Fluorescent Guest Molecules Report Ordered Inner Phase of Host Capsules in Solution

Dalgarno, Scott J.; Tucker, Sheryl A.; Bassil, Daniel B.; Atwood, Jerry L.

doi:10.1126/science.1116579

Cited by 220 publications

(120 citation statements)

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“…The solvents can be the only occupants of the capsule 1 6 , or they can share it with additional guests (16)(17)(18)(19), when the interaction between coguests is favorable. The recent solid-state studies by Atwood and colleagues (20) indicate that strong host-guest interactions relative to the interactions between coencapsulated guests are also possible.…”

Section: Resultsmentioning

confidence: 99%

Resorcinarenes are hexameric capsules in solution

Evan-Salem

Baruch

Avram

et al. 2006

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

142

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The host-guest complexes of resorcin[4]arenes with small molecules in organic solutions are examined using modern NMR spectroscopic methods. The complexation of glutaric acid and ␤-methyl D-glucopyranoside in chloroform were investigated through 2D COSY, 2D NOESY, 1D NOE, and diffusion-ordered NMR spectroscopy (DOSY) techniques. These methods indicate that the complex is a self-assembled capsule composed of six resorcinarenes that surround six guest molecules of glutaric acid or three molecules of ␤-methyl D-glucopyranoside inside. The multiplicity of guest proton signals shows that the capsule provides an asymmetric magnetic environment that persists on the 1 H NMR time scale. The encapsulation of these guests and common solvents suggests that the phenomenon of reversible encapsulation in chemistry may be a century old. 2). They provided the modules from which open-ended container molecules, the cavitands, were elaborated and led to the first covalent structures that completely surrounded other molecules, the carcerands (3). These shallow, bowl-shaped structures have intrinsic properties as receptors for molecular recognition as introduced by Aoyama and coworkers (4, 5). They described complexes of 1 in organic solvents with a number of guests, small diacids, alcohols, and even steroids, featuring a 1:1 stoichiometry. Intermolecular hydrogen bonding was proposed to hold the guest in the concavity of the resorcinarene host, as shown for glutaric acid in Fig. 2. The NMR spectra confirmed that the signals of the guest were upfield-shifted, as expected for their positions above the four aromatic units of the resorcinarene. However, the same spectra showed an unexpected feature: guest exchange took place slowly on the NMR time scale, with separate signals for free and bound guests. The broad range of molecules recognized and the slow on͞off dynamics appeared at odds with the simple structures proposed for the complexes, and raised some questions as to the extent of the intermolecular forces involved. We have now examined the glutaric acid, ␤-methyl D-glucopyranoside, and related complexes of 1 in solution through modern NMR techniques and report on them here. We find that the unprecedented behavior can be reconciled through encapsulation complexes involving the self-assembly of six resorcinarenes in a capsular host. The host surrounds six glutaric acid or three ␤-methyl D-glucopyranoside guests.A blueprint to the solution structure came from the crystallographic studies of Atwood and MacGillivray (6). They found that, unlike the many previous solid-state structures of resorcinarenes and guests that involve layered arrays of the molecules (7-10), resorcin[4]arene 1Ј crystallized from hot nitrobenzene as a rather large closed shell, a hexameric capsule surrounding a space of nearly 1,400 Å 3 (6). The six resorcin [4]arene molecules appear at the sides of a notional cube, and one molecule of water is at each of the eight corners (Fig. 1). An unknown number of highly disordered solvent molecules are inside the cavity. S...

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Section: Resultsmentioning

confidence: 99%

Resorcinarenes are hexameric capsules in solution

Evan-Salem

Baruch

Avram

et al. 2006

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

142

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“…26,[48][49][50] It should be pointed out that pyrogallol [4]arenes contain four additional upper rim hydroxyl groups, as compared with resorcinarenes; this fact results in a larger number of hydrogen-bonding interactions in formed hexamers and, as a consequence, the higher stability than in the case of resorcinarene-based hexameric capsules. 50,51 Resorcinarenes and pyrogallolarenes form hexameric capsules in the solid state and in solution via a network of hydrogen bonds. Usually water molecules are involved to complete the hydrogen bond network of resorcinarene-based hexameric capsules, 49 while assembly of pyrogallolarenes does not require water molecules.…”

Section: Hexameric Capsulesmentioning

confidence: 99%

Trimeric and hexameric calixarene-based capsules

Śliwa¹,

Dondela²

2007

Arkivoc

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“…Pyrogallol- [4]arenes often form a variety of superstructures other than hexameric capsules [4][5][6][7] including dimeric capsules 8 and bilayers depending on the selection of solvent conditions.…”

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confidence: 99%

Synthesis, Crystal Structure, and Spectroscopic Investigation of C-Cyanophenyl Pyrogallol[4]arene

Jeon

Kim²,

Kim³

et al. 2008

Bulletin of the Korean Chemical Society

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Pyrogallol [4]arenes have drawn much attention since their emergence as new hydrogen-bonded hexameric 1 or metalseamed 2,3 capsule-forming molecular receptors. arenes often form a variety of superstructures other than hexameric capsules 4-7 including dimeric capsules 8 and bilayers depending on the selection of solvent conditions. 1,9-12It is well established that the substitution of aryls for alkyls on methine units connecting the pyrogallols of pyrogallol-[4]arene yields a chair conformation, while alkyl-substituted pyrogallol[4]arene mostly adopts a cone conformation. In these reports, the hydroxyl groups of pyrogallols were acetylated to enhance solubility because of the poor solubility of unacetylated forms in common organic solvents. 13Herein, we describe the synthesis, crystal structure, and spectroscopic investigation of C-cyanophenyl pyrogallol-[4]arene (1) without any modification of the hydroxyl groups of pyrogallols, which might be the first crystal structure formed in unacetylated aryl-substituted pyrogallol[4]-arenes. These findings might be useful for the design of receptors based on pyrogallol [4]arenes for the construction of the superstructure derived from hydrogen bonds or metal coordinations. Experimental SectionAll the chemicals were used as received without further purification. The synthesis of pyrogallol[4]arene were performed according to the method in the literature method. 13The 1 H NMR and 13 C NMR spectra were recorded on a Bruker AVANCE II spectrometer at a Larmor frequency of 400.13 MHz. The infrared (IR) spectra were recorded on a MIDAC M series IR spectrometer. MALDI-TOF mass spectra were obtained on a Bruker Reflex III MALDI-TOF mass spectrometer. Data collection for 1 was performed with the beamline (6C1 MXII) at the Pohang Accelerator Laboratory (PAL).Synthesis of 2,8,14,20-cyanophenyl pyrogallol[4]arenes (1). The synthesis of 1 has been reported elswhere.1 Briefly, equimolar amounts of pyrogallol (1.2 g, 10 mmol) and 4-cyanobenzaldehyde (1.3 g, 10 mmol) were mixed in a round-bottom flask containing 30 mL of ethanol and 10 mL of concentrated HCl with a flow of nitrogen; the solution was stirred under a reflux at 70-80 o C for 1 day. The resulting solution was cooled to room temperature. Filtration and washing with water and ethanol several times followed by drying in vacuum gave the desired product (yield = ~65%).

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Fluorescent Guest Molecules Report Ordered Inner Phase of Host Capsules in Solution

Cited by 220 publications

References 18 publications

Resorcinarenes are hexameric capsules in solution

Resorcinarenes are hexameric capsules in solution

Trimeric and hexameric calixarene-based capsules

Synthesis, Crystal Structure, and Spectroscopic Investigation of C-Cyanophenyl Pyrogallol[4]arene

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