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Selective Coordination of Gallium(III), Zinc(II), and Copper(II) by an Asymmetric Dinucleating Ligand: A Model for Metallophosphatases
Author(s) -
Bosch Simone,
Comba Peter,
Gahan Lawrence R.,
Hanson Graeme R.,
Noble Christopher,
Schenk Gerhard,
Wadepohl Hubert
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201503348
Subject(s) - chemistry , steric effects , zinc , ligand (biochemistry) , amide , copper , amine gas treating , metal , pyridine , electron paramagnetic resonance , titration , metal ions in aqueous solution , stereochemistry , inorganic chemistry , crystallography , medicinal chemistry , organic chemistry , biochemistry , physics , receptor , nuclear magnetic resonance
Complexation studies of the dinucleating ligand H 3 L (H 3 L=2‐{[bis(pyridin‐2‐ylmethyl)amino]methyl}‐6‐{[bis(6‐pivaloylamidopyridin‐2‐ylmethyl)amino]methyl}‐4‐methylphenol), with metal‐binding sites A and B, which both provide four donors to a metal ion; a tertiary amine; two pyridines (substituted with amide hydrogen‐bond donors in site B), and a bridging phenolate, with Zn II , Cu II , and Ga III are reported. The titration of H 3 L with the three metal ions in solution was monitored by NMR spectroscopy or EPR and UV/Vis/near‐IR spectroscopy, as well as by ESI‐MS to analyze the selectivity of the two metal‐ion sites A and B of this model ligand for metallophosphatases; the spectroscopic assignments are supported by X‐ray crystallography results. The first Zn II ion coordinates to site A with unsubstituted pyridine donors and, upon addition of a second equivalent of Zn II , this coordinates to the sterically less accessible site B. From a similar titration with Ga III , it emerges that only a mononuclear complex is obtained, with the Ga III center coordinated to site A. When one equivalent of Ga III is reacted with the mononuclear Zn II complex, Zn II is forced by Ga III to exchange the site; this results in a dinuclear complex with Ga III in site A and Zn II in site B. With Cu II , two isomers are observed: one with and the other without a bridging phenolate; these differ significantly in their spectroscopic and magnetic properties.