Exploring the Strength of the H-Bond in Synthetic Models for Heme Proteins: The Importance of the N-H Acidity of the Distal Base.
The distal hydrogen bond (H-bond) in dioxygen-binding proteins is crucial for the discrimination of O2 with respect to CO or NO. We report the preparation and characterization of a series of Zn(II) porphyrins, with one of three meso-phenyl rings bearing both an alkyl-tethered proximal imidazole ligand and a heterocyclic distal H-bond donor connected by a rigid acetylene spacer. Previously, we had validated the corresponding Co(II) complexes as synthetic model systems for dioxygen-binding heme proteins and demonstrated the structural requirements for proper distal H-bonding to Co(II) -bound dioxygen. Here, we systematically vary the H-bond donor ability of the distal heterocycles, as predicted based on pKa values. The H-bond in the dioxygen adducts of the Co(II) porphyrins was directly measured by Q-band Davies-ENDOR spectroscopy. It was shown that the strength of the hyperfine coupling between the dioxygen radical and the distal H-atom increases with enhanced acidity of the H-bond donor.
Laboratorium für Organische Chemie, ETH Zurich, Vladimir-Prelog-Weg 3, 8093, Zurich, Switzerland.
Mariza N
MN
Alberti
Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093, Zurich, Switzerland.
Yevhen
http://orcid.org/0000-0002-6009-1077
Y
Polyhach
Laboratorium für Organische Chemie, ETH Zurich, Vladimir-Prelog-Weg 3, 8093, Zurich, Switzerland.
Manolis D
http://orcid.org/0000-0002-8591-2038
MD
Tzirakis
Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093, Zurich, Switzerland.
Laura
L
Tödtli
Laboratory of Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093, Zurich, Switzerland. gunnar.jeschke@phys.chem.ethz.ch.
Gunnar
http://orcid.org/0000-0001-6853-8585
G
Jeschke
Laboratorium für Organische Chemie, ETH Zurich, Vladimir-Prelog-Weg 3, 8093, Zurich, Switzerland. diederich@org.chem.ethz.ch.
François
F
Diederich
D002352:Carrier Proteins / Q000737:chemistry*; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D013057:Spectrum Analysis
D002352:Carrier Proteins; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D008024:Ligands; D011166:Porphyrins; D010100:Oxygen
ENDOR spectroscopy; NMR spectroscopy; dioxygen binding; heme proteins; hydrogen bond; model systems; porphyrins