Nanoporosity – where is it useful in chemistry? David Avnir Institute of Chemistry

1. 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

2. 1. The material at focus - silica

3. Silica

4. Controlled nanoporosity Surface area and pore volume of silica as a function of pH and water/silane ratio in the sol-gel process

5. Functionality within a sol-gel matrix Monoliths Powders Particles This-films

7. 2. Chemical sponges – diffusion considerations

8. Sol-Gel Sponges Hagit Frenkel-Mullerad

9. The reaction kinetics can be followed in two ways: • Following the visible absorption of bromine • 2. Following the decrease in pH

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

11. 2.4 2.35 2.3 2.25 2.2 0 10 20 30 40 50 Kinetics of the reaction as detected by HBr release X10 slower pH Time (min) Kinetics of reactivity in nanopores depends on the analytical probe!

12. 1.1 1 0.9 0.8 0.7 VTS ATS 0.6 BTS OTS 0.5 0 2 4 6 8 10 12 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? Time (s) A/Ao Initial rates Time (s)

13. A schematic view of the possible micellar nano-phase zones Reactivity depends on the specific nano structure of the hybrid material

14. 3. Photochemistry

15. Example 1: 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

16. 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 Py*@silica + TV2+ TV+ + Py+@silica MV2+@silica + TV+ TV+2 + MV+@silica Four hours, 5% yield of separated pair TV2+ Py MV2+ The redox potential of the MV pair is smaller than that of the TV pair TV+ + Py+@silica Py@silica + TV2+ A. Slama-Schwok, M. Ottolenghi

17. Example 2: Affecting the direction of photochromism by tailoring the surface of the nanopores Isomerization of spiropyrans D. Levy

18. Controlling the directionality of photochromism Colorless Colored Reversed photochromism in silica sol-gel matrices

19. …but normal photochromism in ethylated silica Colorless Colored

20. 3. Sensors: Extraction of a library of reactivities from a single molecule

21. Getting a library of acid/base sensors from a single molecule nanopore effects Anionic AF Zwitterionic ET(30) + Claudio Rottman

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

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

24. Continuous range of acids/bases by using a surfactant mixture at varying proportions ET(30)

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

26. 4. Catalysis

27. 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 1st example: Superior synergistic catalyst for green chemistry Two components in a nano-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 R. Abu-Reziq, J. Blum

28. Mechanism suggested by Bianchini, Psaro et al: The confinement of the two catalysts within a cage C. Bianchini, R. Psaro et al, J. Am. Chem. Soc.

29. 2nd example: One-pot multistep catalytic processes with opposing reagents Cutting the need for separation steps F. Gelman, J. Blum

30. Three steps oxidation/reductions in one pot RhCl[P(C6H5)3]3 91% F. Gelamn, J. Blum

31. 5. Imprinted nanoporosity

32. 4th example: Tailored nanoporosity by imprinting 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

33. Electrochemical recognition of the imprinting molecule: Dopa L-Dopa D-Dopa Silica sol-gel thin films, 70 nm Current (mA) Current / mA D. Mandler, S. Fireman

34. 6. Enzymatic reactions - enhanced stability

35. Protection from heat New, very mild entrapment method in alumina: Al(C3H7O)3, pH 7.3, ultrasound OVA@alumina Very large shifts in the denaturing temperatures V. Vinogradov, 2014/5

36. Not only thermal stability, but increase in activity up to 60oC Acid phosphatase@Alumina … and stability to repeated cycles of heating to 60oC and cooling The activity at 750C, is higher than at room temperature by about two orders of magnitude. # (AcP, 1): Treatment of enzyme deficiency diseases

37. Arrhenius analysis ACP@Alumina The pre-factor of the entrapped enzyme A = 3.54.1014 sec-1 six orders of magnitude higher (!) than that of the free enzyme 4.34.108 sec-1 60-70oC 60-70oC

38. 7. Merging all of the above

39. Protection of an enzyme from strong oxidative conditions: Alkaline phosphatase protected from bromine H. Frenkel-Mullerad, R. Ben-Knaz, 2014

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

41. Conclusion Better materials based on chemistry Better chemistry based on materials