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Amino Acid Adhesion on TiO2 Surface DFT Model. Francesco Buonocore Caterina Arcangeli , Massimo Celino , Ivo Borriello ENEA - C.R. Casaccia and NAST Centre Computational Material Science and technology (CMAST) Laboratory www.afs.enea.it/project/cmast - PowerPoint PPT Presentation
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Amino Acid Adhesion on TiO2 Surface DFT Model
Francesco BuonocoreCaterina Arcangeli, Massimo Celino, Ivo Borriello
ENEA - C.R. Casaccia and NAST CentreComputational Material Science and technology (CMAST) Laboratorywww.afs.enea.it/project/cmast
”Biosystems, Energy, and Cultural Heritage:Materials Enhancement for technological application”
July 3rd 2013 - Università di Roma Tor Vergata
Density functional theory (DFT) let us model the following interactions that molecular dynamics cannot describe:
• Covalent bond formation• Electron charge distribution
Therefore we give a close look to the region of the amino acid/TiO2 surface interaction by means of DFT methods
Why density functional theory?
We focus on the following amino acids
-NH-C-(NH2)2-CH2-COO
Terminal groups of side-chains interacting with TiO2 surface
R D
Bulk O are bonded to 3 Ti atoms -> O(3c)
Bulk Ti are bonded to 6 O atoms -> Ti(6c)
Low coordinated Ti(5c) and O(2c) on surface layer: they represent the most reactive points of the surface
TiO2 (101) anatase reconstructed surface
•Anatase is the most probable phase of TiO2 oxide surface formation•The 101 orientation represents the most stable recontruction in TiO2 anatase phase
TiO2 (101) anatase recontruction
Ti(6c) O(2c) Ti(5c) O(3c)
ARGININE on TiO2 (101) anatase: bound configurations
5) O(2c) & O(2c)
O(2c)-H bonds lenght lying in 1.7 – 2.2 Å
2) O(2c)
3) O(2c) & O(3c) 4) 2 x O(2c)
1 2 3 4 5
-6.5
-6.0
-5.5
-5.0
-4.5
-4.0
configuration
Bin
din
g E
ne
rgy (
eV
)Free ARG
Free ARG = 10 Å far away from TiO2 surface
ASPARTIC ACID on TiO2 (101) anatase : bound configurations
6) 2 x Ti(5c)COOH towards O(3c)
Ti-O bonds lenght lying in
1.9 – 2.2 Å
2) Ti(5c)
4) 2 x Ti(6c)5) 2 x Ti(5c)
COOH towards O(2c)
1 2 3 4 5 6
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
1.6B
ind
ing
En
erg
y (
eV
)
configuration
Free ASP
Free ASP = 10 Å far away from TiO2 surface
ARGININE on TiO2 (101) anatase: charge density analysis
Negative charge density difference charge depletion
charge density
Positive charge density difference
charge accumulation
Electron charge is removed from H and TiO2
Electron charge moves on N and H-O bond
ASPARTIC ACID on TiO2 (101) anatase: charge density analysis
Negative charge density difference charge depletion
charge density
Positive charge density difference
charge accumulation
Electron charge
moves on O-Ti bond and TiO2
Electron charge is not removed from TiO2
• The mediation of a water layer can be included in the DFT models
• The role of van der Waals interactions can also be investigated
• How to include environmental water effects?
Challenges
• The adhesion of the amino acid side-chains to TiO2 substrate has been modeled for arginine and aspartic acid.• The most stable configurations and their binding energies have been calculated.• Arginine (positive ion) adhesion does involve a charge transfer from TiO2 to amino acid. In aspartic acid (negative ion) this effect is reversed.• DFT models provide information complementary to that provided by MD
Conclusions