Contacts Between Alcohols in Water Are Random Rather than Hydrophobic.
Given the importance of water-mediated hydrophobic interactions in a wide range of biological and synthetic self-assembly processes, it is remarkable that both the sign and the magnitude of the hydrophobic interactions between simple amphiphiles, such as alcohols, remain unresolved. To address this question, we have performed Raman hydration-shell vibrational spectroscopy and polarization-resolved femtosecond infrared experiments, as well as random mixing and molecular dynamics simulations. Our results indicate that there are no more hydrophobic contacts in aqueous solutions of alcohols ranging from methanol to tertiary butyl alcohol than in random mixtures of the same concentration. This implies that the interaction between small hydrophobic groups is weaker than thermal energy fluctuations. Thus, the corresponding water-mediated hydrophobic interaction must be repulsive, with a magnitude sufficient to negate the attractive direct van der Waals interaction between the hydrophobic groups.
†Purdue University, Department of Chemistry, West Lafayette, Indiana 47907, United States.
Blake M
BM
Rankin
†Purdue University, Department of Chemistry, West Lafayette, Indiana 47907, United States.
Dor
D
Ben-Amotz
‡FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
Sietse T
ST
van der Post
‡FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
Huib J
HJ
Bakker
D000438:Alcohols / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D014867:Water / Q000737:chemistry*
D000438:Alcohols; D014867:Water
Raman spectroscopy; femtosecond IR spectroscopy; hydrophobic interactions; random mixing