Research

10 pages, 4015 KiB

Open AccessArticle

Breaking Azacalix[4]arenes into Induline Derivatives

by Zhongrui Chen, Gabriel Canard, Olivier Grauby, Benjamin Mourot and Olivier Siri

Molecules 2023, 28(24), 8113; https://doi.org/10.3390/molecules28248113 - 15 Dec 2023

Cited by 1 | Viewed by 535

Tetraamino-tetranitro-azacalixarene 5 is at the crossroad of two different families of compounds depending on the conditions and the agent used to reduce the NO₂ groups: (1) azacalixphyrin 7 in neutral medium, or (2) phenazinium of type 8 in acidic medium. The key [...] Read more.

Tetraamino-tetranitro-azacalixarene 5 is at the crossroad of two different families of compounds depending on the conditions and the agent used to reduce the NO₂ groups: (1) azacalixphyrin 7 in neutral medium, or (2) phenazinium of type 8 in acidic medium. The key role of the N-substituted amino functions at the periphery is highlighted by investigating octaaminoazacalixarene as a model compound, and by using the corresponding tetrahydroxy-tetranitro-azacalixarene 15 as a precursor, which behaves differently. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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15 pages, 2555 KiB

Open AccessArticle

Detection of Aromatic Hydrocarbons in Aqueous Solutions Using Quartz Tuning Fork Sensors Modified with Calix[4]arene Methoxy Ester Self-Assembled Monolayers: Experimental and Density Functional Theory Study

by Shofiur Rahman, Mahmoud A. Al-Gawati, Fatimah S. Alfaifi, Wadha Khalaf Alenazi, Nahed Alarifi, Hamad Albrithen, Abdullah N. Alodhayb and Paris E. Georghiou

Molecules 2023, 28(19), 6808; https://doi.org/10.3390/molecules28196808 - 26 Sep 2023

Viewed by 899

Abstract

Quartz tuning forks (QTFs), which were coated with gold and with self-assembled monolayers (SAM) of a lower-rim functionalized calix[4]arene methoxy ester (CME), were used for the detection of benzene, toluene, and ethylbenzene in water samples. The QTF device was tested by measuring the [...] Read more.

Quartz tuning forks (QTFs), which were coated with gold and with self-assembled monolayers (SAM) of a lower-rim functionalized calix[4]arene methoxy ester (CME), were used for the detection of benzene, toluene, and ethylbenzene in water samples. The QTF device was tested by measuring the respective frequency shifts obtained using small (100 µL) samples of aqueous benzene, toluene, and ethylbenzene at four different concentrations (10⁻¹², 10⁻¹⁰, 10⁻⁸, and 10⁻⁶ M). The QTFs had lower limits of detection for all three aromatic hydrocarbons in the 10⁻¹⁴ M range, with the highest resonance frequency shifts (±5%) being shown for the corresponding 10⁻⁶ M solutions in the following order: benzene (199 Hz) > toluene (191 Hz) > ethylbenzene (149 Hz). The frequency shifts measured with the QTFs relative to that in deionized water were inversely proportional to the concentration/mass of the analytes. Insights into the effects of the alkyl groups of the aromatic hydrocarbons on the electronic interaction energies for their hypothetical 1:1 supramolecular host–guest binding with the CME sensing layer were obtained through density functional theory (DFT) calculations of the electronic interaction energies (ΔIEs) using B3LYP-D3/GenECP with a mixed basis set: LANL2DZ and 6-311++g(d,p), CAM-B3LYP/LANL2DZ, and PBE/LANL2DZ. The magnitudes of the ΔIEs were in the following order: [Au4-CME⊃[benzene] > [Au4-CME]⊃[toluene] > [Au4-CME]⊃[ethylbenzene]. The gas-phase BSSE-uncorrected ΔIE values for these complexes were higher, with values of −96.86, −87.80, and −79.33 kJ mol⁻¹, respectively, and −86.39, −77.23, and −67.63 kJ mol⁻¹, respectively, for the corresponding BSSE-corrected values using B3LYP-D3/GenECP with LANL2dZ and 6-311++g(d,p). The computational findings strongly support the experimental results, revealing the same trend in the ΔIEs for the proposed hypothetical binding modes between the tested analytes with the CME SAMs on the Au-QTF sensing surfaces. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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13 pages, 3945 KiB

Open AccessArticle

Hexahexyloxycalix[6]arene, a Conformationally Adaptive Host for the Complexation of Linear and Branched Alkylammonium Guests

by Veronica Iuliano, Carmen Talotta, Paolo Della Sala, Margherita De Rosa, Annunziata Soriente, Placido Neri and Carmine Gaeta

Molecules 2023, 28(12), 4749; https://doi.org/10.3390/molecules28124749 - 13 Jun 2023

Viewed by 706

Abstract

Hexahexyloxycalix[6]arene 2b leads to the endo-cavity complexation of linear and branched alkylammonium guests showing a conformational adaptive behavior in CDCl₃ solution. Linear n-pentylammonium guest 6a⁺ induces the cone conformation of 2b at the expense of the 1,2,3-alternate, which is [...] Read more.

Hexahexyloxycalix[6]arene 2b leads to the endo-cavity complexation of linear and branched alkylammonium guests showing a conformational adaptive behavior in CDCl₃ solution. Linear n-pentylammonium guest 6a⁺ induces the cone conformation of 2b at the expense of the 1,2,3-alternate, which is the most abundant conformer of 2b in the absence of a guest. In a different way, branched alkylammonium guests, such as tert-butylammonium 6b⁺ and isopropylammonium 6c⁺, select the 1,2,3-alternate as the favored 2b conformation (6b⁺/6c⁺⊂2b^1,2,3-alt), but other complexes in which 2b adopts different conformations, namely, 6b⁺/6c⁺⊂2b^cone, 6b⁺/6c⁺⊂2b^paco, and 6b⁺/6c⁺⊂2b^1,2-alt, have also been revealed. Binding constant values determined via NMR experiments indicated that the 1,2,3-alternate was the best-fitting 2b conformation for the complexation of branched alkylammonium guests, followed by cone > paco > 1,2-alt. Our NCI and NBO calculations suggest that the H-bonding interactions (⁺N–H···O) between the ammonium group of the guest and the oxygen atoms of calixarene 2b are the main determinants of the stability order of the four complexes. These interactions are weakened by increasing the guest steric encumbrance, thus leading to a lower binding affinity. Two stabilizing H-bonds are possible with the 1,2,3-alt- and cone-2b conformations, whereas only one H-bond is possible with the other paco- and 1,2-alt-2b stereoisomers. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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13 pages, 4449 KiB

Open AccessArticle

A Combined Solution and Solid-State Study on the Tautomerism of an Azocalix[4]arene Chromoionophore

by Laura Baldini, Davide Balestri, Luciano Marchiò and Alessandro Casnati

Molecules 2023, 28(12), 4704; https://doi.org/10.3390/molecules28124704 - 12 Jun 2023

Cited by 1 | Viewed by 786

Abstract

Azocalixarenes functionalized with cation binding sites are popular chromoionophores due to the ease of synthesis and the large complexation-induced shifts of their absorption band that originate from an azo-phenol–quinone-hydrazone tautomerism. Despite their extensive use, however, a thorough investigation of the structure of their [...] Read more.

Azocalixarenes functionalized with cation binding sites are popular chromoionophores due to the ease of synthesis and the large complexation-induced shifts of their absorption band that originate from an azo-phenol–quinone-hydrazone tautomerism. Despite their extensive use, however, a thorough investigation of the structure of their metal complexes has not been reported. We describe herein the synthesis of a new azocalixarene ligand (2) and the study of its complexation properties with the Ca²⁺ cation. Through a combination of solution (¹H NMR and UV-vis spectroscopies) and solid-state (X-ray diffractometry) techniques, we demonstrate that metal complexation induces a shift of the tautomeric equilibration towards the quinone-hydrazone form, while deprotonation of the complex results in the reversion to the azo-phenol tautomer. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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15 pages, 5571 KiB

Open AccessArticle

Critical Analysis of Association Constants between Calixarenes and Nitroaromatic Compounds Obtained by Fluorescence. Implications for Explosives Sensing

by Alexandre S. Miranda, Paula M. Marcos, José R. Ascenso, Mário N. Berberan-Santos, Peter J. Cragg, Rachel Schurhammer and Christophe Gourlaouen

Molecules 2023, 28(7), 3052; https://doi.org/10.3390/molecules28073052 - 29 Mar 2023

Cited by 1 | Viewed by 1130

Abstract

The binding behaviour of two ureido-hexahomotrioxacalix[3]arene derivatives bearing naphthyl (1) and pyrenyl (2) fluorogenic units at the lower rim towards selected nitroaromatic compounds (NACs) was evaluated. Their affinity, or lack of it, was determined by UV-Vis absorption, fluorescence and [...] Read more.

The binding behaviour of two ureido-hexahomotrioxacalix[3]arene derivatives bearing naphthyl (1) and pyrenyl (2) fluorogenic units at the lower rim towards selected nitroaromatic compounds (NACs) was evaluated. Their affinity, or lack of it, was determined by UV-Vis absorption, fluorescence and NMR spectroscopy. Different computational methods were also used to further investigate any possible complexation between the calixarenes and the NACs. All the results show no significant interaction between calixarenes 1 and 2 and the NACs in either dichloromethane or acetonitrile solutions. Moreover, the fluorescence quenching observed is only apparent and merely results from the absorption of the NACs at the excitation wavelength (inner filter effect). This evidence is in stark contrast with reports in the literature for similar calixarenes. A naphthyl urea dihomooxacalix[4]arene (3) is also subject to the inner filter effect and is shown to form a stable complex with trinitrophenol; however, the equilibrium association constant is greatly overestimated if no correction is applied (9400 M⁻¹ vs 3000 M⁻¹), again stressing the importance of taking into account the inner filter effect in these systems. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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17 pages, 5622 KiB

Open AccessArticle

Calix[4]arene Derivative for Iodine Capture and Effect on Leaching of Iodine through Packaging

by Loredana Ferreri, Marco Rapisarda, Melania Leanza, Cristina Munzone, Nicola D’Antona, Grazia Maria Letizia Consoli, Paola Rizzarelli and Emanuela Teresa Agata Spina

Molecules 2023, 28(4), 1869; https://doi.org/10.3390/molecules28041869 - 16 Feb 2023

Cited by 1 | Viewed by 1560

Abstract

A hydrophobic calix[4]arene derivative was investigated for its iodine (I₂) capture efficiency from gaseous and liquid phase. The iodine uptake was followed by UV-vis spectroscopy. Additionally, the influence of the calix[4]arene derivative–polyolefin system on the leaching of iodine through packaging from [...] Read more.

A hydrophobic calix[4]arene derivative was investigated for its iodine (I₂) capture efficiency from gaseous and liquid phase. The iodine uptake was followed by UV-vis spectroscopy. Additionally, the influence of the calix[4]arene derivative–polyolefin system on the leaching of iodine through packaging from a povidone-iodine-based (PVP-I) formulation was evaluated. In fact, iodine is a low-cost, multi-target, and broad-spectrum antiseptic. However, it is volatile, and the extended storage of I₂-based formulations is challenging in plastic packaging. Here, we investigated the possibility of reducing the loss of I₂ from an iodophor formulation by incorporating 4-tert-butylcalix [4]arene-tetraacetic acid tetraethyl ester (CX) and its iodine complex in high-density polyethylene (HDPE) or polypropylene (PP) via a swelling procedure. Surface and bulk changes were monitored by contact angle, thermogravimetric analysis (TGA), and UV-vis diffuse reflectance spectra. The barrier effect of the different polymeric systems (embedded with CX, iodine-CX complex, or I2) was evaluated by monitoring the I2 retention in a buffered PVP-I solution by UV-vis spectroscopy. Overall, experimental data showed the capability of the calix[4]arene derivative to complex iodine in solution and the solid state and a significant reduction in the iodine leaching by the PP-CX systems. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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11 pages, 2296 KiB

Open AccessArticle

New Supramolecular Hypoxia-Sensitive Complexes Based on Azo-Thiacalixarene

by Farida Galieva, Mohamed Khalifa, Zaliya Akhmetzyanova, Diana Mironova, Vladimir Burilov, Svetlana Solovieva and Igor Antipin

Molecules 2023, 28(2), 466; https://doi.org/10.3390/molecules28020466 - 04 Jan 2023

Cited by 4 | Viewed by 1429

Abstract

Hypoxia accompanies many human diseases and is an indicator of tumor aggressiveness. Therefore, measuring hypoxia in vivo is clinically important. Recently, complexes of calix[4]arene were identified as potent hypoxia markers. The subject of this paper is new hypoxia-sensitive host–guest complexes of thiacalix[4]arene. We [...] Read more.

Hypoxia accompanies many human diseases and is an indicator of tumor aggressiveness. Therefore, measuring hypoxia in vivo is clinically important. Recently, complexes of calix[4]arene were identified as potent hypoxia markers. The subject of this paper is new hypoxia-sensitive host–guest complexes of thiacalix[4]arene. We report a new high-yield synthesis method for thiacalix[4]arene with four anionic carboxyl azo fragments on the upper rim (thiacalixarene L) and an assessment of the complexes of thiacalixarene L with the most widespread cationic rhodamine dyes (6G, B, and 123) sensitivity to hypoxia. Moreover, 1D and 2D NMR spectroscopy data support the ability of the macrocycles to form complexes with dyes. Rhodamines B and 123 formed host–guest complexes of 1:1 stoichiometry. Complexes of mixed composition were formed with rhodamine 6G. The association constant between thiacalixarene L and rhodamine 6G is higher than for other dyes. Thiacalixarene L-dye complexes with rhodamine 6G and rhodamine B are stable in the presence of various substances present in a biological environment. The UV-VIS spectrometry and fluorescence showed hypoxia responsiveness of the complexes. Our results demonstrate that thiacalixarene L has a stronger binding with dyes compared with the previously reported azo-calix[4]arene carboxylic derivative. Thus, these results suggest higher selective visualization of hypoxia for the complexes with thiacalixarene L. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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14 pages, 2390 KiB

Open AccessArticle

The Formation of Inherently Chiral Calix[4]quinolines by Doebner–Miller Reaction of Aldehydes and Aminocalixarenes

by Martin Tlustý, Václav Eigner, Hana Dvořáková and Pavel Lhoták

Molecules 2022, 27(23), 8545; https://doi.org/10.3390/molecules27238545 - 04 Dec 2022

Cited by 1 | Viewed by 1483

Abstract

The formation of inherently chiral calix[4]arenes by the intramolecular cyclization approach suffers from a limited number of suitable substrates for these reactions. Here, we report an easy way to prepare one class of such compounds: calixquinolines, which can be obtained by the reaction [...] Read more.

The formation of inherently chiral calix[4]arenes by the intramolecular cyclization approach suffers from a limited number of suitable substrates for these reactions. Here, we report an easy way to prepare one class of such compounds: calixquinolines, which can be obtained by the reaction of aldehydes with easily accessible aminocalix[4]arenes in acidic conditions (Doebner–Miller reaction). The synthetic procedure represents a very straightforward approach to the inherently chiral macrocyclic systems. The complexation studies revealed the ability of these compounds to complex quaternary ammonium salts with different stoichiometries depending on the guest molecules. At the same time, the ability of enantioselective complexation of chiral N-methylammonium salts was demonstrated. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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13 pages, 2038 KiB

Open AccessArticle

Electronic Tuning of Host-Guest Interactions within the Cavities of Fluorophore-Appended Calix[4]arenes

by Varun Rawat and Arkadi Vigalok

Molecules 2022, 27(17), 5689; https://doi.org/10.3390/molecules27175689 - 03 Sep 2022

Cited by 1 | Viewed by 1134

Abstract

A series of fluorescent calix[4]arene scaffolds bearing electron-rich carbazole moiety conjugated at the lower rim have been prepared. Studies of the fluorescence quenching in the presence of the N-methyl pyridinium guest revealed that the electronic properties of the distal phenolic ring play a [...] Read more.

A series of fluorescent calix[4]arene scaffolds bearing electron-rich carbazole moiety conjugated at the lower rim have been prepared. Studies of the fluorescence quenching in the presence of the N-methyl pyridinium guest revealed that the electronic properties of the distal phenolic ring play a major role in the host–guest complexation. In particular, placing an electron-donating piperidine fragment at that ring significantly increased the host–guest interactions, while introducing the same fragment into the proximal phenolic ring weakened the fluorescence response. These results suggest that the dominant interactions between the guest and calixarene cavity involve the oxygen-depleted fluorophore-bearing aromatic ring and not the more electron-rich unsubstituted phenolic fragments. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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16 pages, 3165 KiB

Open AccessArticle

Anion Binding by Fluorescent Ureido-Hexahomotrioxacalix[3]arene Receptors: An NMR, Absorption and Emission Spectroscopic Study

by Alexandre S. Miranda, Paula M. Marcos, José R. Ascenso, Mário N. Berberan-Santos and Filipe Menezes

Molecules 2022, 27(10), 3247; https://doi.org/10.3390/molecules27103247 - 19 May 2022

Cited by 6 | Viewed by 1453

Abstract

Fluorescent receptors (4a–4c) based on (thio)ureido-functionalized hexahomotrioxacalix[3]arenes were synthesised and obtained in the partial cone conformation in solution. Naphthyl or pyrenyl fluorogenic units were introduced at the lower rim of the calixarene skeleton via a butyl spacer. The binding [...] Read more.

Fluorescent receptors (4a–4c) based on (thio)ureido-functionalized hexahomotrioxacalix[3]arenes were synthesised and obtained in the partial cone conformation in solution. Naphthyl or pyrenyl fluorogenic units were introduced at the lower rim of the calixarene skeleton via a butyl spacer. The binding of biologically and environmentally relevant anions was studied with NMR, UV–vis absorption, and fluorescence titrations. Fluorescence of the pyrenyl receptor 4c displays both monomer and excimer fluorescence. The thermodynamics of complexation was determined in acetonitrile and was entropy-driven. Computational studies were also performed to bring further insight into the binding process. The data showed that association constants increase with the anion basicity, and AcO⁻, BzO⁻ and F⁻ were the best bound anions for all receptors. Pyrenylurea 4c is a slightly better receptor than naphthylurea 4a, and both are more efficient than naphthyl thiourea 4b. In addition, ureas 4a and 4c were also tested as ditopic receptors in the recognition of alkylammonium salts. Full article

(This article belongs to the Special Issue Calixarene Complexes: Synthesis, Properties and Applications II)

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