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Guest recognition in a partially bridged deep cavitand.

ABSTRACT: The synthesis of a new deep cavitand partially bridged via disulfide bonds is described. Its thermodynamic and kinetic complexation parameters are compared with those of an unbridged analogue. The disulfide bridges cause deviations in ?H and ?S but result in only small differences in ?G of complexation. The bridges increase the activation barrier for guest dissociation and lead to complexes with enhanced kinetic stability.

SUBMITTER: Busseron E

PROVIDER: S-EPMC2966534 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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Guest recognition in a partially bridged deep cavitand.

Busseron Eric E Rebek Julius J

Organic letters 20101101 21

The synthesis of a new deep cavitand partially bridged via disulfide bonds is described. Its thermodynamic and kinetic complexation parameters are compared with those of an unbridged analogue. The disulfide bridges cause deviations in ΔH and ΔS but result in only small differences in ΔG of complexation. The bridges increase the activation barrier for guest dissociation and lead to complexes with enhanced kinetic stability. ...[more]

PMID: 20923195

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Project description:A hexacationic triangular covalent organic cage, AzaEx2Cage 6+, has been synthesized by means of a tetrabutylammonium iodide-catalyzed SN2 reaction. The prismatic cage is composed of two triangular 2,4,6-triphenyl-1,3,5-triazine (TPT) platforms bridged face-to-face by three 4,4'-bipyridinium (BIPY 2+) spacers. The rigidity of these building blocks leads to a shape-persistent cage cavity with an inter-platform distance of approximately 11.0 Å. This distance allows the cage to accommodate two aromatic guests, each of which is able to undergo π-π interactions with one of the two TPT platform simultaneously, in an A-D-D-A manner. In the previously reported prism-shaped cage, the spacers (pillars) are often considered passive or non-interactive. In the current system, the three BIPY 2+ spacers are observed to play an important role in guest recognition. Firstly, the BIPY 2+ spacers are able to interact with the carbonyl group in a pyrene-1-carbaldehyde (PCA) guest, by introducing lateral dipole-cation or dipole-dipole interactions. As a consequence, the binding affinity of the cage towards the PCA guest is significantly larger than that of pyrene as the guest, even although the latter is often considered to be a better π-electron donor. Secondly, in the case of the guest 1,5-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]naphthalene (BH4EN), the pillars can provide higher binding forces compared to the TPT platform. Hence, peripheral complexation occurs when AzaEx2Cage 6+ accommodates BH4EN in MeCN. Thirdly, when both PCA and BH4EN are added into a solution of AzaEx2Cage 6+, inclusion and peripheral complexation occur simultaneously to PCA and BH4EN respectively, even though the accommodation of the former guest seems to attenuate the external binding of the latter. This discovery of the importance of lateral interactions highlights the relationship between the electrostatic properties of a highly charged host and its complexation behavior, and as such, provides insight into the design of more complex hosts that bind guests in multiple locations and modes.

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Guest recognition in a partially bridged deep cavitand.

Publications

Guest recognition in a partially bridged deep cavitand.

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