Researchers have investigated for the first time how two different forms of voda (ortho- and para-) behave differently when undergoing chemical reactions.
voda is a chemical entity, a molecule in which a single kyslík atom is linked to two hydrogen atoms (H2O). voda exists as liquid, solid (ice) and gas (vapours). It is among the few chemicals which do not contain uhlík and still can be liquid at room temperature (about 20 degrees). voda is ubiquitous and important for life. At the molecular level it is well known that everyday voda exists in two different forms but this information is not of common knowledge. These two forms of voda are called isomers and are referred to as ortho- or para- voda. The main difference between these forms is very subtle and is simply the relative orientation of the nuclear spins of the two hydrogen atoms which are aligned in either same or opposite direction, hence their names. This spin of hydrogen atoms is due to atomic physics though this phenomenon is not yet fully understood. These two forms have identical physical properties and it has been believed so far that they should also then have identical chemical properties.
V nedávné studii publikované v Příroda Communications, researchers from the University of Basel, Hamburg have for the first time investigated the difference in chemical reactivity of these two forms of voda and have proven that ortho- and para- forms react very differently. Chemical reactivity means the way or the ability by which a molecule undergoes a chemical reaction. The study involved separation of voda into its two isomeric forms (ortho- and para-) using an electrostatic deflector by involving electric fields. Since both these isomers are practically the same and have identical physical properties, this separation process is complex and challenging. The separation was achieved by this group of researchers by using a method based of electric fields developed by them for Free-Electron Laser Science. The deflector introduces an electric field to a beam of atomized water. Since there is crucial difference in nuclear spin in the two isomers, this slightly impacts the way by which atoms interact with this electric field. Therefore, as the water travels through the deflector it starts separating into its two forms ortho- and para-.
Researchers have demonstrated that para- voda reacts around 25 percent faster than ortho-water and its able to attract to a reakce partnera silněji. To je jednoznačně vysvětleno rozdílem v jaderném spinu, který ovlivňuje rotaci molekul vody. Také elektrické pole para-vody je schopno přitahovat ionty rychleji. Skupina dále provedla počítačové simulace molekul vody, aby potvrdila svá zjištění. Všechny experimenty byly provedeny s molekulami při velmi nízkých teplotách téměř -273 stupňů Celsia. To je důležitý faktor, jak autoři vysvětlují, že pouze za takových podmínek mohou být jednotlivé kvantové stavy a energetický obsah molekul dobře definovány a lépe kontrolovány. Což znamená, že molekula vody se stabilizuje jako jedna z jejích dvou forem a jejich rozdíly se stanou zjevnými a jasnými. Zkoumání chemických reakcí tak může odhalit základní mechanismy a dynamiku vedoucí k lepšímu porozumění. Praktické využití této studie však v současné době nemusí být příliš vysoké.
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Zdroje)
Kilaj A et al 2018. Pozorování různých reaktivit para a orto-vody vůči zachyceným diazenyliovým iontům. Nature Communications. 9 (1). https://doi.org/10.1038/s41467-018-04483-3
