Tetra-2,3-pyrazinoporphyrazines with Peripherally Appended Pyridine Rings. 20. Mono- and Pentanuclear AlIII and GaIII Complexes: Synthesis and Physicochemical and Photoactivity Studies

Giulia Saltini; Lei Cong; Maria Pia Donzello; Claudio Ercolani; Elisa Viola; Ida Pettiti; Pavel A Stuzhin; Karl M Kadish

doi:10.1021/acs.inorgchem.9b02279

Tetra-2,3-pyrazinoporphyrazines with Peripherally Appended Pyridine Rings. 20. Mono- and Pentanuclear Al^III and Ga^III Complexes: Synthesis and Physicochemical and Photoactivity Studies

Inorg Chem. 2019 Nov 18;58(22):15269-15282. doi: 10.1021/acs.inorgchem.9b02279. Epub 2019 Oct 30.

Authors

Giulia Saltini¹, Lei Cong², Maria Pia Donzello¹, Claudio Ercolani¹, Elisa Viola¹, Ida Pettiti¹, Pavel A Stuzhin³, Karl M Kadish²

Affiliations

¹ Dipartimento di Chimica , Università di Roma Sapienza , P.le A. Moro 5 , I-00185 Rome , Italy.
² Department of Chemistry , University of Houston , Houston , Texas 77204-5003 , United States.
³ Department of Organic Chemistry , Ivanovo State University of Chemistry and Technology , 153460 Ivanovo , Russian Federation.

PMID: 31663723
DOI: 10.1021/acs.inorgchem.9b02279

Abstract

The autocyclotetramerization of the precursor 2,3-dicyano-5,6-di(2'-pyridyl)pyrazine [(CN)₂Py₂Pyz] in the presence of MCl₃ compounds (M = Al^III, Ga^III) leads to the formation of the new mononuclear porphyrazine complexes [Py₈TPyzPzMCl]·xH₂O (Py₈TPyzPz = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato anion). From these species, the hydroxide analogues [Py₈TPyzPzMOH]·xH₂O were obtained by contact with hot water, and their corresponding pentanuclear species [(PdCl₂)₄Py₈TPyzPzMCl]·xH₂O could be easily formed by the reaction with PdCl₂. Physicochemical characterization of the mono- and pentanuclear macrocycles was based on elemental analysis, and mass, powder X-ray, and IR spectra. UV-vis spectral studies of the mononuclear species in solutions of DMF, DMSO, or pyridine (c ≈ 10^-5-10^-6 M) indicate (mainly in DMF and DMSO) the initial presence of aggregation, in some cases accompanied by the concomitant occurrence for the complex of a one-electron reduction. While disaggregation into a single species evolves spontaneously over time, the -1 charged species, eventually also found present, can be brought back to its neutral form by addition of a slight amount of HCl, the final spectrum showing the presence of the starting neutral species in its pure monomeric form. Similar aspects were faced also for the parent pentanuclear complexes. Cyclic voltammetry experiments, conducted for the mono-/pentanuclear complexes in DMF and DMSO (c ≈ 10^-4 M), exhibit progressive one-electron reductions (1 → 4) characterized by E_1/2 values (V vs SCE) positioned to significantly less negative values than those known for the phthalocyanine (Pc) analogues, these data confirming the previously already proven higher electron-deficient character of the M^II derivatives of the Py₈TPyzPz macrocycle with respect to Pc. The role of the present new series of Al^III and Ga^III macrocyclic species to act as photosensitizers for the generation of singlet oxygen, ¹O₂, the cytotoxic agent in the anticancer treatment known as photodynamic therapy (PDT), has been explored in DMF/HCl. Among the quantum yields Φ_Δ, the value found for the Ga^III complex [Py₈TPyzPzGaCl] (0.68), practically coincident with that observed for the TTDPz analogue (0.69), is well above those of most porphyrazines analogues (Φ_Δ = 0.4-0.6), a result encouraging further research work for potential applications in the biochemical field.