Testing the Core/Shell Model of Nanoconfined Water in Reverse Micelles Using Linear and Nonlinear IR Spectroscopy

Piletic, Ivan R.; Moilanen, David E.; Spry, D. B.; Levinger, Nancy E.; Fayer, M. D.

doi:10.1021/jp061065c

Cited by 331 publications

(817 citation statements)

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“…The anisotropy decay of HOD in pure water is a single exponential with a time constant of 2.6 ps (18,41). However, the anisotropy decays in aqueous NaBr solutions are clearly not a single exponential and are fit very well by a biexponential function of the form…”

Section: Resultsmentioning

confidence: 98%

“…Experiments on HOD in water nanopools in small AOT reverse micelles (18) and in nanoscopic water channels in Nafion fuel cell membranes (19) also displayed biexponential decays of the anisotropy. Both of these systems have interfacial layers composed of sulfonate head groups with associated sodium counter ions.…”

Section: Resultsmentioning

confidence: 99%

“…However, this is not necessarily true. For example, it has been shown recently that the blue-shift of the water spectrum in small sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles is actually caused by the superposition of two distinct spectra of water molecules (18). One of the spectra is the bulk-like spectrum of water molecules in the core of the reverse micelle.…”

Section: Resultsmentioning

confidence: 99%

“…Orientational relaxation dynamics are determined from the anisotropy decay, r(t), which is calculated from the parallel and perpendicular components of the pump-probe signals (18).…”

Section: Resultsmentioning

confidence: 99%

“…These experiments directly examine the dynamics of water rather than study the indirect influence of water dynamics on a probe molecule (13). The ultrafast 2D IR vibrational echo experiments on water (7,8) and other hydrogen-bonded systems (14) build upon earlier IR pump-probe experiments that have been extensively used to study the vibrational population relaxation and orientational relaxation dynamics of pure water (15,16), water in nanoscopic environments (17)(18)(19), and ionic solutions (20). Pump-probe experiments have also been used to investigate the hydrogen bond dynamics in aqueous solutions (20) and other hydrogen-bonded liquids (21).…”

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confidence: 99%

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Hydrogen bond dynamics in aqueous NaBr solutions

Park

Fayer

2007

Proc. Natl. Acad. Sci. U.S.A.

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294

403

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Hydrogen bond dynamics of water in NaBr solutions are studied by using ultrafast 2D IR vibrational echo spectroscopy and polarization-selective IR pump-probe experiments. The hydrogen bond structural dynamics are observed by measuring spectral diffusion of the OD stretching mode of dilute HOD in H2O in a series of high concentration aqueous NaBr solutions with 2D IR vibrational echo spectroscopy. The time evolution of the 2D IR spectra yields frequency-frequency correlation functions, which permit quantitative comparisons of the influence of NaBr concentration on the hydrogen bond dynamics. The results show that the global rearrangement of the hydrogen bond structure, which is represented by the slowest component of the spectral diffusion, slows, and its time constant increases from 1.7 to 4.8 ps as the NaBr concentration increases from pure water to Ϸ6 M NaBr. Orientational relaxation is analyzed with a wobbling-in-a-cone model describing restricted orientational diffusion that is followed by complete orientational randomization described as jump reorientation. The slowest component of the orientational relaxation increases from 2.6 ps (pure water) to 6.7 ps (Ϸ6 M NaBr). Vibrational population relaxation of the OD stretch also slows significantly as the NaBr concentration increases.ultrafast 2D IR spectroscopy ͉ water dynamics in ionic solutions W ater plays an important role in chemical and biological processes. In aqueous solutions, water molecules dissolve ionic compounds, charged chemical species, and biomolecules by forming hydration shells (layers) around them. Pure water undergoes rapid structural evolution of the hydrogen bond network that is responsible for water's unique properties (1). A question of fundamental importance is how the dynamics of water in the immediate vicinity of an ion or ionic group differ from those of pure water. For monatomic ions, molecular ions, charged groups of large molecules, or charged amino acids on the surfaces of proteins, the basic structure of hydration shells is determined by ion-dipole interactions between water molecules and the charged group (2, 3). Such ion-dipole interactions will influence both the structure and dynamics of water in the proximity of ions. Water dynamics in ion hydration shells play a significant role in the nature of systems such as proteins and micelles (3) and in processes such as ion transport through transmembrane proteins (4).Over the last several years, the application of ultrafast IR vibrational echo spectroscopy (5, 6), particularly 2D IR vibrational echo experiments, (7, 8) combined with molecular dynamics (MD) simulations (9-12) have greatly enhanced understanding of the hydrogen bond dynamics in pure water. These experiments directly examine the dynamics of water rather than study the indirect influence of water dynamics on a probe molecule (13). The ultrafast 2D IR vibrational echo experiments on water (7, 8) and other hydrogen-bonded systems (14) build upon earlier IR pump-probe experiments that have been extensively used to study ...

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…Orientational relaxation dynamics are determined from the anisotropy decay, r(t), which is calculated from the parallel and perpendicular components of the pump-probe signals (18).…”

Section: Resultsmentioning

confidence: 99%