Abstract
Searching for functional polyesters with stability and degradability is important due to their potential applications in biomedical supplies, biomass fuel, and environmental protection. Recently, a cyclobutane-fused lactone (CBL) polymer was experimentally found to have superior stability and controllable degradability through hydrolysis reactions after activation by mechanical force. In order to provide a theoretical basis for developing new functional degradable polyesters, in this work, we performed a detailed quantum chemical study of the alkaline and acidic hydrolysis of CBL using dispersion-corrected density functional theory (DFT-D3) and mixed implicit/explicit solvent models. Various possible hydrolysis mechanisms were found: BAC2 and BAL2 in the alkaline condition and AAC2, AAL2, and AAL1 in the acidic condition. Our calculations indicated that CBL favors the BAC2 and AAC2 mechanisms in alkaline and acidic conditions, respectively. In addition, we found that incorporating explicit water solvent molecules is highly necessary because of their strong hydrogen-bonding with reactant/intermediate/product molecules.
Highlights
A cyclobutane-fused lactone (CBL) polymer was proposed and demonstrated to have superior stability and controllable degradability [1]
Our calculations indicated that using a purely implicit solvation model will underestimate activation free energies by ~4 kcal/mol in BAC2 when compared with incorporating additional explicit water solvent molecules, and the activation free energies will not change much when including more than two explicit water molecules
This study indicates that it is highly possible for CBL to follow the BAC2 and AAC2 mechanisms in alkaline and acidic conditions, respectively
Summary
A cyclobutane-fused lactone (CBL) polymer was proposed and demonstrated to have superior stability and controllable degradability [1]. A comprehensive theoretical calculation work by Gómez-Bombarelli et al, summarized the features of the various possible hydrolysis mechanisms of two linear esters and eight lactones [3,4]. In this work, they directly adopted a model of one ester molecule including six water molecules. Though employing explicit solvation models is reliable for studying reaction mechanisms [5,6,7,8,9,10,11,12,13], they ignored the effect of a varying number of water molecules on the hydrolysis processes. Our calculations indicated that using a purely implicit solvation model will underestimate activation free energies by ~4 kcal/mol in BAC2 when compared with incorporating additional explicit water solvent molecules, and the activation free energies will not change much when including more than two explicit water molecules
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