Nonpolar Water Clusters: Proton Nuclear Magnetic Resonance Spectroscopic Evidence for Transformation from Polar Water to Nonpolar Water Clusters in Liquid State

Abstract

The hydrophilic/hydrophobic interactions of water are important in biological and chemical self-assembly phenomena. Water clusters in hydrophobic environments exhibit a unique morphology. Their process of formation and nonpolar properties have been extensively studied, but no direct experimental evidence has been available until now. This study provides spectroscopic evidence for the transformation of water to nonpolar configuration via clustering. Although individual water molecules form hydrogen bonds with the hydroxyl protons of n-hexanol when codissolved in a nonpolar solvent (toluene-d 8 ), the water clusters are comprised solely of hydrogen bonds between water molecules and do not form hydrogen bonds with the hydroxyl protons of n-hexanol. This behavior indicates that the water clusters are nonpolar rather than polar. This study reports the first example of nonpolar water configuration produced via a liquid-state clustering. This property is a common and important interfacial phenomenon of water in chemistry, biology, materials science, geology, and meteorology.

Solvent Effects in the Preparation of Catalysts Using Activated Carbon as a Carrier

“…Substances with similar structures dissolve each other. Water is a polar material, whereas AC is a nonpolar material [ 26 ]; thus, AC is not dissolved well in solutions prepared using water. To demonstrate that the reduction in solution polarity can make AC better wetted by the solution, contact angle tests were conducted for water and four mixed solvents using AC as the substrate, as shown in Figure 2 .…”

Ice-Like Dynamics of Water Clusters

“…Furthermore, the dynamics of water in cells are key to biological processes, and water molecules confined in hydrophobic nanochannels have attracted considerable interest in materials science because the water dynamics in these nanochannels change drastically even under the same thermodynamic conditions . Using 1 H nuclear magnetic resonance ( 1 H NMR) spectroscopy, we have recently identified a metastable state of water molecules (water clusters) in hydrophobic solvents, in addition to water molecules dissolved in the solvents and a small bulk water domain that was phase-separated from the solvents. − Water clusters are formed from supersaturated dissolved water and are associated with a temperature increase and decrease (or sonication). As the solubility of water in hydrophobic solvents increases with increasing temperature, the dissolution of water clusters increases.…”

Two States of Water Converge to One State below 215 K

“…1 H NMR spectroscopy is one of many techniques that has been used to study the dynamics of water in confined geometries. − It is an excellent method for observing hydrogen bonding in water. When water forms hydrogen bonds, the electron density around hydrogen decreases due to the highly electronegative oxygen atom.…”

“…Proton signals of methanol (3.0 and 0.0 ppm) and residual proton signals of toluene- d 8 (7.0 and 2.1 ppm) were also observed. We have previously discussed the sharp low-entropy water clusters signal as cubic octamer, and the precise structure and properties have been investigated. , …”

“…We have previously discussed the sharp low-entropy water clusters signal as cubic octamer, 19 and the precise structure and properties have been investigated. 20,25 The signal from the hydroxyl proton of methanol with a low chemical shift (0.0 ppm) indicates a small contribution of hydrogen bonding, suggesting that methanol is dissolved in toluene-d 8 as single molecules and does not aggregate with water molecules. 30 Upon cooling, the chemical shifts of the low-entropy water clusters and small bulk water, which are composed of hydrogen bonds, increase because the length of the hydrogen bond is shortened and the electron shielding of the hydrogen nucleus decreases (Figure 2b).…”