Department of Chemistry , Indian Institute of Science Education and Research (IISER), Pune Dr. Homi Bhabha Road , Pashan, Pune , India 411008.
Centre for Energy Science, Department of Chemistry , Indian Institute of Science Education and Research (IISER) , Pune , India 411008.
J Phys Chem B. 2019 May 9;123(18):4118-4128. doi: 10.1021/acs.jpcb.9b01559. Epub 2019 Apr 30.
Water molecules present inside the lipid-based cubic liquid crystalline phases are found to play a major role in wide range of applications, such as protein crystallization, virus detection, delivery of drug and biomolecules, etc. In this regard, it is crucial to elucidate static and dynamic properties of the water molecules in the nanochannels and to explore the effect of geometrical topology on the nature of the water inside the different cubic phases. In the present work, we have incorporated two probes, coumarin-343 (C-343) and coumarin-480 (C-480), in two cubic phases with different symmetries, namely gyroid ( Ia3 d) and double diamond ( Pn3 m) with the same water content (22%), to probe the micropolarity, the microviscosity, and the hydration dynamics at different hydrophobic depths in the mesophases. Steady state results estimate the polarity at the lipid-water interface to be similar to that of ethanol, and the polarity near the more hydrophilic parts of the nanochannel resembles that of ethylene glycol. We have also observed a gradient in the microviscosity inside the LLC nanochannels from time-resolved fluorescence anisotropy studies. The hydration dynamics, which play a key role in the numerous applications of the mesophases, have been probed by the time-dependent Stokes shift method of the two probes, revealing the existence of three kinds of dynamics. The difference in the hydration dynamics inside the two mesophases, where the water molecules confined in the Ia3 d phase exhibit a slower dynamics compared to that in Pn3 m, is the prime importance of this work. The underlying reason for this disparity is majorly associated with the differences in the topology of the two structures including the hydrophobic packing stress, the negative interfacial curvature, and the curvature elastic energy of the lipid-water interface. We believe that this kind of correlation between the structural topology of the different cubic LLC mesophases and nature of the water nanochannel will help to boost the applications of the cubic phases in the future.
水是生命之源，在生命科学中扮演着重要的角色。水在脂质立方液晶相中扮演着重要的角色，在许多应用中都有广泛的应用，如蛋白质结晶、病毒检测、药物和生物分子的传递等。在这方面，阐明纳米通道中水分子的静态和动态性质，以及探索几何拓扑对不同立方相内水的性质的影响，是至关重要的。在本工作中，我们在两种具有不同对称性的立方相中分别掺入了两种探针，香豆素-343（C-343）和香豆素-480（C-480），这两种立方相具有相同的含水量（22%），分别为：二十面体（Ia3d）和双菱形（Pn3m），以探测中间相在不同疏水区的微极性、微粘度和水合动力学。稳态结果估计脂质-水界面的极性与乙醇相似，而靠近纳米通道更亲水部分的极性类似于乙二醇。我们还通过时间分辨荧光各向异性研究观察到 LLC 纳米通道内微粘度的梯度。通过两种探针的时间依赖斯托克斯位移方法探测水合动力学，该动力学在中间相的许多应用中起着关键作用，揭示了三种动力学的存在。两种中间相（Ia3d 和 Pn3m）内的水合动力学存在差异，其中 Ia3d 相中的水分子表现出比 Pn3m 相更慢的动力学，这是这项工作的主要重点。这种差异的根本原因主要与两种结构的拓扑差异有关，包括疏水区的堆积应力、负界面曲率和脂质-水界面的曲率弹性能。我们相信，这种不同的立方 LLC 中间相的结构拓扑与水纳米通道的性质之间的相关性将有助于推动立方相在未来的应用。
