A new view of water dynamics in immobilized proteins

Halle, Bertil; Денисов, В И

doi:10.1016/s0006-3495(95)79895-2

Cited by 50 publications

(49 citation statements)

References 38 publications

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“…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. We previously presented this argument in connection with 2 H MRD profiles (31,32), and Eq. [33] and Fig.…”

Section: Other Modelsmentioning

confidence: 96%

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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: Other Modelsmentioning

confidence: 96%

“…7, the adiabatic regime is reached for I Ϸ 10 -3 s and the midpoint frequency is 17 kHz, as predicted by Eqs. [32] and [33] valid for an internal water molecule in the adiabatic regime, but then the dipole frequency is (see Eq. [26])…”

Section: Adiabatic Regimementioning

confidence: 99%

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

Halle

2006

Magnetic Resonance in Med

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“…The homonuclear case might represent a serine side-chain with the I spin in the labile hydroxyl proton and the S spin in one of the adjacent methylene protons (chemical shifts have no significant effect). The heteronuclear case might represent an 15 N-labeled lysine side-chain, with the I spin in one of the labile amino protons and the S spin in the directly bonded nitrogen atom so that κ = γ S /γ I = −0.1014. In both cases, we excite nonselectively but observe only the I spin.…”

Section: B Heteronuclear Spinsmentioning

confidence: 99%

“…The EMOR SLE theory was first developed for quadrupolar relaxation 10,11 and it has been extensively applied to water 2 H MRD studies of colloidal silica, 12 polymer gels, 13,14 cross-linked proteins, [15][16][17][18] and cells. 19 As compared to quadrupolar relaxation, which only involves single spins, dipolar relaxation is theoretically more challenging.…”

Section: Introductionmentioning

confidence: 99%

Nuclear magnetic relaxation by the dipolar EMOR mechanism: General theory with applications to two-spin systems

Chang

Halle

2016

The Journal of Chemical Physics

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On the theory of the proton dipolar-correlation effect as a method for investigation of segmental displacement in polymer melts The Journal of Chemical Physics 147, 074904 (2017); 10.1063/1.4998184 THE JOURNAL OF CHEMICAL PHYSICS 144, 084202 (2016) Nuclear magnetic relaxation by the dipolar EMOR mechanism: General theory with applications to two-spin systems In aqueous systems with immobilized macromolecules, including biological tissue, the longitudinal spin relaxation of water protons is primarily induced by exchange-mediated orientational randomization (EMOR) of intra-and intermolecular magnetic dipole-dipole couplings. We have embarked on a systematic program to develop, from the stochastic Liouville equation, a general and rigorous theory that can describe relaxation by the dipolar EMOR mechanism over the full range of exchange rates, dipole coupling strengths, and Larmor frequencies. Here, we present a general theoretical framework applicable to spin systems of arbitrary size with symmetric or asymmetric exchange. So far, the dipolar EMOR theory is only available for a two-spin system with symmetric exchange. Asymmetric exchange, when the spin system is fragmented by the exchange, introduces new and unexpected phenomena. Notably, the anisotropic dipole couplings of non-exchanging spins break the axial symmetry in spin Liouville space, thereby opening up new relaxation channels in the locally anisotropic sites, including longitudinal-transverse cross relaxation. Such cross-mode relaxation operates only at low fields; at higher fields it becomes nonsecular, leading to an unusual inverted relaxation dispersion that splits the extreme-narrowing regime into two sub-regimes. The general dipolar EMOR theory is illustrated here by a detailed analysis of the asymmetric two-spin case, for which we present relaxation dispersion profiles over a wide range of conditions as well as analytical results for integral relaxation rates and time-dependent spin modes in the zero-field and motional-narrowing regimes. The general theoretical framework presented here will enable a quantitative analysis of frequency-dependent water-proton longitudinal relaxation in model systems with immobilized macromolecules and, ultimately, will provide a rigorous link between relaxation-based magnetic resonance image contrast and molecular parameters. C 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

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“…The experimental study of the structure and dynamics of water in the vicinity of a large molecule, such as DNA or a protein is a challenge but the importance of the problem justifies a lot of efforts essentially achieved by NMR (Halle and Denisov 1995) and, in a more exhaustive way, by neutron scattering (Ball 2008, and references therein). One of the main problems is the fact that water molecules are structurally in many different situations, as for example, deeply inserted on grooves, forming "bridges" between different residues, or exchanging rapidly with the external aqueous media.…”

Section: Dynamics Of Hydration Watermentioning

confidence: 99%

Dynamics of hydration water in proteins

Teixeira

2009

gpb

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Abstract. Thermodynamic and transport properties of liquid water are determined essentially by inter-molecular hydrogen bonds and their dynamics. Because the molecular dynamics depends mostly on geometric constrains and dynamics of hydrogen bonds, it is shown that a simple statistics on the number of bonds, including at the vicinity of hydrophilic substrates describes well the temperature dependence of water diffusion on the surface of a small peptide.Experiments were performed by incoherent quasi-elastic neutron scattering giving information about the hydrogen bond lifetime and the residence time of the water molecules. In order to study the interactions between water molecules and a small hydrophobic peptide (an assembly of five monomers of alanine), the hydration level is changed step by step. The only motion of the first single water molecule of the structure is due to hydrogen libration. The first two added water molecules bind with the hydrophilic site of the peptide and have only the dynamics of the bond breaking. The other hydration molecules show fast diffusive motions on the surface of the peptide.

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A new view of water dynamics in immobilized proteins

Cited by 50 publications

References 38 publications

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

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

Nuclear magnetic relaxation by the dipolar EMOR mechanism: General theory with applications to two-spin systems

Dynamics of hydration water in proteins

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