Unveiling two deuteration effects on hydrogen-bond breaking process of water isotopomers
The physicochemical and biological properties of hydrogen-bonded systems are significantly affected by nuclear quantum effects including zero-point energies of vibrational modes, proton delocalization, and tunneling effect.
These originate from the extremely low nuclear mass of hydrogen; thus, hydrogen-bonded systems show remarkable isotope effects upon deuteration. In the 1930s, Ubbelohde first proposed that deuteration elongates and weakens hydrogen bonds in many hydrogen-bonded systems.
Ever since, such an isotope effect has been widely confirmed and is nowadays well known as the "Ubbelohde effect." In contrast, deuterating water molecules in liquid water and ice elongates but strengthens hydrogen bonds.
Despite intensive experimental and theoretical studies in more than three-quarters of a century, the molecular-level origin of this peculiar isotope effect on water hydrogen bonds has been unclear.
Very recently, researchers led by Toshiki Sugimoto, Associate Professor at the Institute for Molecular Science, have tackled the longstanding mystery: how do more expanded D2O aggregates form stronger hydrogen bonds than H2O aggregates, in contrast to the hydrogen-bonded systems composed of bulky constituent molecules?
By means of isotope selective measurements on sublimation of isotope-mixed ice with various H/D isotopic compositions, the researchers have made a new discovery to unravel the mystery; the isotope effect on the strength of hydrogen bonds are governed by two deuteration effects: (1) the bond-strengthening effect derived from zero-point energy of hindered rotational motion, and (2) the bond-weakening (and elongating) effect derived from quantum anharmonic coupling between inter- and intramolecular modes.
The most important concept is that the deuteration effect (1) derived from rotational motion plays crucial roles in the bond breaking process of extremely small and light molecules. In the case of water aggregates, huge isotopic difference in the zero-point energy of hindered rotation brings out a peculiar nature of the bond strengthening effect (1) overwhelming over the bond-weakening effect (2), leading to the unique isotope effect: deuterated water molecules form longer but stronger hydrogen bonds than hydrogenated water molecules.
In contrast, in the case of other typical hydrogen-bonded systems composed of larger and heavier constituent molecules, such as oxalic acid dihydrate, benzoic acid, succinic acid, and cyclohexane/Rh(111), the isotopic differences in the zero-point energy of hindered rotation are negligibly small. Therefore, only the bond-weakening effect (2) is predominant in the isotope effect on their binding energy, resulting in the longer and weaker hydrogen bonds in deuterated systems than hydrogenated systems.
Thus, the isotopic differences in the strength of hydrogen bonds are determined by a delicate balance between the competing two deuteration effects (1) and (2), while those in hydrogen-bond length, i.e. geometrical isotope effect, are basically dominated by the deuteration effect (2). "These results and concepts provide a new basis for our fundamental understanding of the highly quantum water hydrogen bonds," says Sugimoto.
Toshiki Sugimoto | EurekAlert!
New treatment for brain tumors uses electrospun fiber
03.12.2019 | University of Cincinnati
A window into evolution
03.12.2019 | Leibniz Institute of Plant Genetics and Crop Plant Research
With ultracold chemistry, researchers get a first look at exactly what happens during a chemical reaction
The coldest chemical reaction in the known universe took place in what appears to be a chaotic mess of lasers. The appearance deceives: Deep within that...
Abnormal scarring is a serious threat resulting in non-healing chronic wounds or fibrosis. Scars form when fibroblasts, a type of cell of connective tissue, reach wounded skin and deposit plugs of extracellular matrix. Until today, the question about the exact anatomical origin of these fibroblasts has not been answered. In order to find potential ways of influencing the scarring process, the team of Dr. Yuval Rinkevich, Group Leader for Regenerative Biology at the Institute of Lung Biology and Disease at Helmholtz Zentrum München, aimed to finally find an answer. As it was already known that all scars derive from a fibroblast lineage expressing the Engrailed-1 gene - a lineage not only present in skin, but also in fascia - the researchers intentionally tried to understand whether or not fascia might be the origin of fibroblasts.
Fibroblasts kit - ready to heal wounds
Research from a leading international expert on the health of the Great Lakes suggests that the growing intensity and scale of pollution from plastics poses serious risks to human health and will continue to have profound consequences on the ecosystem.
In an article published this month in the Journal of Waste Resources and Recycling, Gail Krantzberg, a professor in the Booth School of Engineering Practice...
Conventional light microscopes cannot distinguish structures when they are separated by a distance smaller than, roughly, the wavelength of light. Superresolution microscopy, developed since the 1980s, lifts this limitation, using fluorescent moieties. Scientists at the Max Planck Institute for Polymer Research have now discovered that graphene nano-molecules can be used to improve this microscopy technique. These graphene nano-molecules offer a number of substantial advantages over the materials previously used, making superresolution microscopy even more versatile.
Microscopy is an important investigation method, in physics, biology, medicine, and many other sciences. However, it has one disadvantage: its resolution is...
03.12.2019 | Event News
15.11.2019 | Event News
15.11.2019 | Event News
03.12.2019 | Medical Engineering
03.12.2019 | Life Sciences
03.12.2019 | Physics and Astronomy