Bennett H F, Brown R D, Keana J F, Koenig S H, Swartz H M
Department of Nuclear Engineering, University of Illinois, Urbana-Champaign 61801.
Magn Reson Med. 1990 Apr;14(1):40-55. doi: 10.1002/mrm.1910140106.
Nitroxide stable free radicals (nitroxides) have potential utility as MRI contrast-enhancing agents with the additional capability of reflecting redox metabolism. In order to gain a better understanding of their potential interactions in vivo, we have studied the longitudinal NMRD profiles (1/T1 as a function of field strength) and ESR spectra for lipophilic and aqueous-soluble nitroxides in blood, plasma, and plasma components. Typical water-soluble nitroxides do not interact appreciably with blood, plasma, or plasma proteins. Fatty acid nitroxides do interact physically with blood, predominantly by intercalation within red blood cell membranes and binding to albumin. The latter interaction results in significantly enhanced relaxivity for the nitroxide/HSA complex. Relaxation of water protons in this case is dominated by inner sphere processes, ostensibly due to water molecules hydrogen bonded to nitroxide moieties. The rotational reorientation time for the complex, the electronic relaxation time, and the exchange time for the water molecule reversably bound to the nitroxide, all appear significantly to influence the correlation time (approximately 16 ns) for this inner sphere contribution.
氮氧化物稳定自由基（氮氧自由基）作为磁共振成像（MRI）造影剂具有潜在用途，还具备反映氧化还原代谢的额外能力。为了更好地理解它们在体内的潜在相互作用，我们研究了亲脂性和水溶性氮氧自由基在血液、血浆及血浆成分中的纵向核磁共振弛豫分散曲线（1/T1作为场强的函数）和电子顺磁共振（ESR）谱。典型的水溶性氮氧自由基与血液、血浆或血浆蛋白之间没有明显相互作用。脂肪酸氮氧自由基确实与血液发生物理相互作用，主要是通过插入红细胞膜内并与白蛋白结合。后一种相互作用导致氮氧自由基/人血清白蛋白（HSA）复合物的弛豫率显著提高。在这种情况下，水质子的弛豫主要由内球过程主导，表面上是由于与氮氧自由基部分形成氢键的水分子所致。该复合物的旋转重取向时间、电子弛豫时间以及与氮氧自由基可逆结合的水分子的交换时间，似乎都对这种内球贡献的相关时间（约16纳秒）有显著影响。
