1. Sol-gel matrix effects in organic chemistry
David Avnir
Institute of Chemistry
The Hebrew University of Jerusalem, Israel
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences
April 19, 2019 

2. Molecularly doped sol-gel materials
Background:
Molecularly doped sol-gel materials

3. The preliminary motivation:
To merge the small family of glasses and ceramics with the huge library of organic molecules and biomolecules: There are ~40 millions of these

4. The sol-gel porous glass formation by polycondenstation
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
Monomers of the type R-Si(OCH3)3 leading to(R-SiOmHn)p
H+ or OH-

5. The Sol-Gel Process Sol Stage Gel Stage Xerogel Stage Thin Films
Fibers
Powders, patricles
Hollow Spheres
Membranes
Porous Monoliths
Dense Ceramic
Aerogels

6. Sol-gel silica

7. Functionality within a sol-gel matrix
* Molecules
* Polymers
* Proteins
* Nanoparticles

8. Functionalization by entrapment of active components
Porous
Monomers,
oligomers
Sol
Sol
Gel
Gel
Xerogel
monomer
* Small molecules
* Polymers
* Proteins
* Nanoparticles
oligomer
sol - -
particle
The concept is general and of very wide scope
entrapped
molecule

10. Organically doped sol-gel objects

11. Reactivity of the dopant through the nanopores
An important and useful property:
The entrapped functionalities are accessible to diffusing molecules from the outside, and to diffusing products from the inside, with minimal or no leaching.
The reason:

12. From “Better Ceramics Through Chemistry” to
“Better Chemistry Through Ceramics“
Matrix parameters which affect reactivity:
The heterogenization by entrapment
The confinement within cages and their rigidity
3. The porosity
4. The structure of the material
5. The chemical modification of the matrix
6. Co-entrapment of dopants

13. Matrix effects on reactivity
2. Opening example:
Matrix effects on reactivity

14. Double-bond derivatized sol-gel silica
Polymerization of monomers of the type R-Si(OCH3)3
Hydrobromination
H. Frenkel

15. The hydrobromination reaction
Bromine sponge
The hydrobromination reaction
We can see that the reaction kinetics can be followed in two ways:
Following the visible absorption of bromine
2. Following the decrease in pH

16. Kinetics of the reaction through follow-up of Br2 consumption
Vinylated silica

17. Kinetics of the reaction as detected by HBr release
2.2
2.25
2.3
2.35
2.4
X10 slower pH 10 20 30 40 50
Time (min)
Kinetics of reactivity in nanopores depends on the analytical probe!

18. Bromine sponge: chain length effect
n = 0, R = vinyl, (VTS): CH2=CH-Si
n = 1, R = allyl, (ATS): CH2=CH-CH2-Si
n = 2, R = butenyl, (BTS): CH2=CH-CH2-CH2-Si
n = 6, R = octenyl, (OTS): CH2=CH-(CH2)6-Si
The shorter chains are much more reactive than the longer ones - why?
Time (s)
0.5
0.6
0.7
0.8
0.9 1
1.1
A/Ao
VTS
ATS
BTS
OTS
Initial rates 2 4 6 8 10 12
Time (s)

19. % hydrobromination
vinyl allyl butyl octyl
Material
Total Br/Si molar ratio 5 10 15 20 25 30 35 40
VTS
ATS
BTS
OTS 50 60 70 80 90
100
% Hydrobromination
Reactivity depends on the specific nano structure of the hybrid material

20. 3. Matrix effect on catalysis

21. A. Porosity effects:
Size-discrimination in catalytic disproportionation
The catalyst:
R: (C8H17), R’: Me
A. Rosenfeld, J. Blum

22. B. Cage effects: Synergistic catalyst for green chemistry
Two components in a cage
Hydrogenation of chlorinated environmental pollutants OH O OH =
Chlorophenols
2,4,5-T
PCBs
DDT
Cl-dioxins
6 h
(44%) +
(26%) H 2 O Cl
The combined catalyst:
Pd nanoparticles + [Rh(cod)Cl]2
OCH 2 CO H Cl
24 h
(75 % ) Cl
ClCH 2 CH Cl Cl
24 h
(99%)
hexane Cl 3 Cl 3 H H
24 h Cl C Cl
hexane C
(90%)
CCl 3 C H 3 Cl Cl O O
24 h
(93%)
ClCH 2
CH2Cl O O Cl
R. Abu-Reziq, J. Blum

23. Mechanism suggested by Bianchini, Psaro et al:

24. C. Matrix hydrophobization effects:
All-hydrophobic catalytic reactions in water
Three-phase catalysis:
The EST process
A novel three-phase microemulsion/solid
heterogenization and transport
method for catalysis
R. Abu-Reziq, J. Blum

25. EST: Matrix induced selectivity
Ethyl derivatized matrix
Octyl derivatized matrix
Catalyst: [CH3(C8H17)3N]+[RhCl4]-
Surfactant: Cetyl(trimethylammonium)(p-toluenesulfonate)
Conditions: 200 psi of H2 and heated at 80°C for 20 h

26. The sol-gel imprinting approach
D. Imprinting effects:
The sol-gel imprinting approach

27. Imprinting for catalysis Directing the seterochemistry of a reaction
Forcing a cis-product in the Pd-acetate catalyzed Heck reaction
9:1
1:1
D. Tsvelikhovsky, J. Blum

28. 4. Biocatalysis

29. Entrapped enzymes in sol-gel nanocages
Protection against extreme pH
Alkaline-phosphatase is active at pH 1!
Blue: silica
Green: with AOT
Red: with CTAB
H. Frenkel

30. Entrapped enzymes in sol-gel nanocages
Protection against heat
Acid
Increase in activity up to 60oC
The activity at 750C, is higher than at room temperature by about two orders of magnitude.
V. Vinogradov

31. Two protonated water molecules out of 100 is ~”pH=0”!
The entrapped enzyme with few water molecules inside a pore, two of which are protonated: The nominal "pH" is very low
Two protonated water molecules out of 100 is ~”pH=0”!

32. 5. Opposing reactions in one reaction pot

33. The concept: Sol-gel isolation of mutually destructive chemical reagents
F. Gelman, J. Blum

34. One-pot acid/base reactions
Acid: Nafion
Base: TBD
Faina Gelamn, J. Blum

35. Oxidation/reductions in one pot
RhCl[P(C6H5)3]3
91%

36. One-pot enzyme/catalyst pair
0.6 mmol acid, 2.5 mmol alcohol
0.01 mmol catalyst, 11U lipase
F. Gelman, J. Blum

37. 6. Getting a library of reactivities from a single molecule

38. Getting a library of acid-base equilibria from a single molecule
Nanopore effects on the co-entrapment of an indicator-with a surfactant
Anionic indicator AF
Zwitterionic indicator
ET(30) +
Claudio Rottman

39. Affecting the immediate environment by co-entrapment of surfactants within the nanocages

40. ET(30), an acid or a base – your choice: The interpretation

41. Huge pKi shift for AF: 8 orders of magnitude

42. Surfactant-dye interactions

43. 7. Matrix effect on photochemistry

44. Affecting the direction of photochromism Isomerization of spiropyrans
D. Levy

45. Controlling the directionality of photochromism
Colorless Colored
Reversed photochromism in silica sol-gel matrices
D. Levy et al, J. Phys. Chem., 92, (1988).

46. …but normal photochromism in ethylated silica
Colorless Colored
D. Levy

47. Solar energy storage - solving the problem of back-reaction
Light
Py* - the donor Py
Electron transfer
Py* +
MV.+ + Py+
MV2+ - the acceptor
Energy storing pair
2MV.+ + 2H3O+
2MV2+ + H2 + 2H2O
Useful reaction
The classical problem:
MV.+ + Py+
MV2+ + Py
back-reaction
M. Ottolenghi

48. The nanoporosity approach:
I. Separate spatially the donor and the acceptor by entrapment in a sol-gel matrix
II. Allow them to communicate through the nanopores with a shuttler
+ TV2+
TV+ +
+ TV+
TV+2 +
Four hours, 5% yield of separated pair
TV Py MV2+
The redox potential of the MV pair is smaller than that of the TV pair
TV+ +
+ TV2+
A. Slama-Schwok, M. Ottolenghi

49. 8. Conclusion
Traditionally, variations in chemical reactivity have been affected by changing reagents and starting materials, that is by changing the molecules.
Here we have seen that changing the heterogeneous environment of the molecules without changing them, opens a new way to control chemical reactivity:
Catalysis, biochemistry, sensing, photochemistry

50. Abu-Reziq, R. , Armon, R. , Babonneau, F. , Banin, U. , Behar-Levy, H
Abu-Reziq, R., Armon, R., Babonneau, F., Banin, U., Behar-Levy, H., Ben-David, O., Birenbaum, H., Blum, J., Braun, S., Ciriminna, R., Coradin, T., Elimelech, H., Fireman-Shoresh, S., Frenkel-Mullerad, H., Fuchs, I., Gelman, F., Ghattas, A., Grader, G.S., Hamza, K., Kaufman, V.R., Keinan, E., Khalfin, R., Kogan, A., Lev, O., Levy, A., Levy, D., Livage, J., Mandler, D., Marx, S., Mokari, T., Nairoukh, Z., Naor, H., Nedelec, J-M., Ottolenghi, M., Pagliaro, M., Polevaya, Y., Popov, I., Prior, Y., Rappoport, S., Reetz, M.T., Reisfeld, R.,
Rojanski, D., Rosenfeld, A., Rottman, C., Rouquerol, J., Samuel, J., Sarussi, L., Schubert, U., Schumann, H., Seri-Levy, A., Sertchook, H., Shabat, D., Shacham, R., Shtelzer, S., Shter, G.E., Shuster, M., Shvalb, A., Slama-Schwok, A., Tsvelikhovsky, D., Turiansky, A., Turyan, I., Vinogradov, V.V., Wellner, E., Zolkov, Ch., Zusman, R.