Arene In Solution Research Articles

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The cover image is based on the Research Article Reaction of hydroxyl radical with arenes in solution—On the importance of benzylic hydrogen abstraction by Abygail R. Waggoner, Yahya Abdulrahman, Alexis J. Iverson, Ethan P. Gibson, Mark A. Buckles and James S. Poole, https://doi.org/10.1002/poc.4278.

Saucer[n]arenes: Synthesis, Structure, Complexation, and Guest‐Induced Circularly Polarized Luminescence Property

AbstractMacrocycles denoted as saucer[n]arenes (n=4,5) were easily synthesized by the one‐pot condensation of 2,7‐dimethoxynaphthalene (2,7‐DMN) and paraformaldehyde in the presence of TFA or catalytic BF3⋅OEt2. With 1,1‐dimethylpiperidin‐1‐ium as the template, saucer[4]arene was selectively obtained. Crystal structures show that saucer[n]arenes are all composed of 2,7‐DMN moiety bridged by the methylene groups at 1,6‐positions: all of the 7‐methoxy groups lie on one face, and all of the 2‐methoxy groups lie on the other. Saucer[n]arenes exhibit strong fluorescence properties with the quantum yields of 19.6 % and 23.4 %. They form 1:1 complexes with ammonium salts in both solution and solid state (association constant up to 105 M−1 in CDCl3). Chiral quaternary ammonium salts can induce the chirality of the dynamically racemic inherently chiral saucer[n]arenes in solution, and thus show mirror‐imaged circular dichroism signals and circularly polarized luminescence (CPL) properties.

Saucer[n]arenes: Synthesis, Structure, Complexation, and Guest-Induced Circularly Polarized Luminescence Property.

Macrocycles denoted as saucer[n]arenes (n=4,5) were easily synthesized by the one-pot condensation of 2,7-dimethoxynaphthalene (2,7-DMN) and paraformaldehyde in the presence of TFA or catalytic BF3 ⋅OEt2 . With 1,1-dimethylpiperidin-1-ium as the template, saucer[4]arene was selectively obtained. Crystal structures show that saucer[n]arenes are all composed of 2,7-DMN moiety bridged by the methylene groups at 1,6-positions: all of the 7-methoxy groups lie on one face, and all of the 2-methoxy groups lie on the other. Saucer[n]arenes exhibit strong fluorescence properties with the quantum yields of 19.6 % and 23.4 %. They form 1:1 complexes with ammonium salts in both solution and solid state (association constant up to 105 M-1 in CDCl3 ). Chiral quaternary ammonium salts can induce the chirality of the dynamically racemic inherently chiral saucer[n]arenes in solution, and thus show mirror-imaged circular dichroism signals and circularly polarized luminescence (CPL) properties.

Reaction of hydroxyl radical with arenes in solution—On the importance of benzylic hydrogen abstraction

AbstractThe regioselectivity of hydroxyl radical reactions with alkylarenes was investigated using a nuclear magnetic resonance (NMR)‐based methodology capable of trapping and quantifying addition and hydrogen abstraction products of the initial elementary step of the oxidation process. Abstraction products are relatively minor components of the product mixtures (15–30 mol%), depending on the magnitude of the overall rate coefficient and the number of available hydrogens. The relative reactivity of addition at a given position on the ring depends on its relation to the methyl substituents on the hydrocarbons under study. The reactivity enhancements for disubstituted and trisubstituted rings are approximately additive under the conditions of this study.

New terpyridine derivatives of thiacalix[4]arenes in solution and at the water-air interface

New di- and tetrasubstituted thiacalix[4]arenes in cone and 1,3-alternate configurations containing terpyridine and triazole fragments at the lower rim of the macrocycle, as well as model triazole-terpyridine, are synthesized. The structures and purity of the compounds are confirmed by NMR spectroscopy and high-resolution MALDI mass spectrometry. The compounds form luminescent complexes with lanthanide cations (europium and terbium) in a chloroform-methanol (10: 1) system during fluorimetric titration. The possibility of antenna ef ect during fluorescence sensitization in lanthanides by the thiacalixarene ligands is demonstrated. Successful immobilization of the terpyridine receptors on a solid substrate makes it possible to consider the Langmuir-Blodgett films on the basis of these receptors as promising adsorbents of lanthanide from nonaqueous media or organic salts and also provides new opportunities for the investigation of the luminescence characteristics of lanthanide complexes in thin films.

Physicochemical and Ion-Sensing Properties of Benzofurazan-Appended Calix[4]arene in Solution and on Gold Nanoparticles: Spectroscopy, Microscopy, and DFT Computations in Support of the Species of Recognition.

A calix[4]arene conjugate (L) functionalized at the lower rim with a benzofurazan fluorophore (NBD) and at the upper rim with a thioether moiety has been synthesized and characterized by 1H NMR, 13C NMR, and mass spectrometry techniques. Both the absorption and emission spectral data for L in different solvents exhibited progressive changes with an increase in polarity. Ion recognition studies were performed by absorption and fluorescence spectroscopy using 10 different metal ions. Among these, Hg2+ exhibited greater changes in these spectra, whereas Cu2+ showed only significant changes and all other ions showed no change in the spectral features. Although the Hg2+ has dominant influence on the spectral features and provides a detection limit of 56.0 ± 0.6 ppb, the selectivity was hampered because of the presence of the derivatizations present on both the rims of L for ion interaction in solution. Therefore, L was immobilized onto gold nanoparticles (AuNPL’s) so that the upper rim derivatizations anchor onto the gold surface through Au–S interactions, and this leaves out only the lower rim NBD derivatization for interaction with ions selectively. The AuNPL’s were characterized by transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses. The surface characteristics were analyzed by contact angle measurements. The AuNPL’s exhibit greater selectivity and enhanced sensitivity for Hg2+ ions with a lowest detection limit of 48.0 ± 0.8 ppb. The immobilization of L onto AuNPs was reflected in the corresponding fluorescence lifetime values, and the addition of Hg2+ to either L or AuNPL showed fluorescence quenching. The reversible recognition of Hg2+ by L was demonstrated by titrating L or AuNPL with Hg2+ followed by tetra-butyl ammonium iodide for several cycles. The structural features of Hg2+-bound species were demonstrated by density functional theory computations and were supported by the XPS data. The Hg2+ induces aggregated fibrillar morphology into supramolecular L, as demonstrated by microscopy when Hg2+ was added either to L or to AuNPL, supporting aggregation-caused quenching.

Photophysical and conformation properties of luminescent-labeled star poly-2-isopropyl-2-oxazolines based on octa-tert-butylcalix[8]arene in solution

The synthesis of luminescent-labeled copolymers of octa-tert-butylcalix[8]arene with 8 poly-2-isopropyl-2-oxazoline arms is carried out. Each macromolecule involves one luminescent label of the anthracene structure located at the end of one of the arms. The luminescent properties of the copolymers in water and methanol are studied. It is shown that, in aqueous solutions, the formation of intermolecular aggregates with a hydrophobic core and a hydrophilic shell results in a new photophysical process of migration of electron excitation energy accompanied by a decrease in the solution luminescence polarization. The interaction of oxazoline arms with poly(methacrylic acid) via the mechanism of interpolymer complex formation implies a weakening of the efficiency of energy migration.

Conformational diversity and dynamics of distally disubstituted calix and thiacalix[4]arenes in solution

According to the quantum chemical calculations and Dynamic NMR experiments in the distally disubstituted classical and thiacalix[4]arenes (CCA and TCA) in addition to the C2v symmetrical pinched cone (PC) conformation, the distorted cone (DC) form with an approximate Cs overall symmetry (with two OH groups bonded to one oxygen atom) also corresponds to the energy minimum. Moreover, in DC form, two different mutual orientations of O–R groups at a lower rim lead to two stable conformations: the first - with both these groups directed outward, the second - with both these groups pointing toward the same direction. In CCA, the PC is essentially favoured over the DC, while in TCA, energies of these forms are similar or the latter may be even preferable. Copyright © 2013 John Wiley & Sons, Ltd.

Absorption spectrophotometric, NMR and theoretical investigations on ground state non-covalent interaction of C60 and C70 with a designed trihomocalix[6]arene in solution

The present paper reports the spectroscopic investigations on non-covalent interaction of fullerenes C60 and C70 with a designed trihomocalix[6]arene (2) in toluene. UV–vis studies reveal appreciable ground state interaction between fullerenes and 2. Jobs method of continuous variation establishes 1:1 stoichiometry for fullerene–2 complexes. Binding constant (K) data reveals that 2 binds C70 more strongly compared to C60, i.e. KC60–2=47,540dm3mol−1 and KC70–2=86,360dm3mol−1. Proton NMR studies provide very good support in favor of strong binding between C70 and 2. Estimation of solvent reorganization energy (RS) evokes that C70–2 complex is stabilized more compared to C60–2 complex as RS(C60–2)=−1.162eV and RS(C70–2)=−1.244eV. Semiempirical calculations at third parametric level of theory in vacuo evoke the single projection structures of the fullerene–2 complexes and interpret the stability difference between C60 and C70 complexes of 2 in terms of enthalpies of formation values.

The role of preorganization of hydrazone moieties on tetrathiacalix[4]arene platform for their conformational and binding properties from the view of structural investigation

The IR, 1H and 13C NMR data, as well as conformation and dynamic behaviour of tetrathiacalix[4]arenes functionalized by hydrazone fragments are reported. The influence of isomers of thiacalix[4]arenes, the removal of tert-butyl groups from upper rim of macrocycle and the replacement of a phenyl substituents in the hydrazone fragments by 2-pyridyl ones on conformational properties of the compounds are discussed. The structural peculiarities of the cone isomer of 25,26,27,28-tetrakis[N 2-(2-pyridinylmethylidene)hydrazinocarbonylmethyloxy]-2,8,14,20-tetrathiacalix[4]arene and the 1, 3-alternate isomer of 25,26,27,28-tetrakis[N 2-(benzylidene)hydrazinocarbonylmethyloxy]-2,8,14,20-tetrathiacalix[4]arene in solution are compared with their crystal structures obtained by X-ray analysis. The correlation between extraction efficiency data obtained for these compounds earlier and the conformational features of calix[4]arene hydrazone derivatives studied in this work was performed.

Absorption Spectrophotometric, NMR and Quantum Chemical Investigations of Ground State Non-Covalent Interactions between Fullerenes and a Designed Trihomocalix[6]arene in Solution

Ground state non-covalent interactions between a newly designed macrocyclic 1,3,5-trihomo calix[6]arene receptor, designated as 1, and the C60 and C70 fullerenes have been studied in toluene solutions. It was observed that the absorbances of both C60 and C70 solutions increased upon the addition of increasing concentrations of compound 1. Job’s method of continuous variation established 1:1 stoichiometry for these fullerene-1 complexes. The binding constant (K) data reveal that compound 1 binds to C70 more strongly compared to C60, i.e., \(K_{C60\mbox{-}\boldsymbol{1}} = 230~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1}\) and \(K_{C70\mbox{-}\boldsymbol{1}}= 517~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1}\). Proton NMR analysis provides very good support for strong binding between C70 and 1. Estimations of the solvent reorganization energy (RS) suggest that the C70-1 complex is stabilized more than the corresponding C60-1 complex, with \(R_{S(C60\mbox{-}\boldsymbol{1})} = -1.970~\mathrm{eV}\) and \(R_{S(C70\mbox{-}\boldsymbol{1})}= -2.300~\mathrm{eV}\). Molecular mechanics force field method calculations established that the binding pattern of C70 towards 1 occurs in the side-on rather than end-on orientation, and that the C70-1 complex gains 5.23 kJ⋅mol−1 of extra stabilization energy with this side-on geometrical arrangement.

Encapsulated or Not Encapsulated? Mapping Alcohol Sites in Hexameric Capsules of Resorcin[4]arenes in Solution by Diffusion NMR Spectroscopy

Encapsulated or Not Encapsulated? Mapping Alcohol Sites in Hexameric Capsules of Resorcin[4]arenes in Solution by Diffusion NMR Spectroscopy

Encapsulated or Not Encapsulated? Mapping Alcohol Sites in Hexameric Capsules of Resorcin[4]arenes in Solution by Diffusion NMR Spectroscopy

Knock, knock! Despite the similar high-field 1H NMR spectra of different alcohols in the presence of hexameric capsules of resorcin[4]arenes, diffusion NMR spectroscopy showed that only some of these alcohols are truly encapsulated in the hexameric capsules, whereas other alcohols are part of the hexameric structure of the capsules (see schematic representation; R=C11H23).

Experimental evidence for interactions between anions and electron-deficient aromatic rings

This feature article summarizes our research aimed at using electron-deficient aromatic rings to bind anions in the context of complementary research in this active field. Particular attention is paid to the different types of interactions exhibited between anions and electron-deficient arenes in solution. The 120+ references cited in this article underscore the flurry of recent activity by numerous researchers in this field, which was relatively nascent when our efforts began in 2005. While the interaction of anions with electron-deficient aromatic rings has recently garnered much attention by supramolecular chemists, the observation of these interactions is not a recent discovery. Therefore, we begin with a historical perspective on early examples of anions interacting with electron-deficient arenes. An introduction to recent (and not so recent) computational investigations concerning anions and electron-deficient aromatic rings as well as a brief structural survey of crystalline examples of this interaction are provided. Finally, the limited solution-based observations of anions interacting with electron-deficient aromatic rings are summarized to introduce our current investigations in this area. We highlight three different systems from our lab where anion-arene interactions have been investigated. First, we show that tandem hydrogen bonds and anion-arene interactions augment halide binding in solution. Second, a crystallographic and computational study highlights the multiple types of interactions possible between anions and electron-deficient arenes. Third, we summarize the first example of a class of designed receptors that emphasize the different types of anion-arene interactions possible in solution.

The conformation and dynamic behaviour of tetrathiacalix[4]arenes functionalized by hydrazide and hydrazone groups

The 1H, 13C and 15N NMR data, conformation and dynamic behaviour of the new tetrathiacalix[4]arenes functionalized by hydrazide and hydrazone groups are reported and compared with the result of earlier investigations of 4- tert-butylphenoxyacetylhydrazones. The unusual fact of formation of N, N′-diacetylhydrazine bridge and factors leading to its formation in the cone conformer of calixarene has been discussed. The barriers of rotation of hydrazone fragments of tetrathiacalix[4]arenes were determined by NMR-measurements at various temperatures. The structure of 1,3- alternate conformer of 5,11,17,23-tetra- tert-butyl-25,26,27,28-tetrakis[hydrazinocarbonylmethyl]-2,8,14,20-tetrathiacalix[4]arene in solution is compared with crystal structure obtained by the X-ray analysis.

Frozen 1,3-Alternate Conformation of Exhaustively Methylated Azacalix[4]arene in Solution: Successful Immobilization by Small but yet Sufficiently Bulky O-Methyl Group

Abstract Conformational flexibility of exhaustively methylated azacalix[4]arene in solution has been investigated. Relaxation time measurements revealed that its 1,3-alternate conformation was inflexible even in solution. Intramolecular small annulus plays a central role in suppressing the conformational inversion by the small but yet sufficiently bulky O-methyl groups. Without regard to the small anulus, the azacalix[4]arene has a room to selectively accommodate potassium ion in the cavity.

Lanthanide complexation with CMPO and CMPO-calix[4]arenes in solution: Spectrophotometric and electrospray mass spectrometric approaches

The binding of lanthanide(III) cations with organophosphorous ligands like CMPO and related calix[4]arene-based derivatives have been investigated using two experimental methods. The stability constants of the lanthanum, europium and ytterbium complexes were first determined in methanol by UV absorption spectrophotometry in the presence of nitrate or chloride anions. The results showed that the stoichiometry and the stability of the complexes formed depend on the position of the CMPO moieties either on the wide or the narrow rim of the calixarene scaffold, the nature of the medium, the conformational mobility of the ligands. Complexation of lanthanum was also followed by ESI-mass spectrometry in the same solvent. This method confirmed the stoichiometry of the complexes, giving also structural information, like coordination of anion or solvent molecules to the complexes, and allowed the calculation of distribution curves in good agreement with those derived from the spectrophotometric results. This is an important result showing that ESI-MS can be used to provide with quantitative information when absorption spectrophotometry is not applicable, i.e. for systems where complexation leads to weak spectral changes.

Regioselective Synthesis and Inclusion Properties of distal-Bis[(2-pyridylmethyl) oxy]tetrathiacalix[4]arenes

Regioselective synthesis of bis[(2-pyridylmethyl)oxy]tetrathiacalix[4]arenes was accomplished by a protection–deprotection method using benzyl groups as a protecting group. The conformational studies of distal-bis[(2-pyridylmethyl)oxy]thiacalix[4]arenes in solution and solid state are described. The two-phase solvent extraction data indicated that bis[(2-pyridylmethyl)oxy]tetrathiacalix[4]arenes show strong Ag+ (E%, 97%) affinity. In contrast, no significant E% is observed for K+. A good Job plots proves 1:1 coordination of 1,3-alternate-3 with Ag+ cation. 1H-NMR Titration of 1,3-alternate-3 with AgSO3CF3 also clearly demonstrates that a 1:1 complex is formed with retention of the original symmetry. The conformational changes of pyridine moiety from the original outward orientation of the ring nitrogen to the inside orientation toward the thiacalixarene cavity were observed in the process of Ag+ complexation. The down-field shifts of the benzene protons of the benzyl group were also observed and attributed to the conformational deviation from the original face to face overlapping.

New materials based on tubular nanodimensional structures 1. Synthesis, structural studies and determination of interproton distances in solutions of functionalized thiacalix[4]arenes according to NMR spectroscopic data (NOESY)

New derivatives of p-tert-butylthiacalix[4]arene were synthesized. The conformation of the macrocycles and interproton distances in the synthesized thiacalix[4]arenes in solutions were determined by NMR spectroscopy. p-tert-Butylthiacalix[4]arene distally disubstituted at the lower rim adopts the cone conformation, and the tetrasubstituted products are formed in the 1,3-alternate conformation.

The use of a lyotropic liquid-crystalline medium and residual dipolar coupling constants for determination of the spatial structure of thiacalix[4]arenes in solutions

The possibility of using an approach for the elucidation of the spatial structure of functionalized thiacalix[4]arenes based on the determination the residual dipolar coupling constants between the 1H and 13C nuclei separated by one chemical bond (1 D CH) in lyotropic liquid-crystalline media (poly-γ-benzyl-L-glutamate and CDCl3) is demonstrated for the first time. This approach was used to distinguish between the cone and 1,3-alternate conformations of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-oxopropyloxy)-2,8,14,20-tetrathiacalix[4]arene. The results were confirmed by the data from 2D NMR (1H—1H) NOESY experiments for these compounds in an isotropic solvent (CDCl3).