Boek E S, Padding J T, den Otter W K, Briels W J
Schlumberger Cambridge Research, High Cross, Madingley Road, Cambridge CB3 0EL, United Kingdom.
J Phys Chem B. 2005 Oct 27;109(42):19851-8. doi: 10.1021/jp054372b.
We use simulations to predict the stability and mechanical properties of two amphiphilic bilayer membranes. We carry out atomistic MD simulations and investigate whether it is possible to use an existing coarse-grained (CG) surfactant model to map the membrane properties. We find that certain membranes can be represented well by the CG model, whereas others cannot. Atomistic MD simulations of the erucate membrane yield a headgroup area per surfactant a(0) of 0.26 nm(2), an elastic modulus K(A) of 1.7 N/m, and a bending rigidity kappa of 5 k(B)T. We find that the CG model, with the right choice for the size and potential well depth of the head, correctly reproduces a(0), kappa, as well as the fluctuation spectrum over the whole range of q values. Atomistic MD simulations of EHAC, on the other hand, suggest that this membrane is unstable. This is indicated by the fact that kappa is of the order of k(B)T, which means that the interface is extremely flexible and diffuse, and K(A) is close to zero, which means that the surface tension is zero. We argue that the CG model can be used if the headgroups are uncharged, dipolar, or effectively dipolar due to headgroup charge screening induced by counterion condensation.
我们使用模拟来预测两种两亲性双层膜的稳定性和力学性能。我们进行了原子尺度的分子动力学（MD）模拟，并研究是否有可能使用现有的粗粒度（CG）表面活性剂模型来描绘膜的性质。我们发现某些膜可以被CG模型很好地表示，而其他膜则不能。芥酸膜的原子尺度MD模拟得出每个表面活性剂的头基面积a(0)为0.26 nm²，弹性模量K(A)为1.7 N/m，弯曲刚度κ为5k(B)T。我们发现，通过对头的大小和势阱深度做出正确选择，CG模型能够正确地再现a(0)、κ以及整个q值范围内的涨落谱。另一方面，EHAC的原子尺度MD模拟表明这种膜是不稳定的。这表现为κ的量级为k(B)T，这意味着界面极其灵活且弥散，并且K(A)接近于零，这意味着表面张力为零。我们认为，如果头基不带电、呈偶极或者由于反离子凝聚引起的头基电荷屏蔽而有效地呈偶极，那么CG模型就可以使用。
