Bovine serum albumin (BSA) nonspecifically binds to well-dispersed multiwalled carbon nanotubes (MWCNTs), forming a stable bioconjugate. After accounting for the inner filter effect, we found the fluorescence intensity of BSA was quenched by MWCNTs in static mode, which was authenticated by lifetime measurements and Stern-Volmer calculations. The thermodynamic parameters DeltaG(o), DeltaS(o), and DeltaH(o) were -9.67 x 10(3) + 2.48 x 10(3) ln lambda J x mol(-1), 41.0 - 0.828 ln lambda J x mol(-1) x K(-1), and 7.30 x 10(3) + 2.23 x 10(3) ln lambda J x mol(-1) (lambda < 1 x 10(-4)), respectively, which shows a spontaneous and electrostatic interaction. Scatchard analysis and UV-visible results provide statistical data concerning changes in the microenvironment of amide moieties in response to different doses of MWCNTs, revealing different behavior of the BSA molecules. The absorption spectra also show that the tertiary structure of the protein was partially destroyed. The content of secondary structure elements of BSA was changed by the tubes. This work elucidates the interaction mechanism of BSA and MWCNTs from a spectroscopic angle.

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p-Phenylenediamines (PPDs) have been extensively used in the rubber industry and found to be pervasive in various environmental compartments for decades, while their transformation products and associated ecological and human health risks remain largely unknown. Herein, we developed and implemented a mass spectrometrybased platform combined with self-synthesized standards for the investigation of rubber-derived quinones formed from PPD antioxidants. Our results demonstrated that five quinones are ubiquitously present in urban runoff, roadside soils, and air particles. All of the identified sources are closely related to mankind's activities. Among the identified quinones, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone has been recently found to be highly toxic, causing acute mortality of coho salmon in the Pacific Northwest. Ultrahigh-performance liquid chromatography coupled with triple quadrupole mass spectrometry was then applied for quantification of the five quinones and their corresponding PPD antioxidants. The results revealed interesting distinct distribution and concentration patterns of PPD-derived quinones in different environmental matrices. Daily intake rates of these quinones in a compact city of Hong Kong were estimated to be varied from 1.08 ng/(kg•day) for adults to 7.30 ng/(kg•day) for children, which were higher than the exposure levels of their parent compounds. Considering the prevalence of the use of rubber products, the outcome of this study strongly suggests for additional toxicological studies to investigate potential ecological and human health risks of the newly discovered quinones.

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Understanding the mechanism of nanosilver-dependent antibacterial activity against microorganisms helps optimize the design and usage of the related nanomaterials. In this study, we prepared four kinds of 10 nm-sized silver nanoparticles (AgNPs) with dictated surface chemistry by capping different ligands, including citrate, mercaptopropionic acid, mercaptohexanoic acid, and mercaptopropionic sulfonic acid. Their surface-dependent chemistry and antibacterial activities were investigated. Owing to the weak bond to surface Ag, short carbon chain, and low silver ion attraction, citrate-coated AgNPs caused the highest silver ion release and the strongest antibacterial activity against Escherichia coli , when compared to the other tested AgNPs. The study on the underlying antibacterial mechanisms indicated that cellular membrane uptake of Ag, NAD + /NADH ratio increase, and intracellular reactive oxygen species (ROS) generation were significantly induced in both AgNP and silver ion exposure groups. The released silver ions from AgNPs inside cells through a Trojan-horse-type mechanism were suggested to interact with respiratory chain proteins on the membrane, interrupt intracellular O 2 reduction, and induce ROS production. The further oxidative damages of lipid peroxidation and membrane breakdown caused the lethal effect on E. coli . Altogether, this study demonstrated that AgNPs exerted antibacterial activity through the release of silver ions and the subsequent induction of intracellular ROS generation by interacting with the cell membrane. The findings are helpful in guiding the controllable synthesis through the regulation of surface coating for medical care purpose.

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