Chiral Nanoporosity in silicates Institute of Chemistry The Hebrew University of Jerusalem...
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Transcript of Chiral Nanoporosity in silicates Institute of Chemistry The Hebrew University of Jerusalem...
Chiral Nanoporosity in silicates
Institute of ChemistryThe Hebrew University of Jerusalem
Nanocenter meeting, Ashkelon, 21.6.10
David Avnir
Zeolites:Highly porous, highly symmetric crystalline materials
ZSM-5, a silicate zeolite: NanAlnSi96-nO192•16H2O
Major industrial applications: *Catalysis
*Heterogeneous chemistry *Separation *Adsorbents
Chiral zeolites
Prime importance because of their enantioselective potential applications in:
*Enantioselective catalysis *Enantiomers separation
Known:Zeolite-like, open-pore crystals, MOF’s, etc.
Out of over 700 zeolite structures only 5 are recognized as chiral
Desired:Chiral aluminosilicate zeolitesOnly one was reported
We found 21(!) chiral silicate zeolites
which have been under the nose all the time!
a. Goosecreekite. b. Bikitaite. c. The two enantiomeric forms of Nabesite
Ch. Dryzun et al, J. Mater. Chem., 19, 2062 (2009)Editor’s Choice, Science, 323, 1266 (2009)
2 .The route to that finding:
.IChiral nanoporosity of amorphous materials
II. The chiral crystal of quartz
Here is how one can induce chiral porosity in silicates:
*Adsorb on the surface a chiral molecule
*Silylate the surface with a chiral silylating agent
*Polymerize a chiral trialkoxysilane
*Entrap a chiral molecule using the sol-gel polycondenstion
*Prepare a hybrid of silica with a chiral polymer
*Imprint chirally the silica
Synthesis of silica by the sol-gel polycondensation
Si(OCH3)4 + H2O (SiOmHn)p + CH3OH
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
Entrapped species
monomer
oligomer
-
Physical entrapment of molecules within sol-gel matrices
*Small molecules
*Polymers
*Proteins
*Nanoparticles
Monomers,oligomers
The concept is general and of very wide scope
Sol Gel XerogelSol Gel Xerogel
sol-particle
Entrapped species
monomer
oligomer
-
Physical entrapment of molecules within sol-gel matrices
*Small molecules
*Polymers
*Proteins
*Nanoparticles
Monomers,oligomers
The concept is general and of very wide scope
CHO
HC
CH3
H
N
CH3
CH2(CH2)10CH3
CH3
+
CH3O
CH C
O
OH
H3C
OCH2CHCH2NHCHCH3
HOH CH3
PO
OH
O
O
Silica imprinted with aggregates of DMB
was capable of separating the enantiomer-pairs of:
BINAP
PropranololNaproxen
Pirkle’s alcohol
With S. Fireman, S. Marx, J. Am. Chem. Soc. 127, 2650 (2005)
)1R,2S-(-)-(N-dodecyl-N-methylephedrinium bromide (DMB)
0.93
1.03
1.13
1.23
1.33
Dis
crim
inat
ion
Rat
io
SR
R
General enantioselectivity by chirally imprinted silica
With S. Fierman, S. Marx, Adv. Mater., 19, 2145 (2007)
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
Comparison of two methods: Doping and imprinting
Before extraction: Chiral dopant (DMB) After extraction: Chiral holes
The recognition handedness changes!
If an amorphous 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?
Conceptual questions :
The building blocks of quartz: All are chiral!
SiO4 SiSi4 -O(SiO3)7-Si(OSi)4
D. Yogev-Einot, Chem. Mater. 15, 464 (2003)
Induced circular dichroism of Congo-Red within silica
SO3Na
NH2
N
SO3Na
NH2
NNNCHO
HC
CH3
H
N
CH3
CH2(CH2)10CH3
CH3
+
The chiral inducer: DMB The achiral probe: CR
With S. Fireman, S. Marx, J. Mater. Chem., 17, 536 - 544 (2007)
We shall compare:* Co-doping * Adsorption of CR on silica doped with DMB
CR-DMB@SG (red line) and CR-DMB@OSG (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)
Does CR “feel” the chirality of only DMB?
-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@silica
Reversal of the ICD signal indicates that the chirality-inducer is different in the two cases.
The building blocks of quartz: All are chiral!
SiO4 SiSi4 -O(SiO3)7-Si(OSi)4
D. Yogev-Einot, Chem. Mater. 15, 464 (2003)
SiSi4 is much more chiral than SiO4
Calculating the degree of chirality
1001
)(2
12
n
kkk NP
nDGS
G: The nearest achiral symmetry point group
Achiral molecule: S(G) = 0
The more chiral the molecule is, the higher is S(G)
H. Zabrodski Hel-Or, J. Am. Chem. Soc., 117, 462(1995); 120, 6152 (1998); 126 , 1755 (2004). A. Zayit et al, Chirality, in press (2010)
Le Chatelier, H. Com. Rend de I'Acad Sciences 1889, 109, 264.
The optical rotation of quartz: 120 years ago
Le Chatelier and his contemporaries
0.97
1.02
1.07
1.12
1.17
98 298 498 698 898 1098
Temperature ( K)
0.54
0.56
0.58
0.6
0.62
0.64
Temperature (°K)
Le
Cha
teli
er
t
Ch
irality, SiSi4
Chirality t
More than 120 years later :An exact match with quantitative chirality changes
D. Yogev, Tetrahedron: Asymmetry 18, 2295 (2007)
SiSi4
The symmetry space groups of quartz
-O(SiO3)7-
D. Yogev-Einot, Chem. Mater. 15, 464 (2003)
A helical chiral space group: P3121 or P3221
#The relevant space group symmetries which are indicative of a chiral crystal, are the
65 space groups which lack any improper symmetry element )reflection, inversion, glide or roto-inversion ,(collectively known as
Sohncke space groups
#Surprisingly, not all are chiral
#22 of the 65 are chiral (helical)
Systematic search for Sohncke space groups in zeolites
#43 of the 65 are non-helical
#They are achiral space groups, despite the fact that they do not contain improper symmetries!
The non-helical Sohncke space groups
#They provide chiral crystals if the asymmetric unit is chiral
All of the chiral zeolites we found belong to that category
The main finding: Out of 120 classical silicate zeolites, we found 21 that must be chiral, but were not recognized as such
Ch. Dryzun et al, J. Mater. Chem., 19, 2062 (2009)Editor’s Choice, Science, 323, 1266 (2009)
Goosecreekite (GOO)
Chiral zincophosphate I
(CZP)α-Quartz
TT’42.052.940.55
SBU0.860.37------
A.U.14.761.280.00
Unit cell4.908.911.28
The chirality values are comparable or larger than the chirality values of the known chiral zeotypes and of quartz
Adsorption of D-histidine (the lower curve) or L-histidine (the higher curve) on Goosecreekite (GOO): The heat flow per injection
The isothermal titration calorimetry (ITC) experiment
L-histidine
With Y. Mastai and A. Shvalb, Bar-Ilan
The building blocks of quartz and of chiral zeolites
SiO4 SiSi4
So, what is a left-handed SiO4 tetrahedron?
CIP rules distinguish between the enantiomers of A(bcde) molecules:
F
Cl
Br
I
F
Cl
Br
I
Si(OSi)4
The steps:
1. Find the triangle with the maximal perimeter.
2. Check the direction from the
longest edge to the shortest one, facing the triangle.
3. Clockwise rotation (shown) is a right handed tetrahedron.
(The CIP logic of hierarchy)
1
2
3
R*
1 :5.774
2 :4.913
3 :4.369
D. Yogev et al Tetrahedron: Asymmetry 18, 2295 (2007)
A method to assign handedness to AB4 species
The Triangle-Method