Counterion Effect on Vibrational Relaxation and the Rotational Dynamics of Interfacial Water and an Anionic Vibrational Probe in the Confined Reverse Micelles Environment

Dexia Zhou; Qianshun Wei; Shuyan Wang; Xiaoqian Li; Hongtao Bian

doi:10.1021/acs.jpclett.8b03389

Counterion Effect on Vibrational Relaxation and the Rotational Dynamics of Interfacial Water and an Anionic Vibrational Probe in the Confined Reverse Micelles Environment

J Phys Chem Lett. 2019 Jan 17;10(2):176-182. doi: 10.1021/acs.jpclett.8b03389. Epub 2018 Dec 31.

Authors

Dexia Zhou¹, Qianshun Wei¹, Shuyan Wang¹, Xiaoqian Li¹, Hongtao Bian¹

Affiliation

¹ Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering , Shaanxi Normal University , Xi'an , 710119 , China.

PMID: 30582817
DOI: 10.1021/acs.jpclett.8b03389

Abstract

Vibrational relaxation and the rotational dynamics of water molecules encapsulated in reverse micelles (RMs) have been investigated by ultrafast infrared (IR) spectroscopy and two-dimensional IR (2D IR) spectroscopy. By changing the counterion of the hydrophilic headgroup in the RMs formed by Aerosol-OT (AOT) from Na⁺ to K⁺, Cs⁺ and Ca²⁺, we could determine the specific counterion effects on the rotational dynamics of water molecules. The orientational relaxation time constant of water decreases in the order Ca²⁺ > Na⁺ > K⁺ > Cs⁺. The SCN^- anionic probe and counterion can form ion pairs at the interfacial region of the RMs. The rotational dynamics of SCN^- anion significantly decreases because of the synergistic effects of confinement and the surface interactions in the interfacial region of the RMs. The results can provide a new understanding of the cationic Hofmeister effect at the molecular level observed in biological studies.