The Overlooked Photochemistry of Iodine in Aqueous Suspensions of Fullerene Derivatives

Abstract

Fullerene’s low water solubility was a serious challenge to researchers aiming to harness their excellent photochemical properties for aqueous applications. Cationic functionalization of the fullerene cage provided the most effective approach to increase water solubility, but common synthesis practices inadvertently complicated the photochemistry of these systems by introducing iodide as a counterion. This problem was overlooked until recent work noted a potentiation effect which occurred when photosensitizers were used to inactivate microorganisms with added potassium iodide. In this work, several photochemical pathways were explored to determine the extent and underlying mechanisms of iodide’s interference in the photosensitization of singlet oxygen by cationic fulleropyrrolidinium ions and rose bengal. Triplet excited state sensitizer lifetimes were measured via laser flash photolysis to probe the role of I – in triplet sensitizer quenching. Singlet oxygen production rates were compared across sensitizers in the presence or absence of I – , SO 4 2– , and other anions. 3,5-Dimethyl-1 H -pyrazole was employed as a chemical probe for iodine radical species, such as I·, but none were observed in the photochemical systems. Molecular iodine and triiodide, however, were found in significant quantities when photosensitizers were irradiated in the presence of I – and O 2 . The formation of I 2 in these photochemical systems calls into question the interpretations of prior studies that used I – as a counterion for photosensitizer materials. As an example, MS2 bacteriophages were inactivated here by cationic fullerenes with and without I – present, showing that I – moderately accelerated the MS2 deactivation, likely by producing I 2 . Production of I 2 did not appear to be directly correlated with estimates of 1 O 2 concentration, suggesting that the relevant photochemical pathways are more complex than direct reactions between 1 O 2 and I – in the bulk solution. On the basis of the results here, iodine photochemistry may be underappreciated and misunderstood in other environmental systems.

Ultraefficient OG-Mediated Photodynamic Inactivation Mechanism for Ablation of Bacteria and Biofilms in Water Augmented by Potassium Iodide under Blue Light Irradiation

“…3,5-Dimethyl-1 H -pyrazole (DMPZ), as a probe for iodine radicals (I • , I 2 •– ), was likely to form I – DMPZ under light irradiation through the addition reaction . The mixture solution of OG (0.15 mM) and KI (250 mM) with DMPZ (10 μM) was under BL irradiation for 0, 30, 60, and 90 min (420 nm, 210 mW/cm 2 ).…”

Carboxyfullerene C60 preserves sperm by enhancing antioxidant capacity and inhibiting apoptosis and harmful bacteria

“…As a result, it is only soluble in benzene, toluene, and other aromatic solvents [21]. It has been reported that underived fullerene C 60 has low solubility in polar solvents and a solubility of only 1.3 × 10 − 11 g/L in water at 17°C [22]; these properties limit its application in the biomedical eld. Therefore, chemical modi cation methods based on the amino, carboxyl, and hydroxyl groups are often used to modify its physical and chemical properties and improve its bioavailability.…”