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Relative contributions of chemical exchange and other relaxation mechanisms in protein solutions and tissues
Author(s) -
Zhong Jianhui,
Gore John C.,
Armitage Ian M.
Publication year - 1989
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910110304
Subject(s) - relaxation (psychology) , chemistry , heavy water , magnetic relaxation , proton , chemical shift , chemical physics , nuclear magnetic resonance , magnetic field , deuterium , atomic physics , magnetization , physics , nuclear physics , psychology , social psychology , quantum mechanics
Abstract Transverse relaxation times T 2 of water protons were measured in 5% protein solutions and soaked rat liver in different static magnetic fields (0.15 to 11 T). Protein molecular weight varied between 1.4 and 480 kDa in solutions of yarying degrees of deuteration. The data obtained are analyzed in terms of a model system consisting of three phases of different relaxation characteristics: protein protons, hydration layer water protons, and bulk water protons. The contributions to relaxation due to hydrodynamic effects on water protons, cross relaxation between the hydration layer water protons and the protein protons, and chemical exchange between the hydration layer water protons and the bulk water protons are separately estimated. The experimental results indicate that the “hydrodynamic interactions” are about the same magnitude in rat liver and all the proteins studied, but the contribution of the cross relaxation differs by several orders in different protein systems. Fast chemical exchange between the hydration layer water and the bulk water causes considerable shortening of T 2 at high magnetic fields for all the protein solutions and rat tissue studied. Selected samples were studied at different temperatures (2 13‐3 18 K) and with different intervals in the CPMG sequence. The rates of chemical exchange and fractional populations of different phases are determined, and the results obtained provide support for the model in which fast exchange among the different water phases is an important feature of the overall relaxation behavior.