We found that molecular baskets 1–3, with amino acids at their rim, undergo photoinduced decarboxylations to give baskets 4–6 forming a solid precipitate in water. Furthermore, organophosphonates 7–9 ...(OP), akin in size and shape to G-type nerve agents, form inclusion complexes with baskets 1–3 (K = 6–2243 M–1). Light irradiation (300 nm) of an aqueous solution of 1–3⊂OP led to the formation of precipitate containing an OP compound thereby amounting to a novel strategy for light-induced sequestration of nerve agents or, perhaps, other targeted compounds. Importantly, the stability of basket⊂OP complexes in addition to functional groups at the basket’s rim play a role in the efficiency (up to 98%) by which OPs are removed from water.
In this study, we report the preparation, conformational dynamics, and recognition characteristics of novel molecular capsule 1 comprising a bowl-shaped framework conjugated to a ...tris(2-pyridylmethyl)amine (TPA) lid. With the assistance of experiment (1H NMR spectroscopy) and theory (MM and DFT) we found that C 3 symmetric 1 is poorly preorganized with three pyridines at the rim adopting a propeller-like orientation and undergoing P-to-M (or vice versa) stereoisomerization (ΔG ⧧ < 8 kcal/mol, VT 1H NMR). Capsule 1 binds CH4, CH3Cl, CH2Cl2, CHCl3, and CCl4 with K a < 7 M–1. Protonation of 1 with HCl, however, gives 1·H–Cl, with the solid-state structure showing the TPA lid being “flattened” and the +N–H---Cl hydrogen-bonded group residing outside. Importantly, the P-to-M stereoisomerization would for 1·H–Cl occur with ΔG ⧧ = 11 kcal/mol (VT 1H NMR). Less dynamic and more preorganized 1·H–Cl binds CH4, CH3Cl, CH2Cl2, CHCl3, and CCl4 guests with a greater affinity (K a = 100–400 M–1) than 1. The results of our studies suggest that the complexation of increasingly larger guests takes place in an induced-fit fashion, with 1·H–Cl (a) elongating along its vertical axis and concurrently potentially (b) twisting pyridines fromP into M (and vice versa) orientation. The addition of Et3N to 1·H–Cl⊂CH2Cl2 causes deprotonation of the capsule and the release of CH2Cl2 with the process being fully reversed after the addition of HCl. Allosteric capsule 1 with unique structural and dynamic characteristics is expected to, in the future, assist the construction of complex molecular machines and smart functional materials.
A Hexapodal Capsule for the Recognition of Anions Xie, Han; Finnegan, Tyler J; Liyana Gunawardana, Vageesha W ...
Journal of the American Chemical Society,
03/2021, Letnik:
143, Številka:
10
Journal Article
Recenzirano
We herein describe the preparation, characterization, and recognition characteristics of novel hexapodal capsule 1 composed of two benzenes joined by six hydrogen bonding (HB) groups to encircle ...space. This barrel-shaped host was obtained by reversible imine condensation of hexakis-aldehyde 2 and hexakis-amine 3 in the presence of oxyanions or halides acting as templates. Fascinatingly, capsule 1 includes 18 HB donating (Csp2–H and N–H) and 12 HB accepting groups (CO and CN) surrounding a binding pocket (78 Å3). In this regard, the complexation of fluoride, chloride, carbonate, sulfate, and hydrogen phosphate was probed by NMR spectroscopy (DMSO) and X-ray diffraction analysis to disclose the adaptive nature of 1 undergoing an adjustment of its conformation to complement each anionic guest. Furthermore, the rate by which encapsulated chloride was substituted by sulfate or hydrogen phosphate was slow (>7 days) while the stability of SO4⊂12– was greatest in the series with K a > 107 M–1 in highly competitive DMSO. With facile access to 1, the stage is set to probe this modular, polyvalent, and novel host to further improve the extraction of tetrahedral oxyanions from waste and the environment or control their chemistry in living systems.
Two molecular baskets 1 6–, each with three (S)-glutamic acids at its rim, were found (NMR, ITC) to complex diammonium alkanes 2 2+ –5 2+ (+H3N(CH2) n NH3 +, n = 7–10) giving ternary 2–5⊂1 210– ...assemblies (K = 107 –109 M–2). From the magnetic perturbation of proton nuclei (1H NMR, NICS), we deduced that each guest assumed a U shape within the binary complex, 2–5⊂14–. Two ammonium groups were bound in the “anionic nest” at the top of 1 6–, while the hydrocarbon chain resided in its nonpolar cavity. From detailed ITC analyses, we showed that the binary complex 2–5⊂14– forms first and then another 1 6– capped 2–5⊂14– to give 2–5⊂1 210–, via interactions of the carboxylates at the rims with ammoniums on the guest. Long-range NOEs revealed that U-shaped 2 2+ and 5 2+ coiled into highly strained twist–turn–twist formations, for the first time observed within an abiotic host while curiously resembling helix–turn–helix motif found in DNA binding proteins.
We describe a preparative method for directing Mizoroki-Heck cyclotrimerization of enantioenriched bromonorbornenes into molecular baskets having increasingly deeper and extendable aromatic cavities. ...Such diastereoselective cyclotrimerizations of the bromo-olefinic substrates resulted from prevalent β migratory insertions without the formation of palladacycle intermediate(s). The facile access to multigram quantity of a new series of basket-like hosts clears the way for creating novel supramolecular materials for storage, sequestration and catalysis.
A novel synthetic method for obtaining multigram quantities of uniquely functionalized and deep molecular baskets is now available, clearing the way toward useful supramolecular materials.
Host-guest complexations can be described by two competing mechanisms, conformational selection (CS) and induced fit (IF). In this work, we used a combination of nudged elastic band (NEB), adaptive ...steered molecular dynamics (ASMD), and density functional theory (DFT, with a correction for dispersion) to study the dynamics of the pathways (IF/CS) by which two conformers of basket B(+) and B(−) interconvert and trap CX
4
guests (X = Cl and Br). While the results from NEB/DFT studies disclosed host-guest noncovalent contacts reducing the basket's conformational dynamics, ASMD methodology suggested an associative mechanism for the guest complexation. With theory in excellent agreement with experiments, NEB and ASMD emerge as the methods of choice for studying dynamics of supramolecular systems.
Adaptive steered molecular dynamics in combination with a nudged elastic band study of CS and IF, operating in an abiotic system, permits an accurate prediction of the system's dynamics.
Fluorinated piperidines find wide applications, most notably in the development of novel therapies and agrochemicals. Cyclization of alkenyl N-tosylamides promoted by BF3-activated aryliodine(III) ...carboxylates is an attractive strategy to construct 3-fluoropiperidines, but it suffers from selectivity issues arising from competitive oxoaminations and the inability to easily modulate the reactions diastereoselectivity. Herein, we report an itemized optimization of the reaction conditions carried out on both cyclic and acyclic substrates and outline the origins of substrate- and reagent-based stereo-, regio-, and chemoselectivity. Extensive mechanistic studies encompassing multinuclear NMR spectroscopy, deuterium labeling, rearrangements on stereodefined substrates, and careful structural analyses (NMR and X-ray) of the reaction products are performed. This revealed the processes and interactions crucial for achieving controlled preparation of 3-fluoropiperidines using I(III) chemistry and has provided an advanced understanding of the reaction mechanism. In brief, we propose that BF3-coordinated I(III) reagents attack CC to produce the corresponding iodiranium(III) ion, which then undergoes diastereodetermining 5-exo-cyclization. Transiently formed pyrrolidines with an exocyclic σ-alkyl-I(III) moiety can further undergo aziridinium ion formation or reductive ligand coupling processes, which dictate not only the final product’s ring size but also the chemoselectivity. Importantly, the selectivity of the reaction depends on the nature of the ligand bound to I(III) and the presence of electrolytes such as TBABF4. Reported findings will facilitate the usage of ArI(III)-dicarboxylates in the reliable construction of fluorinated azaheterocycles.
The synergy among twelve carboxylates from two hexavalent baskets
1
6−
assisted the encapsulation of one divalent diammonium guest
3
2+
-
6
2+
and the formation of ternary
3
-
6
⊂1
2
10−
. The ...reduction of basket's multivalency, by photoinduced α-decarboxylation of 1
6−
to give
2
3−
, intercepted the interannular cooperativity operating in the stabilization of capsulpex
3
-
6
⊂1
2
10−
to dramatically diminish the binding affinity towards diammonium guests. As a result, the cationic guests were released into bulk water with
2
3−
assembling into nanoparticles. With numerous drugs carrying positive sites, the finding reported here could now be examined for their light-promoted spatiotemporal delivery.
Photoinduced decarboxylation of two hexaanionic baskets, surrounding a divalent cationic guest, reduced the interannular cooperativity (
i.e.
multivalency) holding the complex together to result in the release of guests.
Discovering novel and functional photoresponsive materials is of interest for improving controlled release of molecules and scavenging toxic compounds for cleaning our environment or designing ...chemosensors. In this study, we report on the photoinduced decarboxylation of basket 16−, containing three glutamic acids at its rim. This concave compound is, in an aqueous environment (30 mm phosphate buffer at pH 7.0), monomeric (1H NMR DOSY, DLS) with glutamic acid residues randomly oriented about its rim (1H NMR and MM‐OPLS3). The irradiation (300 nm) of 16− leads to the exclusive removal of its α‐carboxylates to give amphiphilic 23− possessing γ‐carboxylates. The photochemical transformation is a consecutive reaction with mono‐ and bis‐decarboxylated products observed with 1H NMR spectroscopy and ESI mass spectrometry. Amphiphilic 23− is a preorganized molecule (MM‐OPLS3) that, in water, aggregates into organic nanoparticles (ca. 50–200 nm in diameter; DLS, TEM and cryo‐TEM) having a critical aggregation concentration of 12 μm (UV/Vis). As the transition of monomeric 16− into nanoparticulate 23− is triggered with light, we reasoned that stimuli‐responsive formation of the soft material lends itself to nanotechnology applications such as controlled release or scavenging of targeted compounds.
Filling the basket: Photoinduced decarboxylation of molecular baskets functionalized with glutamic acids was found to, in water, give amphiphilic cavitands. These cavitands assemble into organic nanoparticles that could be used for scavenging toxic molecules, promoting chemical reactions or delivering drugs.
Covalent capsule 1 was designed to include two molecular baskets linked with three mobile pyridines tucked into its inner space. On the basis of both theory (DFT) and experiments (NMR and X‐ray ...crystallography), we found that the pyridine “doors” split the chamber (380 Å3) of 1 so that two equally sizeable compartments (190 Å3) became joined through a conformationally flexible aromatic barrier. The compartments of such unique host could be populated with CCl4 (88 Å3; PC=46 %), CBr4 (106 Å3; 56 %) or their combination CCl4/CBr4 (PC=51 %), with thermodynamic stabilities ΔG° tracking the values of packing coefficients (PC). Halogen (C−X⋅⋅⋅π) and hydrogen bonding (C−H⋅⋅⋅X) contacts held the haloalkane guests in the cavities of 1. The consecutive complexations were found to occur in a negative allosteric manner, which we propose to result from the induced‐fit mode of complexation. Newly designed 1 opens a way for probing the effects of inner conformational dynamics on noncovalent interactions, reactivity and intramolecular translation in confined spaces of hollow molecules.
A newly designed covalent capsule incorporates three revolving pyridine “doors” splitting its inner space into two chambers that may coalesce into one. The chambers accommodate up to two haloalkanes in the allosteric fashion therefore opening a way for studying the effect of host internal dynamics on reactivity, noncovalent interaction or trafficking of guests residing in such unique environment.
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