A mini review: supramolecular gels based on calix[4]arene derivatives
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REVIEW ARTICLE
A mini review: supramolecular gels based on calix[4]arene derivatives Xiuqin Cai1 · Qiuling Zhao2 Received: 25 February 2020 / Accepted: 17 October 2020 © Springer Nature B.V. 2020
Abstract Supramolecular gels, materials with reversible phase that respond to external stimuli, form via multiple noncovalent interactions of gelator/gelator or gelator/solvent. Calix[4]arene, with an adjustable cavity and multiple modified sites, enriches the properties of supramolecular gels. The synthesis and properties of calix[4]arene supramolecular gels will be discussed and reviewed. There are three methods for constructing calix[4]arene supramolecular gels: (1) using cation- or anion-directed and assisted calix[4]arene derivatives to build a gel network; (2) using a calix[4]arene derivative and another compound together to construct a binary supramolecular gel; and (3) forming a calix[4]arene derivative self-assembled gel network. Moreover, increased interest has been shown in the application of calix[4]arene supramolecular gels. Keywords Calix[4]arene · Supramolecular gel · Assembly
Introduction Supramolecular gels, solid-like materials, have attracted great attention for their reversible phase and smart response to external stimuli [1] and are widely applied in controlled drug release [2], mild separation [3], smart cleaning [4], and new media for preparation [5] and purification [6, 7]. Supramolecular gels are usually formed by noncovalent interactions between gelators (Fig. 1), and their properties are enriched via introducing new interacting sites, introducing new functional groups or exploiting new noncovalent interactions and assembly [8]. Some special and functional structures, such as cholesterol [9], amino acids [10], glucose [11] and so on, are widely used as building blocks of supramolecular gels. In recent years, macrocyclic hosts such as crown ether [12], cyclodextrin [13], cucurbituril [14] and so on have been incorporated into gelators to construct excellent supramolecular gels [15].
* Xiuqin Cai [email protected] Qiuling Zhao [email protected] 1
College of Chemistry and Materials Science, Weinan Normal University, Weinan 714099, China
School of Biomedical and Chemical Engineering, Liaoning Institute of Science and Technology, Benxi 117004, China
2
Calix[4]arene, a cyclic oligomer condensed through phenol and formaldehyde units, has an adjustable cavity, variable conformation, an easily modified structure, convenient synthesis and unique molecular recognition of low-molecular-weight compounds, anions and cations via hydrogen bonding, electrostatic interactions, π-π stacking interactions and intermolecular forces [16]. Calix[4]arene is an excellent core structure for supramolecular assembly [17]. To date, supramolecular gels based on calix[4]arene have been reported in the following categories: (1) cation- or aniondirected and assisted calix[4]arene derivatives used to build gel networks; (2) a calix[4]arene derivative and another compound used together to construct a binary supra
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