Switching Processes in Cavitands, Containers and Capsules

Azov, Vladimir A.; Diederich, François

doi:10.1002/9783527634408.ch8

Cited by 6 publications

(5 citation statements)

References 253 publications

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“…[34] During the last decades, resorcin [4]arenes involving many different functionalizations have been synthesized and investigated. [35][36][37] These functionalizations mainly aimed at tuning properties such as the solubility in various solvents, [6][10] [38][39][40] the guest-binding capabilities, [10] [34][37] [41][42][43][44][45][46] the position of the equilibrium between the VASE and KITE forms, [11] [47 -49] and its control by means of external stimuli. [11] [16] [17] [36] [49 -60] For a given resorcin [4]arene, the VASE-KITE equilibrium is influenced by environmental factors including temperature, [1] solvent size and polarity, [61] proton concentration [62] (pH), and ion concentration.…”

Section: Introductionmentioning

confidence: 99%

Vase‐Kite Equilibrium of Resorcin[4]arene Cavitands Investigated Using Molecular Dynamics Simulations with Ball‐and‐Stick Local Elevation Umbrella Sampling

Hahn

Milić

Hünenberger

2019

Helvetica Chimica Acta

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A key feature of resorcin[4]arene cavitands is their ability to switch between a closed/contracted (Vase) and an open/expanded (Kite) conformation. The mechanism and dynamics of this interconversion remains, however, elusive. In the present study, the Vase‐Kite transitions of a quinoxaline‐based and of a dinitrobenzene‐based resorcin[4]arene are investigated using molecular dynamics (MD) simulations in three environments (vacuum, chloroform, and toluene) and at three temperatures (198.15, 248.15, and 298.15 K). The challenge of sampling the Vase‐Kite transition, which occurs experimentally on the millisecond time scale, is overcome by calculating relative free energies using ball‐and stick local elevation umbrella sampling (B&S‐LEUS) to enhance the statistics on the relevant states and to promote interconversion transitions. Associated unbiased MD simulations also evidence for the first time a complete Vase‐to‐Kite transition, as well as transitions between degenerate Kite1 and Kite2 forms and solvent‐exchange events. The calculated Vase‐to‐Kite free‐energy changes ΔG are in qualitative agreement with the experimental magnitudes and trends. The level of quantitative agreement is, however, limited by the force‐field accuracy and, in particular, by the approximate treatment of intramolecular interactions at the classical level. The results are in line with a less stable Vase state for the dinitrobenzene compared to the quinoxaline compound, and a negative entropy change ΔS for the Vase‐to‐Kite transition of the latter compound. Relative free energies calculated for intermediates also suggest that the Vase‐Kite transition does not follow a concerted mechanism, but an asynchronous one with sequential opening of the flaps. In particular, the conformation involving two adjacent flaps open in a parallel direction (cis‐p) represents a likely intermediate, which has not been observed experimentally to date.

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Section: Introductionmentioning

confidence: 99%

Vase‐Kite Equilibrium of Resorcin[4]arene Cavitands Investigated Using Molecular Dynamics Simulations with Ball‐and‐Stick Local Elevation Umbrella Sampling

Hahn

Milić

Hünenberger

2019

Helvetica Chimica Acta

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“…that act as hosts for smaller, complementary guests. They are built up from a resorcinarene core (Figure 1) by covalent attachment of walls [1][2][3][4][5][6][7] and features such as rigidified walls, [8][9][10][11] intramolecular hydrogen bonding patterns [12,13] and even solvent water, [14] or metal coordination [15,16] are often recruited to stabilize the receptive vase-like shapes. Further refinement of the rims often allows cavitands to dimerize through weak intermolecular forces to form capsules as shown in Figure 2, relevant examples of these modifications are summarized in the folllowing.…”

Section: Deep Cavitands Are Container Molecules With One Open Endmentioning

confidence: 99%

Binding and Assembly of a Benzotriazole Cavitand in Water

et al. 2022

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A water-soluble cavitand bearing a benzotriazole upper rim was prepared and characterized. It exists as a dimeric velcraplex in D 2 O, but forms hostguest complexes with hydrophobic and amphiphilic guests. Alkanes (C5 to C10), cyclic ketones (C6-C10), cyclic alcohols (C6-C8) and various amphiphilic guests form 1 : 1 cavitand complexes. A cyclic array of hydrogen bonds, bridged by solvent/water (D 2 O) molecules, stabilizes the vase conformation of the complexes. With longer alkanes (C12-C15), symmetrical dialkyl amine, urea and phosphate, 2 : 1 host:guest capsules are formed. Computations indicate that additional waters on the upper rim create a self-complementary hydrogen-bonding pattern for capsule formation.

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“… , In the expanded kite form, these groups fold outward in an unsymmetrical fashion, creating two degenerate, equilibrating C 2 v -symmetric structures (kite 1 and kite 2). , In the C 4 v -symmetric vase form, the heteroaryl groups are oriented upward, forming an extended bowl-type structure with an internal cavity. Switching between vase and kite conformations was originally observed in response to changes in temperature. ,, The favorable solvation of the larger surface area makes the kite form predominant at low temperatures (≤213 K for 1 ), whereas this solvation becomes entropically disfavored at higher temperatures (≥293 K for 1 ), resulting in the transition to the more compact vase form. ,,, Many groups have focused on inducing conformational switching in response to a variety of other stimuli, including pH changes, metal ion concentration, solvent effects, ,, and the presence of guest molecules, ,, as well as studying the kinetics and thermodynamics of the vase–kite switching process. , Significantly, efficient guest binding occurs only in the vase conformation, whereas the kite form, which lacks a cavity, shows poor binding affinities for guests.…”

Section: From Conformational Switching To Molecular Switchesmentioning

confidence: 99%

Molecular Recognition with Resorcin[4]arene Cavitands: Switching, Halogen-Bonded Capsules, and Enantioselective Complexation

2018

Self Cite

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The development of synthetic host-guest chemistry to investigate and quantify weak, non-covalent interactions has been key to unraveling the complexity of molecular recognition in chemical and biological systems. Macrocycles have shown great utility in the design of receptors, enabling the development of highly preorganized structures. Among macrocycles, resorcin[4]arene-based cavitands have become privileged scaffolds due to their synthetic tunability, which allows access to structures with precisely defined geometries, as well as receptors that display conformational switching between two distinct states with a large difference in guest-binding properties. Here, we highlight three case studies demonstrating redox- and photoredox-controlled switching of molecular recognition properties, the formation of guest-binding supramolecular capsules based solely on halogen-bonding interactions, and enantioselective encapsulation of chiral, substituted cyclohexanes by enantiopure cage compounds as a result of perfect shape complementarity, dispersion interactions, and halogen bonding. The high geometrical and conformational control that can be achieved with resorcin[4]arene-derived host systems will continue to be a powerful resource in future molecular recognition studies.

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Switching Processes in Cavitands, Containers and Capsules

Cited by 6 publications

References 253 publications

Vase‐Kite Equilibrium of Resorcin[4]arene Cavitands Investigated Using Molecular Dynamics Simulations with Ball‐and‐Stick Local Elevation Umbrella Sampling

Vase‐Kite Equilibrium of Resorcin[4]arene Cavitands Investigated Using Molecular Dynamics Simulations with Ball‐and‐Stick Local Elevation Umbrella Sampling

Binding and Assembly of a Benzotriazole Cavitand in Water

Molecular Recognition with Resorcin[4]arene Cavitands: Switching, Halogen-Bonded Capsules, and Enantioselective Complexation

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