Cumulative Submillisecond All-Atom Simulations of the Temperature-Induced Coil-to-Globule Transition of Poly(N-vinylcaprolactam) in Aqueous Solution

Less-Ordered Hydration Shell around Poly(N,N-diethylacrylamide) Is Insensitive to the Clouding Transition

Raman multivariate curve resolution (Raman-MCR) is applied to examine how the hydration shell around poly(N,N-diethylacrylamide) (PDEAM) changes upon heating, in comparison with poly(N-isopropylacrylamide) (PNIPAM), both of which undergo a clouding transition near room temperature. We report that PDEAM possesses a less-ordered and smaller hydration shell than PNIPAM. Furthermore, the PDEAM hydration-shell structure is insensitive to the occurrence of clouding, indicating the coil-globule transition and aggregation of multiple chains can be achieved without the hydration-shell structural transformation.

Implementation of the Freely Jointed Chain Model to Assess Kinetics and Thermodynamics of Thermosensitive Coil-Globule Transition by Markov States

We revived and implemented a method developed by Kuhn in 1934, originally only published in German, that is, the so-called "freely jointed chain" model. This approach turned out to be surprisingly useful for analyzing state-of-the-art computer simulations of the thermosensitive coil-globule transition of N-Isopropylacrylamide 20-mer. Our atomistic computer simulations are orders of magnitude longer than those of previous studies and lead to a reliable description of thermodynamics and kinetics at many different temperatures. The freely jointed chain model provides a coordinate system, which allows us to construct a Markov state model of the conformational transitions. Furthermore, this guarantees a reliable reconstruction of the kinetics in back-and-forth directions. In addition, we obtain a description of the high diversity and variability of both conformational states. Thus, we gain a detailed understanding of the coil-globule transition. Surprisingly, conformational entropy turns out to play only a minor role in the thermodynamic balance of the process. Moreover, we show that the radius of gyration is an unexpectedly unsuitable coordinate to comprehend the transition kinetics because it does not capture the high conformational diversity within the different states. Consequently, the approach presented here allows for an exhaustive description and resolution of the conformational ensembles of arbitrary linear polymer chains.