An Ion's Perspective on the Molecular Motions of Nanoconfined Water: a Two-dimensional Infrared Spectroscopy Study

Overview

Journal J Phys Chem B

Publisher American Chemical Society

Specialty Chemistry

Date 2013 Jul 17

PMID 23855349

Citations 2

Authors

Prabhat K Singh

Daniel G Kuroda

Robin M Hochstrasser

Affiliations

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Abstract

The vibrational population relaxation and hydration shell dynamics of the symmetric tricyanomethanide (TCM) anion are investigated in a sodium bis(2-ethylhexyl)sulfosuccinate reverse micelle as a function of the water pool radius. Two-dimensional infrared (IR) spectroscopy in combination with linear absorption and ultrafast IR pump-probe spectroscopy is utilized in this study. Spectroscopic measurements show that the anion has two bands in the 2160-2175 cm(-1) region, each with its own spectroscopic signatures. Analysis of the vibrational dynamics shows that the two vibrational bands are consistent with the anion located either at the interface or in the water pool. The sensitivity of the TCM anion to the environment allows us to unequivocally monitor the vibrational and hydration dynamics of the anion in those two different environments. A TCM anion located at the interface does not show any significant variation of the vibrational dynamics with the water pool size. On the contrary, the TCM anion inside the water pool exhibits a large and nonlinear variation of the vibrational lifetime and the frequency-frequency correlation time with the pool radius. Moreover, for the solvated anion in water pools of 49 Å in radius (W0 = 30), the vibrational lifetime reaches the values observed for the anion in bulk water while the frequency-frequency correlation time shows a characteristic time higher than that observed in the bulk. In addition, for the first time a model is developed and used to explain the observed nonlinear variation of the spectroscopic observables with the pool size. This model attributes the changes in the vibrational dynamics of the TCM anion in the water pool to the slow and radius-dependent water dynamics present in the confined environment of a reverse micelle.

Citing Articles

Assessing the Location of Ionic and Molecular Solutes in a Molecularly Heterogeneous and Nonionic Deep Eutectic Solvent.

Chen X, Cui Y, Gobeze H, Kuroda D J Phys Chem B. 2020; 124(23):4762-4773.

PMID: 32421342 PMC: 7304071. DOI: 10.1021/acs.jpcb.0c02482.

Properties of water confined in ionic liquids.

Saihara K, Yoshimura Y, Ohta S, Shimizu A Sci Rep. 2015; 5:10619.

PMID: 26024339 PMC: 4448549. DOI: 10.1038/srep10619.

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