This project is funded by SSF, MISTRA and FORMAS. Published papers using SNIC 2022/5-49: 2, and 1 paper under revision in Nature communications The low use of allocated resources at KTH PDC from the previous round was due to parental leave of Per-Olof Syrén, and long waiting times for editor and referee reports (Syrén et al. Nat. Commun. 2023, now in revision). The PI is now back and ready to lead and perform work in this project. The main goal of this research project is to construct novel green biocatalytic pathways for expedient generation of sustainable monomers and biomaterials from CO2. This will be achieved by retrofitting existing metalloenzymes - driven by computations - for new-to-nature chemistries for mild CO2 upcycling. CO2 is the most oxidized form of carbon and is inert towards further chemical transformations. Thus, harsh reaction conditions and high pressure has up to now been needed to activate CO2 and to enable its use as a chemical feedstock (Beller et al. Nat. Commun. 2015). This project will instead use enzymes as green catalysts to upcycle CO2 under mild conditions into platform chemicals with applications in polymers and additives to Lithium-ion battery electrolytes. Existing enzymes for CO2 upcycling are limited to (de)carboxylation and reduction chemistries, whereas applications in material science require formation of carbonates; a new type of transformation that is hitherto unknown in biology. Using computational methods, we will fill current gaps in available biocatalytic transformations to enable biosynthesis of carbonates from CO2. This will be achieved by implementing new reactions and mechanisms in existing metalloenzymes, such as carbonic anhydrase and decarboxylases so that they instead enable formation of carbonates. The proposed project utilizes quantum mechanical (QM) calculations to explore the chemistry that governs the new biological activity: high-level QM calculations will be used to elucidate the reaction mechanism and the resulted knowledge will be used to guide enzyme engineering efforts. Together, the project’s pipeline allows for generation of enzyme variants with improved catalytic properties in CO2 upcycling. The PI has experience in modelling reaction mechanism in metalloenzymes. Great progress was made in previous PDC-supported projects, as we unraveled how tertiary amide bonds undergo hydrolysis in nature by metallopeptidases. This demonstrates necessary expertise of the main applicant in performing state of the art quantum mechanical calculations on metalloenzymes (see e.g. Syrén et al. J. Org. Chem. 2018). Cyclic carbonates are important monomers and platform chemicals generated mainly by harsh metal catalysis in scales of 100,000 tons/y. It is envisaged that the present investigation centered on generating novel enzymatic reactions for CO2 upcycling will be of high value in industrial biotechnology and chemistry. Motivation to Dardel: Per-Olof Syrén (PI) has several funded projects from FORMAS, MISTRA and SSF whose success are entirely dependent on running US-GAMESS. Calculations are based on very large models of complex biocatalysts containing metals.