Ion mobility studies of Pyrroloquinoline Quinone Aza-Crown Ether-Lanthanide Complexes

20 January 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Lanthanide-dependent enzymes and their biomimetic complexes have arisen as an interesting target of research in the last decade. These enzymes, specifically, pyrroloquinoline quinone (PQQ)-bearing methanol dehydrogenases, efficiently turn over alcohols to the respective aldehydes. To rationally design bioinspired alcohol dehydrogenation catalysts, it is imperative to understand the species involved in catalysis. However, given the extremely flexible coordination sphere of lanthanides, it is often difficult to assess the number and nature of the active species. Here we show how such questions can be addressed by using a combination of ion mobility spectrometry, mass spectrometry and quantum chemical calculations to study the test systems PQQ and lanthanide-PQQ-crown ether ligand complexes. Specifically, we determine the gas phase structures of [PQQH2]-, [PQQH2+H2O]-, [PQQH2+MeOH]-, [PQQ-15c5+H]+ and [PQQ-15c5+Ln+NO3]+ (Ln=La to Lu, except Pm). In the latter case a trend to smaller collision cross sections across the lanthanide series is clearly observable, in line with the well-known lanthanide contraction. We hope that in future such investigations will help to guide the design and understanding of lanthanide based biomimetic complexes optimized for catalytic function.

Keywords

ion mobility spectrometry
mass spectrometry
lanthanide complexes
pyrroloquinoline quinone

Supplementary materials

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Description
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Supporting Information
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Geometry restricted DFT calculations, temperature dependent NMR, CSM
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DFT-optimized structures are available as xyz-files
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All DFT-optimized structures
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