Mihai C.,Pacific Northwest National Laboratory |
Chrisler W.B.,Fundamental and Computational science Direct. |
Xie Y.,Pacific Northwest National Laboratory |
Hu D.,Pacific Northwest National Laboratory |
And 6 more authors.
Nanotoxicology | Year: 2013
Airborne nanoparticles (NPs) that enter the respiratory tract are likely to reach the alveolar region. Accumulating observations support a role for zinc oxide (ZnO) NP dissolution in toxicity, but the majority of in-vitro studies were conducted in cells exposed to NPs in growth media, where large doses of dissolved ions are shed into the exposure solution. To determine the precise intracellular accumulation dynamics and fate of zinc ions (Zn2+) shed by airborne NPs in the cellular environment, we exposed alveolar epithelial cells to aerosolized NPs at the air-liquid interface (ALI). Using a fluorescent indicator for Zn2+, together with organelle-specific fluorescent proteins, we quantified Zn2+ in single cells and organelles over time. We found that at the ALI, intracellular Zn2+ values peaked 3 h post exposure and decayed to normal values by 12 h, while in submerged cultures, intracellular Zn2+ values continued to increase over time. The lowest toxic NP dose at the ALI generated peak intracellular Zn2+ values that were nearly three-folds lower than the peak values generated by the lowest toxic dose of NPs in submerged cultures, and eight-folds lower than the peak values generated by the lowest toxic dose of ZnSO4 or Zn2+. At the ALI, the majority of intracellular Zn2+ was found in endosomes and lysosomes as early as 1 h post exposure. In contrast, the majority of intracellular Zn2+ following exposures to ZnSO4 was found in other larger vesicles, with less than 10% in endosomes and lysosomes. Together, our observations indicate that low but critical levels of intracellular Zn2+ have to be reached, concentrated specifically in endosomes and lysosomes, for toxicity to occur, and point to the focal dissolution of the NPs in the cellular environment and the accumulation of the ions specifically in endosomes and lysosomes as the processes underlying the potent toxicity of airborne ZnO NPs. © 2014 Informa UK Ltd. All rights reserved.
Cantu D.C.,Fundamental and Computational science Direct. |
McGrail B.P.,Pacific Northwest National Laboratory |
Glezakou V-A.,Fundamental and Computational science Direct.
Chemistry of Materials | Year: 2014
A detailed mechanism, based on density functional theory calculations and simulation, is presented outlining the formation of the secondary building unit (SBU) of MIL-101, a chromium terephthalate metal organic framework (MOF). Formation of the metal core and of the SBU is key to MOF nucleation, the rate-limiting step in the synthesis process of many MOFs. A series of reactions that lead to the formation of the SBU of MIL-101 is proposed in this work. The highest barrier (∼35 kcal/mol) involves the formation of a dimetal-linker intermediate and high to low spin transition as a third Cr-linker moiety joins to form a three metal-linker group joined by a central oxygen. The terephthalate linkers play an important, key mechanistic role with the carboxylates first joining chromium atoms prior to the formation of bridging oxygens. Subsequent to metal core formation, stepwise linker addition reactions generate different assembly pathways due to structural isomers that are limited by the removal of water molecules in the first chromium coordination shell. A simple kinetic model based on transition state theory gave a rate of SBU formation similar to a reported rate of MOF nucleation. The least energy path was identified with all linkers on the same face of the metal center added first. These first steps in developing a modeling framework for SBU formation will hopefully lay the groundwork for future comprehensive predictive models of the full MOF framework structure assembly and synthesis conditions required to support the self-assembly process. © 2014 American Chemical Society.