A versatile fluorescence approach to kinetic studies of hydrocarbon autoxidations and their inhibition by radical-trapping antioxidants

Abstract

We report a simple coumarin-triarylphosphine conjugate that undergoes fluorescence enhancement upon reaction with hydroperoxides and demonstrate its use to follow autoxidations of 7-dehydrocholesterol (at 37 °C) and hexadecane (at 160 °C) and their inhibition by antioxidants.

Acid Is Key to the Radical-Trapping Antioxidant Activity of Nitroxides

“…The concentration of hydroperoxide was determined from the rate of phosphine oxidation using the rate constant for the reaction of the dye with secondary hydroperoxides in tert-amyl alcohol (1.2 M −1 s −1 ) assuming pseudo-first-order kinetics. 31 In tandem, four duplicates (1.2 μL) of each sample were loaded into separate wells of a 96-well microplate; the automated reagent dispenser of the microplate reader was used to dilute each sample with 25% isopropyl alcohol in methanol (280 μL), and the plate was stirred for 15 s. Afterward, a solution of fluorogenic amine 3 (20 μL of a 630 μM stock in methanol) was added. The plate was stirred for 8 s, and the fluorescence of each well was measured every second for 10 s (excitation = 315 nm; emission = 395 nm) and the acid concentration was determined from the average fluorescence reading.…”

“…Paraffin autoxidations were carried out using an analogous procedure to hexadecane autoxidations previously carried out by our group. 30,31,43 Light paraffin oil (100 mL) was thoroughly degassed with N 2 and then heated to 160°C in a stirred flow reactor. Once the temperature stabilized, 0.04 mmol of bis(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl) decanedioate (2), the appropriate amount of either palmitic acid or 2,4,6-tri-tert-butylpyridine, and 82 mg (0.5 mmol) of tetralin hydroperoxide 49 were added to the solution.…”

“…Aliquots were removed at regular time intervals, and the hydroperoxide concentration in each was determined using our previously described profluorescent phosphine (1). 31 Since TEMPO is somewhat volatile at 160°C, a higher molecular weight analogue (2) was investigated, along with palmitic acid in lieu of the acetic acid used at ambient temperatures. 32 The results are shown in Figure 6A.…”

Relevance of Copper and Organic Cation Transporters in the Activity and Transport Mechanisms of an Anticancer Cyclometallated Gold(III) Compound in Comparison to Cisplatin

“…Solvents were dried and distilled under argon before use. Cisplatin was purchased at Sigma, while the precursor [Au(py b -H)Cl 2 ] and the coumarin-phosphine have been synthesized according to literature procedure (Cinellu et al, 1995 ; Hanthorn et al, 2012 ). The identity and purity (≥95%) of the gold complexes under investigation were unambiguously established using high-resolution mass spectrometry and NMR.…”

“…Here, we report on the synthesis and characterization of a novel cyclometallated C ∧ N gold(III) compound (Figure 2 ) [Au(py b -H)(PPh 2 Ar)Cl]PF 6 (PPh 2 Ar = 3-[4-(diphenylphosphino)phenyl]-7-methoxy-2H-chromen-2-one] ( 1 ) featuring a coumarin ligand endowed with “smart” fluorescence properties for imaging in cells by fluorescence microscopy (Hanthorn et al, 2012 ; Ali et al, 2015 ; Dondaine et al, 2016 ). The smart character of this probe involves a dramatic drop of the fluorescence when the metal is released, allowing a reliable tracking of the complex: if strong fluorescence is observed it means that the “P-Au” bond is intact.…”