chirality in amorphous and crystalline materials - experimental aspects david avnir
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Chirality in amorphous and crystalline materials - experimental aspects David Avnir Institute of Chemistry, The Hebrew University Summer School on Chirality Mainz, August, 15-17, 2011, sponsored by. Main general questions to be addressed:. - PowerPoint PPT PresentationTRANSCRIPT
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Chirality in amorphous and crystalline materials - experimental aspects
David Avnir
Institute of Chemistry, The Hebrew University
Summer School on ChiralityMainz, August, 15-17, 2011, sponsored by
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#How is it possible to induce chirality in a material?
# How is it possible to extract chiral activity from a material?
Our main road:
SiO2-based amorphous materials
and crystalline metals
Main general questions to be addressed:
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Amorphous silica
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The classical approach:
Attach covalently a chiral molecule to the surface of the (porous) material
Often, a silylating reaction
How is it possible to induce chirality in a material?
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Photophysical Recognition of Chiral Surfaces
With E. WellnerM. Ottolenghi
J. Am. Chem. Soc., 111, 2001 (1989)
The quencher:
DMP, R-Q or S-Q
The excited chiral surface: Silica derivatized with R- or S-BNP
N
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For the R-surface (shown):
S-Q/R-Q = 1.3
For the S-surface:
R-Q/S-Q = 1.2
The S-quencher recognizes better the R-surface
Stern-Volmer quenching analysis
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The second, newer approach
Dope the material with a chiral molecule
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DOPING OF SILICA IS MADE POSSIBLE
BY THE SOL-GEL POLYCONDENSATION
Si(OCH3)4 + H2O (SiOmHn)p + CH3OH
(unbalanced)
Variations on this theme:
–the metals, semi-metals and their combinations
–the hydrolizable substituent
–the use of non-polymerizable substituents
–organic co-polymerizations (Ormosils)
–non-hydrolytic polymerizations
H+ or OH-
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Sol Gel XerogelSol Gel Xerogel
sol-particle
entrappedmolecule
monomer
oligomer
-
Organic functionalization
by physical entrapment of molecules within sol-gel matrices
* Small molecules
* Polymers
* Proteins
* Nanoparticles
Monomers,oligomers
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Doping the material with a chiral molecule:
# A chiral catalyst
# A protein
# A chiral surfactant
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Entrapment of a chiral catalyst
With
F. Gelman
J. Blum
J. Molec. Catal., A: Chem., 146, 123 (1999)
ee = 78% (BPPM)
The advantages
# Covalent bonding chemistry is not needed
# Working with a hydrophobic catalyst in water
# Recyclability
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Doping the material with a chiral surfactant
CHO
HC
CH3
H
N
CH3
CH2(CH2)10CH3
CH3
+
(1R,2S)-(-)-N-dodecyl-N
-methylephedrinium bromide
(DMB)
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The experiment:
Inducing Circular Dichroism in Congo-Red
Within Silica Sol
SO3Na
NH2
N
SO3Na
NH2
NNNCHO
HC
CH3
H
N
CH3
CH2(CH2)10CH3
CH3
+
The chiral inducer: DMB The achiral probe: CR
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CR-DMB@SG sol (red line) and CR-DMB@OSG sol (blue line)
The ICD spectra of co-entrapped CR-DMB in hydrophilic and hydrophobic silica sols
S. Fireman
-40
-20
0
20
40
60
80
300 400 500 600
Wavelength (nm)
CD
(m
deg)
CR-DMB in solution (blue line) and CR solution (red line)
Has the silica matrix become chiral?
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Second experiment with doped surfactant:
NMR detection of diastereomeric interactions
within phenylated-silica sols and gels
With S. FiremanS. Marx
PO
OH
O
O
S-BINAP
CHO
HC
CH3
H
N
CH3
CH2(CH2)10CH3
CH3
+
1R,2S-DMB
The possible interactions:
DMB/S-BINAP
DMB/R-BINAP
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SiO
Si
O-
O
Si
Si
O
Si
O
O
Si
O
O-
(H3C)2N
(H3C)2N
O-
CHCH
H3C
CH CH
OHH3C
OH
+
+
OO
POO
CHCH
OH
H3CNH(CH3)2
OO
P OO
Si
+
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31P-NMR spectrum of BINAP-DMB diastereomers:Looking inside the sol and the gel of silica
S-BINAP R-BINAP
5.99
5.85.96.06.1ppmppm
5.9 4
S-BINAP interacts better with the chiral surfactant
6.00
5.98
5.85.96.06.1ppmppm
In the gel
In solution
In the sol
5.85.96.06.16.2ppm
6.13
26.
146
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Is it possible to induce structural chirality in a material?
Make a hole which is chiral -
imprint the material; make a chiral silicate skeleton
What have we seen so far?
# Covalent attachment of a chiral molecule
# Physical entrapment of a chiral dopant
Dickey, 50’s
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With
S. Marx
S. Fireman
General methodology for chiral imprinting of
sol-gel based thin-films
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Silica thin-film chiral imprinting
Where is “Smart porosity” needed?
for evaluating ee,
for chiral separations,
for selective sensing,
for chiral catalysis
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PropranololPropranolol
OCH2CHCH2NHCHCH3
HOH CH3
The functional monomers
Film thickness: 700 nm
Si
H3CO
H3CO
H3CO
CH3Si
H3CO
H3CO
H3CO
Si
OCH3
H3CO
OCH3
OCH3
TMOS PTMOS MTMOS
Two different cases:
I. Selectivity towards an enantiomer of the imprinting molecule
Chem. Mater. ,15, 3607 (2003)
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Immersed in solutions of R or S, for adsorption, and radio-assay; or:
Fluorescencemeasurement
Imprinted films Adsorbed molecules are leached out
The enantioselectivity adsorption experiment
Fluorescence: (ex = 288nm; em= 335 nm)
Radio ligand binding of 3H-S-Propranolol
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Enantioselectivity towards Propranolol enantiomers
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
S imprinted R imprinted Blank
Ads
orpt
ion
(nm
ole)
S solutionR solution
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Cu
rren
t /
A
0
0.5
1
1.5
2
2.5
3
3.5
4
L Dopa D Dopa Dopamine Dopac Catechol
L imprinted
D imprinted
Electrochemical detection of enantioselectivity and molecular selectivity in very thin silica films
Cur
rent
(A
)
OH
OH
CH2CHNH2
COOH
OH
OHOH
OH
CH2CO2H
OH
OH
CH2CH2NH2
L-Dopa D-Dopa
70 nm films
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The more general case:
Enantioselectivity towards enantiomers of
non-imprinting molecules
Why is that important?
Because a small, recyclable chiral imprinting molecules can be used and reused
S. Fireman
S.Marx
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CHO
HC
CH3
H
N
CH3
CH2(CH2)10CH3
CH3
+
CH3O
CH C
O
OH
H3COCH2CHCH2NHCHCH3
HOH CH3
PO
OH
O
O
Silica imprinted with aggregates of DMB
Was capable of separating the enantiomer-pairs of:
BINAP Propranolol Naproxen
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0.9
1.2
1.5
1.8
2.1
2.4
Propranolol Anthracene
extracted-DMB@PSG
extracted-CTAB@PSG
Dis
crim
inat
ion
Rat
io
R
R
General enantioselectivity in imprinted thin films
20% phenylated silica, 270nm J. Am. Chem. Soc. 127, 2650 (2005)
PO
OH
O
O
OCH2CHCH2NHCHCH3
HOH CH3
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0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
Dis
crim
inat
ion
Rat
io
S
R R
0.93
1.03
1.13
1.23
1.33
Dis
crim
inat
ion
Rat
io
SR
R
General enantioselectivity in granules:
Comparison of two methods of inducing chirality
Before extraction: Chiral dopant (DMB)
After extraction:
Chiral holes
The recognition handedness changes!
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Next:
If an SiO2 material is made chiral by a foreign molecule which either remains there or not, then:
#How are the building blocks of the material affected?
#Is it possible that an SiO4 tetrahedron which is neighboring to the chiral event, becomes chiral itself?
#Is it possible that the material becomes chiral deeper inside?
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Nature has already provided an answer -Yes, it is possible!
Quartz
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A:P3121 & B:P3221
A:P3121 & B:P3221
31 Right Helix31 Right Helix
32 Left Helix32 Left Helix
SiO4
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1. Each of the chiral SiO4 tetrahedra is a single enantiomer event.
#A statistically similar counter enantiomer maybe defined.
2 .Silica is a racemic mixture of chiral SiO4 tetrahedra :
#Half comprise a homochiral left-handed set, and half a right-handed
set.
#This is true for ANY handedness definition; but each definition will
divide the set differently into two equal halves.
Silica is composed of randomly distorted SiO4 tetrahedra. Therefore:
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3 .Induction of chirality by any of the methods,
will enrich the chiral population of SiO4 tetrahedra
with one type of handedness.
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-6
-5
-4
-3
-2
-1
0
1
2
300 400 500 600
Wavelength (nm)C
D (
mde
g)
The ICD signal of CR adsorbed on DMB@silica
The only possibility is chiral skeletal porosity induced by the doped DMB
Co-doping:CR/DMB@silica
CR adsorbed on DMB@silicaReversal of the ICD signal indicates that the chirality-inducer is different in the two cases.
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Inducing chirality in metals
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Motivation: Why should one dope metals with organic molecules?
* Hybrid materials of metals and organics have been unknown
* Most elements are metals
* Metals are everywhere – any new methodology of affecting their properties is interesting
* The library of organic compounds is huge; the number of metals is small
* Placing a molecule in a sea of electrons may affect its properties; and the properties of the metal
* Synergetic effects between the metal and the dopant may emerge
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Synthetic methods: Reduction in the presence of the dopant
AgNO3
Reducing aqueous solution
Reduction
Doping through metal synthesis
Dopant
Reducing agent
Aggregation and
entrapment
Ag metal
Hanna Behar-Levy et al, Chem. Mater., 14, 1736 (2002)
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Ag
CR@Ag1:100 molar
Congo-Red
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Noble metals
Coin metals
Scope: The metals
Magnetic metal
Alloys: Cu-Pd, Cu-Pt, Au-Ag
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Small molecules, hydrophilic or hydrophobic: Sudan III
Scope: The dopants
Polymers, hydrophobic or hydrophilic: Polyacrylonitrile
Biologicals: D-Tryptophan
Proteins: Alkaline phosphatase
Nanoparticles:Carbon nanofibers
Complexes: [Rh]
Inorganic compounds:H3[P(Mo3O10)4]
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Nafion@Ag PSSA@Au CR@Co CR@Cu
The New Materials
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Scope: The entrapment range
0.2% (doped metals) - 10% by weight (hybrid materials)
For instance for PSSA@Ag:Molar ratio - PSSA-monomer units : Ag = 1:250Weight ratio - 0.42 carbon w/w%Atomic molar ratio - C : Ag = 1:30
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Hierarchical structure: PSSA@Ag
H. Behar-Levy, G. Shter, G. Grader, Chem. Mater., 16, 3197 (2004)
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aa bbaa bbbb
First taken after a few secondsFirst taken after a few seconds
Rhodium-Rhodium-complex@silver@silver
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Thionin@Ag
Thionin@Ag - Coin
Thionin@Ag - Powder
compression
DMSO
No extraction with water, although water is a solvent of the dye
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Adsorption of CR compared to entrapment
Adsorbed Doped
Adsorption on Adsorption on Entrapment in Ag commercial Ag Ag
1% 1% 100%
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Starting solution: 6.2x10-4 M
Supernatant after entrapment:3.5x10-
7 M
Thionin@Cu-Pt: Entrapment vs adsorption
Adsorption: 4%
Y. Ben-Efraim
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Dopant@metal - the picture of the entrapment
* Aggregated crystallite metal system* Porous material* The dopant is tightly entrapped in narrow pores and cages * The molecules are entrapped intact* Adsorption and entrapment are different processes
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Scope: Properties and functionalities
*Affecting the metal properties - conductivity
*Affecting the reactivity characteristics – “acidic metal”
*Affecting the metal structure – chiral metals
*Affecting the catalytic properties of the metal
*Using a metal as a support for heterogeneous catalysis
*Bioapplication: Synergism in antibacterial activity
*Bioapplication: Enzyme entrapment within metals
*Corrosion prevention
*New concept in batteries
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Chlorhexidine digluconate@Ag
0 100 200 300 400 500 600 700 800 900
0
20
40
60
80
100
98.8
99.0
99.2
99.4
99.6
99.8
100.0W
eig
ht
(%
)
Temperature (oc)
CHD
CHD@Ag
Racheli Ben-Knaz, Rami Pedahzur, Adv. Funct. Mater., 20, 2324 (2010)
HN
HN
HN
NH
NH
NH
ClNH NH
NH NHCl
O
OH
OH
OH
OH
OH
HO
O
HO
OH
OH
OH
OH
OH
Thermal gravimetric analysis
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Enzymatic activity of acid-phospatase@gold
Michaelis-Menten dose-response kinetics is obeyed
Km = 9.3 mM (free enzyme: 1.25 mM )
0 30 60 90 1200.00
0.03
0.06
0.09
0.12
0.15
0.18
0.21A
bso
rbance
at
405 n
m (
a.u
)
Time (min)
AcP@Au AcP Adsorbed on Au Adsorption supernatant
Racheli Ben-Knaz, Biomaterials, 30 126 (2009)
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What is chiral doping doing to the metal?Is it inducing chirality in it?
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Circularly polarized 193 nm
Laser source
Sample:Chiral gold
Electron beam
Detector
Vacuum chamber
Detection of chirality of metals using photoelectrons
Photoelectrons are emitted from the conducting band with different kinetic energies.
H. Behar-Levy, O. Neumann, Ron Naaman, Adv. Mater. 19, 1207 (2007)
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D- or L-Tryptophan
L-Glutathione Quinine (R=COH3)
Entrapped chiral molecules in gold or silver for the photoelectron experiment
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Blank: Scattering from undoped Au
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0.0 0.5 1.0 1.5 2.0 2.50.0
0.1
0.2
0.3
0.4
cw
ccw
I nte
nsity
(ar
b. u
nits
)
Energy (eV)
Scattering from gold doped with L-quinine
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Reversal of scattering behavior by switching between the enantiomers of tryptophan
Silver was made chiral too!
Two enantiomers of gold
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Chiral doping of palladium
L. Duran Pachon, I. Yosef, T. Markus, R. Naaman, D. Avnir, G. Rothenberg, Nature-Chemistry, 1, 160 (2009)
N
OH
R
N N
N
R
OH
2: (+)-Cinchonine (CN)
1: (–)-Cinchonidine (CD)
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Pd SDS@Pd
Clockwise irradiation, Counterclockwise, Linearly polarized
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Photoelectron emission spectroscopy of chirally doped Photoelectron emission spectroscopy of chirally doped palladiumpalladium
CD@PdCN@Pd
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What is chiral in the metal?
# The chiral dopant affects the metal molecular orbitals, distorting them chirally
# The geometry of the metal pore around the doped molecule is chiral
These are two different chiral entities!
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Doping Doping vsvs chiral imprinting chiral imprinting with with cinchonine
CN@Pd after extractionCN@Pd
Doped Imprinted
Similar but mirror behavior with CD@Pd
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CD adsorption on dopant-free PdCN adsorption on dopant-free Pd
CD readsorption on CN imprinted Pd
CN readsorption on CN imprinted Pd
Enantioselectove adsorption on CN-imprinted palladium
N
OH
R
N N
N
R
OH
CD CN
Concentration in solution
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Chiral catalysis in the context of metals
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α-ketogluterate + NH4+ + NADPH
L-Glu + NADP+ +H2O
L-glutamic dehydrogenase@Au
O
O
O
O
OO
O
NH3
O
O
Level 1: The metal serves as a heterogenization matrix for a chiral catalyst
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L. Duran Pachon, I. Yosef, T. Markus, R. Naaman, D. Avnir, G. Rothenberg, Nature-Chemistry, 1, 160 (2009)
Level 2:Level 2: A Catalytic metal is chirally doped A Catalytic metal is chirally dopedHydrogenation of isopreneHydrogenation of isoprene
Isophorone (R)-3,3,5-Trimethyl-cyclohexanone
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A Catalytic metal is chirally imprintedA Catalytic metal is chirally imprinted
CN-imprinted Pd
Motivation: Chiral catalysis with a pure metal
A challenge to be met!