Structural Transformation of a Multicompartment Micelle Induced by Photo-Switchable Spiropyran–Merocyanine Transition: Dissipative Particle Dynamics Simulation Approach

Abstract

This work highlights the structural transformation of a multicompartment micelle consisting of an amphiphilic A-b-(C-spiropyran) diblock copolymer in water, induced by the photo-switched transition between hydrophobic nonionic spiropyran and hydrophilic zwitterionic merocyanine, using a set of computational methods such as density functional theory (DFT), molecular dynamics (MD) simulation, and dissipated particle dynamics (DPD) simulation. By employing a new computational framework for the Flory–Huggins χ-parameter, which is improved by considering solvation free energy, it is demonstrated that the χ-parameter for a merocyanine–water pair is significantly smaller than that for a spiropyran–water pair, indicating that hydrophobic spiropyran becomes hydrophilic merocyanine through the photo-switched transition. Our computational procedure of χ-parameter calculation is further validated by investigating the deprotonation of syndiotactic and isotatic acrylic acid in water. It is revealed that a reasonable χ-parameter of −0.717 and −1.23 can be calculated from a singly deprotonated syndiotactic and isotatic trimer acrylic acid in water, respectively, which is consistent with the weak acidity of acrylic acid. Finally, using a set of calculated χ-parameters, DPD simulations are performed employing two different block copolymers with two different block lengths: A10-b-(C6-Spiro12) (Micelle I) and A6-b-(C10-Spiro12) (Micelle II), demonstrating that both micelles undergo distinctive inside-out transformations as a function of the block length ratio. Through the structure analysis, it turns out that Micelle I keeps a well-defined core–shell structural feature before and after the transformation, whereas Micelle II loses such structural feature because short Block A is not capable of forming the core of micelle.

Catalytically Active Multicompartment Micelles

“…Here, the Flory–Huggins χ-parameter for a pair of polymer blends A and B is defined as eq : where χ A – B and Δ E AB mix indicate χ-parameter and mixing energy between molecules A and B, respectively. In the previous study, , we established a computational procedure to evaluate the χ-parameter consistently and precisely by using the enhanced Δ E AB mix calculation via implementation of coordination number of B surrounding A ( Z AB ), the volume enclosed by the solvent-excluded molecular surface over a pair of molecules A and B ( V AB ), the number of monomeric units ( n ), reference volume ( V ref ), and interaction energy between molecules A and B ( E AB * ), respectively,…”

Multiscale Modeling Approach for the Aldol Addition Reaction in Multicompartment Micelle-Based Nanoreactor

“…To characterize the internal morphology of the MCM, we performed DPD simulations. For DPD simulation, we calculated the Flory–Huggins χ AB -parameter for molecular A–B pairs such as polymer–water, water–water, and polymer–polymer pairs, from the mixing energy Δ E AB mix by eq χ ij = normalΔ E ij mix RT In the previous study, , we developed a computational method to estimate the χ-parameter consistently and accurately using the improved mixing energy as defined by eq normalΔ E ij mix = V ref 2 n [ E ij * V ij true( Z italicij n i + Z italicji n j true) − true( E italicii * V italicii Z italicii n i + E italicjj * V italicjj Z italicjj n j true) ] where Z ij , V ij , n , V ref , and E ij refer to the coordination number of the molecule j around the molecule i , the volume enclosed by the Connolly surface over the combined pair of molecules i and j , the number of monomeric units, reference volume, and interaction energy between molecules i and j , respectively. Since the Δ E ij mix in eq utilizes more molecular information compared with the original form of mixing energy, normalΔ E ij mix = E ij * − 1 ...…”

“…In the previous study, 29,34 we developed a computational method to estimate the χ-parameter consistently and accurately using the improved mixing energy as defined by eq 2…”

“…This arrangement facilitates the reactivity of organic substrates within the aqueous system. As the molecular variables such as block sequence, block ratio, and catalyst location of the polymer play a pivotal role in determining the micelle morphology that impacts the catalytic activity, we considered these molecular variables in the design criteria. − Among various types of micelles, we reported that “clover-like” H- L-Proline-F sequenced bottlebrush copolymers, illustrated in Figure a, exhibited the highest yield and selectivity due to the Proline catalyst adjacent to the L domain within the micelle. However, it should be noted that the underlying mechanism for such enhancement remains unclear as cryogenic transmission electron microscopy (cryo-TEM) images cannot provide detailed information about the local microstructures surrounding the catalyst.…”

Nonorthogonal Cascade Catalysis in Multicompartment Micelles

“…Additional references cited within the Supporting Information. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]…”