Speaker
Ira Weinstock, Ph.D.
Speaker's Institution
Ben Gurion University
Date
8/26/19
Time
4:00 PM
Location
Chemistry A101
Mixer Time
3:45 PM
Mixer Location
Chemistry B101E
Additional Information

About the Seminar:

In recent years, we have used porous icosahedral-symmetry metal-oxide capsules, of the type,[{MoVI6O21(H2O)6}12{MoV2O4(L)}30]42– {Mo132} (L = an endohedrally-coordinated carboxylate anion), to investigate organic reactions within nano-confined domains in water. Using the capsule as a soluble analogue of porous solid-state (rigid) oxides, we initially showed that branched-alkane carboxylate “guests” could enter the capsule’s interior by negotiating passage through flexible subnanometer Mo9O9 apertures whose geometrical dimensions were smaller than the entering species themselves [1]. Nano-containers in which structurally integral metal centers serve as catalytic sites for encapsulated substrates are relatively rare, and the {Mo132} capsules provide a unique opportunity for exploring this class of reactions. These include the cleavage of methyl tert-butyl ether under mild conditions in water, and for the Michaelis-Menten compliant hydrolysis of epoxides, with an enzyme-like rate acceleration (kcat / kuncat) of 182,800, the largest yet reported for a cage or container at room temperature in water [2-3]. Regarding self-assembly a {Mo132} capsule was used to reveal the energetics of individual steps in the formation of a “micelle”-like organic aggregate of n-butyrate ions [4] (see also ref. [5]), and in related work, two distinct host domains within the capsule were found to be preferentially populated as a function of alkane-guest size [6]. Most recently[7], we demonstrated that confined conditions can release a latent potential for entropically driven (i.e., ‘hydrophobic’) uptake and assembly of alcohol guests. Namely, the spontaneous uptake of L-glycerate ligands by a {Mo132} capsule was shown to be entropically driven, revealing the inherently “hydrophobic” nature of poly-alcohols, whose sequestration from water bears an energetic signature closely analogous to that of “classical” hydrophobes.

[1] Ziv, A.; Grego, A.; Kopilevich, S.; Zeiri, L.; Miro, P.; Bo, C.; Müller, A.; Weinstock, I. A. “Flexible Pores of a Metal-Oxide-Based Capsule Permit Entry of Comparatively Larger Organic Guests” J. Am. Chem. Soc. 2009, 131, 6380-6382.

[2] Kopilevich, S.; Gil, A.; Garcia-Ratés, M.; Avalos, J. B.; Bo, C.; Müller, A.; Weinstock, I. A. “Catalysis in a Porous Molecular Capsule: Activation by Regulated Access to Sixty Metal Centers Spanning a Truncated Icosahedron” J. Am. Chem. Soc. 2012, 134, 13082-13088.

[3] Kopilevich, S; Müller, A.; Weinstock, I. A. “Amplified Rate Acceleration by Simultaneous Up-Regulation of Multiple Active Sites in an Endo-Functionalized Porous Capsule” J. Am. Chem. Soc. 2015, 137, 12740–12743.

[4] Grego, A.; Müller, A.; Weinstock, I. A. “Stepwise-Resolved Thermodynamics of Hydrophobic Self-Assembly” Angew. Chem. Int. Ed. 2013, 52, 8358 –8362.

[5] Garai, S.; Bögge, H.; Merca, A.; Petina, O.P.; Grego, A.; Gouzerh, P.; Haupt, E.T.K.; Weinstock, I.A.; Müller, A. “Densely packed hydrophobic clustering: Encapsulated valerates form a high-temperature-stable {Mo132} capsule system” Ang. Chem. Int. Ed. 2016, 55, 6634 –6637.

[6] Kopilevich, S.; Gottlieb, H.; Keinan-Adamsky, K.; Müller, A.; Weinstock, I.A. “The uptake and assembly of alkanes within a porous nanocapsule in water: New information about hydrophobic confinement” Ang. Chem. Int. Ed., 2016, 55, 4476 –4481.

[7] Chakraborty, S.; Shnaiderman-Grego, A.; Garai, S.; Baranov, M.; Müller, A.; Weinstock, I. A. Alcohols as Latent Hydrophobes: Entropically Driven Uptake of 1,2-Diol Functionalized Ligands by a Porous Capsule in Water. J. Am. Chem. Soc. 2019, 141, 9170−9174.

 

Image of Ira Weinstock
Back to top of page
Image of Peng LiuCSU Ram logo 2