Ionic interactions. Subnanoscale hydrophobic modulation of salt bridges in aqueous media.
Polar interactions such as electrostatic forces and hydrogen bonds play an essential role in biological molecular recognition. On a protein surface, polar interactions occur mostly in a hydrophobic environment because nonpolar amino acid residues cover ~75% of the protein surface. We report that ionic interactions on a hydrophobic surface are modulated by their subnanoscale distance to the surface. We developed a series of ionic head groups-appended self-assembled monolayers with C2, C6, C8, and C12 space-filling alkyl chains, which capture a dendritic guest via the formation of multiple salt bridges. The guest release upon protonolysis is progressively suppressed when its distance from the background hydrophobe changes from 1.2 (C2) to 0.2 (C12) nanometers, with an increase in salt bridge strength of ~3.9 kilocalories per mole.
Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Shuo
S
Chen
Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. itoh@macro.t.u-tokyo.ac.jp aida@macro.t.u-tokyo.ac.jp.
Yoshimitsu
Y
Itoh
Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan.
Takuya
T
Masuda
York Structural Biology Laboratory, Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
Seishi
S
Shimizu
Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China.
Jun
J
Zhao
Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China.
Jing
J
Ma
Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Shugo
S
Nakamura
Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Kou
K
Okuro
Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan. International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan. Graduate School of Chemical Science and Engineering, Hokkaido University, Sapporo 060-0810, Japan.
Hidenori
H
Noguchi
Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan. International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan. Graduate School of Chemical Science and Engineering, Hokkaido University, Sapporo 060-0810, Japan.
Kohei
K
Uosaki
Department of Chemistry and Biotechnology, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. itoh@macro.t.u-tokyo.ac.jp aida@macro.t.u-tokyo.ac.jp.
Takuzo
T
Aida
D000596:Amino Acids; D050091:Dendrimers / Q000737:chemistry; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D007477:Ions / Q000737:chemistry; D011506:Proteins / Q000737:chemistry*; D012492:Salts / Q000737:chemistry; D055672:Static Electricity; D014867:Water / Q000737:chemistry*
D000596:Amino Acids; D050091:Dendrimers; D007477:Ions; D011506:Proteins; D012492:Salts; D014867:Water