The dynamics of hydration water (HW) in 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) was investigated by means of quasi-elastic neutron scattering (QENS) and compared with those observed in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The headgroup dynamics of DMPE was investigated using a mixture of tail-deuterated DMPE and D2O, and the QENS profiles were interpreted as consisting of three modes. The fast mode comprised the rotation of hydrogen atoms in –NH3+ and –CH2– groups in the headgroup of DMPE, the medium-speed mode comprised fluctuations in the entire DMPE molecule, and the slow mode comprised fluctuations in the membrane. These interpretations were confirmed using molecular dynamics (MD) simulations. The HW dynamics analysis was performed on a tail-deuterated DMPE and H2O mixture. The QENS profiles were analyzed in terms of three modes: (1) a slow mode, identified as loosely bound HW in the DMPC membrane; (2) a medium-speed mode similar to free HW in the DMPC membrane; and (3) a fast mode, identified as rotational motion. The relaxation time for the fast mode was approximately six times shorter than that of rotational water in DMPC, consistent with the results of terahertz time-domain spectroscopy. The activation energy of medium-speed HW in DMPE differed from that of free HW in DMPC, suggesting the presence of different hydration states or hydrogen-bonded networks around the phosphocholine and phosphoethanolamine headgroups.

中文翻译：

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准弹性中子散射揭示了磷脂头基与水合水动力学行为之间的关系

通过准弹性中子散射 (QENS) 研究了 1,2-二肉豆蔻酰基-sn-甘油-3-磷酸乙醇胺 (DMPE) 中的水合水 (HW) 动力学，并与 1,2-二肉豆蔻酰基-3-磷酸乙醇胺 (DMPE) 中观察到的水合水 (HW) 动力学进行了比较。 sn-甘油-3-磷酸胆碱 (DMPC)。使用尾部氘代 DMPE 和 D2O 的混合物研究 DMPE 的头基动力学，并将 QENS 曲线解释为由三种模式组成。快速模式包括 DMPE 头基中 –NH3+ 和 –CH2- 基团中氢原子的旋转，中速模式包括整个 DMPE 分子的波动，慢速模式包括膜中的波动。这些解释已通过分子动力学 (MD) 模拟得到证实。HW 动力学分析是在尾部氘化 DMPE 和 H2O 混合物上进行的。QENS 曲线按三种模式进行分析：（1）慢速模式，被识别为 DMPC 膜中松散结合的 HW；(2) DMPC膜中类似于游离HW的中速模式；(3)快速模式，称为旋转运动。快速模式的弛豫时间大约比 DMPC 中旋转水的弛豫时间短六倍，这与太赫兹时域光谱的结果一致。DMPE 中中速 HW 的活化能与 DMPC 中游离 HW 的活化能不同，表明磷酸胆碱和磷酸乙醇胺头基周围存在不同的水合状态或氢键网络。