====== Proton Hopping ======

Proton hopping - a.k.a. the// Grotthuss Mechanism// has been said to be "the fastest known chemical reaction". The effects of which were first noted by [[https://en.wikipedia.org/wiki/Theodor_Grotthuss|Theodor Grotthuss]] in 1805, who was investigating the [[https://books.googleusercontent.com/books/content?req=AKW5QacC161-t2SdQxcf_fTrSh5Xm0QjX2lHsiXai2vEpVJxVESbWMsLdpBWjzoHpSNcIr_XFqeeNuoH68x6BheS7HKN9xfWzp1k7XIlnQJsHdiEd-hZLkY2HWKePCtSXfE8JqGNbWD4K6S5gOpv6YQSs5ISJamfW0TnPaEFx0tnPPd3fl2tmg7EczKpGQc33MvFWRDEU-OF3ujqjEum6RD8wxKXTj5gzbtPlmdph2Ph2_fvnJkDJOK-zys3orkpcM2nhnF84O6fI-K14q5ircQGWK-x_TBH-N5axGxniN48q03vBlJNlUk|decomposition of water]] under electrolysis.

In the process, an 'excess' proton (or its opposite, a proton-deficit) 'tunnels' through the hydrogen bond network of water molecules (or other hydrogen-bonded liquids). Leading to the formation, and simultaneous breaking, of covalent bonds with neighbouring molecules. On a local scale, this can occur in less than 2 picoseconds.

It has not yet been accurately explained.

>Although well studied for over 200 years, excess proton solvation and transport remains to this day mysterious, surprising, and perhaps even misunderstood."\\ \\ Source : [[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2548316/|J Phys Chem B. 111(17): 4300–4314. ]]

There are currently two hypotheses :

>1) Eigen to Zundel to Eigen (E–Z–E), on the basis of experimental NMR data, \\ 2) Zundel to Zundel (Z–Z), on the basis of molecular dynamics simulation.\\ \\ See: [[https://en.wikipedia.org/wiki/Grotthuss_mechanism|Wikipedia]]\\ \\ Editor's clarification :  The so-called //'Eigen'// cation is H<sub>9</sub>O<sub>4</sub><sup>+</sup> and the //'Zundel'// ion is H<sub>5</sub>O<sub>2</sub><sup>+ </sup>

It's also likely that some quantum physics effects are operating :

>Despite its widespread importance, the quantum character of proton transfer has not been satisfactorily elucidated."\\ \\ Source : [[https://science.sciencemag.org/content/275/5301/817|Science, Vol. 275, Issue 5301, pp. 817-820]]

//Note: //Proton hopping can occur in any solution or structure where the water content exceeds 20%. Therefore it's //probably in operation in the majority of biological systems.//

//Example :// It has recently been suggested that proton hopping may be an important mechanism for the rapid operation of electro-chemical nerve impulses. [[http://www.eurekaselect.com/144578/article|Proton Hopping as the Nerve Conduction Message]] C//urrent Computer Aided Drug Design,// 2016;12(4): 255-258.

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Also see: [[content:chemistry:water_clusters|Water clusters]]

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