Quantitative Evaluation of Anion–π Interactions in Solution

Gil-Ramírez, Guzmán; Escudero‐Adán, Eduardo C.; Benet‐Buchholz, Jordi; Ballester, Pablo

doi:10.1002/anie.200800636

Cited by 208 publications

(151 citation statements)

References 33 publications

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“…This conformation has also been routinely observed in the crystal structure of aryl extended calixpyrroles grown from hydrogen bonding solvents (e.g., acetonitrile, acetone and N,Ndimethylformamide) (26,27). In contrast, the few X-ray structures of aryl extended calixpyrroles from crystals grown in nonpolar solvents (e.g., dichloromethane) show that the calixpyrrole core is in the 1,3-alternate conformation (26). Taken together, these results suggest that the conformational features of aryl extended calixpyrroles could be considered analogous to those of the related octaalkyl calix [4]pyrroles.…”

Section: Conformational Features Of Calix[4]pyrrolessupporting

confidence: 56%

“…Although there are no detailed studies on the conformational features of aryl extended calixpyrroles, we (25,26) and others (19) have observed that their chloride and fluoride complexes adopt the cone conformation in solution and in the solid state. This conformation has also been routinely observed in the crystal structure of aryl extended calixpyrroles grown from hydrogen bonding solvents (e.g., acetonitrile, acetone and N,Ndimethylformamide) (26,27). In contrast, the few X-ray structures of aryl extended calixpyrroles from crystals grown in nonpolar solvents (e.g., dichloromethane) show that the calixpyrrole core is in the 1,3-alternate conformation (26).…”

Section: Conformational Features Of Calix[4]pyrrolesmentioning

confidence: 71%

“…Experimental and theoretical studies have also shown that, in nonpolar solvents, the binding of a chloride anion induces a conformational change in the calixpyrrole core from the alternate conformation to the cone conformation (24). Although there are no detailed studies on the conformational features of aryl extended calixpyrroles, we (25,26) and others (19) have observed that their chloride and fluoride complexes adopt the cone conformation in solution and in the solid state. This conformation has also been routinely observed in the crystal structure of aryl extended calixpyrroles grown from hydrogen bonding solvents (e.g., acetonitrile, acetone and N,Ndimethylformamide) (26,27).…”

Section: Conformational Features Of Calix[4]pyrrolesmentioning

confidence: 85%

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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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Section: Conformational Features Of Calix[4]pyrrolessupporting

confidence: 56%

Section: Conformational Features Of Calix[4]pyrrolesmentioning

confidence: 71%

Section: Conformational Features Of Calix[4]pyrrolesmentioning

confidence: 85%

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

Ballester

Gil-Ramírez²

2009

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

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“…Phenyl units connected to the meso-positions of calix [4]pyrroles are known to increase the anion binding affinity of these structures via anion−π interactions. 43 Furthermore, the presence of cyclohexyl units at the meso-positions was expected to increase the solubility of the calix [4]pyrroles in common organic solvents. Thus, incorporation of the phenyl and cyclohexyl derivatives was expected to increase the anion binding affinity of the calix [4]pyrroles via additional anion−π interactions while maintaining the high solubility in organic solvents.…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

Calix[4]pyrroles with bulky substituents and their anion binding studies

Akar¹,

Aydogan²

2017

Turk J Chem

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“…1,2,3 The four pyrrole rings are linked by meso-carbon bridges, which carry eight substituents, such as alkyl chains or aryl substituents in the aryl-extended calixpyrroles. The three dimensional structure of an aryl-extended calixpyrrole ( Fig.…”

Section: Introductionmentioning

confidence: 99%

Solid lipid nanoparticles from amphiphilic calixpyrroles

Helttunen

Galán

Ballester

et al. 2016

Journal of Colloid and Interface Science

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HypothesisMacrocyclic amphiphiles form interesting self-assembling structures, including solid lipid nanoparticles, which have potential applications in drug encapsulation. Aryl-extended calixpyrroles, which act as anion binding hosts, are expected to form solid lipid nanoparticles, even though the alkyl chains have unusual perpendicular geometry with respect to the hydrophilic head group. The preparation conditions and the alkyl chain length should affect the size and stability of the particles. ExperimentsSolid lipid nanoparticles of two aryl-extended calixpyrroles with resorcinol walls and either meso-dodecyl or meso-methyl alkyl chains were compared. Ethanolic solutions of the calixpyrroles were mixed with water and the resulting nanoparticle dispersions were studied with dynamic light scattering and nanoparticle tracking analysis. The effect of different calixpyrrole/ethanol/water ratios on particle size was tested. The surface charge of the particles at different pH and NaCl concentration was determined by zeta potential measurements. 2 FindingsThe meso-dodecyl calixpyrrole produced small nanoparticles with mean hydrodynamic diameters between 40-70 nm in 0.86-4.28 M ethanol. The particles were stable in solution for several months. Particles prepared from meso-methyl calixpyrrole were larger and less stable.The smallest particles were obtained with low calixpyrrole concentration and calixpyrrole/ethanol ratio. Larger ethanol/water ratio induced broader particle size distributions. Increasing pH aided the stability of the particles due to increased negative surface charge.

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Quantitative Evaluation of Anion–π Interactions in Solution

Cited by 208 publications

References 33 publications

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

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

Calix[4]pyrroles with bulky substituents and their anion binding studies

Solid lipid nanoparticles from amphiphilic calixpyrroles

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