Structural Consequences of Anionic Host−Cationic Guest Interactions in a Supramolecular Assembly

Pluth, Michael D.; Johnson, Darren W.; Szigethy, Géza; Davis, Anna V.; Teat, Simon J.; Oliver, Allen G.; Bergman, Robert G.; Raymond, Kenneth N.

doi:10.1021/ic8012848

Cited by 72 publications

(107 citation statements)

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“…Previously measured cavity volumes (~250 Å 3 ) suggest 8-10 water molecules can occupy the host interior. 24 The weight loss observed in TGA is consistent with this estimate of the number of encapsulated solvent molecules. Despite the enthalpic cost of host and guest desolvation, the overall encapsulation equilibrium is an enthalpically favored process.…”

Section: H Nmr Titrationssupporting

confidence: 80%

“…20 The highly anionic exterior surface of 1 imparts solubility in water and other polar solvents, as well as an affinity for external ion-association of cationic molecules ( Figure 2a); indirect observation of external ion-association has previously been observed in kinetic studies, 21,22 diffusion-based 1 H NMR experiments, 23 as well as solid-state structures. 24 The species distribution of these competing interior and exterior host-guest equilibria (Figure 2b), which cannot be deconvoluted by NMR, UV-vis or ITC alone, here has been elucidated by analyzing together the different observables measured by each technique.…”

Section: Introductionmentioning

confidence: 99%

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External and Internal Guest Binding of a Highly Charged Supramolecular Host in Water: Deconvoluting the Very Different Thermodynamics

et al. 2009

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Abstract. NMR, UV-vis and isothermal titration calorimetry (ITC) measurements probe different aspects of competing host-guest equilibria as simple alkylammonium guest molecules interact with both the exterior (ion-association) and interior (encapsulation) of the [Ga 4 L 6 ] 12-supramolecular assembly in water. Data obtained by each independent technique measure different components of the host-guest equilibria and only when analyzed together does a complete picture of the solution thermodynamics emerge. Striking differences between the internal and external guest binding are found. External binding is enthalpy driven and mainly due to attractive interactions between the guests and the exterior surface of the assembly while encapsulation is entropy driven as a result of desolvation and release of solvent molecules from the host cavity.

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Section: H Nmr Titrationssupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

External and Internal Guest Binding of a Highly Charged Supramolecular Host in Water: Deconvoluting the Very Different Thermodynamics

et al. 2009

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“…[10][11][12][13][14] The host ligand framework is flexible: apertures between ligands expand and contract to accommodate guest exchange and the volume of the interior cavity ranges from 250 to 450 Å 3 in the solid state, depending on the encapsulated guest (Figure 1, right). [15][16][17] Host 1 can also catalyze a variety of chemical transformations with altered regio-, stereo-or enantioselectivities, and enzyme-like rate accelerations of up to 10 6 . [18][19][20][21][22][23][24][25][26] .…”

Section: Introductionmentioning

confidence: 99%

“…[18][19][20][21][22][23][24][25][26] . 17 The large variation in the size and shape of these cavities illustrates the flexibility of the host ligand framework.…”

Section: Introductionmentioning

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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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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“…[11,12] The host assembly 1 has a hydrophobic interior cavity that can encapsulate a variety of monocationic [13,14] and neutral [15,16] guest molecules, and has been shown to mediate the chemical reactivity of encapsulated guests. [17,18] Guest molecules can exchange between the interior and exterior of the host assembly via one of four C 3 -symmetric apertures (Figure 1) in the ligand framework, which expand and contract to accommodate guest exchange without Ga-L bond breakage (Figure 2).…”

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Does Size Really Matter? The Steric Isotope Effect in a Supramolecular Host–Guest Exchange Reaction

2010

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an NSF predoctoral fellowship to J.S.M. We thank M. D. Pluth for helpful discussions and Dr. Ulla Andersen for assistance with mass spectrometry experiments.Isotope effects (IEs), which arise from differences in zero point energies (ZPEs) between a parent and isotopically substituted bond, have been used extensively by chemists to probe molecular interactions and reactivity. [1,2] Due to the anharmonicity of the C-H/D vibrational potential energy function and the lower ZPE of a C-D bond, the average C-D bond length is typically ~0.005 Å shorter than an equivalent C-H bond. [3][4][5] It is this difference in size that is often invoked to explain the observation of secondary, inverse kinetic isotope effects (KIEs) in chemical processes which proceed through a sterically strained transition state. This so-called "steric isotope effect" (SIE) has been observed in processes such as the racemization of ortho-substituted biphenyls [6] and phenanthrenes, [7] ring flipping of cyclophanes, [8] and more recently in the deslipping of rotaxanes, [9] where substitution of the sterically less demanding deuterium for protium results in rate accelerations for these processes. [10] Herein, we use deuterium substitution in a cationic guest molecule to probe the sensitivity limits of the guest exchange process from a highly-charged supramolecular host.The self-assembling [Ga 4 L 6 ] 12-supramolecular host (1, Figure 1) is composed of six ligands (L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene) that span the edges of a tetrahedron and four Ga metal centers which sit at the vertices. [11,12] The host assembly 1 has a hydrophobic interior cavity that can encapsulate a variety of monocationic [13,14] and neutral [15,16] guest molecules, and has been shown to mediate the chemical reactivity of encapsulated guests. [17,18] Guest molecules can exchange between the interior and exterior of the host assembly via one of four C 3 -symmetric apertures (Figure 1) in the ligand framework, which expand and contract to accommodate guest exchange without Ga-L bond breakage (Figure 2). [19] Due to the large distortion of the host framework required for guest exchange, drastically different exchange rates are observed for guests of different size and shape. [20] These observations prompted us to investigate whether the tiny difference between C-H and C-D bond lengths is enough to produce a measurable effect on the guest exchange kinetics. In other words, just how much does guest size matter? The KIEs observed in this study demonstrate that host 1 is able to distinguish between guests with even as small a structural difference as isotopic substitution. This is the pre-peer reviewed version of the following article: Angew. Chem. Int. Ed. 2010, 49, 3635 -3637. which has been published in final form at

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Structural Consequences of Anionic Host−Cationic Guest Interactions in a Supramolecular Assembly

Cited by 72 publications

References 50 publications

External and Internal Guest Binding of a Highly Charged Supramolecular Host in Water: Deconvoluting the Very Different Thermodynamics

External and Internal Guest Binding of a Highly Charged Supramolecular Host in Water: Deconvoluting the Very Different Thermodynamics

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

Does Size Really Matter? The Steric Isotope Effect in a Supramolecular Host–Guest Exchange Reaction

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