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  4. Challenges in preparing, preserving and detecting para-water in bulk: overcoming proton exchange and other hurdles
 
research article

Challenges in preparing, preserving and detecting para-water in bulk: overcoming proton exchange and other hurdles

Mammoli, Daniele  
•
Salvi, Nicola  
•
Milani, Jonas  
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2015
Physical Chemistry Chemical Physics

Para-water is an analogue of para-hydrogen, where the two proton spins are in a quantum state that is antisymmetric under permutation, also known as singlet state. The populations of the nuclear spin states in para-water are believed to have long lifetimes just like other Long-Lived States (LLSs). This hypothesis can be verified by measuring the relaxation of an excess or a deficiency of para-water, also known as a "Triplet-Singlet Imbalance'' (TSI), i.e., a difference between the average population of the three triplet states T (that are symmetric under permutation) and the population of the singlet state S. In analogy with our recent findings on ethanol and fumarate, we propose to adapt the procedure for Dissolution Dynamic Nuclear Polarization (D-DNP) to prepare such a TSI in frozen water at very low temperatures in the vicinity of 1.2 K. After rapid heating and dissolution using an aprotic solvent, the TSI should be largely preserved. To assess this hypothesis, we studied the lifetime of water as a molecular entity when diluted in various solvents. In neat liquid H2O, proton exchange rates have been characterized by spin-echo experiments on oxygen-17 in natural abundance, with and without proton decoupling. One-dimensional exchange spectroscopy (EXSY) has been used to study proton exchange rates in H2O, HDO and D2O mixtures diluted in various aprotic solvents. In the case of 50 mM H2O in dioxane-d(8), the proton exchange lifetime is about 20 s. After dissolving, one can observe this TSI by monitoring intensities in oxygen-17 spectra of H2O (if necessary using isotopically enriched samples) where the AX(2) system comprising a "spy'' oxygen A and two protons X-2 gives rise to binomial multiplets only if the TSI vanishes. Alternatively, fast chemical addition to a suitable substrate (such as an activated aldehyde or ketone) can provide AX2 systems where a carbon-13 acts as a spy nucleus. Proton signals that relax to equilibrium with two distinct time constants can be considered as a hallmark of a TSI. We optimized several experimental procedures designed to preserve and reveal dilute para-water in bulk.

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Type
research article
DOI
10.1039/c5cp03350k
Web of Science ID

WOS:000362679300039

Author(s)
Mammoli, Daniele  
Salvi, Nicola  
Milani, Jonas  
Buratto, Roberto  
Bornet, Aurelien  
Sehgal, Akansha Ashvani
Canet, Estel  
Pelupessy, Philippe  
Carnevale, Diego  
Jannin, Sami  
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Date Issued

2015

Publisher

Royal Society of Chemistry

Published in
Physical Chemistry Chemical Physics
Volume

17

Issue

40

Start page

26819

End page

26827

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LRMB  
Available on Infoscience
December 2, 2015
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/121354
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