Synthesis and Self-Assembly of Pseudo-Spherical Homo- and Heterodimeric Capsules

Valdés, Carlos; Spitz, Urs; Toledo, Leticia M.; Kubik, Stefan; Rebek, Julius

doi:10.1021/ja00156a010

Cited by 102 publications

(58 citation statements)

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“…[1][2][3][4][5][6][7]). Correspondingly, there has been considerable interest in studying the structural and dynamical aspects of ligand binding in these systems.…”

Section: Introductionmentioning

confidence: 99%

Inclusion Complexes Oriented in Thermotropic Liquid-Crystalline Solvents Studied with Carbon-13 NMR

et al. 2003

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The inclusion complex of cryptophane-A and chloroform dissolved in two non-chiral liquid crystalline environments was investigated via 13 C NMR. Stable solutions of oriented complexes were prepared using aromatic (ZLI 1132) and aliphatic (ZLI 1695) thermotropic nematic liquid crystals as solvents; ordering of the complexes was manifested by the 1 H-13 C dipolar splitting of the 13 C resonance of labeled chloroform. In both solutions, the dipolar splitting for the bound ligands was substantially larger than that obtained These results demonstrate the potential for using restored dipolar couplings to investigate structural and dynamical aspects of inclusion complexes in solution.2

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“…[1][2][3][4][5][6][7]). Correspondingly, there has been considerable interest in studying the structural and dynamical aspects of ligand binding in these systems.…”

Section: Introductionmentioning

confidence: 99%

Inclusion Complexes Oriented in Thermotropic Liquid-Crystalline Solvents Studied with Carbon-13 NMR

et al. 2003

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“…Besides cyclic and hence well-preorganized receptors (e.g. cyclodextrins, [9] cyclophanes, [10] carcerands, [11] and cryptophanes [12] ) and the more recently reported supramolecular capsules [13] formed by selfassembly of suitable building blocks, noncyclic receptors with cavities of flexible size proved to be effective. [1,14] Recently, we have described the synthesis of the benzene-and naphthalene-spaced receptors 1 and 2.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Supramolecular Properties of Trimethylene‐Bridged Clips

Klärner¹,

Lobert²,

Naatz³

et al. 2003

Chemistry A European J

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The novel trimethylene-bridged clips 3 and 4 have been synthesized by using repetitive stereoselective Diels-Alder reactions of the benzo- and naphthobismethylenenorbornenes 8 and 19 as dienes and norbornadiene 9 as bisdienophile, and subsequent dehydrogenation of the primary cyclobisadducts 10 and 20 by using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Clips 3 and 4 serve as receptors for a variety of electron-deficient neutral and cationic aromatic substrates, comparable to the molecular tweezers 1 and 2. The thermodynamic parameters of the complex formation, K(a) and DeltaG, were determined by (1)H NMR titration experiments and, in the case of the highly stable complex TCNB 32@4, by the use of isothermal titration microcalorimetry. The finding that clip 4 forms more stable complexes than 3 can be explained by the larger van der Waals contact surfaces of the naphthalene sidewalls in 4 compared to the corresponding benzene systems in 3. In the complexes with 4 as receptor, the plane of each aromatic substrate molecule is calculated to be oriented almost parallel to the naphthalene sidewalls. However, in the complexes of tweezers 2, the substrate is usually oriented parallel to the central naphthalene spacer unit. Due to the more open topology of 4, most complexes were calculated to consist of two or more equilibrating noncovalent conformers.

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“…A number of longer alkanes were encapsulated in this host assembly, but the expanded capsule also offered broadened possibilities for isomerism and accommodated other guests that we elaborate on here. The results indicate that highly complex molecular assemblies can emerge from only a few modules acting as hosts and guests (20,21). …”

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Adaptations of guest and host in expanded self-assembled capsules

Ajami

Rebek

2007

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

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Reversible encapsulation complexes create spaces where two or more molecules can be temporarily isolated. When the mobility of encapsulated molecules is restricted, different arrangements in space are possible, and new forms of isomerism (''social isomerism'') are created: the orientation of one encapsulated molecule influences that of the other in the confined space. Expansion of a capsule's length is possible through addition of small-molecule spacer elements. The expanded capsules have dimensions that permit the observation of social isomerism of two identical guests, and they adopt arrangements that properly fill the host's space. The host also can adapt to longer guests by incorporating additional spacers, much as protein modules are added to a viral capsid in response to larger genomes. Arachidonic and related fatty acid derivatives act in this way to induce the assembly of further extended capsules having sufficient length to accommodate them.encapsulation ͉ self-assembly ͉ social isomers E ncapsulation complexes are synthetic, self-assembled hosts that more or less completely surround their guest molecules. They are dynamic and form reversibly in solution with lifetimes ranging from milliseconds to days. The capsules isolate molecules from the bulk solution, and they reveal behaviors that cannot be seen otherwise. They have become a tool of modern physical organic chemistry (1). For example, cylindrical host 1.1 (Fig. 1) self-assembles only in the presence of suitable guests to give encapsulation complexes (2-4). Combinations of different guests (5) inside this capsule have allowed its use as a reaction chamber (6), a chiral receptor (7), and a space where singlemolecule solvation can be observed (8). Elsewhere, reversible encapsulation complexes have been used to stabilize reactive intermediates (9, 10) and even transition states (11, 12) as well as to alter the course of reactions in the limited quarters (13). New forms of stereochemistry also have emerged from coencapsulation studies (14). For example, with benzene and p-ethyl toluene, two complexes coexist (Fig. 1). The two molecules are too large to slip past each other, and the p-ethyl toluene is too long to tumble freely while inside the capsule. Either of these motions could interconvert the complexes, but they are slow on the NMR time scale and separate spectra are seen for the two isomers. These ''social isomers'' are different arrangements in space that arise from the interactions of at least two encapsulated molecules. They also are constitutional isomers, but mechanical barriers hold these arrays in place rather than covalent bond ''connectedness.'' Accordingly, the term supramolecular diastereomers better describes the relationships. This stereoisomerism is related to the carceroisomerism (15) observed in covalently bound capsules with one guest.The self-assembly of the benzene/p-ethyl toluene pair owes its stability to the optimal filling of the capsule's space. Two benzene molecules can assemble the capsule as guests in that solvent and f...

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Synthesis and Self-Assembly of Pseudo-Spherical Homo- and Heterodimeric Capsules

Cited by 102 publications

References 0 publications

Inclusion Complexes Oriented in Thermotropic Liquid-Crystalline Solvents Studied with Carbon-13 NMR

Inclusion Complexes Oriented in Thermotropic Liquid-Crystalline Solvents Studied with Carbon-13 NMR

Synthesis and Supramolecular Properties of Trimethylene‐Bridged Clips

Adaptations of guest and host in expanded self-assembled capsules

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