This can be a bit shocking, but technically speaking, not all water on Earth is made up of H2A molecule.
Less than a century ago, the discovery of the isotope deuterium hydrogen – 2H, but often simplified to D – revealed the existence of another type of water with a chemical formula 2H2O or simply D2A.
Here’s how it differs. A typical hydrogen atom contains a proton in its nucleus. However, the deuterium isotope has an neutron in addition to the proton, giving the hydrogen atom a larger mass. Therefore, water formed with this type of heavy hydrogen is usually called … heavy water.
In addition to the key difference between H2O and D2O – which gives heavy water a density about 10% higher than ordinary water – these two types of water are chemically the same, although deuterium has a slightly different binding behavior from ordinary hydrogen (which is also known as protium). ).
Because of the altered bonding behavior – which can affect body chemistry if you ingest deuterium in D.2Oh – scientists generally say it’s not a great idea to drink heavy water, at least not in large doses.
However, small amounts are considered harmless to humans and are, in fact, often administered to participants in scientific experiments.
Due to such incidental consumption, which now returns almost a century ago, there has long been a question whether heavy water tastes the same as regular drinking water – or whether its subtle isotopic variation produces a different taste that humans she might perceive it.
“There is anecdotal evidence from the 1930s that the taste of pure D.2O is distinct from the neutral of pure H2Oh, being described mostly as “sweet,” explains in a new study an international team of researchers led by leading authors and biochemists Natalie Ben Abu and Philip E. Mason.
“However, Urey and Failla [the former being Harold Urey, the scientist who discovered deuterium] addressed this question in 1935, authoritatively concluding that on tasting “none of us could detect the slightest difference between the taste of ordinary distilled water and the taste of pure heavy water.”
But was this conclusion a little premature? Ben Abu and Mason say that Urey and Failla’s unequivocal opinion on this subject has effectively stifled further research in this area for much of the next century, at least in terms of testing human taste.
Tests in rats have shown that consuming too much water can be fatal for animals, but evidence as to whether rats can taste the difference remains unclear.
In the last two decades or so, advances in understanding human taste receptors have led to the reopening of old cases like these – and in their new research, Ben Abu, Mason and their team can finally confirm that there is something different about the taste of heavy water.
“Despite the fact that the two isotopes are chemically identical, we have conclusively shown that humans can distinguish by taste (which is based on chemical detection) between H2O and D2Oh, with the latter having a distinct sweet taste, “explains lead author and physical chemist Pavel Jungwirth of the Czech Academy of Sciences.
In a taste test experiment with 28 participants, most people were able to distinguish between H2O and D2O and tests with mixed amounts of water showed that higher proportions of heavy water were perceived as having a sweeter taste.
However, in the mice tests, the animals did not prefer to drink heavy water than ordinary water, although they showed a preference for sweetened water – suggesting that in mice, D2It doesn’t get the same sweet taste that people can perceive.
Other taste tests performed by the team suggest why this is the case, indicating that the receptivity of human taste to D2It is mediated by the TAS1R2 / TAS1R3 taste receptor, which is known to respond to sweetness in both natural sugars and artificial sweeteners.
Laboratory experiments with HEK 293 cells confirmed the same, showing solid responses in cells expressing TAS1R2 / TAS1R3 when exposed to D2A.
In addition, computational modeling with molecular dynamics simulations revealed slight differences in the interactions between proteins and H2O versus D.2Oh, which the team says needs further study to fully explain, but agrees with previous research and provides another example of quantum nuclear effects in chemical systems, including water.
“Our findings indicate that the human sweet taste receptor TAS1R2 / TAS1R3 is essential for sweetness D2Oh, “the authors conclude.
“At the molecular level, this general behavior can be traced back to the slightly stronger hydrogen bond in D2O vs H2Oh, that is due to a nuclear quantum effect, namely the difference in energy at zero point … Although clearly not a practical sweetener, heavy water provides a look into the wide open chemical space of sweet molecules. “
The findings are reported in Biology of communications.