Recent development of pillar[n]arene-based amphiphiles

Pillar[n]arene-based amphiphiles,mainly including amphiphilic pillar[n]arenes and supra-amphiphilic pillar[n]arenes,have obtained considerable interests in recent years due to their fascinating chemical structures,various self-assembly behaviors,and widely applications.Thanks to the pillar-like frameworks and the rich host-guest recognitions of the cavities,these amphiphiles can be easily controlled to form dimensional and morphologic assemblies for multiple applications.Compared with traditional linear covalent amphiphiles,the introduction of host-guest recognitions facilitated the preparation and controllability of these supramolecular amphiphilic systems.Moreover,the host-guest recognitions endow the assemblies from pillar[n]arene-based amphiphiles with stimuli-responsive functions.In this mini-review,we summarized the chemical structures,self-assembly features,and the applications of pillar[n]arene-based amphiphiles.However,several research topics of pillar[n]arenebased amphiphiles can be further developed in the future,such as larger cavity amphiphilic pillar[n]arenes,co-assembly with 2 D materials and utilization of the host-guest interactions.     

柱芳烃的合成及主客体化学研究进展

柱芳烃是由对苯二酚或对苯二酚醚通过亚甲基桥在苯环的对位连接而成的一类环状低聚物, 是一类新型的大环主体分子. 本文介绍了柱芳烃和功能化柱芳烃分子的合成, 以及在分子识别、 自组装等主客体化学方面的最新研究进展, 并对其研究前景进行展望.     

Self-assembled dendrimers with uniform structure

Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly processes occur independently. Therefore, molecules have been prepared in which a tetra-urea calix[4]arene and a tri-urea mono acetamide derivative are covalently connected between their narrow rims by a long, mainly aliphatic chain [-O-(CH(2))(n)-C(O)-NH-(CH(2))(m)-O-] (7). In the presence of an equimolar amount of tetra-tosyl urea calix[4]arene () they form dendritic assemblies since the well known heterodimerization of tetra-tosyl and tetra-aryl urea calix[4]arenes prevents the formation of a cross-linked structure. Covalent connection of adjacent urea residues leads to tetra-loop derivatives (3) that cannot form homodimers, but instead form heterodimers with tetra-aryl or tetra-tosylureas. Therefore, similar dendrimers should be available using the selective dimerization observed for 3. The formation of a single, structurally uniform dendrimer from eight building blocks is confirmed by (1)H NMR spectra, showing only peaks that are also found for respective model assemblies. Translational diffusion coefficients of the assemblies have been determined using (1)H DOSY NMR.     

Facile synthesis of oligophenylene-substituted calix[4]arenes and their enhanced binding properties

[reaction: see text] A facile and efficient protocol for the synthesis of oligophenylene OPP(n)-substituted calix[4]arenes (with n up to 4) via iodo-substituted oligoarylcalix[4]arenes has been developed. The cooperation effect of the proximate fluoroionophores in hexylsulfanyl end-capped OPP(n)-substituted calix[4]arene assemblies leads to metal ion binding enhancement.     

Controlled self-assembly by mono-p-sulfonatocalix[n]arenes and bis-p-sulfonatocalix[n]arenes

The complexation-induced critical aggregation concentrations of 1-pyrenemethylaminium by mono-p-sulfonatocalix[n]arenes and bis-p-sulfonatocalix[n]arenes (n=4, 5) were systemically measured by fluorescence spectroscopy. In all cases, the complexation-induced critical aggregation concentration decreases by about 3 times upon addition of p-sulfonatocalix[n]arenes. However, the optimal molar ratios for the aggregation of 1-pyrenemethylaminium by mono-p-sulfonatocalix[n]arenes and bis-p-sulfonatocalix[n]arenes are distinctly different: For mono-p-sulfonatocalix[n]arenes, the optimum mixing ratio for the aggregation of 1-pyrenemethylaminium is 1:4 mono-p-sulfonatocalix[n]arenes/1-pyrenemethylaminium, whereas only 2.5 molecules of 1-pyrenemethylaminium can be bound by one cavity of bis-p-sulfonatocalix[n]arenes. The intermolecular complexation of mono-p-sulfonatocalix[n]arenes and bis-p-sulfonatocalix[n]arenes with 1-pyrenemethylaminium led to the formation of two distinctly different nanoarchitectures, which were shown to be nanoscale vesicle and rod aggregates, respectively, by using dynamic laser scattering, TEM, and SEM. This behavior is also different from the fiber-like aggregates with lengths of several micrometers that were formed by 1-pyrenemethylaminium itself above its critical aggregation concentration. Furthermore, the obtained nanoaggregates exhibit benign water solubility, self-labeled fluorescence, and, more importantly, temperature responsiveness.     

Water-soluble molecular capsules: self-assembly and binding properties

The self-assembly and characterization of water-soluble calix[4]arene-based molecular capsules (12) is reported. The assemblies are the result of ionic interactions between negatively charged calix[4]arenes 1 a and 1 b, functionalized at the upper rim with amino acid moieties, and a positively charged tetraamidiniumcalix[4]arene 2. The formation of the molecular capsules is studied by (1)H NMR spectroscopy, ESI mass spectrometry (ESI-MS), and isothermal titration calorimetry (ITC). A molecular docking protocol was used to identify potential guest molecules for the self-assembled capsule 1 a2. Experimental guest encapsulation studies indicate that capsule 1 a2 is an effective host for both charged (N-methylquinuclidinium cation) and neutral molecules (6-amino-2-methylquinoline) in water.     

Water as a building block in solid-state acetonitrile-pyrogallol[4]arene assemblies: structural investigations

Under various conditions, water molecules dramatically affect a number of solid-state C-alkylpyrogallol[4]arene assemblies. In the absence of water, hydrogen-bonded hexameric capsules are formed for the C-butyl, pentyl, hexyl, and heptyl pyrogallol[4]arenes. Introduction of water to acetonitrile solutions containing C-propyl-C-octylpyrogallol[4]arenes resulted in the formation of markedly different bilayer structures and the structural identification of two new dimer-type motifs.     

Water‐Soluble Molecular Capsules: Self‐Assembly and Binding Properties

The self‐assembly and characterization of water‐soluble calix[4]arene‐based molecular capsules ( 1?2 ) is reported. The assemblies are the result of ionic interactions between negatively charged calix[4]arenes 1 a and 1 b , functionalized at the upper rim with amino acid moieties, and a positively charged tetraamidiniumcalix[4]arene 2 . The formation of the molecular capsules is studied by ¹H NMR spectroscopy, ESI mass spectrometry (ESI‐MS), and isothermal titration calorimetry (ITC). A molecular docking protocol was used to identify potential guest molecules for the self‐assembled capsule 1 a?2 . Experimental guest encapsulation studies indicate that capsule 1 a?2 is an effective host for both charged (N‐methylquinuclidinium cation) and neutral molecules (6‐amino‐2‐methylquinoline) in water.     

Recent progress in the research on the host-guest chemistry of pillar[n]arenes

Pillar[n]arene, as a new kind of macrocyclic host molecule, is a cyclic oligomer, which has a unique rigid structure with a hydrophobic cavity and can interact with many size-matched guest molecules. In this review, the molecular recognition, self-assembly and applications of the pillar[n]arenes in the past two years were described. On the basis of previous scientific research, a variety of pillar[n]arene-based supramolecular systems responsive to specific external stimuli such as pH, redox, gas, light, etc. has been constructed. Pillar[n]arenes have exhibited great potential in constructing these fantastic supramolecular systems based on host-guest recognition, including nanomaterials, controllable drug delivery, transmembrane channels, chemosensors and catalytic entities. These supramolecular systems have a wide range of applications in the material, biology, detection and catalysis field, but their applications are not limited to these fields.     

Alignment and Dynamic Inversion of Planar Chirality in Pillar[n]arenes

Pillar[n]arenes are symmetrical macrocyclic compounds composed of benzene panels with para-methylene linkages. Each panel usually exhibits planar chirality and prefers chirality-aligned states. Because of this feature, pillar[n]arenes are attractive scaffolds for chiroptical materials that are easy to prepare and optically resolve and show intense circular dichroism (CD) signals. In addition, rotation of the panels endows the chirality of pillar[n]arenes with a dynamic nature. The chirality in tubular oligomers and supramolecular assemblies sometimes show time- and procedure-dependent alignment phenomena. Furthermore, the CD signals of some pillar[n]arenes respond to the addition of chiral guests when their dynamic chirality is coupled with host–guest properties. By using diastereomeric pillar[n]arenes with additional chiral structures, the response can also be caused by achiral guests and changes of the environment, providing molecular sensors.     

Biochemistry of anionic calix[n]arenes

This review treats the biological properties of the various anionic calix[n]arenes, both as soluble forms and in the colloidal state. The complexation of these molecules with amino-acids, peptides and proteins is discussed, as is their interaction with model membranes. The complexations with various Active Pharmaceutical Ingredients as complexes, for tamoxifen as solid state and colloidal structures, are treated in depth. Two sections deal with the direct biological action of the calix[n]arenes and their use as biosensors. A final section deals with the toxicity, in reality the lack of toxicity of the calix[n]arenes.     

Calixarenes in analytical and separation chemistry

Discovered in the 1940's, [1n]metacyclophanes with the common name calix[n]arenes which is derived from for the molecule's shape enjoyed a remarkable interest in almost all fields of chemistry since the 1980's, which is highlighted by several books [1-8]. Over 50 reviews concerning their synthesis, properties and applicabilities were published, many of those with emphasis on organic synthesis and structural properties are cited in [P. 5-6 in 2]. Of interest for analytical chemists are reviews on calixarenes and the structurally related resorcin[n]arenes (or calix[n]resorcarenes) and calixpyrroles concerning potentiometric sensors [9-12], chromo- and fluorophores [13, 14], molecular switches [15], metal ion binding in solution [16-19], redox properties [20] and anion binding [21-24]. Other recent reviews deal with thermodynamic aspects [25], organometallic compounds [26], P-containing calixarenes [27-29], as well as molecular dynamics modeling [30-33]. It is a vital field with over 200 publications per year. Therefore, this article presents only selected results on complexation, solvent extraction and membrane transport with the emphasis on ion and molecular recognition which can be used for analytical purposes, without attempting to cover all available references.     

Fourfold [2]rotaxanes based on calix[4]arenes

Tetraurea calix[4]arenes with four loops form exclusively heterodimers with open-chain urea calix[4]arenes when they are dissolved in aprotic solvents. These assemblies can be considered as pseudorotaxanes. If open-chain tetraureas ending with maleic imide functions are used, their Diels-Alder reaction with 1,4,5,8-tetrapentoxyanthracene leads to tetra[2]rotaxanes which cannot be split into the single calixarene parts by hydrogen bond breaking solvents.     

Hydrogen bond energies and cooperativity in substituted calix[n]arenes (n = 4, 5)

Hydrogen-bonded interactions in para-substituted calix[n]arenes (CX[n]) (n = 4, 5) and their thia analogues are analyzed using the recently proposed molecular tailoring approach. The cooperative contribution toward the hydrogen-bonding network within the CX[5] host is shown to be nearly 5 times larger than that in its thia analogue. Hydrogen bond strengths in the O-H···O network are enhanced on substitution of an electron-donating group. The cooperativity contributions are reflected in the electron density at the bond critical point in the quantum theory of atoms in molecules.     

Self-recognition, structure, stability, and guest affinity of pyrogallol[4]arene and resorcin[4]arene capsules in solution

In the present study, we used diffusion NMR to probe the structures and characteristics of the products obtained from the self-assembly of resorcin[4]arenes 1a and 1b and pyrogallol[4]arenes 2a and 2b in CDCl(3) solutions. It was found that all four molecules self-assemble into hexameric capsules. The hexameric capsules of pyrogallol[4]arenes 2a and 2b were found to be more stable than the capsules of resorcin[4]arenes 1a and 1b in polar media. We also studied the role of water molecules in the self-assembly of the different capsules and found that water molecules are part of the hexameric capsules of resorcin[4]arenes 1a and 1b but not in the capsules of pyrogallol[4]arenes 2a and 2b. It was found that the self-assembly process between the resorcin[4]arenes and pyrogallol[4]arenes proceeds with self-recognition. When mixing two macrocycles of different types in a chloroform solution, no heterohexamers are formed, only the capsule constructed from the same macrocycle is detected. However, when two resorcin[4]arenes (i.e., 1a and 1b) or two pyrogallol[4]arenes (i.e., 2a and 2b) are mixed, heterohexamers are formed over time. In addition, we found that resorcin[4]arenes and pyrogallol[4]arenes differ significantly in their guest affinity. The capsules of 1a and 1b can accommodate both the tertiary alkylamines and their respective ammonium salts, while the capsules of 2a and 2b encapsulate only the neutral tertiary alkylamines.     

Biochemistry of the para-sulfonato-calix[n]arenes

The biochemistry of the para-sulfonato-calix[n]arenes has shown rapid development during the past ten years, the highly diverse biomedical applications of these molecules now include anti-viral, anti-thrombotic activities, enzyme blocking and protein complexation. The future is even more promising as para-sulfonato-calix[n]arenes have, now, been shown to have potential in the diagnosis of prion-based diseases. Their innocuous nature, as far as is known at present, may open up their future use in medications.     

Calixarenes in analytical and separation chemistry

Discovered in the 1940’s, [1_n]metacyclophanes with the common name calix[n]arenes which is derived from for the molecule’s shape enjoyed a remarkable interest in almost all fields of chemistry since the 1980’s, which is highlighted by several books [1–8]. Over 50 reviews concerning their synthesis, properties and applicabilities were published, many of those with emphasis on organic synthesis and structural properties are cited in ¶[P. 5–6 in 2]. Of interest for analytical chemists are reviews on calixarenes and the structurally related resorcin[n]arenes (or calix[n]resorcarenes) and calixpyrroles concerning potentiometric sensors [9–12], chromo- and fluorophores [13, 14], molecular switches [15], metal ion binding in solution [16–19], redox properties [20] and anion binding [21–24]. Other recent reviews deal with thermodynamic aspects [25], organometallic compounds [26], P-containing calixarenes [27–29], as well as molecular dynamics modeling [30–33]. It is a vital field with over 200 publications per year. Therefore, this article presents only selected results on complexation, solvent extraction and membrane transport with the emphasis on ion and molecular recognition which can be used for analytical purposes, without attempting to cover all available references.     

Dynamic materials fabricated from water soluble pillar[n]arenes bearing triethylene oxide groups

Recent advance on dynamic materials fabricated from water soluble pillar[n]arenes with triethylene oxide groups was summarized.     

Calix[4]arenes as molecules for second order nonlinear optics

Abstract

The synthesis of a novel class of molecules for second order nonlinear optics, i.e. calix[4]arenes with extended π-systems, is described. These compounds are obtained via Wittig-Horner reactions of the formylated calix[4]arenes 5 and 6 to give the stilbene derivatives 7–9, or by diazotization of calix[4]arene, 1, followed by alkylation to give the phenylazocalix[4]arenes 11 and 12. The molecular second order nonlinear optical properties (β_z) of these calix[4]arenes have been measured by electric field-induced second harmonic generation. The influence of different acceptors as well as the influence of the different conformations of the calix[4]arenes on β_z values were determined. Surprisingly, the wavelength of the charge-transfer band λ_max is lower when β_z increases upon increasing the number of acceptors.