College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha Hunan 410081, P. R. China.
Phys Chem Chem Phys. 2018 Jul 4;20(26):17990-17998. doi: 10.1039/c8cp03092h.
Cooperativity is a widely used chemical concept whose existence is ubiquitous in chemical and biological systems but whose quantification is still controversial and origin much less appreciated. In this work, using the interaction energy of a molecular system, which is composed of multiple copies of a building block, we propose a quantitative measurement to evaluate the cooperativity effect. This quantification approach is then applied to six molecular systems, i.e., water cluster, argon cluster, protonated water cluster, zinc atom cluster, water cluster on top of a graphene sheet, and alpha helix of glycine amino acids, each with up to 20 copies of the building block. Cooperativity is seen in all these systems. Both positive and negative cooperativity effects are observed. Employing the two energy partition schemes in density functional theory and the information-theoretic quantities such as Shannon entropy, Fisher information, information gain, etc., we then examine the origin of the cooperativity effect for these systems. Strong linear correlations between the cooperativity measure and some of these theoretical quantities have been unveiled. With these correlations, we are able to quantitatively account for their origin of cooperativity. Our results show that the interactions governing the existence and validity of the cooperativity effect are complicated. An opposite mechanism in enthalpy-entropy compensation for positive and negative cooperativity has been unveiled. These results should provide new insights and understandings from a different viewpoint about the nature and origin of cooperativity to appreciate this vastly important chemical concept.
协同作用是一个广泛使用的化学概念，其存在普遍存在于化学和生物系统中，但对其定量描述仍存在争议，其起源也远未得到充分认识。在这项工作中，我们使用由多个结构单元组成的分子系统的相互作用能，提出了一种定量测量方法来评估协同作用效应。然后，我们将这种定量方法应用于六个分子系统，即水分子簇、氩气簇、质子化水分子簇、锌原子簇、石墨烯片上的水分子簇和甘氨酸氨基酸的α螺旋，每个系统都有多达 20 个结构单元。在所有这些系统中都观察到了协同作用。观察到了正协同和负协同作用效应。我们还使用密度泛函理论中的两种能量划分方案和信息论量，如香农熵、Fisher 信息、信息增益等，研究了这些系统中协同作用效应的起源。我们揭示了协同度量与这些理论量之间的强线性相关性。通过这些相关性，我们能够定量解释其协同作用的起源。我们的结果表明，控制协同作用存在和有效性的相互作用非常复杂。对于正协同和负协同作用，我们揭示了焓熵补偿中的相反机制。这些结果应该从不同的角度提供对协同作用的本质和起源的新的见解和理解，以欣赏这个非常重要的化学概念。
