ฺฺิิิBiochemists often refer to this kind of attraction between nonpolar groups as hydrophobic (see Chapter 12) interaction.Gradually, enough HbS molecules will aggregate to form a "superpolymer.
A general rule about the solubility of a substance is that the larger its molecules, the lowerits solubility because the solvation process becomes unfavorable with increasing molecular surface area. For this reason, proteins generally are not very soluble in water.therefore, the aggregated HbS molecules eventually precipitate out of solution.