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Internal water molecules and magnetic relaxation in agarose gels

Vaca Chavez, Fabian LU ; Persson Sunde, Erik LU and Halle, Bertil LU (2006) In Journal of the American Chemical Society 128(14). p.4902-4910
Abstract
Agarose gels have long been known to produce exceptionally large enhancements of the water H-1 and H-2 magnetic relaxation rates. The molecular basis for this effect has not been clearly established, despite its potential importance for a wide range of applications of agarose gels, including their use as biological tissue models in magnetic resonance imaging. To resolve this issue, we have measured the 2 H magnetic relaxation dispersion profile from agarose gels over more than 4 frequency decades. We find a very large dispersion, which, at neutral pH, is produced entirely by internal water molecules, exchanging with bulk water on the time scale 10(-8)-10(-6) s. The most long-lived of these dominate the dispersion and give rise to a... (More)
Agarose gels have long been known to produce exceptionally large enhancements of the water H-1 and H-2 magnetic relaxation rates. The molecular basis for this effect has not been clearly established, despite its potential importance for a wide range of applications of agarose gels, including their use as biological tissue models in magnetic resonance imaging. To resolve this issue, we have measured the 2 H magnetic relaxation dispersion profile from agarose gels over more than 4 frequency decades. We find a very large dispersion, which, at neutral pH, is produced entirely by internal water molecules, exchanging with bulk water on the time scale 10(-8)-10(-6) s. The most long-lived of these dominate the dispersion and give rise to a temperature maximum in the low-frequency relaxation rate. At acidic pH, there is also a low-frequency contribution from hydroxyl deuterons exchanging on a time scale of 10(-4)S. Our analysis of the dispersion profiles is based on a nonperturbative relaxation theory that remains valid outside the conventional motional- narrowing regime. The results of this analysis suggest that the internal water molecules responsible for the dispersion are located in the central cavity of the agarose double helix, as previously proposed on the basis of fiber diffraction data. The magnetic relaxation mechanism invoked here, where spin relaxation is induced directly by molecular exchange, also provides a molecular basis for understanding the water H-1 relaxation behavior that governs the intrinsic magnetic resonance image contrast in biological tissue. (Less)
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publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of the American Chemical Society
volume
128
issue
14
pages
4902 - 4910
publisher
The American Chemical Society (ACS)
external identifiers
  • wos:000236770300081
  • scopus:33646061977
ISSN
1520-5126
DOI
10.1021/ja058837n
language
English
LU publication?
yes
id
65d9ad73-0e1f-4165-b89b-6a220952ea6d (old id 414008)
date added to LUP
2016-04-01 16:11:16
date last changed
2021-03-09 04:55:00
@article{65d9ad73-0e1f-4165-b89b-6a220952ea6d,
  abstract     = {Agarose gels have long been known to produce exceptionally large enhancements of the water H-1 and H-2 magnetic relaxation rates. The molecular basis for this effect has not been clearly established, despite its potential importance for a wide range of applications of agarose gels, including their use as biological tissue models in magnetic resonance imaging. To resolve this issue, we have measured the 2 H magnetic relaxation dispersion profile from agarose gels over more than 4 frequency decades. We find a very large dispersion, which, at neutral pH, is produced entirely by internal water molecules, exchanging with bulk water on the time scale 10(-8)-10(-6) s. The most long-lived of these dominate the dispersion and give rise to a temperature maximum in the low-frequency relaxation rate. At acidic pH, there is also a low-frequency contribution from hydroxyl deuterons exchanging on a time scale of 10(-4)S. Our analysis of the dispersion profiles is based on a nonperturbative relaxation theory that remains valid outside the conventional motional- narrowing regime. The results of this analysis suggest that the internal water molecules responsible for the dispersion are located in the central cavity of the agarose double helix, as previously proposed on the basis of fiber diffraction data. The magnetic relaxation mechanism invoked here, where spin relaxation is induced directly by molecular exchange, also provides a molecular basis for understanding the water H-1 relaxation behavior that governs the intrinsic magnetic resonance image contrast in biological tissue.},
  author       = {Vaca Chavez, Fabian and Persson Sunde, Erik and Halle, Bertil},
  issn         = {1520-5126},
  language     = {eng},
  number       = {14},
  pages        = {4902--4910},
  publisher    = {The American Chemical Society (ACS)},
  series       = {Journal of the American Chemical Society},
  title        = {Internal water molecules and magnetic relaxation in agarose gels},
  url          = {http://dx.doi.org/10.1021/ja058837n},
  doi          = {10.1021/ja058837n},
  volume       = {128},
  year         = {2006},
}