nanoporosity – where is it useful in chemistry? david avnir institute of chemistry the hebrew...
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Nanoporosity – where is it useful in chemistry?
David Avnir
Institute of Chemistry
The Hebrew University of Jerusalem
Nano Center Meeting, Ashkelon, March 29-30, 2015
1. The material at focus - silica
Silica
Controlled nanoporosity
Surface area and pore volume of silica as a function of pH and water/silane ratio in the sol-gel process
Functionality within a sol-gel matrix
MonolithsPowdersParticlesThis-films
2. Chemical sponges – diffusion considerations
VTS: An efficient bromine sponge
SiOO
O O-
SiOO
CH
SiO
O OH
SiO
Si
H C
O
OHO
OHO
H
Si OH C
OSi
HO O
SiO
OC H
Si OHO
OSiHO O
OSi
OC H O
O
HO
H
SiCH
OO Si
OH
O SiO
OH
OO Si
HC
OO
Si
OH
O Si
OH
O
O
O
H
OH
H
Si
Si
Si
Si
Si OH
O
HOOH
OHHO
O
O
H2C
CH2
CH2H2C
H2C
H2C
H2C
SiOO
OO-
SiOO
CH
SiO
OOH
SiO
Si
H C
O
OHO
O
Si OCH
OSi
HOO
SiO
OC H
Si OHO
OSiHO O
OSi
OCH
O
O
HO
H
Si
CH
OO Si
OH
O SiO
OH
OO Si
HC
OO
Si
OH
O Si
OH
O
O
O
H
Si
Si
Si
Si
Si OH
O
HO
OHOH
HO
O
O
CH2
CH2
CH2H2C
H2C
CH2
H2C
OH
Br
Br
HO
Br
HO
Br
HO
OHBrOH
Br
Br
OHBr-
Br-HO
H
H
Br2/H2O
vinyl groupvinyl group
hydrobromic acidhydrobromic acid
hydrobrominationhydrobromination
silica cagesilica cage
Br2/H2O
Sol-Gel Sponges
Hagit Frenkel-Mullerad
C CH
H H
C C
HO
Br
H HH
Si(CH2)n
Si(CH2)n
Br2 2H2O
H3O Br
The reaction kinetics can be followed in two ways: 1.Following the visible absorption of bromine
2. Following the decrease in pH
Kinetics of the reaction through follow-up of Br2 consumption
Vinylated silica
Kinetics of the reaction as detected by HBr release
2.2
2.25
2.3
2.35
2.4
0 10 20 30 40 50
pH
Time (min)
Kinetics of reactivity in nanopores depends on the analytical probe!
X10 slower
Time (s)
0.5
0.6
0.7
0.8
0.9
1
1.1
0 2 4 6 8 10 12
VTSATSBTSOTS
A/A
o
Time (s)
Kinetics depends also on the fine details of the hybrid material, even if the functionality is the same:
Vinyl, allyl, butyl, octyl.
The shorter chains are much more reactive than the longer ones - why?
Initial rates
A schematic view of the possible micellar nano-phase zones
Si
Si
Si
Si
Si
O
OO
O
O
O
O
O
O
O
OO
OO
O
Si
Si
SiSi
Si
Si
Si
SiSi
O
O
O
O
O
O
O
O
OOOO
O
O
O
O
O
O
O
O
Reactivity depends on the specific nano structure of the hybrid material
3. Photochemistry
Electron transfer
Py
Light Py* - the donor
Py* +
MV2+ - the acceptor
MV.+ + Py+
2MV.+ + 2H3O+ 2MV2+ + H2 + 2H2O
The classical problem:
MV.+ + Py+ MV2+ + Py
Example 1: Solar energy storage - solving the problem of back-reaction
Energy storing pair
Useful reaction
back-reaction
Py*@silica + TV2+
N N
2Br
Four hours, 5% yield of separated pair
The nanoporosity approach:
I. Separate spatially the donor and the acceptor by entrapment in a sol-gel matrixII. Allow them to communicate through the nanopores with a shuttler
A. Slama-Schwok, M. Ottolenghi
TV+ + Py+@silica
MV2+@silica + TV+ TV+2 + MV+@silica
TV+ + Py+@silica Py@silica + TV2+
TV2+ Py MV2+ The redox potential of the MV pair is smaller than that of the TV pair
D. Levy
Example 2: Affecting the direction of photochromism by tailoring the surface of the nanopores Isomerization of spiropyrans
Colorless Colored
Controlling the directionality of photochromism
Reversed photochromism in silica sol-gel matrices
…but normal photochromism in ethylated silica
Colorless Colored
3. Sensors: Extraction of a library of reactivities from a single molecule
Getting a library of acid/base sensors from a single moleculenanopore effects
AnionicAF
ZwitterionicET(30)
+
Claudio Rottman
Affecting the immediate environment by co-entrapment of surfactants within the nanocages
ET(30), an acid or a base – your choice: The interpretation
Continuous range of acids/bases by using a surfactant mixture at varying proportions
ET(30)
Huge pKi shift for AF: 8 orders of magnitude
4. Catalysis
Cl 3
OCH 2 CO 2H
Cl
Cl 3
Cl
24 h (75 % )
Cl
(99%)
C
CCl3
1st example: Superior synergistic catalyst for green chemistryTwo components in a nano-cage: Catalytic synergism
Hydrogenation of chlorinated environmental pollutants
Cl CCl
H
C H 3
(90%)
OH
H
Cl
6 h
H 2 O
ClCH 2CH 2Cl
(44%) + (26%)
=OH
O
O
O
hexane
O
O
hexane24 h
24 h
ClCH 2 CH2Cl
Cl
ClCl
(93%)
24 h
R. Abu-Reziq, J. Blum
The combined catalyst:Pd nanoparticles + [Rh(cod)Cl]2
Chlorophenols
2,4,5-T
PCBs
DDT
Cl-dioxins
C. Bianchini, R. Psaro et al, J. Am. Chem. Soc.
Mechanism suggested by Bianchini, Psaro et al:
The confinement of the two catalysts within a cage
A
B + C
D
acid
base
2nd example: One-pot multistep catalytic processes with opposing reagents
F. Gelman, J. Blum
Cutting the need for separation steps
F. Gelamn, J. Blum
Three steps oxidation/reductions in one pot
RhCl[P(C6H5)3]3 91%
5. Imprinted nanoporosity
4th example: Tailored nanoporosity by imprintingDirecting the seterochemistry of a reaction
Forcing a cis-product in the Pd-acetate catalyzed Heck reaction
D. Tsvelikhovsky, J. Blum
9:1
1:1
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 recognition of the imprinting molecule: DopaC
urre
nt (A
)
OH
OH
CH2CHNH2
COOH
OH
OHOH
OH
CH2CO2H
OH
OH
CH2CH2NH2
L-Dopa D-Dopa
Silica sol-gel thin films, 70 nm
D. Mandler, S. Fireman
6. Enzymatic reactions - enhanced stability
Protection from heat
Very large shifts in the denaturing temperatures
New, very mild entrapment method in alumina:Al(C3H7O)3, pH 7.3, ultrasound
OVA@alumina
V. Vinogradov, 2014/5
Not only thermal stability, but increase in activity up to 60oC
… and stability to repeated cycles of heating to 60oCand cooling
Acid phosphatase@Alumina
The activity at 750C, is higher than at room temperature by about two orders of magnitude.
# (AcP, 1): Treatment of enzyme deficiency diseases
ACP@Alumina
Arrhenius analysis
The pre-factor of the entrapped enzyme A = 3.54.1014 sec-1 six orders of magnitude higher (!) than that of the free enzyme4.34.108 sec-1
RTE a
eAk
60-70oC60-70oC
7. Merging all of the above
Protection of an enzyme from strong oxidative conditions: Alkaline phosphatase protected from bromine
H. Frenkel-Mullerad, R. Ben-Knaz, 2014
VTS: An efficient bromine sponge
SiOO
O O-
SiOO
CH
SiO
O OH
SiO
Si
H C
O
OHO
OHO
H
Si OH C
OSi
HO O
SiO
OC H
Si OHO
OSiHO O
OSi
OC H O
O
HO
H
SiCH
OO Si
OH
O SiO
OH
OO Si
HC
OO
Si
OH
O Si
OH
O
O
O
H
OH
H
Si
Si
Si
Si
Si OH
O
HOOH
OHHO
O
O
H2C
CH2
CH2H2C
H2C
H2C
H2C
SiOO
OO-
SiOO
CH
SiO
OOH
SiO
Si
H C
O
OHO
O
Si OCH
OSi
HOO
SiO
OC H
Si OHO
OSiHO O
OSi
OCH
O
O
HO
H
Si
CH
OO Si
OH
O SiO
OH
OO Si
HC
OO
Si
OH
O Si
OH
O
O
O
H
Si
Si
Si
Si
Si OH
O
HO
OHOH
HO
O
O
CH2
CH2
CH2H2C
H2C
CH2
H2C
OH
Br
Br
HO
Br
HO
Br
HO
OHBrOH
Br
Br
OHBr-
Br-HO
H
H
Br2/H2O
vinyl groupvinyl group
hydrobromic acidhydrobromic acid
hydrobrominationhydrobromination
silica cagesilica cage
Br2/H2O
One-pot enzyme/catalyst pair
+ CH3(CH2)nCH2OH
Catal@S-G Lipase@S-GH2
CH2 CH(CH2)8COOH
CH3(CH2)9COOCH2(CH2)nCH3
Catalysts: Rh2Co2(CO)12
Rh(PPh3)3Cl0.6 mmol acid, 2.5 mmol alcohol0.01 mmol catalyst, 11U lipase
F. Gelman, J. Blum
A
B + C
D
acid
base
Conclusion
Better materials based on chemistry
Better chemistry based on materials