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:
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?
‘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
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
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)
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
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
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 3 2- 7-45 nm: two types of CO 3 2- 120 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
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
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
Acknowledgements Work was supported by NSF grant #0925232
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