Association entropy in adsorption processes
Association entropy in adsorption processes
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DOI：
10.1016/s0006-3495(00)76372-7
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发表时间：
2000-09-01
影响因子：
3.4
通讯作者：
Ben-Shaul, A
中科院分区：
文献类型：
--
作者：
Ben-Tal, N;Honig, B;Ben-Shaul, A
两个物种的结合形成结合络合物，例如配体与蛋白质的结合或肽在脂膜上的吸附，涉及到熵损失，反映了自由平移和旋转自由度转换为结合运动。以前对双分子结合过程中标准熵变的理论估计--S度，是从蛋白质晶体的均方根涨落推导出来的，提出S度近似于-50E，即T，S度近似于-25KT=-15kcal/mol.在这项工作中，我们关注的是吸附，而不是结合过程。我们首先提出了一个简单的统计热力学方案来计算吸附熵，包括它的平移和转动贡献，使用已知的距离取向相关的结合(吸附)势。然后，我们利用这个方案来计算相互作用自由能和戊氨酸在脂膜上的吸附熵。得到T-Delta型S度近似为-1.7kT，近似为-1.3kcal/mol。这种熵变化的大部分原因是一个自由平移转换为约束运动，其余的由两个旋转自由度的限制引起。与结合过程相比，吸附过程中较小的熵损失部分是因为较少的自由度受到限制，但主要是因为结合势要“软得多”。
The association of two species to form a bound complex, e.g., the binding of a ligand to a protein or the adsorption of a peptide on a lipid membrane, involves an entropy loss, reflecting the conversion of free translational and rotational degrees of freedom into bound motions. Previous theoretical estimates of the standard entropy change in bimolecular binding processes, Delta S degrees, have been derived from the root-mean-square fluctuations in protein crystals, suggesting Delta S degrees approximate to -50 e.u., i.e., T Delta S degrees approximate to -25 kT = -15 kcal/mol. In this work we focus on adsorption, rather than binding processes. We first present a simple statistical-thermodynamic scheme for calculating the adsorption entropy, including its resolution into translational and rotational contributions, using the known distance-orientation dependent binding (adsorption) potential. We then utilize this scheme to calculate the free energy of interaction and entropy of pentalysine adsorption onto a lipid membrane. obtaining T Delta S degrees approximate to -1.7 kT approximate to -1.3 kcal/mol. Most of this entropy change is due to the conversion of one free translation into a bound motion, the rest arising from the confinement of two rotational degrees of freedom. The smaller entropy loss in adsorption compared to binding processes arises partly because a smaller number of degrees of freedom become restricted, but mainly due to the fact that the binding potential is much "softer."