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
Nel, Madler, Velegol, Xia, Hoek, Somasundaran, Klaessig, Castranova, Thompson Nature Mat. 8, 2009, 543
‘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 (Mg3Si2O5(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, 273Latin: 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 H38H20
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 ~40nmIt averages acid-base properties of different surface sites
Macroscopic basicity has maximum at ~40nmIt averages acid-base properties of different surface sites
0 50 100 150 200
6.5
7.0
7.5
8.0
8.5
9.0
9.5
PZ
C, I
EP
NP Size, nm
PZC IEP
1800 1600 1400 1200 1000 800
FH, 2nm
7nm
20 nm
38 nm
45 nm
120 nm
200 nm
Wavenumber, cm-1
H2O
Abs
orba
nce,
AU
3s
13as
Adsorption of carbonate vs hematite NPs size/morphology
two-magnons abs-n
in situ FTIR HATR spectra NPs at pH of 5.6
CO32- adsorption is SPECIFIC to NP size
FH: one type of adsorbed CO32-
7-45 nm: two types of CO32-
120 nm: HCO3- dominates
200 nm: no adsorption
3O–C–OFe-OH, 2Fe-O
I I I
IIII
II
IIIIII
in situ FTIR HATR spectra NPs at pH of 5.6
1800 1600 1400 1200 1000 800
FH, 2nm
7nm
20 nm
38 nm
45 nm
120 nm
200 nm
Wavenumber, cm-1
H2O
Abs
orba
nce,
AU
inner-sphere monodentate mononuclear (ISMM)
II
I
I
IIIIII
inner-sphere bidentate binuclear (ISBB)II
Selective adsorption of CO32-: basicity of terminal hydroxyls
DFT molecular modeling => structure of
adsorbed complexes
protonatedinner-sphere monodentate
mononuclear (ISMM-H)
IIIIII
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
