Rhythmic shape change of a vesicle under a pH gradient
Rhythmic shape change of a vesicle under a pH gradient
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DOI：
10.1039/c3sm51100f
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发表时间：
2013-07
期刊：
影响因子：
3.4
通讯作者：
Erika Nawa;Yasuyo Nishigaki;Daigo Yamamoto;A. Shioi
中科院分区：
文献类型：
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作者：
Erika Nawa;Yasuyo Nishigaki;Daigo Yamamoto;A. Shioi
报道了一个囊泡在pH梯度下表现出振荡结构变化。该囊泡由油酸和油酸钠组成，最初呈口细胞型或双球形。内水位于双球形结构的一侧（即膨胀部分）。囊泡的另一侧几乎没有水。当氢氧根阴离子的扩散引起pH梯度时，双球形结构旋转，使其膨胀部分朝向pH值较高的一侧。在此之后，肿胀部位中心的一个小洞开始打开。囊泡转变为环状结构：肿胀部分在外围形成，盘状部分在环体中央形成。形状变化通过环面形状进行，囊泡再次闭合，形成曲率与初始曲率相反的双球形。在这个阶段，肿胀部分朝向ph值较低的一侧。在此事件之后，囊泡旋转回其初始状态，肿胀部分面向ph值较高的一侧。这种有节奏的转变重复了很多次。在这无数的转变过程中，囊泡的大小几乎保持不变。因此，这个囊泡不断地从pH梯度中产生机械功。本文报道了在光学显微镜下的实验观察和转化的模型。
A vesicle that exhibits oscillatory structural changes under a pH gradient is reported. This vesicle is composed of oleic acid and sodium oleate and appears to exhibit a stomatocyte-type or a seemingly double spherical shape initially. The inner water is located at one side of the double spherical structure (i.e., the swollen part). The other side of the vesicle is nearly free of water. When the diffusion of hydroxide anions causes a pH gradient, the double spherical structure rotates such that its swollen part faces the higher-pH side. After this event, a small hole in the center of the swollen part begins to open. The vesicle changes to a torus-like structure: the swollen part is formed at the periphery, and a disk-like part is formed in the central part of the torus. The shape change proceeds via the torus-like shape, and the vesicle closes again to form a double spherical shape with a curvature opposite to the initial curvature. At this stage, the swollen part faces the lower-pH side. After this event, the vesicle rotates back to its initial state, where the swollen part faces the higher-pH side. This rhythmic transformation repeats numerous times. The size of the vesicle remains nearly constant during these numerous transformations. Thus, this vesicle continuously generates mechanical work from a pH gradient. In this study, experimental observations under an optical microscope and a model for the transformation are reported.