Changes to nanoparticle surface charge, colloidal stability, and hydrodynamic properties induced by interaction with natural organic matter (NOM) warrant consideration in assessing the potential for these materials to adversely impact organisms in the environment. Here, we show that acquisition of a coating, or "corona", of NOM alters the hydrodynamic and electrokinetic properties of diamond nanoparticles (DNPs) functionalized with the polycation poly(allylamine HCl) in a manner that depends on the NOM-to-DNP concentration ratio. The NOM-induced changes to DNP properties alter subsequent interactions with model biological membranes and the Gram-negative bacterium Shewanella oneidensis MR-1. Suwannee River NOM induces changes to DNP hydrodynamic diameter and apparent ζ-potential in a concentration-dependent manner. At low NOM-to-DNP ratios, DNPs aggregate to a limited extent but retain a positive ζ-potential apparently due to nonuniform adsorption of NOM molecules leading to attractive electrostatic interactions between oppositely charged regions on adjacent DNP surfaces. Diamond nanoparticles at low NOM-to-DNP ratios attach to model membranes to a larger extent than in the absence of NOM (including those incorporating lipopolysaccharide, a major bacterial outer membrane component) and induce a comparable degree of membrane damage and toxicity to S. oneidensis. At higher NOM-to-DNP ratios, DNP charge is reversed, and DNP aggregates remain stable in suspension. This charge reversal eliminates DNP attachment to model membranes containing the highest LPS contents studied due to electrostatic repulsion and abolishes membrane damage to S. oneidensis. Our results demonstrate that the effects of NOM coronas on nanoparticle properties and interactions with biological surfaces can depend on the relative amounts of NOM and nanoparticles.

In recent years, nanomaterials have entered our daily lives via consumer products; thus, it has become increasingly important to implement activities to introduce these novel materials into chemistry curricula. Here we introduce a newly developed fluorescent nanomaterial, carbon dots, as a more environmentally friendly alternative to heavy-metal semiconductor quantum dots to be used as a model nanomaterial for experiments at multiple educational levels ranging from high school to upper-division college laboratories. These dots, which are polymeric in nature, can be made from a variety of carbon precursors and a cross-linker such as ethylenediamine. The synthesis, which involves heating in a conventional microwave, is quick and straightforward and can be carried out in typical high school chemistry laboratories. The resulting solution is fluorescent without further purification. To increase the complexity for entry-level college students, absorption and emission spectra of the carbon dot solution can be collected as an introduction to spectroscopy. In more advanced undergraduate lab courses, the quantum yield can be determined with a standard reference fluorescent material such as quinine sulfate. Atomic force microscopy or transmission electron microscopy images can also be collected to illustrate the morphology of these particles where such specialty instruments are accessible.

Cobalt phosphate engineered nanomaterials (ENMs) are an important class of materials that are used as lithium ion battery cathodes, catalysts, and potentially as super capacitors. As production of these nanomaterials increases, so does the likelihood of their environmental release; however, to date, there are relatively few investigations of the impact of nanoscale metal phosphates on biological systems. Furthermore, nanomaterials used in commercial applications are often multiphase materials, and analysis of the toxic potential of mixtures of nanomaterials has been rare. In this work, we studied the interactions of two model environmental bacteria, Shewanella oneidensis MR-1 and Bacillus subtilis, with a multiphase lithiated cobalt phosphate (mLCP) nanomaterial. Using a growth-based viability assay, we found that mLCP was toxic to both bacteria used in this study. To understand the observed toxicity, we screened for production of reactive oxygen species (ROS) and release of Co 2+ from mLCP using three abiotic fluorophores. We also used Newport Green DCF dye to show that cobalt was taken up by the bacteria after mLCP exposure. Using transmission electron microscopy, we noted that the mLCP was not associated with the bacterial cell surface. In order for us to further probe the mechanism of interaction of mLCP, the bacteria were exposed to an equivalent dose of cobalt ions that dissolved from mLCP, which recapitulated the changes in viability when the bacteria were exposed to mLCP, and it also recapitulated the observed bacterial uptake of cobalt. Taken together, this implicates the release of cobalt ions and their subsequent uptake by the bacteria as the major toxicity mechanism of mLCP. The properties of the ENM govern the release rate of cobalt, but the toxicity does not arise from nanospecific effectsand importantly, the chemical composition of the ENM may dictate the oxidation state of the metal centers and thus limit ROS production.

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alkaline earth metals alkaline earth metals I 1000 -016Mercaptophenol-Protected Gold Colloides as Nuclei for the Crystallization of Inorganic Minerals: Templated Crystallization on Curved Surfaces.-Deposition and growth of inorganic materials is controlled by use of self-assembled monolayers of ω-substituted alkylthiols on Au(111) surfaces for crystallizing calcium and strontium carbonates from solution. The utility of such a designer seeding is demonstrated by the crystallization of CaCO 3 in the calcite modification and SrCO 3 in the strontionite form. -(KUETHER, J.; SESHADRI, R.; NELLES, G.; ASSENMACHER, W.; BUTT, H.