Axial Imidazole Binding Strengths in Porphyrinoid Cobalt(III) Complexes as Studied by Tandem Mass Spectrometry

Abstract

The Co(II) complexes of twelve meso-tetraaryl-porphyrins, -chlorins, and chlorin analogues containing non-pyrrolic heterocycles were synthesized and converted in situ to the corresponding Co(III) complexes coordinated to one or two imidazoles. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) in conjunction with the energy-variable collision-induced dissociation (CID) technique was used to compare the relative gas-phase binding strength of the axially coordinated imidazoles to the octahedral and square planar Co(III) porphyrinoid complex ions. The observed binding energies of these ligands were rationalized in terms of the effects of porphyrinoid core structure and meso-substitution on the electron density on the central Co(III) centers. Some of these trends were supported by DFT-based computational studies. The study highlights to which extend porphyrins vary from chlorins and chlorin analogues in their coordination abilities and to which extraordinary degree meso-thienyl-substituents influence the electronic structure of porphyrins. The study also defines further the scope and limits CID experiments can be used to interrogate the electronic structures of metalloporphyrin complexes.

Making the invisible visible: improved electrospray ion formation of metalloporphyrins/-phthalocyanines by attachment of the formate anion (HCOO−)

“…4 readily undergo the coordination of the formate anion in the negativeion mode. In light of the pronounced formate addition in the negative-ion mode, the question arises to which extent the established positive-ion mode oxidation [18][19][20][21][22][23][24][33][34][35] would occur in these samples. Therefore, the positive-ion mode formation of radical cations was investigated for all Zn(II)Pors and Zn(II) Pcs by electrospraying from acetonitrile (ACN) solutions as required for oxidation.…”

“…[12][13][14] The characterization of new functional Por-related materials is closely related to the development of modern mass spectrometry. Nowadays, the two most prominent soft ionization methods, namely matrix-assisted laser desorption/ionization (MALDI) [15][16][17] and electrospray ionization (ESI), [18][19][20][21][22][23][24] have both been applied intensively to the analysis of Por-related materials. Both methods have their advantages and disadvantages, almost possessing complementary features in their applicability.…”

“…[18][19][20] Oxidation of M(II)Pors has also been successfully applied to the generation of adducts with imidazoles, allowing the determination of the bond strengths in these complexes. 21,22 ESI oxidation has led to the formation of a stable tricationic dimer of a Zn(II)Por carrying two hexabenzocoronene ligands. 23 The analytical use of ESI oxidation in mixtures of Pors has been examined and it was found that if the oxidation potentials of the two Pors differ by more than 0.1 V, discrimination occurs against the Por with the higher oxidation potential.…”

PEGylated meso-arylporpholactone metal complexes as optical cyanide sensors in water

“…The sensitivity of the zinc lactone complex for CN − is high, with a detection limit of 2.0 mM, i.e., in the same order of magnitude as the platinum complex, and lower than for the parent zinc porphyrin 8Zn-PEG 1000 (3.4 mM). We attribute this to the generally decreased Lewis basicity of the oxidized porpholactone compared to the porphyrin; 26 this renders the coordinated metal ion to be a better Lewis acid, 61 with a corresponding higher binding affinity for cyanide (with a K d of 14 mM for porpholactone complex 6Zn-PEG 1000 compared to 45 mM for the porphyrin complex 8Zn-PEG 1000 ).…”

A Redox-Active Fluorescent pH Indicator for Detecting Plasmodium falciparum Strains with Reduced Responsiveness to Quinoline Antimalarial Drugs

“…Calibration was performed using Tuning mix (Agilent Technologies). CID experiments were performed with a capillary exit (cone voltage) ranging from 120 to 400V with 20V increments 68. Stock solution of hematin ([Fe III PPIX(OH 2 )] 3+ or [Fe III PPIX(OH)] 2+ ) was freshly prepared from hemin (ferriprotoporphyrin chloride, [Fe III PPIX(Cl)] 2+ ) just before use in 50% ammonia.…”