquid-liquid systems. In all of these cases, advantage is taken of the changes in the bulk hydration and molecular cavity properties of the... 

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