The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement

Kopilevich, Sivil; Gottlieb, Hugo E.; Keinan‐Adamsky, Keren; Müller, Achim; Weinstock, Ira A.

doi:10.1002/ange.201511341

Cited by 13 publications

(5 citation statements)

References 55 publications

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“…The Keplerate-type POMs belong to this class of compounds and correspond probably to one of the most fascinating and aesthetic arrangements in these “mesoscopic” species (see Figure ). Resulting from a symmetry-driven self-assembling process, the Keplerate-type structure exhibits a high idealized I h symmetry combining 12 archetypical pentagonal motifs {M(M) 5 O 21 } with M = Mo or W, held together through 30 {Mo 2 E 2 O 2 } linkers with E = O , or S in a spheroidal topology. − In addition to the tunable composition of the inorganic skeleton, the nature of the 30 inner ligands can be changed from acetate (for the most classical inner ligand) to specific ligands, thus giving the possibility of tuning the inner functionalities of the capsule, such as hydrophobicity/hydrophilicity, , charge density, − or coordination properties. ,,− Such chemical and structural features influence the transfer capacities of specific substrates across the 20 channels. − This scenario has been nicely described by Müller and co-workers, who demonstrated that the active pores {Mo 9 O 9 L 3 }, where L = sulfate or phosphate, are able to trap specific cations in specific positions or recently that the large hydrophobic inner cavity is accessible for large organic guests and sequestration of hydrophobic molecules. − Structural characterizations of mixed salts of {Mo 132 } revealed that well-defined sites located in the vicinity of the sulfate-type pores {Mo 9 O 9 (SO 4 ) 3 } coordinate specifically a variety of cations such as alkali (Na + , Rb + , and Cs + ) or organic (guadininium or protonated urea) cations …”

Section: Introductionmentioning

confidence: 99%

Two Compartmentalized Inner Receptors for the Tetramethylammonium Guest within a Keplerate-Type Capsule

et al. 2016

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The host-guest interactions between the spherical porous Keplerate anion, [Mo132O372(CH3CO2)30(H2O)72](42-) (abbreviated {Mo132}) and the tetramethylammonium cation have been investigated extensively by one- and two-dimensional (EXSY, ROESY, and DOSY) and variable-temperature NMR. Evidence of two inner receptor sites specific for a NMe4(+) guest appears consistent with a quite striking compartmentalization phenomenon. ROESY NMR analyses showed that both sites exhibit a close spatial proximity with the hanging inner acetate groups, while a quantitative EXSY study revealed that these two sites are differentiated by their exchange rates. These NMR data support the hypothesis that these two inner sites could be delimited by the hanging inner acetate groups forming triangular (S1) or pentagonal (S2) hydrophobic pockets on the inner side of the capsule wall. Furthermore, the stability constants associated with the trapping process of the NMe4(+) guest on both the S1 and S2 sites have been determined, showing that the stability constant of the S1 sites decreases significantly as the concentration of the capsule increases gradually, while that of the S2 sites remains nearly unaffected. Such an observation has been interpreted as a result of the plugging process of the {Mo9O9} pores by the counterions NH4(+), which causes unfavorable electrostatic interactions for the NMe4(+) coordination on the proximal S1 site. Finally, the thermodynamic parameters of the NMe4(+) transfer from the solvated situation to the interior of the capsule were estimated from variable-temperature NMR experiments that provide the split of the global process into two successive events corresponding to the plugging and transfer across the inorganic shell.

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Section: Introductionmentioning

confidence: 99%

Two Compartmentalized Inner Receptors for the Tetramethylammonium Guest within a Keplerate-Type Capsule

et al. 2016

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“…We report a new class of functional assemblies, wherein the hydrophobic effect 9,10 drives the spontaneous uptake of alkyl and alkylaromatic guests 11 by porous 200 nm diameter supraspheres whose host capacities are orders of magnitude larger than those of individual cages or containers. On a mass-per-volume basis, the level of uptake rivals those of zeolites and metal-organic frameworks, which, for methane at elevated pressures, reach values of 52 and 160 g l , respectively, for a crystalline aluminosilicate (zeolite) with 5 Å pores (100 bar, 293 K) 12 and the metal-organic framework, Fe(bdp), comprising Fe(II) and 1,4-benzenedipyrazolate linkages (70 bar, 298 K) 13 .…”

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Host–guest chemistry with water-soluble gold nanoparticle supraspheres

et al. 2016

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The uptake of molecular guests, a hallmark of the supramolecular chemistry of cages and containers, has yet to be documented for soluble assemblies of metal nanoparticles. Here we demonstrate that gold nanoparticle-based supraspheres serve as a host for the hydrophobic uptake, transport and subsequent release of over two million organic guests, exceeding by five orders of magnitude the capacities of individual supramolecular cages or containers and rivalling those of zeolites and metal-organic frameworks on a mass-per-volume basis. The supraspheres are prepared in water by adding hexanethiol to polyoxometalate-protected 4 nm gold nanoparticles. Each 200 nm assembly contains hydrophobic cavities between the estimated 27,400 gold building blocks that are connected to one another by nanometre-sized pores. This gives a percolated network that effectively absorbs large numbers of molecules from water, including 600,000, 2,100,000 and 2,600,000 molecules (35, 190 and 234 g l ) of para-dichorobenzene, bisphenol A and trinitrotoluene, respectively.H ost-guest phenomena that involve the uptake of gases and small molecules are associated with the supramolecular chemistry of soluble capsules, cages and containers [1][2][3][4][5] or, alternatively, with heterogeneous reactions of porous solid-state materials such as zeolites 6 and metal-organic frameworks 7 . Only now, however, are organized assemblies of metal nanoparticles beginning to serve in a similar capacity as hosts for molecular guests. In organic solvents, for example, light-induced dipoledipole interactions between gold nanoparticles with azobenzenefunctionalized thiolate ligands were recently used to entrap and catalyse the reactions of polar and alkylaromatic substrates 8 . By design, substrates were entrapped during nanoparticle aggregation to overcome the poor uptake and diffusion of molecular guests into colloidal nanocrystal assemblies. However, the uptake of molecular guests, a trait of supramolecular and solid-state chemistry, has so far not been achieved for colloidal nanoparticle assemblies.For that to occur, a thermodynamically favourable driving force must be combined with a porous structure whose interior architecture features host cavities, along with pathways for the effective diffusion of molecular guests from the exterior (bulk solution) to host domains deeply buried in the assembly's interior. If this were achieved, colloidal metal-nanoparticle assemblies could emerge as a new class of functional nano-engineered structures that are uniquely positioned between supramolecular containers and porous solid-state materials.We report a new class of functional assemblies, wherein the hydrophobic effect 9,10 drives the spontaneous uptake of alkyl and alkylaromatic guests 11 by porous 200 nm diameter supraspheres whose host capacities are orders of magnitude larger than those of individual cages or containers. On a mass-per-volume basis, the level of uptake rivals those of zeolites and metal-organic frameworks, which, for methane at elevated pressures, r...

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“…26 In the past decade, porous polyoxometalate capsules consisting of 132 molybdenum atoms have been studied in the context of host−guest chemistry. 27,28 In addition, the guest cavities of these capsules have been used as "nanoreactors" showing very significant acceleration of acid catalyzed hydrolysis of ethers. 29,30 Here, we present the electrochemical cathodic oxygenation of light alkanes and alkenes, notably ethane to acetic acid at 1.8 V under aerobic conditions in water at room temperature using an iron−tungsten porous spherical capsule, {Fe III 30 W VI 72 } in shorthand, 31 as catalyst Figure 1.…”

Section: ■ Introductionmentioning

confidence: 99%

“…36 In addition, previous research has shown that methane is a poorly incorporated guest into nearly isostructural {Mo 132 } capsules, relative to better incorporation of higher alkanes. 27 The lack of reactivity of methane could be associated with this phenomenon.…”

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Aerobic Electrochemical Oxygenation of Light Hydrocarbons Catalyzed by an Iron–Tungsten Oxide Molecular Capsule

2018

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The selective oxidation of light hydrocarbons and their valorization with only dioxygen (O2) are important transformations toward development of efficient chemical processes. Monooxygenase enzymes can catalyze selective aerobic reactions under reducing and protic conditions. The translation of such enzymatic pathways to the practical electrocatalytic oxidation of light, gaseous hydrocarbons, using O2 as sole oxidant is now reported. An iron–tungsten oxide inorganic molecular catalyst with a capsular structure {Fe30W72} stabilized inside by sulfate/bisulfate anions provides a protic environment where three iron atoms are located at each of the pores of the capsule leading to a unique and potent active site for the oxidation reactions. Under mild electrochemical conditions, 1.8 V, in water at room temperature, using O2 from air, we demonstrate the low-pressure (1–2 bar) hydroxylation of alkanes, notably ethane to acetic acid, and the ozone like cleavage of the carbon–carbon double bonds of alkenes. Typical turnover frequencies were 300–400 min–1. Initial mechanistic studies support a reaction through a very active iron-oxo species.

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The Uptake and Assembly of Alkanes within a Porous Nanocapsule in Water: New Information about Hydrophobic Confinement

Cited by 13 publications

References 55 publications

Two Compartmentalized Inner Receptors for the Tetramethylammonium Guest within a Keplerate-Type Capsule

Two Compartmentalized Inner Receptors for the Tetramethylammonium Guest within a Keplerate-Type Capsule

Host–guest chemistry with water-soluble gold nanoparticle supraspheres

Aerobic Electrochemical Oxygenation of Light Hydrocarbons Catalyzed by an Iron–Tungsten Oxide Molecular Capsule

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