Self‐Assembly of Tris(2‐ureidobenzyl)amines: A New Type of Capped, Capsule‐Like Dimeric Aggregates Derived from a Highly Flexible Skeleton

Alajarı́n, Mateo; Pastor, Aurelia; Orenes, Raúl‐Ángel; Steed, Jonathan W.; Arakawa, Ryuichi

doi:10.1002/chem.200305559

Cited by 41 publications

(57 citation statements)

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“…In such dimers, the 2 calixarene units are rotated relative to each other by 45°around their common axis and are held together by a seam of 16 hydrogen bonds that seal the resulting cavity. It is worth mentioning that other urea based dimeric systems that deviate from the rigid calixarenes have also been reported (6,7).…”

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confidence: 90%

Self-assembly of dimeric tetraurea calix[4]pyrrole capsules

Ballester

Gil-Ramírez²

2009

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

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(Fig. 1) (1-3). These are based on the self-assembly of 2 calix[4]arene units 1 in which the so-called ''coneconformation'' is fixed or favored (4, * ) by the presence of ether functions in the lower rim (5, † ). The 2 calixarene units dimerize through upper rim/upper rim interactions mediated by a selfcomplementary hydrogen bonding pattern based on 8 urea functionalities. Oriented in the same direction, all 8 ureas interact in a ''head-to-tail'' topology, which dictates the circular self-assembly. In such dimers, the 2 calixarene units are rotated relative to each other by 45°around their common axis and are held together by a seam of 16 hydrogen bonds that seal the resulting cavity. It is worth mentioning that other urea based dimeric systems that deviate from the rigid calixarenes have also been reported (6, 7).Interest in the construction of molecular capsules by selfassembly and the study of their encapsulation properties has grown steadily since the first report appeared more than a decade ago (8, 9). Using hydrogen bonds, many different types of supramolecular capsules have been synthesized and studied, including examples of free-standing capsules composed of Ͼ2 molecular building blocks (10-14). In general, simple dimeric capsules, such as the ones derived from tetraurea calixarenes, are easier to characterize and manipulate in solution than multimolecular capsular aggregates. Nevertheless, even the design of selfassembled dimers becomes challenging if they are to have internal volumes capable of including Ͼ1 suitable sized guest and enclosing functionality to direct the organization of the housed guests. Although supramolecular capsules with internal volumes ranging from 200 to 1,500 Å 3 have been prepared, there are very few examples in which the guest ordering within the molecular cavity has been controlled by factors other than simple steric constrains or weak nondirectional interactions with the molecular enclosure (15).We report here the use of self-assembling tetraurea calix[4]pyrroles 2 (Fig. 1), which are easily synthesized and possess a sizable endohedral functionalized cavity, for the construction of dimeric capsules in which the included guest is bound through hydrogen bonding to donor sites located within the framework of the molecular enclosure. Results and DiscussionCalix[4]pyrroles, or meso octasubstituted porphyrinogens (16,17), are macrocyclic species having an array of 4 NHs that act as a binding site for anionic and electron rich neutral guests in organic solvents (18). The formation of the complex, for example with a chloride anion, is usually accompanied by a change from the preferred alternate (1,2 or 1,3) conformation of the free calix[4]pyrrole core to the cone conformation (Fig. 2). Aryl extended calix [4]pyrroles are produced by substitution at each of the 4 meso-carbons with 1 aryl group (19). In the cone conformation, the ␣,␣,␣,␣ isomers of aryl extended calix[4]pyrroles have a deep aromatic cavity suitable for including molecular 1 To whom correspondence should be addressed...

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confidence: 90%

Self-assembly of dimeric tetraurea calix[4]pyrrole capsules

Ballester

Gil-Ramírez²

2009

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

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“…After 5 d a value close to the statistical ratio was reached (Table 2). [20] This result seems to be an indication of a predominance of the centrosymmetric dimer in the solid state.…”

Section: F{mentioning

confidence: 85%

“…As we previously reported, [20] triureas 4 a-c (4 a: Conversely, when a sample of 4 a obtained by slow evaporation of a CDCl 3 solution was redissolved in the same solvent and its 1 H NMR spectrum immediately recorded, it showed a 36:64 ratio of C 1 -and C i -symmetric regioisomers. After about 20 min, the mixture of species equilibrated and reached a 57:43 ratio.…”

Section: F{mentioning

confidence: 88%

“…They form capsular dimeric aggregates held together by a seam of six hydrogen-bonded urea groups ( Figure 1). [18] Whereas assemblies 1·1 exist as solvent-free capsular aggregates, [19,20] assemblies 2·2 are able to encapsulate guests of appropriate size and shape. [21,22] The tribenzylamine core provides a high degree of flexibility to triureas 1 and 2, which adopt averaged C 3v symmetry in competitive solvents with hydrogen bonds.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the modular structure of the tribenzylamine skeleton has great potential for modification. The sequential construction "arm-to-arm" of the tertiary amine core would provide access to new triureas of C s symmetry with variation of both the pendant ureido positions [20] and the substitution at the tribenzylamine skeleton. Moreover, triureas with even more flexible branches would be easily available.…”

Section: Introductionmentioning

confidence: 99%

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Novel Capsular Aggregates from Flexible Tripodal Triureas with C_s Symmetry

Alajarı́n

Orenes

Howard

et al. 2012

Chemistry A European J

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Tris(2- and 3-ureidobenzyl)amines with C(s) symmetry self-assemble in solution forming mixtures of regioisomeric capsular aggregates, one of which is chiral and the other centrosymmetric. Under certain conditions, a predominance of the centrosymmetric regioisomer is found before equilibrium, that is, a mixture close to the statistical ratio of the two species is reached. In the solid state, there is a preference for the centrosymmetric capsules. Molecular models of both regioisomeric aggregates have been built and analyzed for comparison. Guests inside capsules formed by self-assembly of desymmetrized tris(3-ureidobenzyl)amines feel different magnetic environments, depending on whether they are inside a chiral or an achiral regioisomeric container. Of special significance are the experiments with a more flexible triurea endowed with an ureidopropylic arm, which self-assembles with the same efficiency as the more rigid tris(ureidobenzyl)amines.

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Self‐Assembly of Organic Supramolecular Capsules

Scarso

Borsato

2012

Supramolecular Chemistry

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The present contribution is aimed at illustrating to the reader the state of the art on the construction of artificial, finite supramolecular assemblies characterized in solution by capsular shape held together by means of weak intermolecular noncovalent forces in solution, except metal‐ligand coordination. These supramolecular assemblies provide cavities of correct size and shape where molecules of guests present in solution can be hosted if the available space is appropriately filled. Guests within the cavity are held for lifetimes ranging from milliseconds to hours, depending on the number and quality of weak intermolecular forces and the number of subunits that compose the capsule. The in–out process of exchange of guests influences their behavior profoundly, enabling a series of applications spanning from molecular recognition of one up to several guests at a time with creation of new forms of isomerism derived by guest–guest interactions to supramolecular catalysis, which is the ultimate goal of such kind of assemblies. A further intriguing aspect of self‐assembled capsules is chirality that can be implemented in the subunits, that forms the capsule, or that can be the result of a particular arrangement of achiral units. In the latter case, the presence of strong attractive forces between the subunits enables to template the formation of enantiomerically enriched capsules with enantiopure guests based on achiral units via the chiral memory effect.

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Self‐Assembly of Tris(2‐ureidobenzyl)amines: A New Type of Capped, Capsule‐Like Dimeric Aggregates Derived from a Highly Flexible Skeleton

Cited by 41 publications

References 60 publications

Self-assembly of dimeric tetraurea calix[4]pyrrole capsules

Self-assembly of dimeric tetraurea calix[4]pyrrole capsules

Novel Capsular Aggregates from Flexible Tripodal Triureas with C_s Symmetry

Self‐Assembly of Organic Supramolecular Capsules

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Self‐Assembly of Tris(2‐ureidobenzyl)amines: A New Type of Capped, Capsule‐Like Dimeric Aggregates Derived from a Highly Flexible Skeleton

Cited by 41 publications

References 60 publications

Self-assembly of dimeric tetraurea calix[4]pyrrole capsules

Self-assembly of dimeric tetraurea calix[4]pyrrole capsules

Novel Capsular Aggregates from Flexible Tripodal Triureas with Cs Symmetry

Self‐Assembly of Organic Supramolecular Capsules

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Product

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Novel Capsular Aggregates from Flexible Tripodal Triureas with C_s Symmetry