Observation of Immobilized Water Molecules around Hydrophobic Groups

Abstract

We have used femtosecond midinfrared spectroscopy to study the orientational mobility of water molecules in the hydration shells of hydrophobic groups. Our results show that hydrophobic groups are surrounded by a number of water molecules that display much slower orientational dynamics than the bulk liquid and that are therefore effectively immobilized. It turns out that each methyl group is surrounded by four immobilized water OH groups.

Reduced coupling of water molecules near the surface of reverse micelles

“…40,41,81,82 Isotopic dilution leads to cancelation of both inter-and intramolecular couplings between OH (or OD) oscillators. In this case, transient anisotropy experiments on an OH/OD oscillator would provide information explicitly on the orientational dynamics of water molecules.…”

Structural Inhomogeneity of Water by Complex Network Analysis

“…Starting with a paper by Röntgen more than a century ago [1], there has been a long-standing debate about the relative importance of local ice-like structures, both in bulk water [2][3][4][5] as well as in the context of the hydrophobic effect [6,7]. The density maximum at 4 • C is a manifestation of the competition between two driving forces, i.e.…”

Effect of Surface Polarity on the Structure and Dynamics of Water in Nanoscale Confinement

“…Experimental techniques such as nuclear magnetic resonance (NMR), dielectric relaxation, and quasielastic neutron scattering (QENS) have shown that water in the proximity of proteins and micelles exhibits an average mobility that is lower than its bulk counterpart. 10 However, since these techniques average a response over all molecules, 24 they are unable to reflect the changes undergone by dynamic properties as they transition from the bulk toward the hydration layer. Moreover, the extent to which confinement affects water dynamics is a matter of much contention.…”

“…26 Other techniques such as atomic force microscopy (AFM) and scanning tunneling microscopy (STM), although intrusive, have proven useful for thin water films on solid surfaces, but less successful at liquid interfaces, while X-ray photoelectron spectroscopy (XPS), X-ray absorption, and attenuated total reflection (ATR) infrared spectroscopy have large penetration lengths (g1 nm and g100 nm, respectively) that hinder the study of the buried interface. 23 Nonetheless, emerging experimental techniques such as sum-frequency vibrational spectroscopy (SFVS), 23,27 and femtosecond mid-infrared spectroscopy 24 hold promise as local probes of water in the (first) hydration layer. Recently, Rezus and Bakker 24 reported what appears to be the first direct proof of the existence of immobilized water molecules in the hydration layer of hydrophobes, thereby confirming certain aspects of the "iceberg" model proposed by Frank and Evans more than 60 years ago.…”

“…23 Nonetheless, emerging experimental techniques such as sum-frequency vibrational spectroscopy (SFVS), 23,27 and femtosecond mid-infrared spectroscopy 24 hold promise as local probes of water in the (first) hydration layer. Recently, Rezus and Bakker 24 reported what appears to be the first direct proof of the existence of immobilized water molecules in the hydration layer of hydrophobes, thereby confirming certain aspects of the "iceberg" model proposed by Frank and Evans more than 60 years ago. 28 Despite the considerable progress shown by different experimental techniques, molecular simulations continue to be a powerful tool for studying interfacial systems, often complementing and guiding the interpretation of experimental results.…”