New Route to Toxic Nitro and Nitroso Products upon Irradiation of Micropollutant Mixtures Containing Imidacloprid: Role of NO and Effect of Natural Organic Matter.

In this study, we reveal the capacity of imidacloprid (a neonicotinoid insecticide) to photoinduce the nitration and nitrosation of three aromatic probes (phenol, resorcinol, and tryptophan) in water. Using a gas-flow reactor and a NO analyzer, the production of gaseous NO/NO was demonstrated during irradiation (300-450 nm) of imidacloprid (10 M). Quantum calculations showed that the formation of NO proceeds via homolytic cleavage of the RN-NO bond in the triplet state.

Contrasting photoreactivity of β2-adrenoceptor agonists Salbutamol and Terbutaline in the presence of humic substances.

The photodegradation reactions of two typical β2-adrenoceptor agonists, salbutamol (SAL) and terbutaline (TBL), alone, and in the presence of Aldrich humic acid (AHA) or Suwannee River fulvic acid (SRFA) were investigated by steady-state photolysis experiments, laser flash photolysis (LFP), kinetic modeling and quantum calculation. AHA and SRFA (2-20 mgC L) accelerated the phototransformation of both SAL and TBL. For SAL, an inhibiting effect of oxygen on the photodegradation was observed that is fully consistent with the main involvement of excited triplet states of HS (HS*).

Unravelling the reactivity of bifenazate in water and on vegetables: Kinetics and byproducts.

In this study, we aimed to better understand the transformation mechanisms of bifenazate, a biphenyl hydrazine derivative insecticide poorly studied up to now. For this, we compared its reactivity in the dark and under simulated solar light irradiation in different media (water, non-aqueous polar solvent, surface of apolar wax films, skin of vegetable). In air-saturated pH = 5.

Sulfate radical induced degradation of β2-adrenoceptor agonists salbutamol and terbutaline: Phenoxyl radical dependent mechanisms.

The present study investigated the reactivity and oxidation mechanisms of salbutamol (SAL) and terbutaline (TBL), two typical β2-adrenoceptor agonists, towards sulfate radical (SO) by using photo-activated persulfate (PS). The reaction pathways and mechanisms were proposed based on products identification using high resolution HPLC-ESI-MS, laser flash photolysis (LFP) and molecular orbital calculations. The results indicated that SO was the dominant reactive species in the UV/PS process.

Photoreactivity of the fungicide chlorothalonil in aqueous medium.

The photoreactivity of chlorothalonil was studied by means of steady-state irradiation and laser-flash photolysis. Experiments were conducted in water containing acetonitrile as a co-solvent. This fungicide undergoes very slow phototransformation in the first stages of the reaction, but the consumption profile is auto-accelerated.

The polysiloxane cyclization equilibrium constant: a theoretical focus on small and intermediate size rings.

The nonlinear dependence of polysiloxane cyclization constants (log(K(x))) with ring size (log(x)) is explained by a thermodynamic model that treats specific torsional modes of the macromolecular chains with a classical coupled hindered rotor model. Several parameters such as the dependence of the internal rotation kinetic energy matrix with geometry, the effect of potential energy hindrance, anharmonicity, and the couplings between internal rotors were investigated. This behavior arises from the competing effects of local molecular entropy that is mainly driven by the intrinsic transformation of vibrations in small cycles into hindered rotations in larger cycles and configurational entropy.

Toward a better understanding of Fe(III)-EDDS photochemistry: theoretical stability calculation and experimental investigation of 4-tert-butylphenol degradation.

The present work describes in detail the chemical structure of the complex Fe(III)–EDDS and the predominance of different species with respect to pH. These results were obtained with ab initio calculations. From the photoredox process, the formation of hydroxyl radical was confirmed, and HO(•) is the main species responsible for the degradation of the organic compound present in aqueous solution.

Phototransformation of azoxystrobin fungicide in organic solvents. Photoisomerization vs. photodegradation.

Azoxystrobin is a systemic fungicide that has a tendency to accumulate at the surface of crop leaves or inside their cuticle where it undergoes photodegradation. Its photochemistry was investigated in n-heptane and isopropanol to mimic the polarity of wax leaves. Using analytical and kinetic data, we demonstrate that azoxystrobin (isomer E) undergoes efficient photoisomerization into the isomer Z with a quantum yield of 0.

Photolysis of cycloxydim, a cyclohexanedione oxime herbicide. Detection, characterization and reactivity of the iminyl radical.

Cyclohexanedione oxime herbicides have been reported to be readily photodegraded in the environment but the reaction mechanism has never been studied in detail. Here we investigated the photolysis of cycloxydim (CD) in acetonitrile and water, solvents in which CD is present as two distinct tautomeric forms: keto form in water and enol form with an intramolecular hydrogen bond between the enolic proton and the nitrogen atom of the oxime in acetonitrile O-H···N. CD (E isomer) undergoes photoisomerization in water but not in acetonitrile.

The role of triplet state keto-enol tautomerism in the photodeamination of metamitron.

Substituted 4-amino-1,2,4-triazin-5-ones undergo photodeamination through cleavage of the N-NH(2) bond in the presence of oxygen and water. To elucidate the mechanism of this reaction, we investigated the photolysis of metamitron (4-amino-6-phenyl-3-methyl-1,2,4-triazin-5-one) by nanosecond laser flash photolysis, steady-state irradiation, and ab initio calculations. Upon pulsed laser excitation of deoxygenated aqueous metamitron, two transient species are clearly detected.

Molecular simulation of excimer fluorescence in polystyrene and poly(vinylcarbazole).

In fluorescence emission spectra of poly(vinylcarbazole) (PVK), two types of excimers are observed, the fully and the partially overlapped excimers, namely, excimers and exciplexes. In this work, we investigated the structural changes induced by the transition between electronic levels S(0) and S(1). Furthermore, the widely used assumption of similar potential energy surfaces in the S(0) and S(1) states and its use in molecular dynamics simulations are thoroughly examined for PVK and polystyrene (PS).