Inorganic Chemistry

PQQ-Aza-Crown Ether Complexes as Biomimetics for Lanthanide and Calcium Dependent Alcohol Dehydrogenases

Abstract

Understanding the role of metal ions in biology can lead to the development of new catalysts for
several industrially important transformations. Lanthanides are the most recent group of metal ions
that have been shown to be important in biology i.e. - in quinone-dependent methanol
dehydrogenases (MDH). Here we evaluate a pyrroloquinoline quinone and 1-aza-15-crown-5 based
ligand platform as scaffold for Ca2+ , Ba2+ , La3+ and Lu3+ biomimetics of MDH and we evaluate the
importance of ligand design, charge, size, counterions and base for the alcohol oxidation reaction
using NMR spectroscopy. In addition, we report a new straightforward synthetic route (3 steps
instead of 11 and 33% instead of 0.6% yield) for biomimetic ligands based on PQQ. We show that
when studying biomimetics for MDH, larger metal ions and those with lower charge in this case
promote the dehydrogenation reaction more effectively and that this is likely an effect of the ligand
design which must be considered when studying biomimetics. To gain more information on the
structures and impact of counterions of the complexes, we performed collision induced dissociation
(CID) experiments and observe that the nitrates are more tightly bound than the triflates. To resolve
the structure of the complexes in the gas phase we combined DFT-calculations and ion mobility
measurements (IMS). Furthermore, we characterized the obtained complexes and reaction mixtures
using Electron Paramagnetic Resonance (EPR) spectroscopy and show the emergence of a quinone-
based radical during the reaction with substrate and base.

Version notes

First Version

Content

Thumbnail image of PQQ Aza Crown Manuscript_Daumann_final.pdf

Supplementary material

Thumbnail image of PQQ Aza Crown Supporting Information_Daumann_final.pdf
PQQ Aza Crown Supporting Information Daumann final
Thumbnail image of PQQ15C-La-NO3-Isomer1.txt
PQQ15C-La-NO3-Isomer1
Thumbnail image of PQQ15C-La-OTf-Isomer1.txt
PQQ15C-La-OTf-Isomer1