Development of N-Cyclopropylanilines to Probe the Oxidative Properties of Triplet-State Photosensitizers

Revisiting triplet state dissolved organic matter (3DOM⁎): Advances in probes, photoreactivity, and environmental implications

Triplet-state dissolved organic matter (3DOM⁎) plays a critical role in the photodegradation of organic pollutants in aquatic environments. This review offers a comprehensive overview of 3DOM⁎, focusing on monitoring methods using various probes, formation mechanisms, and photoreactivity. Traditional probes, such as 2,4,6-trimethylphenol (TMP) and sorbic acid, are widely used, while novel probes promise improved accuracy and sensitivity. The E2:E3 ratio emerges as a promising indicator for 3DOM⁎ due to its simplicity and correlation with photoreactivity, though further validation is needed to confirm its broader applicability. This review highlights the higher photoreactivity of DOM with low molecular weight, low aromaticity, and autochthonous sources, although DOM with contrasting features can also show significant photoreactivity. The presence of inorganic ions and nanomaterials significantly influences 3DOM⁎'s degradation capacity, demonstrating complex interactions with surrounding species. Additionally, the review underscores the importance of various environmental factors, including light source and DOM concentration, in affecting the photodegradation rates of contaminants. Recent literature suggests that future research should focus on developing new probes to capture different aspects of 3DOM⁎, exploring the synergistic effects of plastic leachate, and investigating the role of co-existing ions and nanomaterials on 3DOM⁎ activity. Employing machine learning (ML) techniques to predict 3DOM⁎-related parameters from easily measurable DOM descriptors presents an exciting research avenue. Enhanced understanding of 3DOM⁎ can lead to more effective strategies in wastewater treatment and environmental remediation.

Room-Temperature CuI-Catalyzed N-Arylation of Cyclopropylamine

A general and efficient CuI/N-carbazolyl-1H-pyrrole-2-carbohydrazide catalyst system was developed for the N-arylation of cyclopropylamine using aryl bromides at room temperature. Herein, 5 mol % CuI and 5 mol % of the ligand were used to synthesize N-aryl cyclopropylamines in moderate to excellent yields. This protocol was scaled up to produce the desired product at gram levels and has been generalized for C-N coupling between aryl bromides and amines at room temperature.

Evaluation of Probes to Measure Oxidizing Organic Triplet Excited States in Aerosol Liquid Water

Oxidizing triplet excited states of organic matter (³C*) drive numerous reactions in fog/cloud drops and aerosol liquid water (ALW). Quantifying oxidizing triplet concentrations in ALW is difficult because ³C* probe loss can be inhibited by the high levels of dissolved organic matter (DOM) and copper in particle water, leading to an underestimate of triplet concentrations. In addition, illuminated ALW contains high concentrations of singlet molecular oxygen (¹O₂*), which can interfere with ³C* probes. Our overarching goal is to find a triplet probe that has low inhibition by DOM and Cu(II) and low sensitivity to ¹O₂*. To this end, we tested 12 potential probes from a variety of compound classes. Some probes are strongly inhibited by DOM, while others react rapidly with ¹O₂*. One of the probe candidates, (phenylthiol)acetic acid (PTA), seems well suited for ALW conditions, with mild inhibition and fast rate constants with triplets, but it also has weaknesses, including a pH-dependent reactivity. We evaluated the performance of both PTA and syringol (SYR) as triplet probes in aqueous extracts of particulate matter. While PTA is less sensitive to inhibition than SYR, it results in lower triplet concentrations, possibly because it is less reactive with weakly oxidizing triplets.

Synthesis of new coumarin[1,3]oxazine derivatives of 7-hydroxy-6-isobornyl-4-methylcoumarin and their antioxidant activity

In this work, we synthesized a series of new 9,10-dihydro-2H,8H-chromeno[8,7e][1,3]oxazine-2-on derivatives which incorporate isobornylcoumarin and 1,3-oxazine moieties. A structure-antioxidant activity relationship was analyzed. A comparative evaluation of their radical scavenging activity, antioxidant and membrane-protective properties was carried out in test with DPPH, as well as on the models of Fe²⁺ /ascorbate-initiated lipid peroxidation and oxidative hemolysis of mammalian red blood cells. The results suggest that all the obtained coumarin[1,3]oxazine derivatives of 7-hydroxy-6-isobornyl-4-methylcoumarin are capable of exhibiting antioxidant activity in various model systems. Compound 7 with a phenyl fragment, combining high radical scavenging activity and the ability to inhibit Fe²⁺ /ascorbate-initiated peroxidation of animal lipids in a heterogeneous environment, also proved to be the most effective membrane protector and antioxidant in the model of H₂ O₂ -induced erythrocyte hemolysis.

Activation of aminocyclopropanes via radical intermediates

Aminocyclopropanes are versatile building blocks for accessing high value-added nitrogen-containing products. To control ring-opening promoted by ring strain, the Lewis acid activation of donor-acceptor substituted systems is now well established. Over the last decade, alternative approaches have emerged proceeding via the formation of radical intermediates, alleviating the need for double activation of the cyclopropanes. This tutorial review summarizes key concepts and recent progress in ring-opening transformations of aminocyclopropanes via radical intermediates, divided into formal cycloadditions and 1,3-difunctionalizations.

Copper Inhibition of Triplet-Sensitized Phototransformation of Phenolic and Amine Contaminants

Excited triplet states of natural organic matter (³NOM*) are important reactive intermediates in phototransformation of organic contaminants in sunlit waters. The main goal of this study was to explore the influence of Cu on triplet-sensitized transformation rates of 20 selected phenolic and amine contaminants. Fourteen of the compounds examined exhibited a marked decrease in their 4-carboxybenzophenone (CBBP)-mediated phototransformation rate in the presence of trace amounts of Cu(II) (25-500 nM). Both mathematical modeling of these rate data and transient absorption spectroscopy measurements support the hypothesis that the decrease in the rate and extent of phototransformation of organic contaminants is due to the reduction of radical intermediates of the contaminants by photochemically formed Cu(I). The Cu-induced inhibition of oxidation of organic contaminants photosensitized by Suwannee River NOM (SRNOM) could also take place in the presence of nanomolar concentrations of Cu. The inhibitory effect of Cu on the oxidation rates of amine contaminants in SRNOM solutions was found to be significantly weaker compared to that in CBBP solutions, but little difference was observed on depletion of phenols. This behavior was attributed to the intrinsic inhibitory effect of the antioxidant moieties present in NOM on phototransformation of amine compounds, partially neutralizing the potential for further Cu inhibition.

Secondary organic aerosol formation from 3C⁎-initiated oxidation of 4-ethylguaiacol in atmospheric aqueous-phase

In this study, we investigated aqueous-phase triplet excited states (³C^⁎)-induced photo-degradation of 4-ethylguaiacol (EG) under both simulated sunlight and ultraviolet (UV) light irradiations. Through quencher experiments, the relative contributions of reactive oxygen species (ROS, such as ¹O₂/O₂^-/·OH) and ³C^⁎ were calculated and results showed three reactive species, e.g., ³C^⁎, ¹O₂ and O₂^-, all seemed to play important roles in the photo-degradation of EG, but contribution from ·OH was relatively minor. High steady-state ¹O₂ concentration after 1 h irradiation further revealed the major contribution of ¹O₂ to photo-degradation under Xe light irradiation. The degradation experiment under three saturated gases (air, O₂ and N₂) showed that the degradation rate in air-saturated condition was the largest owing to synergistic effect of ¹O₂ and ³C^⁎. Oxidative capacity of aqueous secondary organic aerosol (aqSOA) increased with reaction time by monitoring oxygen-to‑carbon (O/C) ratio and carbon oxidation state (OS_c) via an aerodyne soot particle aerosol mass spectrometer (SP-AMS). Moreover, aqSOA mass yields were calculated via SP-AMS data. The UV-vis spectral change suggested formation of light-absorbing organics at first stage under simulated sunlight irradiation. Based on the identified products and the reactive intermediates, we postulated that ³C^⁎-induced oxidation might be attributed to direct reactions by ³C^⁎ and ¹O₂, chemical reaction by ROS, as well as oligomerization via H-abstraction. To the best of our knowledge, this is the first time to explore systematically reaction pathways of 4-ethylguaiacol under ³C^∗ radical on the basis of thorough analysis of products and reactive species. Our findings highlight the impacts of aqSOA from biomass burning emissions on air quality and climate change.

Photodegradation of Fludioxonil and Other Pyrroles: The Importance of Indirect Photodegradation for Understanding Environmental Fate and Photoproduct Formation

Fludioxonil is a pyrrole-containing pesticide whose registration as a plant protection product is currently under review in the United States and Europe. There are concerns over its potential persistence and toxicity in the aquatic environment; however, the pyrrole moiety represents a potential reaction site for indirect photodegradation. In this study, the direct and indirect photodegradation of fludioxonil, along with pyrrole, 3-cyanopyrrole, and 3-phenylpyrrole, were investigated. Results showed that pyrrole moieties are capable of undergoing direct photoionization and sensitized photooxidation to form radical cation species, which then likely deprotonate and react with dissolved oxygen. Additionally, pyrrole moieties can undergo reactions with singlet oxygen (¹O₂). Furthermore, the presence of electron-withdrawing or -donating substituents substantially impacted the reaction rate with ¹O₂ as well as the one-electron oxidation potential of the pyrrole that dictates reactions with triplet states of dissolved organic matter (³CDOM*). For fludioxonil, which can undergo both direct and indirect photodegradation, the reaction rate constant with ¹O₂ alone resulted in a predicted t_1/2 < 2 days in waters under sunlit near-surface conditions, suggesting it will not be persistent in aquatic systems. These results are useful for evaluating the environmental fate of fludioxonil as well as other pyrrole compounds.