Functional Molecular Flasks: New Properties and Reactions within Discrete, Self‐Assembled Hosts

Yoshizawa, Michito; Klosterman, Jeremy K.; Fujita, Makoto

doi:10.1002/anie.200805340

Cited by 1,802 publications

(997 citation statements)

References 207 publications

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“…44 The volumes of activation for encapsulated guest bond rotation range between 9 and 17 cm 3 mol -1 ( Figure 4); this corresponds to an increase in the volume of the host-guest complex of between 15 and 30 Å 3 during bond rotation, a roughly 4 -8 % increase relative to the host cavity volume for [2  1] 11-. 27 These activation volumes are similar in magnitude to those previously measured for the guest exchange process from 1 in D 2 O, which were found to be 13 cm 3 Figure 4. Plots used to determine the volumes of activation (ΔV ‡ ) for the Ph-CH 2 bond rotational processes for encapsulated guests 4 (top) and 5 (bottom); k exch is the observed rate constant for Ph-CH 2 bond rotation and Pressure is the applied external pressure.…”

Section: Guestsupporting

confidence: 84%

“…In order to further explore the hypothesis that the observed solvent effects were due to changes in solvent internal pressure, the encapsulated Ph-CH 2 bond rotational rates were measured at elevated external pressures of up to 150 MPa (1500 atm). Encapsulated Ph-CH 2 rotational rates as a function of pressure in different solvents for guest 4 and 5 are listed below in Tables 2 and 3 3 OD at 298 K because the data recorded at 308 K were sufficient to establish the trend in Ph-CH 2 rotational rate with applied pressure and determine a volume of activation for this process. SIR data at 308 K were more robust due to the faster bond rotational rate at this temperature.…”

Section: Guestmentioning

confidence: 99%

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Solvent and Pressure Effects on the Motions of Encapsulated Guests: Tuning the Flexibility of a Supramolecular Host

et al. 2013

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The supramolecular host assembly [Ga 4 L 6 ] 12-(1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) contains a flexible, hydrophobic interior cavity that can encapsulate cationic guest molecules and catalyze a variety of chemical transformations. The Ph-CH 2 bond rotational barrier for encapsulated ortho-substituted benzyl phosphonium guest molecules is sensitive to the size and shape of the host interior space. Here we examine how changes in bulk solvent (water, methanol, or DMF) or applied pressure (up to 150 MPa) affect the rotational dynamics of encapsulated benzyl phosphonium guests, as a way to probe changes in host cavity size or flexibility. When host 1 is dissolved in organic solvents with large solvent internal pressures (∂U/∂V) T , we find that the free energy barrier to Ph-CH 2 bond rotation increases by 1 -2 kcal/mol, compared with aqueous solution. Likewise, when external pressure is applied to the host-guest complex in solution, the bond rotational rates for the encapsulated guests decrease. The magnitude of these rate changes and the volumes of activation obtained using either solvent internal pressure or applied external pressure, are very similar. NOE distance measurements reveal shorter average host-guest distances (~0.3 Å) in organic versus aqueous solution. These experiments demonstrate that increasing solvent internal pressure or applied external pressure reduces the host cavity size or flexibility, resulting in more restricted motions for encapsulated guest molecules. Changing bulk solvent or external pressure might therefore be used to tune the physical properties or reactivity of guest molecules encapsulated in a flexible supramolecular host.

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Section: Guestsupporting

confidence: 84%

Section: Guestmentioning

confidence: 99%

Solvent and Pressure Effects on the Motions of Encapsulated Guests: Tuning the Flexibility of a Supramolecular Host

et al. 2013

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“…39 In addition, there are several classes of host that utilize self-assembly to form water-soluble hosts, [40][41][42] as well as 'foldamers' that, like proteins, are predisposed to fold into a conformation possessing a site for guest recognition. [43][44][45] These hosts provide a great opportunity for the physical community.…”

Section: Host Molecules As Tools For Probing Aqueous Solutionsmentioning

confidence: 99%

Collaborative routes to clarifying the murky waters of aqueous supramolecular chemistry

et al. 2017

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Collaborative routes to clarifying the murky waters of aqueous supramolecular chemistry. AbstractOn planet Earth, water is everywhere: the majority of the surface is covered with it; it is a key component of all life; its vapor and droplets fill the lower atmosphere; even rocks contain it and undergo geomorphological changes because of it. A community of physical scientists largely drives studies of the chemistry of water and aqueous solutions, with expertise in biochemistry, spectroscopy, and computer modeling. More recently however, supramolecular chemistry -with its expertise in macrocyclic synthesis and measuring supramolecular interactions -have renewed their interest in water-mediated non-covalent interactions. These two groups offer complementary expertise that, if harnessed, offers to accelerate our understanding of aqueous supramolecular chemistry and water writ large. This review summarizes the state-of-the-art of the two fields, and highlights where there is latent chemical space for collaborative exploration by the two groups. 4Water is ubiquitous and essential to life on planet Earth. A full understanding of aqueous solutions is therefore of significance to a wide range of fields within the atmospheric, environmental, biological and geological sciences. Within the chemical sciences, a deeper appreciation of how non-covalent interactions and chemical transformations are influenced by water would benefit a variety of fields. However, as we highlight here, there are many open questions regarding the chemical and physical properties of aqueous solutions.The aqueous realm is frequently bifurcated into the Hofmeister and hydrophobic effects, phenomena that respectively deal with the properties of solutions of salts and relatively nonpolar molecules. However, it is becoming increasingly evident that these areas do in fact frequently overlap; two prime examples being the accumulation of large polarizable anions at the air-water interface, 1-5 and the favorable interactions of polarizable anions with non-polar surfaces. [6][7][8][9][10][11][12][13][14][15] Thus the hydrophobic and Hofmeister effects are but part of a greater continuum of aqueous supramolecular chemistry, with many important and outstanding questions regarding the influence of the different kinds of non-covalent interactions involved.Studies of water and aqueous solutions have mostly been driven by the physical sciences community, a broad range of scientists whose expertise in spectroscopy, computer modeling, and biochemistry (to name just three areas) has generally not involved macrocycles or host molecules in general. However, for some time now, supramolecular chemists -with their expertise in macrocyclic synthesis and measuring weak non-covalent interactions -have been travelling a parallel course of exploration. This Review, inspired by discussions between sixteen members of each community at a recent workshop, 16 is an attempt to summarize what we know about aqueous solutions, what we do not know about them, and where the two communit...

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“…Since the realisation that hollow molecular container molecules can accommodate guest molecules in their central cavities, [1][2][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.…”

mentioning

confidence: 99%

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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Functional Molecular Flasks: New Properties and Reactions within Discrete, Self‐Assembled Hosts

Cited by 1,802 publications

References 207 publications

Solvent and Pressure Effects on the Motions of Encapsulated Guests: Tuning the Flexibility of a Supramolecular Host

Solvent and Pressure Effects on the Motions of Encapsulated Guests: Tuning the Flexibility of a Supramolecular Host

Collaborative routes to clarifying the murky waters of aqueous supramolecular chemistry

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

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