The Acid Hydrolysis Mechanism of Acetals Catalyzed by a Supramolecular Assembly in Basic Solution

Pluth, Michael D.; Bergman, Robert G.; Raymond, Kenneth N.

doi:10.1021/jo802131v

Cited by 64 publications

(39 citation statements)

References 49 publications

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“…We note that there is an interesting parallel with the Raymond / Bergman cage based on anionic metal tris-catecholate vertices, in which the high negative charge encourages protonation of bound guests, and thereby facilitates acid-catalysed reactions even in basic conditions. 18,40 These observations imply that our cage may be able to catalyse reactions of a wide range of bound guests that require an anionic base or nucleophile and so could offer a versatile framework for catalysing bimolecular reactions.…”

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confidence: 87%

Highly efficient catalysis of the Kemp elimination in the cavity of a cubic coordination cage

et al. 2016

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The hollow cavities of coordination cages can provide an environment for enzyme-like catalytic reactions of small-molecule guests . We report here a new example (catalysis of the Kemp elimination -reaction of benzisoxazole with hydroxide to form 2-cyanophenolate) in the cavity of a water-soluble M8L12 coordination cage, with two features of particular interest. Firstly, the rate enhancement is amongst the largest so far observed: at pD 8.3, kcat/kuncat is 2 x 10 5 , due to the accumulation of a high concentration of partially desolvated hydroxide ions around the bound guest arising from ion-pairing with the 16+ cage. Secondly, the catalysis is based on two orthogonal interactions: (i) hydrophobic binding of benzisoxazole in the cavity, and (ii) polar binding of hydroxide ions to sites on the cage surface, both of which were established by competition experiments. Hundreds of turnovers occur with no loss of activity due to expulsion of the hydrophilic, anionic product. 2Since the realisation that hollow molecular container molecules can accommodate guest molecules in their central cavities, 1-3 their ability to modify the reactivity of their bound guests has been of great interest. [4][5][6][7][8] Well known examples include Cram's stabilisation of highly-reactive cyclobutadiene; 4 Fujita's 'ship-in-a-bottle' synthesis of cyclic silanol oligomers; 5 Nitschke's stabilisation of P4 in a tetrahedral cage; 6 and the demonstration of unusual regioselectivity in a Diels-Alder reaction when the two reacting molecules are co-confined in a host cavity. 7 The ultimate expression of this behaviour is efficient catalysis of a reaction occurring in the cavity of a container molecule. 8 These synthetic systems have the potential to achieve the selectivity and catalytic rate enhancements displayed by biological systems. For example, artificial container molecules provide relatively rigid and hydrophobic central cavities that may mimic binding pockets in enzymes. These containers may be purely organic hydrogen-bonded assemblies (such as Rebek's 'softball' dimer) 9 or may be metal-ligand polyhedral coordination cages [such as Fujita's Pd6/tris(pyridyl)triazine cage]. 10 Coordination cages offer particular promise in this field because of the ease with which they can be formed by a self-assembly process from very simple component parts, using the predictable coordination geometries of metal ions to provide the three-dimensional ordering of the components which generates the necessary cavity. [1][2][3]8,11,12 In order for a container molecule to act as an efficient catalyst it needs to (i) recognise and bind the guest(s); (ii) accelerate the reaction by increasing the local concentration of reactants and/or stabilising the transition state; and (iii) expel the product to allow catalytic turnover. 8 Guest binding in cage cavities has been very well studied and is becoming a mature field, 1 to the extent that a modeling tool for quantitative prediction of guest binding has recently been reported by us. 13 For a reaction of t...

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confidence: 87%

Highly efficient catalysis of the Kemp elimination in the cavity of a cubic coordination cage

et al. 2016

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“…We hoped to gain further information about the simultaneous encapsulation through the use of naturalabundance 14 N and 15 N NMR experiments; however, neither of these methods was amenable to this system. Methylphospholane, the phosphorus analog of 2, was also prepared in hopes that 31 P NMR experiments could be used to investigate protonation. However, methylphospholane is encapsulated as a protonated monomer rather than a proton-bound homodimer.…”

Section: Resultsmentioning

confidence: 99%

“…We have previously shown through kinetic analysis that water, in either its neutral or protonated form, can enter 1, so the enthalpy of the hydrogen bond formed between a protonated amine and water molecule ([B⅐⅐H⅐⅐OH 2 ] ϩ ) was also calculated (21,31). The geometry optimized structures for the [B⅐⅐H⅐⅐B] ϩ and [B⅐⅐H⅐⅐OH 2 ] ϩ complexes are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Encapsulation and characterization of proton-bound amine homodimers in a water-soluble, self-assembled supramolecular host

Pluth

Fiedler

Mugridge

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Cyclic amines can be encapsulated in a water-soluble selfassembled supramolecular host upon protonation. The hydrogenbonding ability of the cyclic amines, as well as the reduced degrees of rotational freedom, allows for the formation of proton-bound homodimers inside of the assembly that are otherwise not observable in aqueous solution. The generality of homodimer formation was explored with small N-alkyl aziridines, azetidines, pyrrolidines, and piperidines. Proton-bound homodimer formation is observed for N-alkylaziridines (R ‫؍‬ methyl, isopropyl, tert-butyl), Nalkylazetidines (R ‫؍‬ isopropyl, tert-butyl), and N-methylpyrrolidine. At high concentration, formation of a proton-bound homotrimer is observed in the case of N-methylaziridine. The homodimers stay intact inside the assembly over a large concentration range, thereby suggesting cooperative encapsulation. Both G3(MP2)B3 and G3B3 calculations of the proton-bound homodimers were used to investigate the enthalpy of the hydrogen bond in the protonbound homodimers and suggest that the enthalpic gain upon formation of the proton-bound homodimers may drive guest encapsulation.host-guest chemistry ͉ molecular recognition ͉ guest encapsulation ͉ amine protonation H ydrogen bonding and protonation play vital roles in both chemical and biological phenomena as one of the most prevalent intermolecular forces in nature (1-4). Although hydrogen bonding is often viewed as a weak interaction, the strength of a special class of strong hydrogen bonds, often referred to as ionic hydrogen bonds, can range from 5 to 35 kcal/mol (5). These strong hydrogen bonds are important in nucleation, self-assembly, protein folding, reactivity of enzyme active sites, formation of membranes in biological systems, and biomolecular recognition (5-7). Because of the importance of hydrogen bonding in so many aspects of chemical and biological systems, a number of synthetic and theoretical studies have examined their magnitude and origin (8, 9). Many of the computational studies have focused on simple proton-bound homodimers and heterodimers, where 2 neutral bases are bound by 1 proton (Fig. 1), because experimental energies for these complexes can be obtained from gas phase thermochemical studies such as variable-temperature high-pressure mass spectrometry (5).In simple hydrogen-bonded complexes such as those shown in Fig. 1, the hydrogen bond strength is maximized when the proton donor and the conjugate base of the proton acceptor have similar proton affinities. Therefore, the strongest hydrogen bonds are formed when the 2 basic components, minus the proton, are identical (5). Although the proton-bound homodimers and heterodimers can be observed in the gas phase, solution studies of these types of complexes remain rare. To the best of our knowledge, proton-bound homodimers or heterodimers predominantly form in aprotic organic solvents, rather than protic hydrogen-bonding solvents (5, 10).Previous work in the K.N.R. group has explored the formation, guest exchange dynamics, and mediated reac...

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“…98 Furthermore, cage 4 has been used as catalyst for the hydrolysis of acetals and ketals at pH 10, with an acceleration rate higher than 1000 times. 99,100 Supramolecular capsules assembled via hydrophobic effect…”

Section: Metallo-cage Capsulesmentioning

confidence: 99%

Applications of supramolecular capsules derived from resorcin[4]arenes, calix[n]arenes and metallo-ligands: from biology to catalysis

2015

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Supramolecular architectures developed after the initial studies of Cram, Lehn and Pedersen have become structurally complex but fascinating. In this context, supramolecular capsules based on resorcin[4]arenes, calix[n]arenes or metal-ligand structures are dynamic assemblies inspired by biological systems. The reversible formation of these assemblies, combined with the possibility to modify their dimensions and shapes in the presence of a guest (concepts of reversibility and adaptivity) make them similar to biological macromolecules, such as proteins and enzymes. The small space inside a supramolecular capsule is characterized by different properties compared to the bulk solution. This review describes concrete applications of capsular supramolecular self-assemblies in the biomedical field, in catalysis and in material science.

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The Acid Hydrolysis Mechanism of Acetals Catalyzed by a Supramolecular Assembly in Basic Solution

Cited by 64 publications

References 49 publications

Highly efficient catalysis of the Kemp elimination in the cavity of a cubic coordination cage

Highly efficient catalysis of the Kemp elimination in the cavity of a cubic coordination cage

Encapsulation and characterization of proton-bound amine homodimers in a water-soluble, self-assembled supramolecular host

Applications of supramolecular capsules derived from resorcin[4]arenes, calix[n]arenes and metallo-ligands: from biology to catalysis

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