Multi-perspective analysis of the applicability of bio-based solvents as sustainable options for biocatalysis

• Main Author: Paggiola, Giulia
• Format: Thesis
• Language: English
• Published: University of York 2016
• Subjects: Antarc*; Antarctica
• Online Access: https://etheses.whiterose.ac.uk/15797/; https://etheses.whiterose.ac.uk/15797/14/Giulia%20Paggiola,%20PhD%20thesis,%20York%202016.pdf

Biocatalysis and sustainable solvents are two increasingly popular instruments of the green synthetic toolkit. This thesis explores the use of bio-based solvents in reactions catalysed by Candida Antarctica lipase B, and discusses their greenness and wider applicability. Firstly, to clarify the mechanism of solvent influence on enzyme catalysis, a systematic multi-variable approach is applied for the first time. The results challenge the established theory which relied solely on partition coefficient, logP, revealing that catalytic performance is governed instead by the solvent’s ability to engage in hydrogen bonding. In addition, thermodynamic insight is given, with evidence of isokinetic effect and of genuine enthalpy-entropy compensation. Both effects were previously undocumented for such systems. Secondly, a strong case is made for citrus waste-derived solvents, D-limonene and p-cymene, as effective alternatives to typical petroleum-derived counterparts used in such processes. Their first use as media for biocatalysis is herein reported, in particular applied to the chemo-enzymatic synthesis of the pharmaceutical compound (S,S)-Reboxetine. Finally, novel methods from socio-economic sciences are employed to reveal the main barriers faced by users in the uptake of green solvents. As a result of a survey of stakeholder perception, the most pressing priorities to be addressed appear 1) cost, 2) lack of data, and 3) availability & supply. The third of these aspects is later examined in detail as part of a dedicated case-study, which compares D-limonene potential supply against toluene demand. While complete global substitution appears unlikely, the greatest potential is shown for citrus-growing countries such as Brazil, Spain, India and South Africa which could feasibly implement the substitution as exemplary models of bio-economy.