Multinuclear Relaxation Dispersion Studies of Protein Hydration

Halle, Bertil; Денисов, В И; Venu, K.

doi:10.1007/0-306-47084-5_10

Cited by 76 publications

(280 citation statements)

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“…Depending on the structural details, such buried water molecules typically exchange with bulk water on time scales ranging from 10 -8 to 10 -3 s (16). Depending on pH, the labile protons exchange with water protons on a time scales of 10 -7 s and longer (Vaca Chávez and Halle, this issue) (17)(18)(19). Note that class P includes all labile protons that exchange too slowly to contribute significantly to R 1 .…”

Section: Emor Modelmentioning

confidence: 99%

“…Water-1 H relaxation in aqueous solutions of freely tumbling proteins is well understood (18,19). The relaxation dispersion is produced by labile protein protons and/or buried water molecules, the intra-and intermolecular dipole couplings of which are modulated by the rotational diffusion (tumbling) of the protein molecules.…”

Section: Emor Modelmentioning

confidence: 99%

“…In the absence of I7P crossrelaxation, Ik ϭ 0 so Eq. [19] yields ᑬ I ϭ I , whereby Eq. [18] reduces to the familiar result (27).…”

Section: Dilute Regimementioning

confidence: 99%

“…Although Eq. [19] is numerically impractical for large n, it is useful for deriving approximate analytical results.…”

Section: Dilute Regimementioning

confidence: 99%

“…[17] (or the equivalent Eqs. [18] and [19]) is accurate, it is inconvenient to use in practice because it involves the high-dimensional polymer relaxation matrix P, which, moreover, requires knowledge of all protonproton separations and internal motions in the polymer. Fortunately, Eq.…”

Section: Internal Motionsmentioning

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: Emor Modelmentioning

confidence: 99%

Section: Emor Modelmentioning

confidence: 99%

“…In the absence of I7P crossrelaxation, Ik ϭ 0 so Eq. [19] yields ᑬ I ϭ I , whereby Eq. [18] reduces to the familiar result (27).…”

Section: Dilute Regimementioning

confidence: 99%

“…Although Eq. [19] is numerically impractical for large n, it is useful for deriving approximate analytical results.…”

Section: Dilute Regimementioning

confidence: 99%

Section: Internal Motionsmentioning

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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¹ H NMRD profiles of diamagnetic proteins: a model‐free analysis†

et al. 2000

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A model‐free analysis of the 1H nuclear magnetic relaxation dispersion (NMRD) profiles of 14 proteins in aqueous solution was performed to reproduce the experimental dispersions, that are stretched with respect to Lorentzians. The analysis, according to a recently proposed approach, shows a good correlation of all physically meaningful parameters with the molecular weight of the proteins, spanning the range from 6500 to 480000, and, in particular, of the average correlation time with the Stokes–Einstein estimate of the rotational correlation time. Copyright © 2000 John Wiley & Sons, Ltd.

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