Department of Theoretical Physics, J. Stefan Institute, Ljubljana, Slovenia, EU.
Phys Rev Lett. 2012 Aug 10;109(6):068101. doi: 10.1103/PhysRevLett.109.068101. Epub 2012 Aug 7.
Most helix-coil transition theories can be characterized by three parameters: energetic, describing the (free) energy cost of forming a helical state in one repeating unit; entropic, accounting for the decrease of entropy due to formation of the helical state; and geometric, indicating how many repeating units are affected by the formation of one helical state. Depending on their effect on the helix-coil transition, solvents or cosolutes can be classified with respect to their action on these parameters. Solvent interactions that alter the entropic cost of helix formation by their osmotic action can affect both the stability (transition temperature) and the cooperativity (transition interval) of the helix-coil transition. Consistent inclusion of osmotic pressure effects in a description of helix-coil transition, for poly(L-glutamic acid) in solution with polyethylene glycol, can offer an explanation of the experimentally observed linear dependence of transition temperature on osmotic pressure as well as the concurrent changes in the cooperativity of the transition.
大多数螺旋-卷曲转变理论可以用三个参数来描述：能量，描述在一个重复单元中形成螺旋状态的（自由）能量成本；熵，说明由于形成螺旋状态导致的熵减少；以及几何，表明有多少个重复单元受到形成一个螺旋状态的影响。根据它们对螺旋-卷曲转变的影响，溶剂或共溶剂可以根据它们对这些参数的作用进行分类。通过渗透压作用改变螺旋形成的熵成本的溶剂相互作用可以影响螺旋-卷曲转变的稳定性（转变温度）和协同性（转变区间）。在对聚（L-谷氨酸）在聚乙二醇溶液中的螺旋-卷曲转变的描述中，一致地包含渗透压效应，可以解释实验观察到的转变温度与渗透压的线性关系以及转变协同性的同时变化。
