A unified view of relaxation in protein solutions and tissue, including hydration and magnetization transfer

Koenig, Seymour H.; Brown, Rodney D.; Ugolini, Raphael

doi:10.1002/mrm.1910290114

Cited by 101 publications

(105 citation statements)

References 30 publications

(15 reference statements)

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“…This rigorous result, which is also valid outside the dilute regime, follows from Eqs. [3], [5], [6], [8]- [11], [15], and [38]. Seen in the light of our theoretical analysis, the absence of a pronounced high-frequency step in water-1 H dispersion profiles from tissue (1,2) and biopolymer gels (Vaca Chávez and Halle, this issue) indicates that the effects of internal motions and spin diffusion are unimportant.…”

Section: Spin Diffusionmentioning

confidence: 70%

“…The internal-motion spectral densities in Eq. [5] can therefore be neglected. To assess the accuracy of this approximation, we perform model calculations for a protein with internal motions.…”

Section: Biopolymer Modelmentioning

confidence: 99%

“…The spectral density functions for these dipole couplings are given by Eqs. [3], [5], and [6]. As usual, we neglect cross-correlations between different proton pairs (13).…”

Section: Extended Solomon Equationsmentioning

confidence: 99%

“…This has led to the mistaken belief that the motional correlation time (deduced from the dispersion midpoint) is invariant with respect to system properties and temperature (2,4,5). In fact, the apparent correlation time obtained in this way is not related to molecular motions.…”

Section: Adiabatic Regimementioning

confidence: 99%

“…Previous water-1 H and 2 H MRD studies of chemically cross-linked protein gels revealed a remarkable invariance of the dispersion frequency with respect to temperature and biopolymer (2,4,5). The authors interpreted that finding in terms of the two-pool model by postulating the existence, in all investigated proteins, of a class of water molecules with a long (1 s), but temperature-independent, residence time (2,4,5). Such unphysical assumptions are not required by the EMOR model, which predicts an invariant dispersion frequency that is equal to the residual dipole frequency ⍀ D , in the adiabatic regime.…”

Section: Other Modelsmentioning

confidence: 99%

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Molecular theory of field‐dependent proton spin‐lattice relaxation in tissue

Halle

2006

Magnetic Resonance in Med

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A molecular theory is presented for the field-dependent spinlattice relaxation time of water in tissue. The theory attributes the large relaxation enhancement observed at low frequencies to intermediary protons in labile groups or internal water molecules that act as relaxation sinks for the bulk water protons. Exchange of intermediary protons not only transfers magnetization to bulk water protons, it also drives relaxation by a mechanism of exchange-mediated orientational randomization (EMOR). An analytical expression for T 1 is derived that remains valid outside the motional-narrowing regime. Cross-relaxation between intermediary protons and polymer protons plays an important role, whereas spin diffusion among polymer protons can be neglected. For sufficiently slow exchange, the dispersion midpoint is determined by the local dipolar field rather than by molecular motions, which makes the dispersion frequency insensitive to temperature and system composition. The EMOR model differs fundamentally from previous models that identify collective polymer vibrations or hydration water dynamics as the molecular motion responsible for spin relaxation. Unlike previous models, the EMOR model accounts quantitatively The spin-lattice relaxation time, T 1 , of tissue water is one of the principal contrast modalities in clinical MRI. Although the phenomenology of water-1 H relaxation in soft tissue is well documented (1-3), the molecular determinants of natural and pathological T 1 variations have not been established. Because of the molecular-level complexity of biological tissue, studies aimed at unraveling the relaxation mechanism have often employed aqueous gels as tissue models. The magnetic relaxation dispersion (MRD), that is, the variation of R 1 ϭ 1/T 1 with magnetic field strength (or Larmor frequency) is particularly informative about the molecular motions that induce spin relaxation. However, even though numerous MRD studies of tissue models have been conducted, we still cannot predict the MRD profile from known system properties. There is even disagreement about the nature of the molecular motions that are responsible for the observed relaxation dispersion. For example, some authors invoke slow water dynamics in the hydration layer at the biopolymer surface (4 -6), while others focus on collective biopolymer vibrations (7-10).We recently reported an extensive set of water-2 H MRD data from polysaccharide and polypeptide gels (11) (Vaca Chávez et al., submitted). Since cross-relaxation and spin diffusion can be neglected for the quadrupolar 2 H nuclide, the analysis of 2 H MRD data is relatively straightforward. The 2 H MRD profiles can be accounted for quantitatively by a model that attributes the relaxation dispersion to a small deuteron population in intimate and long-lived association with the biopolymer. These intermediary deuterons either reside in labile groups (such as hydroxyl or amino groups) or belong to water molecules that are temporarily trapped within the biopolymer. According to this model, spin re...

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Section: Spin Diffusionmentioning

confidence: 70%

Section: Biopolymer Modelmentioning

confidence: 99%

“…The spectral density functions for these dipole couplings are given by Eqs. [3], [5], and [6]. As usual, we neglect cross-correlations between different proton pairs (13).…”

Section: Extended Solomon Equationsmentioning

confidence: 99%

Section: Adiabatic Regimementioning

confidence: 99%

Section: Other Modelsmentioning

confidence: 99%

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Molecular theory of field‐dependent proton spin‐lattice relaxation in tissue

Halle

2006

Magnetic Resonance in Med

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Effect of thermal denaturation on water-collagen interactions: NMR relaxation and differential scanning calorimetry analysis

Rochdi¹,

Foucat²,

Renou³

1999

Biopolymers

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1H-NMR study of water dynamics in hydrated collagen: Transverse relaxation-time and diffusion analysis

Traoré¹,

Foucat²,

Renou³

2000

Biopolymers

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Water proton transverse relaxation times (T2) and self‐diffusion coefficients (D) were measured in randomly oriented hydrated collagen fibers. Three T2 relaxation times were discerned indicating the presence of at least three water fractions in the collagen sample. The D values associated with each water fraction were determined. The diffusion time dependence of D suggests water motion is restricted by macromolecular structure. The experimental results are discussed with reference to the structural properties of hydrated collagen fibers. © 2000 John Wiley & Sons, Inc. Biopoly 53: 476–483, 2000

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A unified view of relaxation in protein solutions and tissue, including hydration and magnetization transfer

Cited by 101 publications

References 30 publications

Molecular theory of field‐dependent proton spin‐lattice relaxation in tissue

Molecular theory of field‐dependent proton spin‐lattice relaxation in tissue

Effect of thermal denaturation on water-collagen interactions: NMR relaxation and differential scanning calorimetry analysis

1H-NMR study of water dynamics in hydrated collagen: Transverse relaxation-time and diffusion analysis

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