Composite Silica:Polypeptide Nanoparticles
Sibel Turksen, Brian Fong & Paul S. Russo
Macromolecular Studies Group
Louisiana State University
NSF, ACS, LSU Coates Fund
Kasetsart University
Bangkok, Thailand
Thursday, November 18, 2004
Fuzzballs
a silica interior and synthetic
homopolypeptide exterior.
Silica (SiO2) core
typically 200 nm diameter
Homopolypeptide Shell
typically 100 nm thick
Optional
superparamagnetic
inclusion
Why?
The usual reasons for polymer-coated particles
 Stability studies, probe diffusion, standards, etc.
The better reasons for polypeptide-coated particles




Should allow excellent shell thickness control.
Shell is rigid spacer for assembling silica spheres.
Astounding chemical versatility and functionality, including chirality.
Responsiveness and perfection of structures through reproducible helixcoil transitions.
 Easily attach antibodies for recognition of cancer cells, easily attach
cancer-killing lytic peptides, too.
 When magnetic, good way to self-assemble all this functionality
Our Little Corner of the World:
Silica-Homopolypeptide Composite Particles
Co-Si-homopolypeptide composite systems

Hierarchical structures
Mostly…
unstructured,
random coil polymers

Homopolypeptide
shell – PBLG, PCBL

(can be helix as shown, or coil?)

Superparamagnetic – Fe3O4 or Co core
Silica-Stöber Synthesis
Hydrolysis of tetraethyl orthosilicate (TEOS)
OC2H5 OC2H5
OC2H5
C2H5OH
Si
H5C2O
OC2H5
OC2H5
NH4OH
Si
H5C2O
O
OC2H5
Si
OC2H5
OC2H5
TEOS
OH
HO
OH
HO
Si O Si
hydrolysis
OH
O Si
condensation HO Si O
TEOS
C 2H 5OH
O
O
NH 4OH
Stöber
OH
OH
HO
HO
OH
OH
SEM & TEM of Silica Particles
Synthesis of Magnetite – Fe3O4
2 FeCl3 + FeCl2 + 8 NH4OH
Fe3O4 + 8 NH4Cl
+
-OH
+
-OH
-OH
+
Fe3O4
-OH
-OH
-OH
OMe
H3C
N CH
3
CH3
TMA
tetramethylammonium hydroxide
N
-OH
-OH
+
N
N
OHOH- N+
Fe3O4
OH-+
N
OH- N+
TEM- Silica Coated Fe3O4
Dark:Magnetic inclusions
(~ 10nm)
Gray:Glassy SiO2 matrix
Magnetic silica particles
Superparamagnetic cobalt
cit –
cit –
Co
–
NH2(CH2)3Si(OH)2O
+
NH2(CH2)3Si(OH)3
cit –
Co
NH2(CH2)3Si(OH)2O
NH2(CH2)3Si(OH)2O
+
–
Cit–
–
OH –
O
N
O
TEOS, APS, EtOH
Stöber reaction
N
Co
SiO2
Co
N
OH –
+
OH –
O
OH –
H2O
TEM- Silica Coated Cobalt
Superparamagnetic Particles
Surface Functionalization
MeOH
(CH2)3NH2
Si
MeO
H2O, NH3
OMe
OMe
(CH2)3NH2Si (OH)3
association
condensation
O H
APTMS
3-aminopropyltrimethoxysilane
Si
O H
oligomers
Si
adsorption
on a particle
(CH2)3NH2
HO Si OH
O
NH2(CH2)3
OH
(CH2)3NH2(CH2)3NH2
Si O
Si
OH
O
HO
O
Si
O
Si O Si
OH
O
Si
Si O
O
O
HO
H2O, NH3, C2H5OH
O
H
H
Si O Si
OH
HO
O Si
Si O
O
O
Homopolypeptides
HN
H
C
 PBLG
O
C
R

n


R = CH2CH2CO2CH2C6H5
R = (CH2)4NHCO2CH2C6H5
best understood
homopolypeptide
semiflexible structure
helix-coil transition
for PBLG
for PCBL
 PCBL

helix-coil transition
@ 27 C in m -cresol
Synthesis of homopolypeptides
R
R'
NH2
+
R'
O
1
O
R
N
O
4
H
H
N
R'
OH
+
H
CO2
n
R'
O
O
2
O
H
4
H
N
N
O
H
3
R
N
N
O
2
H
CO2
N
R
H
O
R
H
N
O
R'
H
R
N
O
N
N
O
H
n
H
R
H
5
H
Summary: Particle Preparation
Si
cit –
+
NH2RSi(OH)3
N
O
-
Si
+
N
SiO2-
Cobalt particles
OC2H5
H5C2O
Si
OC2H5
OC2H5
(CH2 )3 NH2
NH2NH2
Si
MeO
NH2
OMe
OMe
Superparamagnetic
domain
NH2
NH2
H2 O , NH3
NH2
O
O
O
O
N
H
CBL-NCA, monomer
O
N
H
O
Si
OH
Is the shell covalently attached?
s our ce : stob ers IR
so urce: bf2cp 33 IR
s ou rc e: b f5 ttIR p1 48
16
(a)
14
(b)
14
10
1628
8
6
802
4
946
2
stober
8
10
8
Transmittance / %
Transmittance / %
Transmittance / %
10
1551
1736
1653
6
PBLG-coated silica
3500
3000
2500
6
1391
4
1654
DMF
Washed
2
4
0
-2
4000
(c)
12
12
2000
1500
Wavenumber / cm-1
1000
500
Figure 2a
Fong and Russo
2
4000
3500
3000
2500
2000
Wavenumber / cm-1
0
1500
1000
500
Figure 2b
Fong and Russo
4000
3500
3000
2500
2000
Wavenumber / cm-1
Almost certainly
(By the way, the polypeptide conformation is mostly
a-helix with some b-sheet)
1500
1000
500
Figure 2c
Fong and Russo
TGA/DTA
0
Silica Spheres Alone
Mixed with 16K and 91K
-20
TG / %
PBLG, then isolated (2 curves)
Composite Particle
-40
-60
-80
PBLG
-100
0
200
400
600
T/
800
1000
1200
oC
Fong and Russo
Figure 3
--Particles with ~ 23% by mass PBLG
--Again, no evidence for binding of loose PBLG
Dynamic Light Scattering
R = 990
5.0
h
4.0
Silica Spheres
C H Spheres
3.5
18
37
Composite Particles
3.0
D
app
/ 10-8cm2s-1
4.5
2.5
R = 973
h
2.0
1.5
R = 1750
h
1.0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
q2/1010 cm-2
Bigger ones may diffuse slower (solvent viscosity effects)
Flat plots indicate excellent, latex-like uniformity
Particle Characteristics
 Silica Core Properties



Radius from DLS: 97 nm
Molar Mass: 4.5 x 109
Surface area: 15.6 m2/g
 PBLG Shell Properties



78 nm.
~90% solvent / 10% polymer.
Polymer density limited by crowding around initiator
sites.
Unfortunately, the shell thickness was not
controlled by [M]/[I]. Why not?
Not all initiators are active: crowding
Challenges:


Controlling initiator density
Attachment of ready-made polymers
Helix-coil Transition of PCBL
Matsuoka, M., Norisuye, T., Teramoto, A., Fujita, H. Biopolymers, 1973, 12,1515-1532
Early attempts showed NO change in the
size of the particles—as if the shells were not
responding.
We reasoned this might be due to
overcrowding on the surface.
Avoiding crowding
OMe
MeO
Si
OMe
NH2
N
H
NH2
AEAPTMS
NH2
OMe
MeO Si
NH2
OMe
APTMS
OMe
MeO Si CH3
OMe
MTMS
25% amino groups
3-(2-furoyl) quinoline-2-carboxaldehyde
(ATTO-TAG™ FQ)
Silica-homopolypeptide Composite Particles
400
350
300
Rapp= 251.6±1.42 nm
Rapp nm
250
200
150
100
50
Si-PCBL core shell particles
0
0
1
2
3
2
4
10
q / 10 cm
5
-1
DLS of Si-PCBL particles in DMF
6
7
Helix-coil transition of Co-PCBL
425.00
400.00
Rapp / nm
375.00
350.00
325.00
1st heating
1st heating
1st heating
cooling
1st cooling
2ndcooling
heating
1st
2nd heating
cooling
2nd heating
2nd cooling
3rd heating
2nd
cooling
3rd heating
4th heating
3rd
4th heating
3rd heating
cooling
4th
3rd cooling
Latex
300.00
275.00
250.00
0
5
10
15
20
25
30
Temperature / °C
35
40
45
50
55
120
It’s Alive!
y=7628x + 68.2
R=0.99804
110
Rapp / nm
100
90
80
70
Si-PCBL
60
0.000
0.001
0.002
0.003
0.004
0.005
0.006
-1
[M] / g.mL
0.10
0.06
2/
2
This plot shows
polydispersity
0.08
0.04
0.02
Si-PCBL
in 3
weeks
0.00
0.002
0.003
0.004
[M]
/
0.005
-1
g.mL
0.006
Hysteresis curve
M Magnetization
-M
Magnetization
in opposite direction
SQUID- hysteresis plot of cobalt particles
25
20
15
Magnetization (emu/g)
10
5
0
-5
-10
-15
-20
-25
-60000
Silica coated cobalt
Latex iron oxide
-40000
-20000
0
Applied Field (Oe)
20000
40000
60000
SQUID- hysteresis plot of Co-PCBL
0.015
Magnetization (emu/g)
0.01
0.005
0
-0.005
Initial
3000 to 0 field
0 field to -3000
-3000 field to 0
0 field to 3000
-0.01
-0.015
-4000
-3000
-2000
-1000
0
Applied Field (Oe)
1000
2000
3000
4000
Formation of colloidal crystals
~ 0.5 m
Sufficiently dense suspensions assemble into
colloidal crystals. With a size that matches that
of visible light, diffraction results. Domains with
different orientations result in different and
quite pure colors.
Colloidal Crystals (PCBL Shell)
~ 2 mm
~ 0.5 m
SiO2
Sufficiently dense suspensions
assemble into colloidal crystals.
With a size that matches that
of visible light, diffraction
results. Domains with different
orientations result in different
and quite pure colors.
Helical homopolypeptide shell
 Why Study?
 Beautiful!
 Fun supramolecular synthesize &
characterize from nm to mm.
 Applies to optical devices,



better lasers, pigment-free paint,
“smart colloids”, artificial muscle,
separations technology
Spectroscopic analysis of the crystal
3.5
3.0
Transmittance measured on
monochromator-equipped
microscope
568 nm
2.5
2.0
593 nm
615 nm
1.5
FWHM of line is ~ 16 nm,
comparable to typical
interference filters
1.0
0.5
0.0
400
500
l / nm
600
700
Achieving population inversion gets progressively harder
for shorter wavelengths; lgreen < lred.
E2
A12
B12
E1
l
l
B12 l

A12 8
3
Conclusions
 Facile synthesis & excellent uniformity
 Responsive shell
 Hierarchical structures, conformal transitions
 Potential applications —optical devices, stationary
phases for chiral separation, model particles, artificial
muscles, medical treatments
 Infinite variation with polypeptide chemistry
Future work




Helix-coil transition effect on magnetization
Crosslinking particles
Asymmetric particles
Application of different grafting techniques


Vapor deposition
Grafting onto
 Controlling cobalt chains-rods
 Investigation of colloidal crystals
 Particles as probe diffusers
Crosslinking
O
H
N
PCy3
O
n
*
Cl
*
O
8
Cl
O
Ph
Ru
L4M
R
PCy3
benzylidene-bis(tricyclohexeylphosphine)
dichlororuthenium
O
8
-dec-1-enyl-L-glutamate
8
O
O
O
O
O
O
8
8
L4M
R
L4M
R
N
Silica
coating
Surface
Functionalization
N
N
N
N
N
N
N
NCA-monomer
N
N
N
N
N
N
N
N
N
N
crosslinking
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
COIL
N
N
N
N
N
HELIX
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N