Water removal, free energy consequence

It is worth noting that the free energy consequence of water removal, the osmotic pressure times the volume of water removed, need not be that great. The 0.15 ionic molarity of mammalian blood translates into an osmotic pressure on the order of 5-10 atm or 5-10 X 106 erg/cm3. One way to comprehend the meaning of this is to say that removal of a 5000-A3 volume of solute-inaccessible water will cost one kT per molecule or one RT per mole of protein. On this scale the osmotic work of removing 60 water molecules with a volume of AV = 30 X 60 = 1800 A3 is not so great. 

Amphiphilic molecules in aqueous solution have a tendency to seek out the surface and to orientate themselves in such a way as to remove the hydrophobic group from the aqueous environment and hence achieve a minimum free energy state (see Fig. 6.1). A consequence of the intrusion of surfactant molecules into the surface or interfacial layer is that some of the water molecules are effectively replaced by hydrocarbon or other nonpolar groups. Since the forces of inter-molecular attraction between water molecules and nonpolar groups are less than those... 

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