Studies of iron(III) porphyrinates containing silanethiolate ligands

Detoxification of hydrogen sulfide by synthetic heme model compounds

Hydrogen sulfide is a lethal toxic gas that disrupts cellular respiration in the mitochondrial system. Currently, no antidote is available for the clinical treatment of hydrogen sulfide poisoning. In this study, we investigated the function of iron(III)porphyrin complexes as hydrogen sulfide scavengers in water and evaluated their potential use as therapeutic agents for hydrogen sulfide poisoning. The compounds, named met-hemoCD-P and met-hemoCD-I, are composed of iron(III)porphyrin complexed with per-methylated β-cyclodextrin dimers that contain a pyridine (met-hemoCD-P) or imidazole axial fifth ligand that is coordinated to Fe(III) (met-hemoCD-I). These compounds formed stable HS-Fe(III) complexes under physiological conditions, with binding constants of 1.2 × 105 and 2.5 × 106 M-1 for met-hemoCD-P and met-hemoCD-I, respectively. The binding constant of met-hemoCD-I was 10-times higher than that reported for native human met-hemoglobin at pH 7.4 and 25oC. Electron paramagnetic resonance (EPR) spectroscopy and H2S quantification assays revealed that after SH- was coordinated to met-hemoCD-I, it was efficiently converted to nontoxic sulfite and sulfate ions via homolytic cleavage of the HS-Fe(III) bond followed by aerobic oxidation. Mouse animal experiments revealed that the survival rate was significantly improved when NaSH-treated mice were injected with met-hemoCD-I. After the injection, mitochondrial CcO function in brain and heart tissues recovered, and met-hemoCD-I injected was excreted in the urine without chemical decomposition.

The contribution of metalloporphyrin complexes in molecular sensing and in sustainable polymerization processes: a new and unique perspective

This review highlights the recent developments in the field of metalloporphyrins as optical probes for biologically relevant molecules, such as nitric oxide (NO) and hydrogen sulfide (H2S), and as catalysts for the preparation of sustainable polymers such as polyesters, by the ring-opening polymerization (ROP) of cyclic esters and the ring-opening co-polymerization (ROCOP) of epoxides and anhydrides, and polycarbonates by the chemical fixation of carbon dioxide (CO2). The great potential of porphyrins is mainly due to the possibility of making various synthetic modifications to the porphyrin ring, such as modifying the coordinated metal, peripheral substituents, or even the molecular skeleton. Due to the strict structure-property relationships, one can use porphyrinoids in several different applications such as, for instance, activation of molecular oxygen or catalysis of photosynthetic processes. These possibilities broaden the application of porphyrins in several different fields of research, further mimicking what nature does. In this context, here, we want to provide evidence for the great flexibility of metalloporphyrins by presenting an overview of results obtained by us and others in the research fields we are currently involved in. More specifically, we report a survey of our most significant achievements regarding their use as optical probes in the context of the results reported in the literature from other research groups, and of the use of porphyrin metal(iii) complexes as catalysts for sustainable polymerization processes. As for the optical probe section, in addition to the metalloporphyrins synthesized ad hoc in the laboratory, the present work also covers the natural proteins containing a porphyrin core.

Synthesis and characterization of six-coordinate iron(II/III) 5,10,15,20-tetrakis(pentafluorophenyl) porphyrinato complexes with non-hindered imidazole ligands

Four bis-imidazole iron(II/III) 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato (TFPP) complexes, [Fe(TFPP)(1-MeIm)[Formula: see text]], [Fe(TFPP)(1-VinylIm)[Formula: see text]], [Fe(TFPP)(4-MeHIm)[Formula: see text]]Cl and [Fe(TFPP)(1-EtIm)[Formula: see text]]BF[Formula: see text] (1-MeIm [Formula: see text] 1-methylimidazole, 1-VinylIm [Formula: see text] 1-vinylimidazole, 4-MeHIm [Formula: see text] 4-methylimidazole and 1-EtIm [Formula: see text] 1-ethylimidazole) were synthesized and characterized by single-crystal X-ray and UV-vis spectroscopy. A negative correlation is found between the absolute imidazole orientation ([Formula: see text] and the Fe–N[Formula: see text] distance for the [Fe(II)(Porph)(Im)[Formula: see text]] (Im [Formula: see text] 1-MeIm or 4-MeHIm) complexes where the smaller [Formula: see text] angle corresponds to a longer axial distance. Hydrogen bonding, which might affect the orientations of the axial imidazoles is found for Fe(TFPP)(4-MeHIm)[Formula: see text]]Cl (A and B). The autoreduction of [Fe(III)(TFPP)]Cl to [Fe(II)(TFPP)(1-MeIm)[Formula: see text]] with 1-methylimidazole has been monitored by UV-vis spectroscopic titration.

Interaction of monohydrogensulfide with a family of fluorescent pyridoxal-based Zn(ii) receptors

We studied the reactivity of HS⁻ with a family of fluorescent zinc complexes. In the case of complexes 1 and 3, we have evidence that the interaction with HS⁻ results in the displacement of the coordinated ligand from the Zn center. For complex 2, our data points to the coordination of HS⁻ to the metal center likely assisted by hydrogen bondings with the OH of the pyridoxal moiety.

Spectroscopic investigation of the reaction of metallo-protoporphyrins with hydrogen sulfide

Hydrogen sulfide (H₂S) is the most recently discovered gasotransmitter molecule joining nitric oxide and carbon monoxide. In addition to being biologically important gases, these gasotransmitters also provide distinct modes of reactivity with biomimetic metal complexes. The majority of previous investigations on the reactivity of H₂S with bioinorganic models have focused on Fe-based porphyrin systems, whereas investigations with other metals remains underinvestigated. To address this gap, we report here an examination of the reactions of H₂S, HS^-, and S₈ with Mg^II, Cu^II, Co^II, Zn^II, Cr^II, Sn^IV, and Mn^II/III protoporphyrins.

Spectroscopic investigations into the binding of hydrogen sulfide to synthetic picket-fence porphyrins

The picket-fence porphyrin system is used a model for a sterically-constrained, protected binding environment to study H₂S and HS⁻ligation.

Carboxyl activation via silylthioesterification: one-pot, two-step amidation of carboxylic acids catalyzed by non-metal ammonium salts

The first organo-catalyzed silylthioesterification of a carboxylic acid and a commercially available mercaptoorganosilane results in the in situ production of an O-silylthionoester. Subsequent amine addition forms amides in an operationally simple one-pot procedure without removal of water. The scope and efficiency of these reactions with respect to the catalyst, carboxylic acid, amine, [Si─S] moiety, and solvent are investigated. A number of functionalities are tolerated in the two-step amidation including alkene, alkyne, alkyl and aryl halides, benzylic ethers, and heterocycles with free coordinating sites.

Organometallic sulfur complexes: reactivity of the hydrogen sulfide anion with cobaloximes

The hydrogen sulfide anion selectively and reversibly displaces pyridine in cobaloxime. A rare trisulfido-bridged dinuclear complex was isolated and characterized.

Synthesis, characterization, and atropisomerism of iron complexes containing the tetrakis(2-chloro-6-fluorophenyl)porphyrinate ligand

The synthesis of iron complexes containing the 5,10,15,20-tetrakis(2-chloro-6-fluorophenyl)porphyrin ligand is presented and the factors surrounding the observed atropisomerism are investigated.

NBu4SH provides a convenient source of HS− soluble in organic solution for H2S and anion-binding research

We report here a simple method to prepare and characterize analytically-pure NBu₄SH, which provides access to an organic-soluble source of HS⁻.

A convenient procedure for the synthesis of fluoro-iron(III) complexes of common synthetic porphyrinates

We report here an improved method for the preparation of fluoro-iron(III) porphyrinate complexes. Treatment of [ Fe 2( P )2(μ- O )] (P = tetraphenylporphyrinate {TPP}, tetra-p-tolylporphyrinate {TTP}, or octaethylporphyrinate {OEP}) or [ Fe ( OH )( OH 2)( TMP )] (TMP = tetramesitylporphyrinate) with the commercially available fluorinating agent, Et 3 N ·3 HF , in dichloromethane affords the desired [ FeF ( P )] complexes in a straightforward fashion and in good yield while avoiding the use of aqueous hydrofluoric acid. All fluoro-iron(III) complexes have been completely characterized by a series of different spectroscopic techniques including cyclic voltammetry. Reaction of a representative complex, [ FeF ( OEP )], with various chloride reagents demonstrates that halide exchange with chloride is facile, but only proceeds at an appreciable rate in the presence of proton sources. Unexpectedly, treatment of [ FeF ( OEP )] with NOBF 4 did not to lead formation of an oxidized species, but rather to formation of the { Fe – NO }6 complex, [ Fe ( NO )( OEP )]( BF 4).

Chemically reversible reactions of hydrogen sulfide with metal phthalocyanines

Hydrogen sulfide (H₂S) is an important signaling molecule that exerts action on various bioinorganic targets. Despite this importance, few studies have investigated the differential reactivity of the physiologically relevant H₂S and HS^– protonation states with metal complexes. Here we report the distinct reactivity of H₂S and HS^– with zinc(II) and cobalt(II) phthalocyanine (Pc) complexes and highlight the chemical reversibility and cyclability of each metal. ZnPc reacts with HS^–, but not H₂S, to generate [ZnPc-SH]⁻, which can be converted back to ZnPc by protonation. CoPc reacts with HS^–, but not H₂S, to form [Co^IPc]⁻, which can be reoxidized to CoPc by air. Taken together, these results demonstrate the chemically reversible reaction of HS^– with metal phthalocyanine complexes and highlight the importance of H₂S protonation state in understanding the reactivity profile of H₂S with biologically relevant metal scaffolds.

The protonation state of H₂S influences its reactivity with different metal phthalocyanine (Pc) complexes. Both ZnPc and CoPc react with H₂S in a chemically reversible manner, with redox-inactive ZnPc binding HS⁻ and redox-active CoPc undergoing reduction. The [ZnPc-SH]⁻ product can be reverted to ZnPc by protonation, and [Co^IPc]⁻ can be redoxidized to CoPc with air.