In 2010, a Van 't Hoff analysis was used to determine whether water preferentially forms a hydrogen bond with the C -terminus or the N -terminus of the amino acid proline. The equilibrium constant for each reaction was found at a variety of temperatures, and a Van 't Hoff plot was created. This analysis showed that enthalpically, the water preferred to hydrogen bond to the C -terminus, but entropically it was more favorable to hydrogen bond with the N -terminus. Specifically, they found that C -terminus hydrogen bonding was favored by 4.2–6.4 kJ/mol. The N -terminus hydrogen bonding was favored by 31–43 J/(K mol).