title: Evaluation of the catalytic activity and cytotoxicity of palladium nanocubes: the role of oxygen.
abstract: Recently, it has been reported that palladium nanocubes (PdNC) are capable of generating singlet oxygen without photoexcitation simply via chemisorption of molecular oxygen on its surface. Such a trait would make PdNC a highly versatile catalyst suitable in organic synthesis and a Reactive Oxygen Species (ROS) inducing cancer treatment reagent. Here we thoroughly investigated the catalytic activity of PdNC with respect to their ability to produce singlet oxygen and to oxidize 3,3',5,5'-tetramethylbenzidine (TMB), and analyzed the cytotoxic properties of PdNC on HeLa cells. Our findings showed no evidence of singlet oxygen production by PdNC. The nanocubes' activity is not necessarily linked to activation of oxygen. The oxidation of substrate on PdNC can be a first step, followed by PdNC regeneration with oxygen or other oxidant. The catalytic activity of PdNC toward the oxidation of TMB is very high and shows direct two-electron oxidation when the surface of the PdNC is clean and the ratio of TMB/PdNC is not very high. Sequential one electron oxidation is observed when the pristine quality of PdNC surface is compromised by serum or uncontrolled impurities and/or the ratio of TMB/PdNC is high. Clean PdNC in serum-free media efficiently induce apoptosis of HeLa cells. It is the primary route of cell death and is associated with hyperpolarization of mitochondria, contrary to a common mitochondrial depolarization initiated by ROS. Again, the effects are very sensitive to how well the pristine surface of PdNC is preserved, suggesting that PdNC can be used as an apoptosis inducing agent, but only with appropriate drug delivery system.
authors.affiliation: †Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, United States.
authors.forename: Eshan
authors.initials: E
authors.lastname: Dahal
authors.affiliation: †Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, United States.
authors.forename: Jessica
authors.initials: J
authors.lastname: Curtiss
authors.affiliation: †Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, United States.
authors.forename: Deepak
authors.initials: D
authors.lastname: Subedi
authors.affiliation: §Department of Chemical Engineering, New Mexico State University, Las Cruces, New Mexico 88003, United States.
authors.forename: Gen
authors.initials: G
authors.lastname: Chen
authors.affiliation: §Department of Chemical Engineering, New Mexico State University, Las Cruces, New Mexico 88003, United States.
authors.forename: Jessica P
authors.initials: JP
authors.lastname: Houston
authors.affiliation: †Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, United States.
authors.forename: Sergei
authors.initials: S
authors.lastname: Smirnov
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001560:Benzidines / Q000737:chemistry; D002384:Catalysis / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D005453:Fluorescence; D006367:HeLa Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D053758:Nanoparticles / Q000633:toxicity* / Q000648:ultrastructure; D010084:Oxidation-Reduction / Q000187:drug effects; D010100:Oxygen / Q000494:pharmacology*; D010165:Palladium / Q000633:toxicity*; D011419:Propidium / Q000378:metabolism; D020112:Rhodamine 123 / Q000378:metabolism; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors
chemical_list: D001560:Benzidines; D012996:Solutions; D020112:Rhodamine 123; D011419:Propidium; C021758:3,3',5,5'-tetramethylbenzidine; D010165:Palladium; D006861:Hydrogen Peroxide; D010100:Oxygen
keywords: Palladium nanocubes; ROS; cancer treatment; catalytic activity; cytotoxicity