Department of Physics, Indiana University Purdue University Indianapolis, Indianapolis, Indiana, USA.
Biophys J. 2011 Jul 20;101(2):362-9. doi: 10.1016/j.bpj.2011.05.062.
Due to thermal motion and molecular polarizability, electrical interactions in biological systems have a dynamic character. Zwitterions are dipolar molecules that typically are highly polarizable and exhibit both a positive and a negative charge depending on the pH of the solution. We use multilamellar structures of common lipids to identify and quantify the effects of zwitterionic buffers that go beyond the control of pH. We use the fact that the repeat spacing of multilamellar lipid bilayers is a sensitive and accurate indicator of the force balance between membranes. We show that common buffers can in fact charge up neutral membranes. However, this electrostatic effect is not immediately recognized because of the concomitant modification of dispersion (van der Waals) forces. We show that although surface charging can be weak, electrostatic forces are significant even at large distances because of reduced ionic screening and reduced van der Waals attraction. The zwitterionic interactions that we identify are expected to be relevant for interfacial biological processes involving lipid bilayers, and for a wide range of biomaterials, including amino acids, detergents, and pharmaceutical drugs. An appreciation of zwitterionic electrodynamic character can lead to a better understanding of molecular interactions in biological systems and in soft materials in general.
由于热运动和分子极化率，生物系统中的电相互作用具有动态特性。两性离子是偶极分子，通常具有高极化率，并根据溶液的 pH 值表现出正电荷和负电荷。我们使用常见脂质的多层结构来识别和量化两性离子缓冲剂的影响，这些影响超出了 pH 值的控制。我们利用这样一个事实，即多层脂质双层的重复间距是膜之间力平衡的敏感和准确指标。我们表明，常见的缓冲剂实际上可以使中性膜带电。然而，由于分散（范德华）力的同时修饰，这种静电效应不会立即被识别。我们表明，尽管表面充电可能很弱，但由于离子屏蔽和范德华吸引力降低，即使在大距离处，静电作用力也很显著。我们所确定的两性离子相互作用预计与涉及脂质双层的界面生物过程以及广泛的生物材料有关，包括氨基酸、清洁剂和药物。对两性离子电动特性的认识可以导致更好地理解生物系统和一般软物质中的分子相互作用。
