The effects of cross-link density and chemical exchange on magnetization transfer in polyacrylamide gels
The effects of cross-link density and chemical exchange on magnetization transfer in polyacrylamide gels
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DOI：
10.1006/jmrb.1996.0042
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发表时间：
1996-03-01
期刊：
影响因子：
--
通讯作者：
Gore, JC
中科院分区：
文献类型：
--
作者：
Kennan, RP;Richardson, KA;Gore, JC
利用磁化传递的定量测量研究了水溶液模型聚合物中聚合物结构和水-大分子相互作用对质子弛豫的影响。本文研究了由95%水、5%共聚单体丙烯酰胺和N，N ′-亚甲基双丙烯酰胺组成的聚丙烯酰胺凝胶，通过改变聚合物的交联密度来改变凝胶的结构和刚性。随着交联密度的增加，聚合物的横向弛豫呈现双相变化，并伴随着在40%以上交联时磁化传递的突然增加。这种变化可能是由于在聚合物中形成刚性域，其表现出固体状行为，具有短T-2（11 μ s）和高斯线形。水-大分子相互作用通过改变凝胶的pH来控制。在高pH（>8）下，存在与水质子和聚合物之间的化学交换介导的相互作用一致的磁化转移和横向弛豫率的增加。通过将系统分析为通过磁化交换耦合的两个质子库，估计质子布居、固有弛豫速率和交换速率，不同程度的交联和pH值。该模型提供了有用的见解，超分子结构和化学交换的相关性在组织中的松弛。(C)出版社：Academic Press，Inc.
The effects of polymer structure and water-macromolecule interactions on proton relaxation in an aqueous model polymer have been investigated using quantitative measurements of magnetization transfer. Polyacrylamide gels composed of 95% water, 5% comonomers acrylamide and N,N'-methylene-bis-acrylamide were studied, The structure and rigidity were varied by changing the cross-linking density of the polymer, The polymer showed a biphasic change in transverse relaxation with increasing cross-linking density which was accompanied by a sudden increase in magnetization transfer above 40% cross-linking. This change may be attributed to the formation of rigid domains in the polymer which exhibit solid-like behavior with a short T-2 (11 mu s) and a Gaussian lineshape, Water-macromolecule interactions were controlled by varying the pH of the gel. At high pH (>8), there was an increase in magnetization transfer and transverse relaxivity consistent with a chemical-exchange-mediated interaction between water protons and the polymer, By analyzing the system as two proton reservoirs coupled by magnetization exchange, the proton populations, intrinsic relaxation rates, and exchange rates were estimated, for different degrees of cross linking and pH. This model affords useful insights into the relevance of both supramolecular structure and chemical exchange on relaxation in tissues. (C) 1996 Academic Press, Inc.