Chirality in amorphous and crystalline materials - experimental aspects David Avnir Institute of...
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Transcript of Chirality in amorphous and crystalline materials - experimental aspects David Avnir Institute of...
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
#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:
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?
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
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
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-
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
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
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)
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
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?
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
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
+
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
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
Silica thin-film chiral imprinting
Where is “Smart porosity” needed?
for evaluating ee,
for chiral separations,
for selective sensing,
for chiral catalysis
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)
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
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
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
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
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
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
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!
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?
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:
3 .Induction of chirality by any of the methods,
will enrich the chiral population of SiO4 tetrahedra
with one type of handedness.
-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.
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
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)
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]
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
aa bbaa bbbb
First taken after a few secondsFirst taken after a few seconds
Rhodium-Rhodium-complex@silver@silver
Thionin@Ag
Thionin@Ag - Coin
Thionin@Ag - Powder
compression
DMSO
No extraction with water, although water is a solvent of the dye
Adsorption of CR compared to entrapment
Adsorbed Doped
Adsorption on Adsorption on Entrapment in Ag commercial Ag Ag
1% 1% 100%
Starting solution: 6.2x10-4 M
Supernatant after entrapment:3.5x10-
7 M
Thionin@Cu-Pt: Entrapment vs adsorption
Adsorption: 4%
Y. Ben-Efraim
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
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
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
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)
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)
D- or L-Tryptophan
L-Glutathione Quinine (R=COH3)
Entrapped chiral molecules in gold or silver for the photoelectron experiment
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
Reversal of scattering behavior by switching between the enantiomers of tryptophan
Silver was made chiral too!
Two enantiomers of gold
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)
Photoelectron emission spectroscopy of chirally doped Photoelectron emission spectroscopy of chirally doped palladiumpalladium
CD@PdCN@Pd
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!
Doping Doping vsvs chiral imprinting chiral imprinting with with cinchonine
CN@Pd after extractionCN@Pd
Doped Imprinted
Similar but mirror behavior with CD@Pd
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
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
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