Proton and deuteron magnetic resonance studies of aqueous polysaccharides

Child, T. F.; Pryce, Norman G.; Tait, M. J.; Ablett, S.

doi:10.1039/c29700001214

Cited by 25 publications

(8 citation statements)

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“…Typical hysteresis loops were observed while cycling an agarose solution/gel between 95 and 5°C at 1°C min −1 using both NMR and small‐deformation rheology, similar to previous reports 38–40. In order to estimate the extent to which the hysteresis loop is governed by kinetic effects, rheological measurements at different cooling and heating rates were performed.…”

Section: Resultssupporting

confidence: 74%

Influence of thermal history on the structural and mechanical properties of agarose gels

et al. 2001

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Using a multitechnique approach, two temperature domains have been identified in agarose gelation. Below 35°C, fast gelation results in strong, homogeneous and weakly turbid networks. The correlation length, evaluated from the wavelength dependence of the turbidity, is close to values of pore size reported in the literature. Above 35°C, gelation is much slower and is associated with the formation of large‐scale heterogeneities that can be monitored by a marked change in the wavelength dependence of turbidity and visualised by transmission electron microscopy. Curing agarose gels at temperatures above 35°C, and then cooling them to 20°C, produces much weaker gels than those formed directly at 20°C. Dramatic reductions in the elastic modulus and failure strain and stress are found in this case as a result of demixing during cure. An interpretation, based on the kinetic competition between osmotic forces (in favor of phase separation) and elastic forces (that prevent it) is proposed. © 2001 John Wiley & Sons, Inc. Biopolymers 59: 131–144, 2001

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Section: Resultssupporting

confidence: 74%

Influence of thermal history on the structural and mechanical properties of agarose gels

et al. 2001

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“…We believe that the contribution from spin diffusion is negligible for the following reasons: (a) As shown in Table II, T1 for deuterons in deuterated water/agarose samples s much shorter than in free D20. A similar result was found by Child et al (17). Spin diffusion would not be effective for deuterons on account of their small magnetic moment, so this indicates the existence of some other relaxation mechanism for water deuterons and hence for water protons.…”

Section: Identification Of the Modified Proton States In Hydrated Agasupporting

confidence: 85%

A Nuclear Magnetic Resonance Study of Hydrated Systems Using the Frequency Dependence of the Relaxation Processes

Outhred¹,

George²

1973

Biophysical Journal

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A practical method is described for determining some characteristics of the spectrum of proton mobilities in a hydrated system from the frequency dependence of the nuclear magnetic resonance (NMR) relaxation processes. The technique is applied to water in association with agarose and gelatin. The results for agarose are consistent with the hypothesis that a fraction of the protons is distributed over states of reduced mobility and exchanges rapidly with the remaining fraction which is attributed to water in the normal state. No variation in the characteristics of the modified fraction could be detected for water concentrations in the range 1.2-50 g H(2)O/g agarose. Within the modified fraction, higher mobilities are more common than low mobilities; at 1.2 g H(2)O/g agarose, not more than 10% of the proton population has mobilities more than 100 times smaller than normal. The modified proton fraction is tentatively identified with agarose hydroxyl protons and possibly water molecules bound to the polymer. Proton states with mobilities intermediate between water and ice have also been detected in hydrated gelatin. As in agarose, higher mobilities are the most common. In contrast to agarose, the characteristics of the modified proton states are markedly dependent on water concentration. They are tentatively attributed to gelatin protons coupled for spinlattice relaxation with those of the bulk phase by exchange and spin diffusion.

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“…Molecular-level information about the structure and dynamics of native gels is contained in the magnetic relaxation rates associated with the water NMR signal. It has long been known that gelation of agarose is accompanied by a dramatic broadening of the water 1 H resonance; the transverse relaxation rate, R 2 , increasing by 2 orders of magnitude even at agarose concentrations of a few percent. − In contrast, little or no relaxation enhancement was observed upon gelation of starch, cellulose derivatives, or gelatin. The exceptional relaxation enhancement in agarose gels was originally attributed to a long-ranged perturbation of the bulk water in the gel, induced by a peculiar matching of the agarose molecule to the presumed “icelike” water structure. , Similar ideas of surface-induced long-range ordering and slowing down of water were invoked to explain water 1 H and 2 H relaxation enhancements in other gels and in biological tissues. − If these ideas were correct, one would also expect a large reduction of the water self-diffusion coefficient, D , in these systems.…”

Section: Introductionmentioning

confidence: 99%

Internal Water Molecules and Magnetic Relaxation in Agarose Gels

2006

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Agarose gels have long been known to produce exceptionally large enhancements of the water 1H and 2H 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 2H 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 1H relaxation behavior that governs the intrinsic magnetic resonance image contrast in biological tissue.

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Proton and deuteron magnetic resonance studies of aqueous polysaccharides

Cited by 25 publications

References 0 publications

Influence of thermal history on the structural and mechanical properties of agarose gels

Influence of thermal history on the structural and mechanical properties of agarose gels

A Nuclear Magnetic Resonance Study of Hydrated Systems Using the Frequency Dependence of the Relaxation Processes

Internal Water Molecules and Magnetic Relaxation in Agarose Gels

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