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DPPH (2,2-Diphenyl-1-picrylhydrazyl) is a cell-permeable, stable free radical commonly used to evaluate the free radical scavenging ability, hydrogen donation capacity of compounds, and to measure the antioxidant activity of tissue extracts.

PAA5, a methide carbon-centered polynuclear gold(I) (Au(I)) cluster, exhibits anticancer activity by releasing Au(I) to induce a pro-oxidant response and accelerated ferroptosis. Additionally, PAA5 increases the expression of pH2AX in a time-dependent manner, further contributing to its anticancer properties [1].

DMPO (5,5-Dimethyl-1-pyrroline N-oxide) is a kind of water-soluble nitric oxide spin trap, which allows the measurement of oxygen-centered free radicals in biological systems at room temperature using electron spin resonance. It has a high reaction rate constant for superoxide and hydroxyl radicals and distinguishes simultaneously among a variety of important biologically generated free radicals.

DEPMPO is a nitrone that is used to spin trap reactive O-, N-, S-, and C-centered radicals and allow their characterization when used in association with electron spin resonance. It is noted for the stability of adducts formed. DEPMPO can be used in vitro or in vivo, as it crosses lipid bilayer membranes and is a good trapping agent in biological systems. DEPMPO-biotin is a biotinylated form of DEPMPO which retains the outstanding persistency of its adducts. The biotin moiety offers an effective means for monitoring biodistribution in cells, tissues, and organs when used with an avidin-conjugated reporter. Importantly, DEPMPO-biotin binds free radicals, such as S-nitroso groups, on proteins, producing adducts that can be analyzed via the biotin tag. This direct labeling of S-nitrosothiols (SNO) thus serves as an effective alternative to the more cumbersome biotin-switch method for monitoring SNO formation.

PAA4, a methide carbon-centered polynuclear Au(I) cluster, exhibits antiproliferative activity and induces pH2AX expression in a time-dependent manner. It also demonstrates an anti-tumor effect in an orthotopic bladder cancer mouse model [1].

Dihydrolipoic acid (USAF XR-12), a dithiol-containing carboxylic acid, acts as a general antioxidant that is highly reactive against a variety of reactive oxygen species, including peroxynitirite, hydroxyl radicals, hydrogen peroxide, and hypochlorite, at concentrations ranging from 0.01-0.5 mM.

MitoPBN is a mitochondria-targeted antioxidant that accumulates in the mitochondria following the generation of a mitochondrial membrane potential by succinate, an effect blocked by the addition of the mitochondrial membrane potential uncoupler FCCP. MitoPBN inhibits superoxide activation of mitochondrial uncoupling protein 1 (UCP1), UCP2, and UCP3 at a concentration of 250 nM in vitro, but does not react with superoxide. It traps hydroxyl (IC50 = ~77 μM) and carbon-centered radicals and inhibits the initiation of lipid peroxidation in isolated bovine heart mitochondria.