nanodiamond mechanical properties and...
TRANSCRIPT
Nanodiamond
mechanical properties and chemistry
George Schatz
Outline:1.
Nanodiamonds
in drug delivery
2.
Ultrananocrystalline
diamond
Molecular Simulation of Nano-diamond Assisted Delivery of Anti-Cancer Drug Doxorubicin
NSF Summer Institute on Nanomechanics, Nanomaterials and Micro/Nanomanufacturing
Northwestern University, Evanston Illinois 60201
May 27th, 2009
Prof. George Schatz
Department of Chemistry, Northwestern University
Diamond
Great Star of Africa, 1915largest rough diamond ever found
530 carats ( 100 grams), 76 facets
58.9 x 54.4 x 27.7 mm
estimated value: $400 million
Crystal Structure of Diamond
8-atom Face-Centered Cubic (FCC) Lattice
predominantly composed of SP3 carbonexcept for SP2 carbon on surface
high density 3.5 g/cm3
Nanodiamond
TEM picture of nanodiamond
particle size: 2 ~ 20 nm
extremely large relative surface area
spontaneous water absorption even at ambient condition
micrometer self-aggregate easily formed
The first successful synthesis was made in 1963
structure of nanodiamond has NOT been well characterized
How nanodiamond was made?
Trinitrotoluene (TNT)
+
Hexogen (RDX)
detonation
yield rate, composition, shape and size sensitive to the reaction condition,particular the cooling capability of reaction chamber
Nanodiamond extracted from combustion soot
Surface Functionalization of Nanodiamond
-OH, -NH2, -CN, -Me, -NCO, -COOH, -COOMe, -COCl, -TMS, -OTS, -Cl, -Br-tBu, -C6, -C18, -C8F17, -Vinyl, -Acrylate, -PEG, -Ph, -PhF5, -APTES, -Bz, -TIPS
Largely available functional groups:
Extension of functionalization can be measured by spectroscopy techniques, including
Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy and Fluorescence
Besides traditional oxidation-reduction chemical methods, ultra-fast functionalization can be accomplished in minutes using cool plasma tecnique
Functionalized nanodiamonds typically have significantly improved solubility
Emerging Applications of NanodiamondMotor engine lubricant: 8% more MPG realized.
Biochip for protein separation, purification and detection.
toxity-free delivery of anti-cancer drug Doxorubicin
Nanodiamond-embedded microfile devices for localized chemotherapeutic elution.R. Lam, M. Chen, E. Pierstorff, H. Huang, E. Osawa and D. Ho. ACS Nano, 2008, 2, 2095
Likely Structures of Nanodiamond
(a) octahedral (b) truncated octahedral (c) cuboctahedral
(d) cuboid
shapes
Crystallinity and surface electrostatics of diamond nanocrystal. A.S. Banard and M. Sternberg. J. Mater. Chem. 2007, 17, 4811.
Optimized by Tight-Binding DFT
Anti-cancer Drug Doxorubicin
Amphiphilichydrophobic aromatic site
hydrophilic sugar site conjugated aggregates observed
DNA duplex intercalated by Doxorubicin
pKa 8.4
Ratio of SP2/SP3 Carbon atoms on reconstructed nanodiamond surface
Surface is largely composed of SP2 type carbon atoms
A handful of SP3 atoms are stillrequired for shape maintenance
π-conjugation is expected at SP2-rich domains.
Cuboctahedral (660)
Rather large solvent accessible area
SAA: 1963 Å2
Volume: 2664 Å3SP2SP3
Surface Electrostatic Potential
Upon hydrogenation, the nanodiamond surface becomes more electropositive.
bare hydrogenated
Technical Details of SimulationsDFT Calculations:
XC Functional: Perdew-Burke-Ernzehor (PBE)Norm-conserving Pseudopotential: Goedecker-Teter-Hutter (GTH)Basis Set: Double-Zeta-Valence-Polarization Gaussian Orbitals (DZVP)Simulation Package: CP2K http://cp2k.berlios.de (GPL license)
MM Force Field Development Protocol:
Amber atom typesIntramolecular and intermolecular parameters derived fromGeneralized Amber Force Field (GAFF)Atomic partial charges fitted to reproduce DFT PES by Restrained ElectroStatic method (RESP) using Amber 9 package
Molecular Dynamics Simulation:
Isothermal-Isobaric Ensemble (NPT) using Gromacs 4 package
Quality of MM force fields
RMSD of MM Optimized Structures with respect to QM: (in Å)
Dipole Moment: (in Debye)
B-C660 H-C660 N-DOX P-DOX
DFT 4.8 1.5 7.3 23.8MM 11.2 9.1 7.3 27.9Please note: a single NaCl possesses a dipole of 9.0 Debye
B-C660 H-C660 N-DOX P-DOX
RMSD 0.01 0.01 0.1 0.2
Binding Energy of Protonated Doxorubicin to Bare and Hydrogenated Nanodiamond
EBinding EDoxND EDox END
Hydrogenation notably decreases binding affinity due to weaker π-stacking
-77.2 kcal/mol -64.5 kcal/mol
pH-dependent Drug Binding Behavior
high pH low pH
Protonation of Doxorubicin is critical for efficient dispersion and binding(water has been removed)
Binding Patterns
π-stacking type binding
micelle type binding
simultaneous binding
Radial Distribution Functions of protonated Dox with respect to ND
Strong binding indicated by the high first peak at 1.2 nm
Binding Free Energy Profiles
Ultrananocrystalline (UNCD) Diamond Films
D. M. Gruen
et al, Appl. Phys. Lett. 64 (1994) 1502: J. Vac. Sci. Tech. A13 (1995) 1628.
Ar/CH4
/N2
-plasma UNCD
•
16 nm diamond grains.
•
2 nm-wide grain boundaries.
•
~50 % sp2
carbon at
the GB’s.•
Electrically conductive
S. Bhattacharyya et al., Appl. Phys. Lett. 79, 1441 (2001).
Σ13 grain boundary structure67.4o
twist perpendicular to 100 plane208 atoms
P. Zapol, M. Sternberg, L. A. Curtiss, T. Frauenheim, D. M. Gruen, Phys. Rev. B 65, 045403 (2002)
DF-TB
(tight binding) studies of diamond film growth, and of grain boundary structures.
UNCD Structural Modeling
Fracture of UNCD grain boundaries
no GB two GBs
UNCD grain boundary fracture: PBE Calculations
•
Significant damage to both GB’s.
•
Complete failure of the bottom GB.
Mechanical properties: UNCD Grain Boundary Fracture
E
-
the Young’s modulus (stiffness).f
-
failure strainf
-
fracture stress.
Jeffrey T. Paci, Ted Belytschko
and George C. Schatz, Chem. Phys. Lett., 414(4-6), 351-358 (2005).
Σ13
Grain Boundary Structure
Single crystal diamond
DFT-PBE Results
Theoretical versus practical strengths
•
Our E values of 1.09 and 1.05 TPa
for single-crystal and UNC diamond, respectively, agree well with the corresponding experimental values of 1.05 and 0.95 TPa.
•
Experimentally measured fracture stress values for single-crystal diamond and UNCD are f
~ 4 GPa
and f~ 1-5 GPa, respectively. We are way-off here. What we have left out is the effect of large (~100 nm) cracks.
•
Cracks lead to regions of stress concentration which result in crack propagation and material failure.
•
The effect of defects on the fracture behavior of a brittle material like diamond can be described using Griffith theory.
Plasma-nitrogen UNCD
•
197 atom cluster based on Σ
13
structure. •
~1nm-wide GB layer.
•
50% sp2, 50% sp3
(close to experiment).
Plasma Nitrogen Results
Decrease in E
and σf
but values still large.
J. Paci, T. Belytschko, G. C. Schatz, Phys. Rev. B, 74, 184112 (2006)
UNCD (PBE) 1.05 0.13 100Amorphous Carbon GB Structure
Σ13
GB Structure
Theoretical versus measured strengths
•
Calculated E values (1.09 and 1.05 TPa) for single-crystal and UNC diamond, respectively, agree well with the corresponding experimental values of 1.05 and 0.95 TPa.
•
Fracture stress values for single-crystal diamond and UNCD are f
~ 1-5 GPa.
What we have left out is the effect of large (~100 nm) cracks.
•
The effect of defects on the fracture behavior of a brittle material like diamond can be described using Griffith theory.
Griffith theory (1920)
•
Basic idea: when the strain energy released by fracture is larger than the energy required to create new surface (the surface energy), a crack will propagate.
•
For a penny-shaped crack of radius c,
the Griffith fracture stress is
where
is the fracture surface energy and
is the Poisson ratio
Practical strength of UNCD•
Typical experimentally observed cracks have radii, c ~ 300 nm.
•
We calculate =2.6 J/m2. So Griffith predicts f
= 3.8 GPa, a value within the f
~ 1-5 GPa
UNCD fracture stress range.
•
Similar argument works for N-doped UNCD.
H. D. Espinosa et al., J. Appl. Phys. 94, 6076 (2003).
Future directions: Nanodiamond research
Effect of nanodiamond size and shape on Doxorubicin bindingInfluence of cosolute concentration and pH environment
Determination of optimal functionalization sites
Optical behavior of fluorescent functionalized nanodiamond
Mechanical property of nanodiamond-polymer composite coating
Charge conduction in doped-nanodiamond based Micro Electro- Mechanical Systems
Automation of molecular model development for nanodiamond
Drug delivery applications:
Diamond films:
Theory:
Models for defect structures