The chirality of the SiO4 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
By Andrea Carter, Vocalist: Jaimsy Kennedy http://www.songlegacy.com/audio/65thBirthdayWomanExcerpt.mp3
The abundance of elements in Earth’s crust The silicates
The most common mineral in Earth’s crust Quartz = 59.7 (%weight)Feldspar = 15.4Haematite = 2.6 MgO = 4.4 Quartz is chiral (https://answers.yahoo.com/question/index?qid=20121205130239AAPOhoq)
Quartz is chiral on all scales: From the macroscopic crystal habit to the molecular building blocks Space groups: A:P3121 & B:P3221 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
Thanks Dina Yogev Chaim Dryzun Michael Ottolenghi Sharon Fireman Sharon Marx Yitzhak Mastai Hagit Zabrodsky
Our focus: Amorphous and crystalline materials based on SiO4
Amorphous silica How is it possible to induce chirality in this amorphous material?
How is it possible to induce chirality in silica? The classical approach: Use of auxiliaries * Adsorb on the surface a chiral molecule * Covalentlysilylate 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 Key question to keep in mind: All of these methods induce chiral functionality, but does the material itself become chiral?
The sol-gel polycondensation reaction 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-
The chiral sol-gel polymerization approach Fibers widths 2 to 5 nm Michel Wong-Chi-Man et al, J. Am. Chem. Soc, 2001, 123, 1509-1510
Imprinting silica with a chiral surfactant DMB: The imprinting molecule The sol-gel monomers # p-pinteractions (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)
Silica (partially phenylated) imprinted with aggregates of DMB was capable of separating the enantiomer-pairs of: BINAP Propranolol Naproxen
S R R General enantioselectivity of imprinted silica With S. Fireman, S. Marx
If an SiO2 material is made chiral by a foreign molecule, then: # How are the building blocks of the material affected? # Is it possible that an SiO4 tetrahedron which is neighboring to the chiral event, becomes chiral itself? # Is it possible that the material becomes chiral farther from the chiral event?
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?
R R S 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!
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 We shall compare: * Co-doping * Adsorption of CR on silica doped with DMB With S. Fireman, S. Marx
CR-DMB in solution (blue line) and CR solution (red line) The ICD spectra of co-entrapped CR-DMB in hydrophilic and hydrophobic silicas CR-DMB@Silica (red line) and CR-DMB@Octylated silica (blue line) Has the silica matrix become chiral? S. Fireman
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@C8-silica
All of the building blocks of quartz are chiral! 32- Left Helix 31- Right Helix C2-symmetry, not exact Td SiO4 Si(OSi)4 SiSi4
If chiral SiO4 is a stable solution in Nature and in amorphous silicas, could it be that it is much more common than previously thought?
Revisiting the aluminosilicate zeolites ZSM-5, NanAlnSi96–nO192·16H2O
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)
The 21 “re-discovered” chiral silicate zeolites The chirality of these x-ray analyzed zeolites is not mentioned in the original reports!
The building blocks of zeolites we analyzed TO4 T(OT’)4 TT’4 The secondary building unit (SBU) The asymmetric unit T, Si, Al, O Goosecreekite The unit cell
The isothermal titration calorimetry (ITC) experiment on Goosecreekite L-histidine Adsorption of D-histidine (the lower curve) or L-histidine (the higher curve) on Goosecreekite (GOO): The heat flow per injection With Y. Mastai and A. Shvalb
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
The continuous chirality measure Major contributions by Santiago Alvarez
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)
The most chiral monodentate complex S. Alvarez, Europ. J. Inorg, Chem., 1499 (2001)
The chirality values are comparable or larger than the chirality values of the known chiral zeotypes and of quartz
The varying degree of chirality of quartz in Nature SiO4 Dina Yogev-Einot
Phase diagram of the SiO2 family Stishovite Cristobalite Coesite Low-Quartz
a SiSi4 a SiO4 Pressure-chirality correlations in quartz
Unit Cell Volume Temperature and pressure effects: Unified picture T P A: d’Amour H (1979), B: Jorgensen J D (1978) , C: Hazen R M (1989), D: Glinneman J (1992), T: Kihara (1990). D. Yogev-Einot
2 2 1 1 0 0 3 3 4 4 Pressure (GPa) Temperature (K) 0.0001 298 838 6.8 The molecular distortion leading to the chirality changes The chirality measure as a single structural parameter
Quartz-germania (GeO2), quatz-silica: Unified picture Chirality-pressure correlation
The optical rotation of quartz: 126 years ago Le Chatelier and his contemporaries Le Chatelier, H. Com. Rend Acad Sci 1889, 109, 264.
Chirality, SiSi4 Le Chatelier a t/a Chirality a t/a 0 Temperature (°K) 126 years later: an exact match with quantitative chirality changes SiSi4 D. Yogev, Tetrahedron: Asymmetry 18, 2295 (2007)
Step 4: What is a left-handed SiO4 tetrahedron?
Reminder of the CIP rules logic • 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 SiO4