1. The chirality of the SiO 4 building block in materials David Avnir Institute of Chemistry, The Hebrew University, Jerusalem Special Symposium on Chemistry Honoring Santiago Alvarez on the Occasion of His 65th Birthday Barcelona, June 18, 2015

2. By Andrea Carter, Vocalist: Jaimsy Kennedy http://www.songlegacy.com/audio/65thBirthdayWomanExcerpt.mp3

3. Motivation

4. The abundance of elements in Earth’s crust The silicates

5. The most common mineral in Earth’s crust ( https://answers.yahoo.com/question/index?qid=20121205130239AAPOhoq ) Quartz = 59.7 (%weight) Feldspar = 15.4 Haematite = 2.6 MgO = 4.4 Quartz is chiral

6. Space groups: A:P3 1 21 & B:P3 2 21 Quartz is chiral on all scales: From the macroscopic crystal habit to the molecular building blocks There are by far more Si species which are chiral than chiral C species which are chiral on planet Earth Si: 28.1%, C: 0.18%, Si/C = 160 But only ~0.1% of the chirality papers are on Si

7. Let us change that a little!

8. Thanks Dina Yogev Chaim Dryzun Michael Ottolenghi Sharon Fireman Sharon Marx Yitzhak Mastai Hagit Zabrodsky

9. Our focus: Amorphous and crystalline materials based on SiO 4

10. Step 1: Amorphous silica

11. Amorphous silica How is it possible to induce chirality in this amorphous material?

12. The classical approach: Use of auxiliaries * Adsorb on the surface a chiral molecule * Covalently silylate the surface with a chiral silylating agent * Polymerize a chiral trialkoxysilane * Entrap physically a chiral molecule * Hybridize the material a with a chiral polymer * Imprint the material with a chiral template How is it possible to induce chirality in silica? Key question to keep in mind: All of these methods induce chiral functionality, but does the material itself become chiral?

13. The sol-gel polycondensation reaction Si(OCH 3 ) 4 + H 2 O (SiO m H n ) p + CH 3 OH 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 -

14. Fibers widths 2 to 5 nm Michel Wong-Chi-Man et al, J. Am. Chem. Soc, 2001, 123, 1509-1510 The chiral sol-gel polymerization approach

15. The sol-gel doping approach

16. The sol-gel chiral imprinting approach

17. Imprinting silica with a chiral surfactant DMB: The imprinting molecule The sol-gel monomers #  interactions (with Si-Ph) # Hydrogen bonding (with Si-OH and Si-O-Si) # Ionic interaction (with Si-O - ) # Hydrophobic interactions (with Si-Ph, Si-O-Si, Si-OEt)

18. Silica (partially phenylated) imprinted with aggregates of DMB was capable of separating the enantiomer-pairs of: BINAP Propranolol Naproxen

19. S R R General enantioselectivity of imprinted silica With S. Fireman, S. Marx

20. If an SiO 2 material is made chiral by a foreign molecule, then: # How are the building blocks of the material affected? # Is it possible that an SiO 4 tetrahedron which is neighboring to the chiral event, becomes chiral itself? # Is it possible that the material becomes chiral farther from the chiral event?

21. Before and after imprinting After imprinting, enantioselective imprinting occurs in the imprinted hole, and non-selective adsorption occurs in the other pores. If the imprinted molecule remains inside, adsorption is still possible in the other pores – have some of them become enantioselective?

22. S R R S R R Adsorption before and after extraction of the imprinting molecule Before extraction: Chiral dopant (DMB) After extraction: Chiral holes The recognition handedness changes!

23. 2nd proof that the building blocks near a chiral event become chiral: Induced circular dichroism of Congo-red within silica The chiral inducer: DMB The achiral probe: CR With S. Fireman, S. Marx We shall compare: * Co-doping * Adsorption of CR on silica doped with DMB

24. CR-DMB@Silica (red line) and CR-DMB@Octylated silica (blue line) The ICD spectra of co-entrapped CR-DMB in hydrophilic and hydrophobic silicas S. Fireman CR-DMB in solution (blue line) and CR solution (red line) Has the silica matrix become chiral?

25. The ICD signal of CR adsorbed on DMB@silica Co-doping:CR/DMB@silica CR adsorbed on DMB@silica What do we see: Reversal of the ICD signal indicates that the chirality-inducer is different in the two cases. The only possibility is that chiral skeletal porosity was induced by the doped DMB Red: Reference silica; black: DMB@silica; blue: DMB@C 8 -silica

26. Step 2: Quartz and chiral silicate-zeolites

27. 3 1 - Right Helix SiO 4 Si(OSi) 4 SiSi 4 All of the building blocks of quartz are chiral! 3 2 - Left Helix C 2 -symmetry, not exact T d

28. If chiral SiO 4 is a stable solution in Nature and in amorphous silicas, could it be that it is much more common than previously thought?

29. Revisiting the aluminosilicate zeolites ZSM-5, Na n Al n Si 96–n O 192 ·16H 2 O

30. The main finding: Out of 120 classical silicate zeolites, we found 21 that must be chiral, but were not recognized as such 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)

31. ZSM – 23 (MTT)Laumontite (LAU)Goosecreekite (GOO) GUS 1 (GON)Edingtonite 10 (EDI)Nabesite (NAB) LTQ (BPH)RUB 23Bikitaite (BIK) LTA (LTA)SSZ-55 (ATS)Gismondine (GIS) ZYT 6 (CHA)H-ZSM-5 (MFI)Franzinite (FRA) ERS 12Zeolite N (EDI)Epistilbite (EPI) RUB 10 (RUT)Zeolite F (EDI)Amicite (GIS) The 21 “re-discovered” chiral silicate zeolites The chirality of these x-ray analyzed zeolites is not mentioned in the original reports!

32. The building blocks of zeolites we analyzed TO 4 TT’ 4 T(OT’) 4 The asymmetric unit T, Si, Al, O The secondary building unit (SBU) The unit cell Goosecreekite

33. 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 on Goosecreekite L-histidine With Y. Mastai and A. Shvalb

34. In all of the examples of Steps 1 and 2, the Si building blocks have been chirally distorted to different levels: Is it possible to evaluate quantitatively the degree of the chirality of the various building blocks? Step 3: Evaluation of the chiral distortion

35. The continuous chirality measure Major contributions by Santiago Alvarez

36. “By how much is one molecule more chiral than the other?”

37. Calculating the degree of symmetry and chirality G: The nearest achiral symmetry point group Achiral molecule: S(G) = 0 The more chiral the molecule is, the higher is S(G)

38. The most chiral monodentate complex S. Alvarez, Europ. J. Inorg, Chem., 1499 (2001)

39. Example in focus: Goosecreekite (GOO)

40. Goosecreekite (GOO) Chiral zincophosphate I (CZP) α-Quartz TT’ 4 2.052.940.55 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

41. SiO 4 The varying degree of chirality of quartz in Nature Dina Yogev-Einot

42. Phase diagram of the SiO 2 family Cristobalite Low-Quartz Stishovite Coesite

43. aSiSi 4 aSiO 4 Pressure-chirality correlations in quartz

44. Temperature and pressure effects: Unified picture A: d’Amour H (1979), B: Jorgensen J D (1978), C: Hazen R M (1989), D: Glinneman J (1992), T: Kihara (1990). Unit Cell Volume P T D. Yogev-Einot

45. Pressure (GPa) 0.0001 6.8 Temperature (K) 298 838 2 1 4 3 0 2 1 4 3 0 The molecular distortion leading to the chirality changes The chirality measure as a single structural parameter

46. Quartz-germania (GeO 2 ), quatz-silica: Unified picture Chirality-pressure correlation

47. Le Chatelier, H. Com. Rend Acad Sci 1889, 109, 264. The optical rotation of quartz: 126 years ago Le Chatelier and his contemporaries

48. Temperature (°K)  Le Chatelier   t  Chirality, SiSi 4 Chirality  t   126 years later: an exact match with quantitative chirality changes D. Yogev, Tetrahedron: Asymmetry 18, 2295 (2007) SiSi 4

49. Step 4: What is a left-handed SiO 4 tetrahedron?

50. Reminder of the CIP rules logic 1.Rank the 4 substituents: purple>red>blue>green 2. Look from the green to the black; two different purple-to-blue rotations are seen: Left handed and right handed. But there is no hierarchy in the 4 oxygen atoms of SiO 4

51. To answer the question “what is a left-handed SiO 4 tetrahedron?” one has to invent a convention of handedness for chiral AB 4 species. Let’s do it!

52. 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 A method to assign handedness to AB 4 species The Triangle-Method

53. Chiral zeolite Goosecreekite is left-handed (Al(1)Si 4 )

54. Yes, but if the definition is arbitrary why this and not another one? Indeed, let us try another one!

55.  1. Project one edge onto the other - three angles form. 2. Select the smallest angle from the three. 3. Check the angle direction from top to bottom and assign the helix notation (Right handedness is shown) The edge-torsion approach:

56. Could it be that the same object is right-handed by one definition and left-handed by the other? Yes. Example: SiO 4 of Low-Cristobalite: Left handed by the torsion rules;right handed by the triangles rules SiO 4 Low-Cristobalite P4 1 2 1 2 (no. 92) D. Peacor (1973)

57. Conclusion: Where does the arbitrariness of handedness labeling leave us? You must be very careful…

58. … because when you encounter your enantiomer, she/he may claim to be the real thing! Me and my enantiomer

59. What does it mean for amorphous silica? # The tetrahedra are chiral because the environment of each is non-isotropic, and because the chance that the distortion retains a reflection mirror, is small. # Silica is a racemic mixture of chiral SiO 4 tetrahedra: - Half comprise a homochiral left-handed set, and half a right- handed set - This is true for ANY handedness definition)

60. What does it mean for amorphous silica? # Each tetrahedron has a unique distortion; - therefore its enantiomer tetrahedron is statistically similar

61. Kelvin’s definition of chirality “I call any geometrical figure, or any group of points, chiral, and say it has chirality, if its image in a plane mirror, ideally realized, cannot be brought to coincide with itself." – Lord Kelvin

62. What does it mean for amorphous silica? # Each tetrahedron has a unique distortion; - therefore its enantiomer tetrahedron is statistically similar # Induction of chirality by any of the auxiliary methods, will enrich the chiral population of SiO 4 tetrahedra with one type of handedness.