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      Kinetics and thermodynamics of enzymatic decarboxylation of α,β-unsaturated acid: a theoretical study†

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      RSC Advances
      The Royal Society of Chemistry

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          Abstract

          Enzymatic decarboxylation of α,β-unsaturated acid through ferulic acid decarboxylase (FDC1) has been of interest because this reaction has been anticipated to be a promising, environmentally friendly industrial process for producing styrene and its derivatives from natural resources. Because the local dielectric constant at the active site is not exactly known, enzymatic decarboxylation to generate β-methylstyrene (β-MeSt) was studied under two extreme conditions ( ε = 1 and 78 in the gas phase and aqueous solution, respectively) using the B3LYP/DZP method and transition state theory (TST). The model molecular clusters consisted of an α-methylcinnamate (Cin) substrate, a prenylated flavin mononucleotide (PrFMN) cofactor and all relevant residues of FDC1. Analysis of the equilibrium structures showed that the FDC1 backbone does not play the most important role in the decarboxylation process. The potential energy profiles confirmed that the increase in the polarity of the solvent could lead to significant changes in the energy barriers, especially for the transition states that involve proton transfer. Analysis of the rate constants confirmed the low/no quantum mechanical tunneling effect in the studied temperature range and that inclusion of the fluctuation of the local dielectric environment in the mechanistic model was essential. Because the computed rate constants are not compatible with the time resolution of the stopped-flow spectrophotometric experiment, the direct route for generating β-MeSt after CO 2 elimination (acid catalyst (2)) is unlikely to be utilized, thereby confirming that indirect cycloelimination in a low local dielectric environment is the rate determining step. The thermodynamic results showed that the elementary reactions that involve charge (proton) transfer are affected by solvent polarity, thereby leading to the conclusion that overall, the enzymatic decarboxylation of α,β-unsaturated acid is thermodynamically controlled at high ε. The entropy changes due to the generation of molecules in the active site appeared more pronounced than that due to only covalent bond breaking/formation or structural reorientation. This work examined in detail for the first time the scenarios in each elementary reaction and provided insight into the effect of the fluctuations in the local dielectric environment on the enzymatic decarboxylation of α,β-unsaturated acids. These results could be used as guidelines for further theoretical and experimental studies on the same and similar systems.

          Abstract

          The kinetically controlled path for enzymatic decarboxylation of α,β-unsaturated acid is proposed based on DFT and TST methods. The mechanism involves fluctuation of the local dielectric environment in the active site of the FDC1 enzyme.

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          Principles of chemical kinetics

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            Author and article information

            Journal
            RSC Adv
            RSC Adv
            RA
            RSCACL
            RSC Advances
            The Royal Society of Chemistry
            2046-2069
            11 May 2022
            5 May 2022
            11 May 2022
            : 12
            : 22
            : 14223-14234
            Affiliations
            [a] School of Chemistry, Institute of Science, Suranaree University of Technology Nakhon Ratchasima 30000 Thailand kritsana@ 123456sut.ac.th +66 44 224635 +66 44 224635
            [b] Chemistry Program, Faculty of Science and Technology, Nakhon Ratchasima Rajabhat University Nakhon Ratchasima 30000 Thailand
            Author information
            https://orcid.org/0000-0002-2076-0969
            https://orcid.org/0000-0002-3822-4654
            Article
            d2ra02626k
            10.1039/d2ra02626k
            9092429
            35558849
            5c3ccbb4-bb34-4205-adbb-5bacf018fa5a
            This journal is © The Royal Society of Chemistry
            History
            : 25 April 2022
            : 3 May 2022
            Page count
            Pages: 12
            Funding
            Funded by: Suranaree University of Technology, doi 10.13039/501100004352;
            Award ID: Unassigned
            Funded by: Thailand Science Research and Innovation, doi 10.13039/501100017170;
            Award ID: Unassigned
            Categories
            Chemistry
            Custom metadata
            Paginated Article

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