Synthetic modeling of the structure and function of the rare-earth dependent methanol dehydrogenase cofactor

Historically, rare-earth ions have been considered irrelevant to biology. Recently, the active sites of certain methanol dehydrogenase (MDH) enzymes have been shown to contain a redox-inactive, rare-earth (RE) cation coordinated by the redox-active pyrroloquinoline quinone (PQQ) cofactor. Importantly, it was demonstrated that rare earths were essential for the growth of certain methylotrophs that incorporated the XoxF-MDH. In this chapter, we summarize the optimized synthesis of a previously published rare-earth complex that serves as a model of the active site of this RE-containing MDH enzyme. The structure and reactivity of the metalated complex, [La(L_QQ)(NO₃)₃] are also discussed. [La(L_QQ)(NO₃)₃] catalytically oxidizes the test alcohol substrate, p-methylbenzyl alcohol, ^4MeBnOH, to p-methylbenzaldehyde, ^4MePhCHO, in the presence of a base (2,6-lutidine) and a terminal oxidant (ferrocenium hexafluorophosphate) with ~17 turnovers. By studying this synthetic model, we have developed a body of evidence about both the reactivity and the mechanism of dehydrogenation of alcohols as a molecular analogue to a native, rare-earth dependent enzyme.

Crystal structure of a calcium(II)-pyrroloquinoline quinone (PQQ) complex outside a protein environment

Pyrrolo­quinoline quinone (PQQ) is an important cofactor of calcium- and lanthanide-dependent alcohol de­hydrogenases. The crystal structure of a Ca–PQQ com­plex (Ca₃PQQ₂·13H₂O) is reported for the first time outside a protein environment.

Pyrrolo­quinoline quinone (PQQ) is an important cofactor of calcium- and lanthanide-dependent alcohol de­hydrogenases, and has been known for over 30 years. Crystal structures of Ca–MDH enzymes (MDH is methanol de­hydrogenase) have been known for some time; however, crystal structures of PQQ with biorelevant metal ions have been lacking in the literature for decades. We report here the first crystal structure analysis of a Ca–PQQ com­plex outside the protein environment, namely, poly[[undeca­aqua­bis­(μ-4,5-dioxo-4,5-di­hydro-1H-pyrrolo­[2,3-f]quinoline-2,7,9-tri­carboxyl­ato)tricalcium(II)] dihydrate], {[Ca₃(C₁₄H₃N₂O₈)₂(H₂O)₁₁]·2H₂O}_n. The com­plex crystallized as Ca₃PQQ₂·13H₂O with Ca²⁺ in three different positions and PQQ³⁻, including an extensive hydrogen-bond network. Similarities and differences to the recently reported structure with biorelevant europium (Eu₂PQQ₂) are discussed.

Insights on Redox Properties of Sumanene Derivatives for High-Performance Organic Cathodes

Despite the potential of large organic molecules for insoluble cathode materials in lithium-ion batteries, they have attracted less attention owing to the penalty in the molecular weight. Herein, an advanced computational modeling approach is employed to comprehensively explore the electrochemical characteristics and theoretical charge/energy storage capability for a series of sumanene derivatives. It is highlighted from this investigation that the carbonyl moiety is generally beneficial to the improvement of the redox properties for the sumanenes. The sumanene with hexagon rings fully functionalized by six carbonyls particularly exhibits both the remarkably high redox potential (3.53 V vs Li/Li⁺) and performance parameters (454 mAh/g and 1129 mWh/g), implying its candidacy as high-potential organic cathodes. It is further demonstrated from a universal relationship of redox potential-electronic property-solvation property that a sumanene derivative would experience a two-stage discharging behavior. This indicates that the sumanene derivative would be cathodically inactive due to a sudden increase of solvation energy.

Application of DFT-based machine learning for developing molecular electrode materials in Li-ion batteries

In this study, we utilize a density functional theory-machine learning framework to develop a high-throughput screening method for designing new molecular electrode materials.