Aminoparathion: A Highly Reactive Metabolite of Parathion. 1. Reactions with Polyphenols and Polyphenol Oxidase

Abstract

Spiking of tomato and apple fruits with parathion at different levels of about 1-4 mg/kg irradiation and under simulated sunlight conditions resulted in nearly complete photodegradation within 13 h, but extractable parathion degradation products could not be found in any case. However, after irradiation of an unrealistically spiked apple (134 mg/kg) different photoproducts including aminoparathion (AP) were detectable by HPLC, proving that the hitherto postulated photochemistry of parathion indeed takes place in the fruit cuticle environment. Besides the photoreduction pathway it was shown for the first time that AP is also easily formed by reduction of the primary photoproduct nitrosoparathion with thiols (cysteine, glutathione), while ascorbic acid only leaves hydroxylaminoparathion. In the presence of polyphenols, AP was effectively bound to quinone intermediates formed by both silver oxide and polyphenol oxidases. For pyrocatechol, a disubstituted o-quinone derivative could be isolated as a dark red addition product and structurally be elucidated. However, in the presence of caffeic acid, catechol, naringin, and quercetin, respectively, insoluble dark colored polymers precipitated within 48 h, while in the supernatants AP was not detectable any more. Polymer-bound and nonextractable AP was proven by transesterification with sodium ethoxide releasing O,O,O-triethyl thiophosphate which was determined by GC. Additionally, AP itself was a substrate for polyphenol oxidases, resulting in a quinone imine intermediate which in turn reacted with excessive AP yielding deep red colored di- and trimerization products.

Usefulness of Fluorescent Probe Prodan To Gain Insight into the Polarity of Plant Cuticles

“…The only difference between the two emission spectra is a small increase of the full width at half-maximum of 2 nm (6%). This finding shows that (1) Prodan is fully impregnated in the paraffin and does not form aggregates that should give an emission around 430 nm, (2) the emission of Prodan is not influenced by the physical state of the medium, but by its chemical nature, and (3) a small band broadening occurs in solid state, which is attributed to interactions of Prodan with the solid environment …”

“…(3) a small band broadening occurs in solid state, which is attributed to interactions of Prodan with the solid environment. 10 Relationship between the Emission Characteristics of Prodan and Properties of the Medium. To explain the experimental shift of emission maximum of Prodan embedded in different solid media, we attempted to establish a correlation between emission frequency and the properties of the heterogeneous media (docosanol and wax paraffin).…”

“…Because the cuticle is a barrier to the uptake of pesticides by plants, better knowledge of compartment is essential for improving the transfer and delivery of such agrochemicals , and in the studies investigating their reactivity/photoreactivity inside the cuticle. , Fluorescence is a nondestructive technique that has been successfully employed to study the cuticle and the interactions with chemicals. For instance, fluorescence was used to visualize the distribution of fluorescent pollutants in leaves, , to monitor the uptake of labeled adjuvants or of xenobiotics through the cuticle, , or to image the cuticle architecture .…”

Studying Lipophilicity Trends of Phosphorus Compounds by 31P-NMR Spectroscopy: A Powerful Tool for the Design of P-Containing Drugs

“…Triethylphosphorothioate (3a). 45 Diethyl phosphorochloridothioate (1.0 g, 0.785 mL, 5.3 mmol) was added dropwise under argon to a solution of sodium ethoxide (21% w/w in ethanol denatured, 2.3 g). The mixture was stirred overnight under argon at room temperature, and afterward, DCM (3 mL) was added.…”

Photochemistry of Imidacloprid in Model Systems

“…Among the products, photoaddition products with alcohols and olefins were detected that deliver reaction mechanisms for the formation of covalently bound residues with constituents of the plant cuticle. As imidacloprid, parathion also contains a nitro group, which was first photoreduced to nitrosoparathion and finally to aminoparathion, both of which are rather reactive toward plant cuticle constituents − . Thus, we conducted photolysis studies using our well-established model systems to study and understand the general photochemistry of imidacloprid to be expected on fruit and leaf surfaces.…”