MadSci Network: Biochemistry

Re: Why does the hydrophobic effect increase with increased temperature?

Date: Fri Apr 12 19:51:44 2002
Posted By: Maggie Guo, Grad student, Plant Physiologu and Molecular Biology Program, Dept.of Plant Biology, UIUC
Area of science: Biochemistry
ID: 1006778718.Bc

You are right, the “motive” behind hydrophobic effect is entropy, the disorder of a system. Hydrophobic effect separates 
hydrophobic(nonpolar) groups from H2O molecules(polar), this can be explained in two ways: 

First, when hydrophobic regions sequestered away from H2O molecules, the orderness of system decreased, entropy thus 
increased. Based on the first and second laws of thermodynamics, free energy *G=*H-T*S, can be negative, means hydrophobic 
effect happens spontaneously, and increased entropy leads to increase hydrophobic effect. 

Second, let’s imagine what would happen if hydrophobic group changes into aqueous system. The first step is like the formation of 
lipid vesicles1, an inner aqueous compartment is separated by segregated hydrophobic group. This process will break the original 
hydrogen bond between H2O molecules, thus *H is positive. The second step is the re-organization of H2O molecules in the inner 
aqueous compartments. Due to the re-organization of hydrogen bonds, orderness of inner aqueous compartments will increase 
(entropy decreases), means *S is negative. Thus *G=*H-T*S has positive result, thus hydrophobic groups can not dissolved in 
aqueous  phase spontaneously. 

In conclusion, *G=*H-T*S tells us increased entropy leads to increase hydrophobic effect; when temperature increases, entropy will 
also increase, hydrophobic effect will happy easier.

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