Institute for Complex Molecular Systems and Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.
J Am Chem Soc. 2012 Aug 15;134(32):13482-91. doi: 10.1021/ja305512g. Epub 2012 Aug 2.
The influence of the ratio between poor and good solvent on the stability and dynamics of supramolecular polymers is studied via a combination of experiments and simulations. Step-wise addition of good solvent to supramolecular polymers assembled via a cooperative (nucleated) growth mechanism results in complete disassembly at a critical good/poor solvent ratio. In contrast, gradual disassembly profiles upon addition of good solvent are observed for isodesmic (non-nucleated) systems. Due to the weak association of good solvent molecules to monomers, the solvent-dependent aggregate stability can be described by a linear free-energy relationship. With respect to dynamics, the depolymerization of π-conjugated oligo(p-phenylene vinylene) (OPV) assemblies in methylcyclohexane (MCH) upon addition of chloroform as a good solvent is shown to proceed with a minimum rate around a critical chloroform/MCH solvent ratio. This minimum disassembly rate bears an intriguing resemblance to phenomena observed in protein unfolding, where minimum rates are observed at the thermodynamic midpoint of a protein denaturation experiment. A kinetic nucleation-elongation model in which the rate constants explicitly depend on the good solvent fraction is developed to rationalize the kinetic traces and further extend the insights by simulation. It is shown that cooperativity, i.e., the nucleation of new aggregates, plays a key role in the minimum polymerization and depolymerization rate at the critical solvent composition. Importantly, this shows that the mixing protocol by which one-dimensional aggregates are prepared via solution-based processing using good/poor solvent mixtures is of major influence on self-assembly dynamics.
通过实验和模拟相结合的方法研究了不良溶剂与良溶剂比例对超分子聚合物稳定性和动力学的影响。逐步向通过协同（成核）生长机制组装的超分子聚合物中添加良溶剂会导致在临界良/不良溶剂比下完全解体。相比之下，对于等规（非成核）体系，在添加良溶剂时会观察到逐渐解体的曲线。由于良溶剂分子与单体的弱结合，溶剂依赖性聚集稳定性可以用线性自由能关系来描述。就动力学而言，当向作为良溶剂的氯仿中添加甲基环己烷（MCH）时，共轭寡聚（对苯撑乙烯基）（OPV）组装体的解聚被证明在临界氯仿/MCH 溶剂比附近以最小速率进行。这种最小的解组装速率与蛋白质变性实验中观察到的现象惊人地相似，在蛋白质变性实验的热力学中点观察到最小速率。开发了一个包含明确依赖于良溶剂分数的速率常数的动力学成核-延伸模型，以合理解释动力学轨迹，并通过模拟进一步扩展见解。结果表明，协同作用，即新聚集体的成核，在临界溶剂组成下的最小聚合和解聚速率中起着关键作用。重要的是，这表明通过使用良/不良溶剂混合物的溶液处理制备一维聚集体的混合方案对自组装动力学有重大影响。
