The incorporation of hydrophobic molecules in water seems very different from what we thought before. In water, hydrophobic molecules are surrounded by two different water populations: the inner shell forms a two-dimensional network of water molecules. The next layer is formed by a second population of water which is almost loose but forms slightly stronger hydrogen bonds with the bulk water. The assumption to date has been that “ice-like” tetrahedral water dominates in the innermost hydration envelope of hydrophobic molecules. The opposite is the case. These new discoveries were published by the team led by Professor Martina Havenith, Chair of Physical Chemistry II at the Ruhr-Universität Bochum (RUB) in the Journal of Physical Chemistry Letters June 18, 2020.
Prospects by THz spectroscopy and simulations
In their study, the researchers studied the network of hydrogen bonds around tert-butanol, a hydrophobic solvated alcohol, because the researchers use alcohols as prototype models of hydrophobic molecules. The team combined the results of terahertz spectroscopy (THz) and simulations.
They obtained a detailed image of the water layers surrounding the molecule. “We refer to the intimate layer like HB-wrap, where HB means water-hydrogen bond “, explains Martina Havenith. The upper layer is called HB-hydration2 in bulk, because it describes the interface with water in bulk. Combined, the two layers of the coating do not are sometimes no thicker than a single layer of water molecules. “Sometimes a single molecule of water can be part of both layers.”
The inner layer is more stable
When the temperature rises, the outer layer melts first and the HP envelope layer remains intact for longer. “The inner layer also has less freedom to form separate patterns due to the hydrophobicity of the solute,” says Havenith. “Since individual water molecules must always turn away from alcohol, they form a loose two-dimensional network.” The water molecules in the outer layer have more freedom of movement and therefore more possibilities to connect with other water molecules; researchers call this phenomenon the greatest entropy.
This type of interaction is relevant for protein folding processes as well as for the biomolecular recognition between a drug and its target molecule. Understanding the role of water plays a crucial role in the process.
V. Conti Nibali et al. Summary of hydrophobic hydration: locality issues, The Journal of Physical Chemistry Letters (2020). DOI: 10.1021 / acs.jpclett.0c00846
Quote: Researchers discover a new form for hydrophobic molecules in water (2020, June 29) retrieved June 29, 2020 from https://phys.org/news/2020-06-hydrophobic-molecules.html
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