Cristina Martí

Aromatic ketones as standards for singlet molecular oxygen O2(1Δg) photosensitization. Time-resolved photoacoustic and near-IR emission studies

Abstract Time-resolved near-IR emission and optoacoustic calorimetry studies were carried out on the aromatic ketones phenalenone, benzanthrone, 4-phenylbenzophenone and the benzophenone-naphthalene (0.1 M) system in order to assess their adoption as solvent-independent standards for singlet molecular oxygen O 2 ( 1 Δ g ) photosensitization. All compounds show quantum yields of O 2 ( 1 Δ g ) production (FΔ) in the range 0.9–1 in cyclohexane. Increasing solvent polarity or protic character reduces the FΔ values for all sensitizers except phenalenone. Laser-induced optoacoustic calorimetry was used to obtain the absolute FΔ values for the latter compound by applying both maximum amplitude and deconvolution methods. The former yields highly precise results (3%–5% uncertainty) and has been chosen for standardization purposes. The deconvolution method yields both kinetic and quantum yield data, albeit with lower precision (10%–15% uncertainty).

Photophysical Properties of Neutral and Cationic Tetrapyridinoporphyrazines

We describe the synthesis and photophysical properties of a series of neutral and cationic 3,4‐tetrapyridinoporphyrazines, potential lead photosensitizers for photodynamic inactivation of bacteria. Tetracationic TPyPzs exist essentially as monomers in aqueous systems, but the presence of trialkylated compounds due to incomplete quaternization of the outer nitrogen atoms induces severe aggregation. The absorption, fluorescence, triplet, and singlet oxygen quantum yields for both the neutral and cationic compounds are comparable to those of the related phthalocyanines.

Time-Resolved Near Infrared Studies on Singlet Oxygen Production by the Photosensitizing 2-Arylpropionic Acids†

Abstract— Time‐resolved near infrared emission studies have been carried out on a series of nonsteroidal anti inflammatory 2‐arylpropionic acids, in order to assess their ability to photosensitize the production of singlet molecular oxygen O2(1Δg). Benoxaprofen, naproxen, tiaprofenic acid, suprofen, ketoprofen and carprofen showed quantum yields for this process (φΔ) in the range 0.2‐0.7 in acetonitrile. Deprotonation of the propionic acid moiety in mixtures of acetonitrile‐ethanol (4:1) basified with KOH produced a systematic decrease in φΔ for all compounds with the exception of naproxen. This effect was even more dramatic in D2O‐based phosphate buffer, where no singlet oxygen could be detected for benoxaprofen, ketoprofen or carprofen. The above results are consistent with the occurrence of competing photochemical reactions of 2‐arylpropionic acids in different media and particularly with the enhanced photodecarboxylation from the carboxylate anions.

Light- and singlet oxygen-mediated antifungal activity of phenylphenalenone phytoalexins.

The light-induced singlet oxygen production and antifungal activity of phenylphenalenone phytoalexins isolated from infected banana plants (Musa acuminata) are reported. Upon absorption of light energy all studied phenylphenalenones sensitise the production of singlet oxygen in polar and non-polar media. Antifungal activity of these compounds towards Fusarium oxysporum is enhanced in the presence of light. These results, together with the correlation of IC50 values under illumination with the quantum yield of singlet oxygen production and the enhancing effect of D2O on the antifungal activity, suggest the intermediacy of singlet oxygen produced by electronic excitation of the phenylphenalenone phytoalexins.

C60 Fullerene-based materials as singlet oxygen O2(1Δg) photosensitizers: a time-resolved near-IR luminescence and optoacoustic study

The triplet properties of a series of fullerene dihydroderivatives of the o-quinodimethane type and of three representative inclusion complexes with γ-cyclodextrin and calix[8]arenes have been studied. It is found that chemical modification results in a decrease of the singlet oxygen quantum yield relative to C60, with an average ΦΔ = 0.76. On the other hand, encapsulation in either γ-cyclodextrin or calix[8]arene produces greatly varying results depending on host and solvent. Thus, in D2O the γ-cyclodextrin complex of C60 sensitizes O2(1Δg) with ΦΔ = 0.77, while the calixarene complex is totally ineffective, probably due to the occurrence of a fast charge transfer-mediated deactivation process. In CCl4 the calixarene complex acts very much like C60, i.e., ΦΔ = 0.84.

Benzoylation at the meso Position of a Zinc(II) Deuteroporphyrin

Summary. By short treatment of zinc(II) deuteroporphyrin-IX dimethyl ester with benzoic anhydride/SnCl4, a mixture of benzoylated derivatives was obtained from which a tribenzoyl derivative with benzoyl groups at the 2, 4, and γ-meso positions could be isolated in low yield. Except for the known Vilsmeier formylation, this constitutes the first example of a Friedel-Crafts acylation taking place at the meso position of a porphyrin chelate. The expected lack of regioselectivity of this reaction, even at low conversion rates, and the difficulty to separate the products limit, of course, its synthetic value for the preparation of the particular benzoyl derivatives. This limitation cannot be overcome by starting with a completely β-substituted porphyrin or with a symmetrically substituted porphyrin, since attempts to benzoylate Zn(II) mesoporphyrin-IX dimethyl ester lead exclusively to demetallation. However, these findings add to the knowledge of the fundamental properties of porphyrin reactivity. A rationalization based on calculations at a semiempirical level, which are in acceptable agreement with the experimental results, is presented.Zusammenfassung. Durch kurzes Behandeln von Zink(II)-Deuteroporphyrin-IX-dimethylester mit Benzoesäureanhydrid/SnCl4 wurde ein Gemisch von benzoylierten Derivaten erhalten, aus welchen in geringer Ausbeute ein Tribenzoylderivat isoliert werden konnte, das die Benzoylgruppen in 2-,4- und γ-meso-Position enthält. Abgesehen von der Vilsmeier-Formylierung stellt diese Reaktion das erste Beispiel einer Friedl-Crafts-Acylierung an der meso-Position eines Porphyrinchelates dar. Mangelnde Selektivität der Reaktion auch bei geringem Umsatz und die Schwierigkeiten bei der Trennung der Produkte engen natürlich ihre Bedeutung für die Synthese bestimmter Benzoylderivate ein. Dieser Mangel konnte auch nicht durch Verwendung von vollständig β-substituierten oder symmetrisch substituierten Porphyrinen behoben werden, da Versuche, Zn(II)-Mesoporphyrin-IX-dimethylester zu benzoylieren, ausschlieβlich das entmetallierte System ergaben. Allerdings tragen diese Resultate zum Wissen über die fundamentalen Reaktionsweisen von Porphyrinen wesentlich bei. Eine Rationalisierung der Ergebnisse kann auf der Basis von semiempirischen Rechen-methoden, deren Resultate mit den experimentellen Daten im Einklang stehen, gegeben werden.