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Problem/Challenge

Problem/Challenge. hematite in cosmetics. Naturally occurring, incidental, and manufactured NPs are of different sizes and nanomorphologies. Which are more bioactive? Why? How NPs respond to facing biosystem?. Problem/Challenge.

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Problem/Challenge

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  1. Problem/Challenge hematite in cosmetics • Naturally occurring, incidental, and manufactured NPs are of different sizes and nanomorphologies. • Which are more bioactive? Why? • How NPs respond to facing biosystem?

  2. Problem/Challenge Nel, Madler, Velegol, Xia, Hoek, Somasundaran, Klaessig, Castranova, Thompson Nature Mat. 8, 2009, 543

  3. ‘Appropriate’ Characterization of NP, protein, system Why This Project is Unique? • In situ probing of • anisotropy in acid-base properties of adsorption sites on metal oxide nanoparticles (NP) in contact with water =LOCAL PROPERTIES IN SITU (!) • molecular structure and binding mode of adsorbed species Interpretation of Data Using Molecular Modeling

  4. Molecular Modeling: Chrysotile (Mg3Si2O5(OH)4) – Human Serum Albumin Artali et. al., J. R. Soc. Interface 2008, 5, 273 Latin: albus = white Modeled Domains of HSA Domains of HSA • Modification of HSA secondary structure • Loss of α-helix structure • Amino acid monolayer on chrysotile surface

  5. Objective of Initial Part of Project • To develop • in situ probe-molecule spectroscopic method to compare acid-base properties of different adsorption sites on basic metal oxide nanoparticles (NPs)

  6. Samples: Hematite and Ferrihydrite NPs H200 H38 H20 H7 Hematite H45 H600 H120 2-Line Ferrihydrite 7, 20, 38, 45, and 120 nm hematite was synthesized by forced hydrolysis; 200 nm hematite and 2-line ferrihydrite – commercial; phase purity was confirmed by XRD

  7. Effect of Nanomorphology on Average Acid-Base Properties of Hematite NPs Isoelectric point (IEP) by electrokinetic measurements; Point of Zero Charge (PZC) – by salt titration Macroscopic basicity has maximum at ~40nm It averages acid-base properties of different surface sites

  8. Adsorption of carbonate vs hematite NPs size/morphology I I II II II FH: one type of adsorbed CO32- 7-45 nm: two types of CO32- 120 nm: HCO3- dominates 200 nm: no adsorption 3O–C–O Fe-OH, 2Fe-O III III two-magnons abs-n CO32- adsorption is SPECIFIC to NP size in situ FTIR HATR spectra NPs at pH of 5.6 in situ FTIR HATR spectra NPs at pH of 5.6 1 3as 3s I

  9. I inner-sphere monodentate mononuclear (ISMM) I I I II II II inner-sphere bidentate binuclear (ISBB) II III III protonated inner-sphere monodentate mononuclear (ISMM-H) III DFT molecular modeling => structure of adsorbed complexes Selective adsorption of CO32-: basicity of terminal hydroxyls

  10. Conclusions • Carbonate adsorption is SPECIFIC for NP size • Selectivity can be correlated with size induced changes in surface structure and basicity of terminal hydroxyls • Heterogeneity in acid-base surface properties of NPs can be characterized using carbonate as a probe molecule • These findings are key to unraveling complex interactions with polypeptides and proteins

  11. Acknowledgements Work was supported by NSF grant #0925232

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