Researchers reveal behaviour of the tiniest water droplets

A new study by researchers at the University of California, San Diego, and Emory University has uncovered fundamental details about the hexamer structures that make up the tiniest droplets of water, the key component of life – and one that scientists still don't fully understand.

The research, recently published in The Journal of the American Chemical Society (JACS), provides a new interpretation for experimental measurements as well as a vital test for future studies of our most precious resource. Moreover, understanding the properties of water at the molecular level can ultimately have an impact on many areas of science, including the development of new drugs or advances in climate change research.

''About 60 per cent of our bodies are made of water that effectively mediates all biological processes,'' said Francesco Paesani, one of the paper's corresponding authors who is an assistant professor in the department of chemistry and biochemistry at UC San Diego and a computational researcher with the university's San Diego Supercomputer Center (SDSC). ''Without water, proteins don't work and life as we know it wouldn't exist. Understanding the molecular properties of the hydrogen bond network of water is the key to understanding everything else that happens in water. And we still don't have a precise picture of the molecular structure of liquid water in different environments.''

Researchers know that the unique properties of water are due to its capability of forming a highly flexible but still dense hydrogen bond network which adapts according to the surrounding environment. As described in the JACS paper, researchers have determined the relative populations of the different isomers of the water hexamer as they assemble into various configurations called 'cage', 'prism', and 'book'.

The water hexamer is considered the smallest drop of water because it is the smallest water cluster that is three dimensional, ie, a cluster where the oxygen atoms of the molecules do not lie on the same plane. As such, it is the prototypical system for understanding the properties of the hydrogen bond dynamics in the condensed phases because of its direct connection with ice, as well as with the structural arrangements that occur in liquid water.

This system also allows scientists to better understand the structure and dynamics of water in its liquid state, which plays a central role in many phenomena of relevance to different areas of science, including physics, chemistry, biology, geology, and climate research. For example, the hydration structure around proteins affects their stability and function, water in the active sites of enzymes affects their catalytic power, and the behavior of water adsorbed on atmospheric particles drives the formation of clouds.