Hodges M W, Cafiso D S, Polnaszek C F, Lester C C, Bryant R G
Department of Chemistry, University of Virginia, Charlottesville 22901, USA.
Biophys J. 1997 Nov;73(5):2575-9. doi: 10.1016/S0006-3495(97)78286-9.
Nuclear magnetic relaxation rates for water protons in aqueous palmitoyloleoylphosphatidylcholine vesicle suspensions containing different nitroxide free radical spin labels are reported as a function of magnetic field strength corresponding to proton Larmor frequencies from 10 kHz to 30 MHz. Under these conditions the water proton relaxation rate is determined by the magnetic coupling between the water protons and the paramagnetic nitroxide fixed on the phospholipid. This coupling is made time-dependent by the relative translational motion of the water proton spins past the nitroxide radical. Using theories developed by Freed and others, we interpret the NMR relaxation data in terms of localized water translational motion and find that the translational diffusion constant for water within approximately 10 A of the phospholipid surface is 6 x 10(-10) m2 s(-1) at 298 K. Similar results are obtained for three different nitroxide labels positioned at different points on the lipid. The diffusion is a thermally activated process with an activation energy only slightly higher than that for bulk water.
报道了在含有不同氮氧化物自由基自旋标记的棕榈酰油酰磷脂酰胆碱囊泡水悬浮液中，水质子的核磁共振弛豫率与对应于10kHz至30MHz质子拉莫尔频率的磁场强度的函数关系。在这些条件下，水质子弛豫率由水质子与固定在磷脂上的顺磁性氮氧化物之间的磁耦合决定。这种耦合通过水质子自旋相对于氮氧化物自由基的相对平移运动而随时间变化。利用弗里德等人提出的理论，我们根据局部水的平移运动来解释核磁共振弛豫数据，发现在298K时，磷脂表面约10埃范围内水的平移扩散常数为6×10⁻¹⁰m² s⁻¹。对于位于脂质上不同点的三种不同氮氧化物标记，也得到了类似的结果。扩散是一个热激活过程，其活化能仅略高于体相水的活化能。
