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Volume 1 of JACS : 1879 Volume 1 of Chem. Mater. : 1989

Volume 1 of JACS : 1879 Volume 1 of Chem. Mater. : 1989. The new motto (80’s) has been: “Better Ceramics Through Chemistry” . Publications in the sol-gel materials field. 25 YEARS OF SOL-GEL RESEARCH: CONTRIBUTIONS TO CHEMISTRY David Avnir Institute of Chemistry

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Volume 1 of JACS : 1879 Volume 1 of Chem. Mater. : 1989

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  1. Volume 1 of JACS: 1879 Volume 1 of Chem. Mater.: 1989

  2. The new motto (80’s) has been: “Better Ceramics Through Chemistry”

  3. Publications in the sol-gel materials field

  4. 25 YEARS OF SOL-GEL RESEARCH: CONTRIBUTIONS TO CHEMISTRY David Avnir Institute of Chemistry The Hebrew University of Jerusalem 75th Meeting of the Israel Chemical Society Tel-Aviv, 25-16.1.2010

  5. “Better Ceramics Through Chemistry”

  6. The motto of this lecture: # What has chemistry gained from sol-gel research # How do solid matrices affect a chemical reaction? # What can be done in heterogeneous chemistry that homogeneous reactions cannot achieve?

  7. My main partners over the years Jochanan Blum Sergei Braun Ovadia Lev Daniel Mandler Sharon Marx Michael Ottolenghi Renata Reisfeld

  8. The Heterogeneous environment: • Silica

  9. Silica

  10. 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-

  11. Controlled nanoporosity and cage geometry Surface area and pore volume of silica as a function of pH and water/silane ratio Y. Polevaya, M. Ottolenghi, D. Avnir, J. Sol-Gel Sci. Tech., 5, 65-70, (1995)

  12. Organic heterogenization Physical entrapment of molecules within sol-gel matrices Monomers, oligomers Sol Sol Gel Gel Xerogel Xerogel • * Small molecules • * Polymers • * Proteins • * Nanoparticles monomer oligomer sol - - particle Entrapped species The concept is general and of very wide scope

  13. Physical entrapment vs covalent entrapment Important property: Reactivity is possible with the entrapped species

  14. Matrix parameters which can affect chemical reactivity: # The fixation by entrapment within the matrix # The confined environment of cages and narrow pores # The porosity # The chemical modification of the matrix # The co-entrapment of a surfactant

  15. 2. Affecting reactivity by the entrapment * Hydrophobic catalysts in water * The back-reaction problem in energy storage * One-pot reactions with mutually destructive reagents

  16. Using hydrophobic catalysts in water ee = 78% (BPPM) The advantages of sol-gel entrapment # Reactivity in incompatible solvents # Covalent bonding chemistry is not needed # Recyclability and separation With F. Gelman. J. Blum, D. Avnir J. Molec. Catal., A: Chem., 146, 123 (1999)

  17. The problem of back-reaction in energy storage 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

  18. The solution: I. Separate spatially the donor and the acceptor in a matrix II. Allow them to communicate with a shuttler Py*@silica + TV2+ TV+ + Py+@silica MV2+@silica + TV+ TV+2 + MV.+@silica Four hours, 5% yield of separated pair TV2+ Py MV2+ Hydrogen evolution, in a related system (Ru/DMB/Ir): JACS113 3984 (1991) TV+ + Py+@silica Py@silica + TV2+ A. Slama-Schwok, M. Ottolenghi and D. Avnir, Nature, 355, 240 (1992)

  19. One-pot reactivity from opposing reagents The concept: Entrapped reagents are not accessible to each other, but are accessible to diffusing substrates The acid and base are entrapped, separately One pot, one step A D Acid, Base, C

  20. One-pot acid/base reactions 32% Acid: Nafion Base: TBD FainaGelamn, J. Blum, D. Avnir, Angew. Chem. Int. Ed., 40, 3647 (2001)

  21. Opposing catalyst and acids F. Gelman, H. Schumann, J. Blum, D. Avnir J. Sol-Gel Sci. Tech., 26, 43 (2003); J. Am. Chem. Soc., 122, 11999 (2000)

  22. Simultaneous oxidation-reduction reactivity RhCl[P(Ph)3]3@silica F. Gelamn, J. Blum, D. Avnir, New J. Chem., 27, 205 (2003)

  23. One-pot lipase / catalyst pair Biocatalysis and organometallic catalysis in one pot F. Gelman, J. Blum, D. Avnir J. Am. Chem. Soc.,124, 14460 (2002)

  24. All possible combinations:

  25. 3. Cage-confinement effects on reactivity # Radical photo-rearrangement # Synergism in catalysis # Unusual enzyme reactivity

  26. The photo-Fries rearrangement

  27. Radical cage effect of silica Only 5% in pentane, but 37% in silica (at 40%, conversion) D. Avnir, P. de Mayo, J. Chem. Soc. Chem. Comm., 1109 (1978)

  28. H O 2 OCH CO H 2 2 (75 % ) ClCH CH Cl 2 2 Cl Cl 3 3 CCl C H 3 3 CH2Cl ClCH 2 Two components in a cage: Catalytic synergism Hydrogenation of chlorinated environmental pollutants OH O OH = Chlorophenols 2,4,5-T PCBs DDT Cl-dioxins 6 h (26%) (44%) + Cl The combined catalyst: Pd nanoparticles + [Rh(cod)Cl]2 Cl 24 h Cl Cl 24 h (99%) hexane H H 24 h Cl Cl C (90%) C hexane Cl Cl O O 24 h (93%) O O Cl A. Ghatas, R. Abu-Reziq, J. Blum, D. Avnir Green Chem.,5, 40 (2003)

  29. Mechanism suggested by Bianchini, Psaro et al: “Pd(0) is able to reduce benzene to cyclohexane with a mechanism that involves disproportionation of the cyclohexa-1,3-diene product and fast cyclohexene hydrogenation; Rh(I) is faster than Pd(0) in reducing cyclohexa-1,3-diene, yet slower in the conversion of cyclohexene to cyclohexane” C. Bianchini, R. Psaro et al, J. Am. Chem. Soc., 128, 7065 (2006)

  30. The confinement of the two catalysts within a cage C. Bianchini, R. Psaro et al, J. Am. Chem. Soc., 128, 7065 (2006)

  31. Un-orthodox reactivity and unusual stability of sol-gel entrapped enzymes Alkaline-phosphatase is active at pH 1! Blue: silica Green: with AOT Red: with CTAB H. Frenkel-Mullerad, D. Avnir J. Am. Chem. Soc.127, 8077 (2005)

  32. Enzymatic activity under very extreme conditions A basic enzyme is active at pH 1! Why is the narrow cage so efficient in protecting the enzyme?

  33. “The collapse of thermodynamics” Two protonated water molecules out of 100 is ~ ”pH=0”!

  34. Acid phosphatase is active under extreme alkaline conditions Right: silica; left: silica/CTAB In solution: Zero activity above pH 10

  35. 4. Porosity effects on reactivity # The inherent porosity of silica # Imprinted porosity

  36. Size-discrimination in disproportionation reactivity The catalyst: [RR’3N]+[RhCl4]-@silica R: (C8H17), R’: Me A. Rosenfeld, J. Blum, D. Avnir J. Catal.164, 363 (1996)

  37. Pore-accessibility effects on the disproportionation reactivity of 1,2-dihydronaphthalene [RR’3N]+[RhCl4]-@silica SG-1: R: (C8H17), R’: Me SG-2: RR’3N: [Me3N(CH2)3Si(OMe)3] naphthalene and tetralin dihydronaphthalene Si(OEt)4 and RSi(OEt)3 SG-1 (—) and SG-2 (– – –)

  38. Directing reactivity through imprinting of the matrix Forcing a cis-product in the Pd-acetate catalyzed Heck reaction 9:1 1:1 D. Tsvelikhovsky, D. Pessing, D. Avnir, J. Blum, Adv. Synth. & Catal., 350, 2856 (2008)

  39. 5. Affecting reactivity by covalent modifying the material Co-polycondensation of Si(OEt)4 and RSi(OEt)3 # All-hydrophobic catalytic reactions in water

  40. All-hydrophobic catalytic reactions in water The emulsion contains the substrate Hydrophobic chains The emulsion spills its content into the porous catalyst material The catalyst is entrapped in a partially hydrophobic silica sol-gel matrix R. Abu-Reziq, J. Blum, D. Avnir Angew. Chem. Int. Ed., 41, 4132 (2002)

  41. A micelle is reassembled and leaves with products inside The catalytic process takes place

  42. 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, D. Avnir Angew. Chem. Int. Ed., 41, 4132 (2002)

  43. 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

  44. 6. Affecting reactivity by co-entrapment of a surfactantGetting a library of acids from a single molecule ET(30) Claudio Rottman et al, J. Am. Chem. Soc., 121, 8533 (1999); 123, 5730 (2001)

  45. Getting a library of acids from a single molecule: ET(30)

  46. Hartley’s rule: The most significant surfactant-induced changes in properties of charged dyes are observed when the charge of the dye is opposite to that of the surfactant G. S. Hartley, Trans. Faraday Soc., 30, 444 (1934) Surfactant-dye interactions greatly enhanced in the cage

  47. Getting a library of acids from a single molecule: ET(30)

  48. Acid fuchsin – CTAB interactions Solution pKi = 13

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