Giuseppe CassoneL’importante lavoro - pubblicato sulla prestigiosissima rivista Science - vede Giuseppe Cassone, ricercatore dell’IPCF di Messina, tra gli autori.
A new spectroscopy reveals water’s quantum secrets
For the first time, researchers have exclusively observed molecules participating in hydrogen bonds in liquid water, measuring electronic and nuclear quantum effects that were previously accessible only via theoretical simulations. The work is the result of an international collaboration supervised by Sylvie Roke (EPFL, Lausanne) and composed by researchers from the Institute for Chemical-Physical Processes of the National Research Council (Messina, Italy), the Ecole Normale Superieure (Paris, France), ICTP (Trieste, Italy), and Queen’s University Belfast (Ireland) and has been published on Science [1].
Water is synonymous with life, but the dynamic, multifaceted interaction that brings H2O molecules together – the hydrogen bond – remains mysterious. Hydrogen bonds result when hydrogen and oxygen atoms between water molecules interact, sharing electronic charge in the process. This charge-sharing is a key feature of the three-dimensional ‘H-bond’ network that gives liquid water its unique properties, but quantum phenomena at the heart of such networks have thus far been understood only through theoretical simulations.
Now, researchers have developed a new method – correlated vibrational spectroscopy (CVS) – that enables them to measure how water molecules behave when they participate in H-bond networks. Crucially, CVS allows scientists to distinguish between such participating (interacting) molecules, and randomly distributed, non-hydrogen-bonded (non-interacting) molecules. By contrast, any other method reports measurements on both molecule types simultaneously, making it impossible to distinguish between them.
The team also conducted additional experiments and advanced supercomputating simulations aimed at using CVS to tease apart the electronic and nuclear quantum effects of H-bond networks, for example by changing the pH of water through the addition of hydroxide ions (making it more basic), or protons (more acidic). Hydroxide ions and protons participate in H-bonding, so changing the pH of water changes its reactivity. With CVS, it is now possible to quantify exactly how much extra charge hydroxide ions donate to H-bond networks (8%), and how much charge protons accept from it (4%) – precise measurements that could never have been done experimentally before. The different values were explained with the help of advanced ab initio and machine learning simulations.
The ability to quantify directly H-bonding strength is a powerful method that can be used to clarify molecular-level details of any solution, for example containing electrolytes, sugars, amino acids, DNA, or proteins. As CVS is not limited to water, it can also deliver a wealth of information on other liquids, systems, and processes.
[1] M. Flòr et al., Science DOI: 10.1126/science.ads4369
