The Big Squeeze:  Guest Exchange in an M<sub>4</sub>L<sub>6</sub> Supramolecular Host

Davis, Anna V.; Raymond, Kenneth N.

doi:10.1021/ja051037s

Cited by 211 publications

(173 citation statements)

References 38 publications

(87 reference statements)

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“…The large binding constant of Et 4 N ϩ and the high stability of these host-guest complexes might explain the greater reliability for obtaining consistent mass spectral data, whereas previous detection of weaker bound host-guest complexes were strongly dependent on experimental conditions [6]. Additionally, regardless of binding constants, neither the Cp* 2 Co ϩ host-guest assembly [19] nor the empty cluster have been previously detected. Cp* 2 Co ϩ represents the largest guest successfully encapsulated in this type of cluster.…”

Section: Resultsmentioning

confidence: 95%

“…In the case of [Cp* 2 Co ʚ Ga 4 L 6 ] 11Ϫ , evidence of encapsulation is based on significant NMR-upfield shifts of the Cp* 2 Co ϩ guest signals in solution over the course of weeks without the encapsulated Cp* 2 Co ϩ guest being released from the cavity [19]. Peaks corresponding to the intact assembly can be observed at m/z 1159.70 (MK 8 3Ϫ ), m/z 860.03 (MK 7 4Ϫ ), and m/z 664.65 (MK 4 H 2 5Ϫ ) for the most abundant isotopes.…”

Section: Resultsmentioning

confidence: 99%

“…The host-guest complexes were prepared according to literature procedures [6,19] in the presence of one equivalent decamethylcobaltocenium, five equivalents of tetra-n-propyl ammonium, and seven equivalents of tetramethyl and tetraethyl ammonium ions. The mass spectra were acquired using a Micromass Q-TOF API US (Micromass, Manchester, UK) equipped with Zspray ion source operated in V mode (where ions travel in the TOF detector in a "V-shape" path) with a resolving power of over 10,000 and in negative ion mode.…”

Section: Methodsmentioning

confidence: 99%

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Characterization of self-assembled supramolecular [Ga₄L₆] host-guest complexes by electrospray ionization mass spectrometry

Andersen

Seeber

Fiedler

et al. 2006

J. Am. Soc. Mass Spectrom.

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Self-assembled supramolecular host-guest complexes have been characterized by electrospray ionization mass spectrometry. The spectra obtained by use of a Q-TOF instrument equipped with a Z-spray ion source show primarily the 3-and 4-charge states of the assemblies. The assemblies have the general formula [guest ʚ Ga 4 L 6 ] 11Ϫ where L represents the chelating bidentate catechol ligand 1,5-bis(2=,3=-dihydroxy-benzamido)naphthalene and guests are tetramethyl ammonium (Me 4 N ϩ ), tetraethyl ammonium (Et 4 N ϩ ), tetra-n-propyl ammonium (Pr 4 N ϩ ) and decamethylcobaltocenium (Cp* 2 Co ϩ ) cations. For the first time, the mass spectrum of the empty assembly [Ga 4 L 6 ] 12Ϫ is reported. This article also reports that provided the electrospray ion source is capable of preserving noncovalent interactions, it is possible to observe host-guest complexes containing both weak binding guests as well as sterically demanding guests in the mass spectra. The present data suggest that electrospray mass spectrometry is a powerful tool for characterization of supramolecular host-guest complexes. ( I n the area of supramolecular chemistry, metal-ligand interactions have been exploited to design highly symmetric closed shell structures that selfassemble from simple metal and ligand components. The formation of discrete molecular architectures relies on labile coordinative bonds that allow for self-correction and exclusive formation of the thermodynamic product. A great variety of self-assembled structures of different molecular sizes and shapes is present in the literature [1][2][3][4][5]. Here, we focus on contributions to this field made by Raymond and coworkers [2, 6 -10]. The common theme in these metal-ligand assemblies is the presence of chelating bidentate catechol amide ligands, which bear certain geometric constraints upon coordination to octahedral metal centers resulting in M 4 L 6 coordination tetrahedra (Figure 1). The complexes are highly charged, rendering them soluble in polar solvents such as water and methanol, yet contain hydrophobic cavities of variable sizes. The presence of these hydrophobic cavities affords rich host-guest chemistry, enabling encapsulation of monocationic guest molecules [2, 6 -8]. Several analytical methods are necessary to efficiently characterize these host-guest complexes. 1 H-NMR spectroscopy shows remarkable upfield shifts in the proton signals of encapsulated guests within the cavities [2]. However, since the structures exhibit high point symmetry and the metal components are often paramagnetic, complete characterization by NMR is not always possible. Although solid-state structures may, in the best of cases, be determined by single crystal X-ray crystallography, intrinsically labile metal-ligand interactions do not always allow for unambiguous characterization of solution state structures. Additionally, mass spectrometry is more sensitive than NMR spectroscopy and allows analysis of lower concentrations, thus observing species with solubility properties insufficient for NMR measureme...

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Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Characterization of self-assembled supramolecular [Ga₄L₆] host-guest complexes by electrospray ionization mass spectrometry

Andersen

Seeber

Fiedler

et al. 2006

J. Am. Soc. Mass Spectrom.

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“…41,42 While the 12-overall charge of 1 imparts water solubility, the naphthalene walls of the assembly provide a hydrophobic interior cavity, able to encapsulate guests, which is isolated from the bulk aqueous solution. A wide variety of small neutral and monocationic guests including aliphatic hydrocarbons, 43 protonated guests, 44 simple organic cations, 45 and reactive organometallic complexes [46][47][48] have been encapsulated in 1. Analysis of the mechanism for guest exchange revealed that 1 stays intact during the guest exchange process and that the apertures along the 3-fold axis of 1 dilate to allow for guest ingress and egress.…”

Section: Introductionmentioning

confidence: 99%

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

et al. 2009

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A water-soluble self-assembled supramolecular host molecule catalyzes the hydrolysis of orthoformates in basic solution. Comparison of the rate constants of the catalyzed and uncatalyzed reactions for hydrolysis displays rate accelerations of up to 3900 for tri-n-propyl orthoformate. Kinetic analysis shows that the mechanism of hydrolysis with the supramolecular host obeys the Michaelis-Menten model.Mechanistic studies, including 13 C-labeling experiments, revealed that the resting state of the catalytic system is the neutral substrate encapsulated in the host. Activation parameters for the k cat step of the reaction revealed that upon encapsulation in the assembly, the entropy of activation becomes more negative in contrast to the uncatalyzed reaction. Furthermore, solvent isotope effects reveal a normal k(H 2 O)/k(D 2 O) = 1.6, confirming that proton transfer is occurring in the transition state and is rate limiting in the catalyzed reaction. In comparison to the uncatalyzed reaction, which operates by an A-1 mechanism in which the decomposition of the protonated substrate is rate limiting, the encapsulated reaction proceeds through an A-S E 2 mechanism in which proton transfer from protonated water to the substrate is rate limiting.

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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%

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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The Big Squeeze: Guest Exchange in an M₄L₆ Supramolecular Host

Cited by 211 publications

References 38 publications

Characterization of self-assembled supramolecular [Ga₄L₆] host-guest complexes by electrospray ionization mass spectrometry

Characterization of self-assembled supramolecular [Ga₄L₆] host-guest complexes by electrospray ionization mass spectrometry

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

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

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The Big Squeeze: Guest Exchange in an M4L6 Supramolecular Host

Cited by 211 publications

References 38 publications

Characterization of self-assembled supramolecular [Ga4L6] host-guest complexes by electrospray ionization mass spectrometry

Characterization of self-assembled supramolecular [Ga4L6] host-guest complexes by electrospray ionization mass spectrometry

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

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

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The Big Squeeze: Guest Exchange in an M₄L₆ Supramolecular Host

Characterization of self-assembled supramolecular [Ga₄L₆] host-guest complexes by electrospray ionization mass spectrometry

Characterization of self-assembled supramolecular [Ga₄L₆] host-guest complexes by electrospray ionization mass spectrometry