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Problem/Challenge hematite in cosmetics Naturally occurring, incidental, and manufactured NPs are of different sizes and nanomorphologies. Which are more.

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Presentation on theme: "Problem/Challenge hematite in cosmetics Naturally occurring, incidental, and manufactured NPs are of different sizes and nanomorphologies. Which are more."— Presentation transcript:

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 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 Why This Project is Unique? Interpretation of Data Using Molecular Modeling

4 Molecular Modeling: Chrysotile (Mg 3 Si 2 O 5 (OH) 4 ) – Human Serum Albumin Domains of HSA Modeled Domains of HSA Modification of HSA secondary structure Loss of α-helix structure Amino acid monolayer on chrysotile surface Artali et. al., J. R. Soc. Interface 2008, 5, 273 Latin: albus = white

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 H7 H38 H20 H200 H600 H120 Samples: Hematite and Ferrihydrite NPs Hematite 2-Line Ferrihydrite H45 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 Macroscopic basicity has maximum at ~40nm It averages acid-base properties of different surface sites

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

9 inner-sphere monodentate mononuclear (ISMM) I I I I II inner-sphere bidentate binuclear (ISBB) II Selective adsorption of CO 3 2- : basicity of terminal hydroxyls DFT molecular modeling => structure of adsorbed complexes protonated inner-sphere monodentate mononuclear (ISMM-H) III

10 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 Conclusions

11 Acknowledgements Work was supported by NSF grant #


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