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Hidden Isolated OH at the Charged Hydrophobic Interface Revealed by Two‐Dimensional Heterodyne‐Detected VSFG Spectroscopy
Author(s) -
Ahmed Mohammed,
Inoue Kenichi,
Nihonyanagi Satoshi,
Tahara Tahei
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202002368
Subject(s) - chemistry , cationic polymerization , hydrogen bond , spectroscopy , hydrophobic effect , molecule , sum frequency generation , infrared spectroscopy , ion , sum frequency generation spectroscopy , chemical physics , molecular dynamics , tetraphenylborate , photochemistry , computational chemistry , organic chemistry , physics , quantum mechanics , nonlinear system , nonlinear optics
Water around hydrophobic groups mediates hydrophobic interactions that play key roles in many chemical and biological processes. Thus, the molecular‐level elucidation of the properties of water in the vicinity of hydrophobic groups is important. We report on the structure and dynamics of water at two oppositely charged hydrophobic ion/water interfaces, that is, the tetraphenylborate‐ion (TPB − )/water and tetraphenylarsonium‐ion (TPA + )/water interfaces, which are clarified by two‐dimensional heterodyne‐detected vibrational sum‐frequency generation (2D HD‐VSFG) spectroscopy. The obtained 2D HD‐VSFG spectra of the anionic TPB − interface reveal the existence of distinct π‐hydrogen bonded OH groups in addition to the usual hydrogen‐bonded OH groups, which are hidden in the steady‐state spectrum. In contrast, 2D HD‐VSFG spectra of the cationic TPA + interface only show the presence of usual hydrogen‐bonded OH groups. The present study demonstrates that the sign of the interfacial charge governs the structure and dynamics of water molecules that face the hydrophobic region.