Self-diffusion of water at the protein surface: a measurement

Polnaszek, Carl F.; Bryant, R. G.

doi:10.1021/ja00314a032

Cited by 58 publications

(48 citation statements)

References 1 publication

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“…It is well known that there is a direct effect of the nitroxide electron spin on the diffusing water spins that has been discussed in detail elsewhere [16,17]. The direct electron-nuclear coupling modulated by translational diffusion, which is dominated by the rapid motion of the water spins, is well characterized, has a different magnetic field dependence, and provides a much smaller contribution to the water spin-lattice relaxation than found here [16,17].…”

Section: Resultsmentioning

confidence: 61%

“…The direct electron-nuclear coupling modulated by translational diffusion, which is dominated by the rapid motion of the water spins, is well characterized, has a different magnetic field dependence, and provides a much smaller contribution to the water spin-lattice relaxation than found here [16,17]. The low field relaxivity associated with the nitroxide bound to a freely rotating and diffusing protein in solution is approximately 1 s −1 mM −1 .…”

Section: Resultsmentioning

confidence: 92%

“…For the relaxation agents presently used, the conjugation of the agent with a macromolecule like a protein causes only a minor increase in the water-proton relaxation rate because of the limitations imposed by short electron-spin relaxation times of the metal center [6] and possibly rapid segmental reorientation about a tether [14]. Conjugation of organic radicals to soluble proteins generally produces small effects in the water-proton relaxation that are related to the rapid modulation of the electron-nuclear coupling by relative translational diffusion [15][16][17]. The relative translational diffusion constant is dominated by the mobile water; therefore, relaxation efficiency is severely limited, and little is gained by attaching the radical to a large macromolecule.…”

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confidence: 99%

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Relaxation of protons by radicals in rotationally immobilized proteins

Korb¹,

Diakova²,

Goddard³

et al. 2007

Journal of Magnetic Resonance

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Proton spin-lattice relaxation by paramagnetic centers may be dramatically enhanced if the paramagnetic center is rotationally immobilized in the magnetic field. The details of the relaxation mechanism are different from those appropriate to solutions of paramagnetic relaxation agents. We report here large enhancements in the proton spin-lattice relaxation rate constants associated with organic radicals when the radical system is rigidly connected with a rotationally immobilized macromolecular matrix such as a dry protein or a cross-linked protein gel. The paramagnetic contribution to the protein-proton population is direct and distributed internally among the protein protons by efficient spin diffusion. In the case of a cross-linked-protein gel, the paramagnetic effects are carried to the water spins indirectly by chemical exchange mechanisms involving water molecule exchange with rare long-lived water molecule binding sites on the immobilized protein and proton exchange. The dramatic increase in the efficiency of spin relaxation by organic radicals compared with metal systems at low magnetic field strengths results because the electron relaxation time of the radical is orders of magnitude larger than that for metal systems. This gain in relaxation efficiency provides completely new opportunities for the design of spin-lattice relaxation based contrast agents in magnetic imaging and also provides new ways to examine intramolecular protein dynamics. Keywords paramagnetic relaxation; MRD; relaxation dispersion; relaxation agentMagnetic relaxation agents or contrast agents for clinical magnetic imaging applications are generally based on soluble chelate complexes of gadolinium(III) that provide one or more coordination positions for labile water molecules that carry the effects of the paramagnetic center to the total water population by chemical exchange of labile protons or water molecules [1][2][3]. In most cases, the relaxation efficiency of these compounds is limited by the short electron spin-lattice relaxation times in the range of tens to hundreds of picoseconds, which in turn defines the concentration range where these compounds may be used as practical contrast agents [4][5][6][7][8][9][10][11]. MRI contrast agents currently in use are generally soluble extracellular and blood-pool agents; however, targeting to provide specific anatomical or biochemical information will necessarily involve binding of an agent to a cell surface site or a specific macromolecular matrix [4,12,13]. For the relaxation agents presently used, the conjugation of

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Section: Resultsmentioning

confidence: 61%

Section: Resultsmentioning

confidence: 92%

mentioning

confidence: 99%

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Relaxation of protons by radicals in rotationally immobilized proteins

Korb¹,

Diakova²,

Goddard³

et al. 2007

Journal of Magnetic Resonance

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“…The spectral densities, j : ( w ) are independent of the electron relaxation rates Tl(S) and T2(S) for nitroxides (2) and in this limit …”

mentioning

confidence: 89%

The magnetic field dependence of transverse water proton relaxation induced by Nitroxide Radicals

Polnaszek

Bryant

1985

Magnetic Resonance in Med

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“…NMR studies suggest the slow down factor for translational diffusion of water near the protein surface is ~ 5 [156], while Molecular Dynamics (MD) simulations show slow down factors similar to those of the water reorientation [140,157]. A MD simulation by Handgraaf and…”

Section: 9 B Restricted Translational Diffusion Of Water In Tissuesmentioning

confidence: 99%

Translational and Rotational Dynamics of Water Molecules in Aligned Collagenous Tissues: Implications for Assessing Collagen Organisation with Magnetic Resonance Imaging

Tourell¹

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Self-diffusion of water at the protein surface: a measurement

Cited by 58 publications

References 1 publication

Relaxation of protons by radicals in rotationally immobilized proteins

Relaxation of protons by radicals in rotationally immobilized proteins

The magnetic field dependence of transverse water proton relaxation induced by Nitroxide Radicals

Translational and Rotational Dynamics of Water Molecules in Aligned Collagenous Tissues: Implications for Assessing Collagen Organisation with Magnetic Resonance Imaging

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