Folding-controlled assembly of <i>ortho</i>-phenylene-based macrocycles

Kirinda, Viraj C.; Hartley, C. Scott

doi:10.1039/d1sc01270c

Cited by 8 publications

(5 citation statements)

References 56 publications

(96 reference statements)

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“…o -Phenylenes are conformationally dynamic, and their geometries can be studied in detail by NMR spectroscopy, making them well-suited to addressing problems in molecular folding. In recent work, we have demonstrated the coassembly of o -phenylenes and rod-shaped linkers into macrocycles comprising multiple foldamer subunits as simple examples of folded systems with higher-order structure. , However, there is essentially no stereocontrol in these systems: the product macrocycles comprise both twist senses of the foldamers ( M and P ) in statistical ratios. As a result, the products are complex racemic mixtures of multiple diastereomers.…”

Section: Introductionmentioning

confidence: 99%

Engineering Chiral Induction in Centrally Functionalized o-Phenylenes

2023

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Work on foldamers, nonbiological oligomers that mimic the hierarchical structure of biomacromolecules, continues to yield new architectures of ever increasing complexity. o-Phenylenes, a class of helical aromatic foldamers, are well-suited to this area because of their structural simplicity and the straightforward characterization of their folding in solution. However, control of structure requires, by definition, control over folding handedness. Control over o-phenylene twist sense is currently lacking. While chiral induction from groups at o-phenylene termini has been demonstrated, it would be useful to instead direct twisting from internal positions to leave the ends free. Here, we explore chiral induction in a series of o-phenylenes with chiral imides at their centers. Conformational behavior has been studied by nuclear magnetic resonance and circular dichroism spectroscopies and density functional theory calculations. Chiral induction in otherwise unfunctionalized o-phenylenes is generally poor. However, strategic functionalization of the helix surface with trifluoromethyl or methyl groups allows it to better interact with the imide groups, greatly increasing diastereomeric excesses. The sense of chiral induction is consistent with computational models that suggest that it primarily arises from a steric effect.

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Section: Introductionmentioning

confidence: 99%

Engineering Chiral Induction in Centrally Functionalized o-Phenylenes

2023

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“…A fundamentally important characteristic that determines the basic properties of polymers is shape. Therefore, the application range of a polymer is highly dependent on its topology, which can nowadays be designed and engineered by exploiting a plethora of synthetic tools. − For instance, the rheological behavior, elasticity, chain entanglements, or even a polymer’s prospect as a gene therapy agent are all features that can be precisely regulated by employing macromolecules with explicit topology and architecture. − Since macromolecular topology had conventionally been considered as a static concept, the question of how a polymer can adopt more than one shape, and consequently display variable properties on-demand without chemically altering the polymer’s environment, arises. Thus far, temperature has been conventionally used as the external stimulus of choice to overcome the static nature of a polymer architecture .…”

Section: Introductionmentioning

confidence: 99%

Reversible Transformations of Polymer Topologies through Visible Light and Darkness

2022

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A fundamentally important characteristic of a macromolecule is its shape. Herein, visible light and darkness are used as the only stimuli to reversibly alter the topology of welldefined polymers in a one-pot procedure. For this, linear naphthalene-containing polyacrylates are used as scaffolds for the visible light-induced cycloaddition with various substituted triazolinediones (i.e., butyl, stearyl, perfluoro, and polymeric), resulting in differently shaped graft polymers, including brushes and combs. The thus-formed cycloadduct linkages dissociate in the dark, resulting in the regeneration of the parent linear polymer at ambient temperature, establishing a dual-topology transformation by only switching green light on and off. By applying different temperatures during the cycloreversion process, the dissociation rate of the cycloadducts can be tuned in a facile manner, thus allowing for time control over the regeneration of the parent polymer. By engineering a polymer that consists of differently substituted naphthalenes at the chain ends and on the side chains, the inherently different cycloreversion rates of the formed cycloadducts are leveraged to achieve in situ multi-topology transformations without external stimuli. The shape transformations have been repeated up to 4 times sequentially in one pot without the need of any purification. The topological alterations are microscopically depicted through reversible self-assembly, with the polymers adopting different morphologies upon visible light or darkness. The versatile yet practical nature of this polymer "reshaping" strategy provides facile access to multifaceted polymer systems and, consequently, to a plethora of potential applications thereof.

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“…Moreover, while not explicitly addressed here, it was obvious that 19 Fbased spectra will be very helpful in combination with 1 H spectra when making initial chemical shift assignments. As work in this area moves toward increasingly complex, dynamic systems, 26,49 the ability to label key sites on o-phenylene backbones and monitor changes in folding should be of great use. That said, we stress that 19 F shielding predictions, at least at the level of theory used here, should not be used on their own to assign geometries to o-phenylene conformations (or those of other sterically congested polyphenylenes), although they may be useful in combination with other data.…”

Section: ■ Introductionmentioning

confidence: 99%

Fluorine Labeling of ortho-Phenylenes to Facilitate Conformational Analysis

et al. 2021

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1 H NMR spectroscopy is a powerful tool for the conformational analysis of orthophenylene foldamers in solution. However, as o-phenylenes are integrated into evermore-complex systems, we are reaching the limits of what can be analyzed by 1 Hand 13 C-based NMR techniques. Here, we explore fluorine labeling of o-phenylene oligomers for analysis by 19 F NMR spectroscopy. Two series of fluorinated oligomers have been synthesized. Optimization of monomers for Suzuki coupling enables an efficient stepwise oligomer synthesis. The oligomers all adopt well-folded geometries in solution, as determined by 1 H NMR spectroscopy and X-ray crystallography. 19 F NMR experiments complement these methods well. The resolved singlets of one-dimensional 19 F{ 1 H} spectra are very useful for determining relative conformer populations. The 1 additional information from two-dimensional 19 F NMR spectra is also clearly valuable when making 1 H assignments. Comparison of 19 F isotropic shielding predictions to experimental chemical shifts is not, however, currently sufficient by itself to establish o-phenylene geometries.

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Folding-controlled assembly of ortho-phenylene-based macrocycles

Abstract: The self-assembly of foldamers into macrocycles is a simple approach to non-biological higher-order structure. Previous work on the co-assembly of ortho-phenylene foldamers with rod-shaped linkers has shown that folding and...

Cited by 8 publications

References 56 publications

Engineering Chiral Induction in Centrally Functionalized o-Phenylenes

Engineering Chiral Induction in Centrally Functionalized o-Phenylenes

Reversible Transformations of Polymer Topologies through Visible Light and Darkness

Fluorine Labeling of ortho-Phenylenes to Facilitate Conformational Analysis

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