Eliav Uzi, Wehrli Felix W, Navon Gil
School of Chemistry, Tel Aviv University, Tel Aviv, Israel.
Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
Magn Reson Med. 2020 Aug;84(2):535-541. doi: 10.1002/mrm.28170. Epub 2020 Jan 21.
Myelin water is commonly characterized by its short proton T relaxation time, suggesting strong association with the polar head groups of the bilayer constituents. Deuterium NMR of water in ordered structures exhibits splittings as a result of quadrupolar interactions that are observable using the double-quantum filter. The purpose of the current study was to identify and characterize the water populations.
The H double-quantum-filtered spectroscopic experiments were conducted at 62 MHz (9.4 T) on a sample of reconstituted myelin from ovine spinal cord after exchange of native water with D O.
Signals passing the double-quantum filter were attributed to 2 water pools: 1 consisting of a doublet of 650-Hz splitting, and a second unsplit signal. Similar signals were observed in the sciatic and optic nerves and in the spinal cord. Further, data suggest that diffusion of water molecules in these 2 pools (D ≤ 5 × 10 cm /s) is either hindered or restricted. An estimate of exchange lifetime of 10-15 ms between water pertaining to the single peak and that of the split peaks suggests exchange occurs in a slow-intermediate rate regime. Further distinction between the 2 pools was obtained from T measurements. Deuterons belonging to the doublet resonance were found to have short T , estimated to be on the order of 10-20 ms, whereas those corresponding to the single peak were close to that of bulk D O.
The results suggest that myelin extract water consists of 2 hindered populations with distinct degrees of anisotropic motion that can be studied by H double-quantum-filtered NMR.
髓鞘水通常以其短的质子T弛豫时间为特征，这表明它与双层成分的极性头部基团有很强的关联。有序结构中水中的氘核磁共振由于四极相互作用而出现分裂，这种分裂可以通过双量子滤波器观察到。本研究的目的是识别和表征水群体。
在将天然水与D₂O交换后，对来自绵羊脊髓的重构髓鞘样本在62MHz（9.4T）下进行¹H双量子滤波光谱实验。
通过双量子滤波器的信号归因于两个水池：一个由650Hz分裂的双峰组成，另一个是未分裂信号。在坐骨神经、视神经和脊髓中观察到类似信号。此外，数据表明水分子在这两个水池中的扩散（D ≤ 5×10⁻⁹cm²/s）受到阻碍或限制。单峰水与分裂峰水之间的交换寿命估计为10-15ms，这表明交换发生在慢-中间速率区域。通过T测量进一步区分了这两个水池。发现属于双峰共振的氘核具有短的T，估计在10-20ms量级，而对应于单峰的氘核接近大量D₂O的T。
结果表明，髓鞘提取水由两个具有不同程度各向异性运动的受阻群体组成，可以通过¹H双量子滤波核磁共振进行研究。
