New artificial receptors from selectively functionalized calix[4]arenes

Abstract

The development of new synthetic methods for the monoalkylation of calix[4]arenes at the lower rim allows the synthesis of a new class of trihydroxamate siderophores. Three chelating hydroxamic acid units are introduced through a sequence of reactions which blocks the macrocycle in the cone conformation. The new ligands obtained form neutral 1:1 complexes (FeL) with iron (III), which are stable in EtOH/H₂O 9:1 at pH 2–7. Calix[4]arene bis-crown ethers are prepared by exploiting the selective 1,2-(proximal) functionalization of calix[4]arenes at the lower rim. These ligands are, however, less effective in complexing alkali metal cations compared with the 1,3-calix[4]arene crown-ethers which, in their partial cone structure, offer a better shielding for the complexed cations. Rigid upper rim-bridged calix[4]arenes potentially useful for the inclusion of neutral molecules are prepared by exploiting the selective 1,3-diformylation of calix[4]arene at the upper rim. Finally a new chloromethylation method for calix[4]arenes blocked in the cone conformation is described together with the synthesis of new cavitands.     

The enhancement of luminescent properties of Tb3+ complexes with tetra-1,3-diketone ligands promoted by the tetrathiacalix[4]arene scaffold

This is the first report on the synthesis and characterization of tetra-1,3-diketone derivatives of tetrthia- and calix[4]arenes substituted by acetylacetonyl or dipivaloylmethanyl moieties at the upper rim and bearing hydroxyl groups at the lower rim as ligands for Tb³⁺ complexes. The spatial structure and tautomeric content for the synthesized ligands have been determined by means of X-ray, IR and NMR spectroscopy. Comparison of the sensitizing properties of tetrathiacalix[4]arenes and their calix[4]arene analogues on the Tb³⁺-centered luminescence in DMF solutions has been performed. A substantial enhancement of the luminescent properties of Tb³⁺- complexes with tetra-1,3-diketone ligands promoted by the tetrathiacalix[4]arene scaffold was established.     

Preorganization of diglycolamides on the calix[4]arene platform and its effect on the extraction of Am(III)/Eu(III)

Different diglycolamide (DGA)-substituted calix[4]arene-based extractants were synthesized and evaluated for the extraction of Am(III) and Eu(III), representative trivalent actinide and lanthanide ions, respectively. On the narrow rim of the calix[4]arene platform, the DGA moiety was either 1,3-di- or tetrasubstituted with a varying spacer length between the oxygen and amide nitrogen atom. In addition, DGA groups were appended both to the wide rim and to both rims of calix[4]arenes and their efficiencies were compared for Am(III) and Eu(III) extraction at three different feed acidities. The extraction and separation efficiencies strongly depended on the N-alkyl substituent as well as the spacer length. 1,3-Di-DGA-substituted calix[4]arenes are inferior extractants to the corresponding tetra-DGA-substituted ones. Narrow rim DGA-functionalized derivatives resulted in high extraction efficiencies, while the wide rim DGA-functionalized calix[4]arenes showed practically no extraction.     

Stilbene-bridged 1,3-alternate calix[4]arene crown ether for selective alkali ion extraction

A series of stilbene-bridged calix[4]arenes was synthesized through an intramolecular reductive McMurry coupling of bisbenzaldehyde calix[4]arene in high yields. Tetra- and pentaethylene glycol chains were tethered to the phenolic groups of calix[4]arene to form stilbene-bridged calix[4]arene crown-5 and crown-6, respectively. The presence of stilbene bridge over the calix[4]arene rim effectively prevented the connection of the polyether chains in the cone conformation resulting in the exclusive formation of 1,3-alternate stilbene-bridged calix[4]arene crown product. Compared to the cone analogues, the 1,3-alternate calix[4]arene crown ethers showed a greater extraction ability and selectivity toward Cs⁺.     

Synthesis, structure, and properties of nitronyl nitroxyl tetraradical with calix[4]arene framework

A reaction of calix[4]arene tetraaldehyde with 2,3-bis(hydroxyamino)-2,3-dimethylbutane in DMF resulted in the corresponding 1,3-dihydroxyimidazolidine tetraadduct, whose oxidation gave a calix[4]arene (1,3-alternate) bearing four nitronyl nitroxyl-containing substituents at the upper rim.     

上端含长链烷基的手性杯[4]芳烃合成

脱叔丁基的杯[4]芳烃与长链的叔醇或者叔氯代烷烃进行傅-克反应, 在其上端引入长链烷基. 然后在下端引入光学活性的1-苯基乙胺基团, 得到了一系列上端含长链烷基的手性杯[4]芳烃.     

The selective preparation of partial cone O-aryl calix[4]arene ethers from 1,3-dimethoxycalix[4]arene: a new platform for the preparation of non-aggregated dyes

We report a new direct route for the selective preparation of novel partial cone O-aryl ether calix[4]arenes to be used as new platforms for the preparation of non-aggregated dyes. These partial cone conformers have the aromatic substituents lying within the calix[4]arene annulus via the upper rim.     

Fourfold tetraurea calix[4]arenes--potential cores for the formation of self-assembled dendrimers

Wide rim tetraurea calix[4]arenes monofunctionalized at the narrow rim by COOH or NH2 have been synthesized in five steps from t-butylcalix[4]arene tripropylether. Their covalent linkage via the narrow rim to a central calix[4]arene fixed in the 1,3-alternate conformation led to pentacalix[4]arenes 9 bearing four tetraurea derivatives in the cone conformation in a flexible tetrahedral arrangement. Their self-assembly via the formation of hydrogen bonded dimeric capsules has been studied under different conditions. A fourfold heterodimerisation of tetrakis-tetraurea derivatives of type 9 with tetratosylurea 10 has been confirmed by 1H NMR-spectroscopy and dynamic light scattering.     

1,3-Alternate calix[4]arene nitronyl nitroxide tetraradical and diradical: synthesis, X-ray crystallography, paramagnetic NMR spectroscopy, EPR spectroscopy, and magnetic studies

Calix[4]arenes constrained to 1,3-alternate conformation and functionalized at the upper rim with four and two nitronyl nitroxides have been synthesized, and characterized by X-ray crystallography, magnetic resonance (EPR and ¹H NMR) spectroscopy, and magnetic studies. Such calix[4]arene tetraradicals and diradicals provide scaffolds for through-bond and through-space intramolecular exchange couplings.     

Exchange coupling mediated through-bonds and through-space in conformationally constrained polyradical scaffolds: calix[4]arene nitroxide tetraradicals and diradical

Calix[4]arenes constrained to the 1,3-alternate conformation and functionalized at the upper rim with four and two tert-butylnitroxides have been synthesized and characterized by X-ray crystallography, magnetic resonance (EPR and (1)H NMR) spectroscopy, and magnetic studies. The 1,3-alternate nitroxide tetraradical and diradical provide unique polyradical scaffolds for dissection of the through-bond and through-space intramolecular exchange couplings. In addition, detailed magnetic studies of the previously reported calix[4]arene nitroxide tetraradical, which possesses cone conformation in solution, reveal conformational dependence of exchange coupling. Through-bond coupling between the adjacent nitroxide radicals is mediated by the nitroxide-m-phenylene-CH(2)-m-phenylene-nitroxide coupling pathway, and through-space coupling is found between the diagonal nitroxide radicals at the conformationally constrained N...N distance of 5-6 A. Magnetic studies of the calix[4]arene polyradical scaffolds in frozen solutions show that the through-bond exchange coupling in the 1,3-alternate calix[4]arene tetraradical is antiferromagnetic, while that in cone calix[4]arene tetraradical is ferromagnetic. The through-space exchange couplings are antiferromagnetic in both cone and 1,3-alternate calix[4]arene tetraradical, as well as in the 1,3-alternate calix[4]arene diradical. The exchange coupling constants (|J/k|) are of the order of 1 K.     

Synthesis and Properties of Upper Rim Schiff Base Calix[4]arenes

The synthesis and properties of upperrim Schiff base calix[4]arenes are described in thisarticle. Tetrakis-p-bromomethylcalix[4]arene(1) reacts with hexamethylenetetramine to givetetrakis-p-formylcalix[4]arene (2) in highyield. Then upper rim Schiff base calix[4]arenes 3 can be easily synthesized by 2 reacting withappropriate alkylamines. The complexation ability of3 toward transition metals Pb²⁺, Cu²⁺and Co²⁺ was studied by UV-VIS spectrophotometry.     

Transition metal-directed self-assembly of calix[4]arene based dithiocarbamate ligands

The transition metal-directed self-assembly of dithiocarbamate ligand functionalized upper and lower rim calix[4]arenes affords novel dimeric bimetallic bis(calix[4]arene) species as determined by a combination of analytical methods including X-ray crystallography. An exception is a zinc(II) dithiocarbamate upper rim calix[4]arene assembly which is monomeric in nature. Electrochemical investigations reveal the bimetallic copper(II) bis(calix[4]arene) systems can electrochemically sense dihydrogen phosphate and carboxylate anions via significant cathodic perturbations of the respective copper(II)/(III) dithiocarbamate oxidation wave.     

Mass spectroscopic investigation of bis-1,3-urea calix[4]arenes and their ability to complex N-protected α-amino acids

We report the ability of urea’s appended onto the upper-rim of conformationally locked ‘cone’ calix[4]arenes to show a preference for binding specific N-protected α-amino acids. Superior complexation (as judged by mass spectroscopy) between N-protected α-amino results and bis-1,3-N-benzylureas calix[4]arenes was observed when methylene bridges were present between the calix[4]arene ‘host’ and the urea motif. Interestingly we also demonstrate that subjecting mixtures of structurally diverse N-Fmoc-α-amino acids to a single bis-1,3-N-benzylurea derived calix[4]arene allows, in some cases, the calix[4]arene ‘host’ to selectively ‘pick out’ and complex a specific N-Fmoc amino acid from the mixture.     

Upper Rim Diester—bridged Calix[4] arenes and Oligocalix [4]—arenes：the Effects of the Length of Bridged Reagents on Their Distribution

A series of monobridged calix [4] arenes 3a-f,cyclic biscalix-[4] arenes 4a-f ,diametrically bridged at the upper rim with saturated aliphatic diester chians,have been synthesized,The results at diluted conditions show that the percentage of yields of mono-,bis- and oligo-calix[4] arenes are related to the legth of the chains ,With the shortening of the chains ,the percent-age of monocalix[4] arenes decreased ,All the calix [4] arene moieties are in a cone conformaiton according to the AB quar-tet pattern of the methylene protons between the phenolic rings in the ^1H NMR spectra.     

Synthesis of upper rim calix[4]arene divalent glycoclusters via amide bond conjugation

Synthetic routes for linking two sugar units at the upper rim of cone calix[4]arenes, through the formation of amide bonds, have been explored. Steric effects prevent the coupling of calix[4]arene dicarboxylic acid with simple aminoglycosides, whereas the corresponding reaction with carbohydrates bearing a two or three carbon atoms spacer, terminating with a primary amino group, allows the synthesis of several difunctionalized calix[4]arene neoglycoconjugates, attractive in chemical glycobiology and supramolecular chemistry.     

Tetrazolecalix[4]arenes as new ligands for palladium(II)

The synthesis of new calix[4]arenes bearing two or four tetrazole liganting groups at the upper rim is decribed. The structures of tetrakis-tetrazolecalix[4]arene and its palladium dichloride (2:2) complex are examined by X-ray crystallography.     

Calix[4]arenequinazolinones. Synthesis and structure

The synthesis of calix[4]arenes bearing two quinazolin-4-ones group at the upper rim is decribed. ¹H NMR spectra and quantum chemical calculations make it possible to suggest that calix[4]arenequinazolinones form three rotamers in solutions at room temperature, due to the restricted rotation of the quinazolinone fragments. The X-ray structure investigation indicates that quinazolin-4-onecalix[4]arene exists in the crystal state as the methanol 1:1 inclusion complex.     

Selectively formylated and bridged calix[6]arene derivatives at the upper rim

The strategy of bridging the anisole units at the upper rim of calix[6]arene has been applied to strain the conformations of calix[6]arene. Based on the selective formylation of the 1,3,5-tri-p-tert-butylcalix[6]arene, several new calix[6]arene derivatives with different 1,3-bridged chains or a 1,3,5-tripod bridge at the upper rim have been prepared with moderate yields. The ¹H NMR spectra indicate that these calix[6]arene derivatives adopt a cone conformation, which has also been confirmed by the theoretical calculation at AM1 level. X-ray crystal structure of 1,3,5-tripod bridged compound 5 discloses that the calix[6]arene host stands in a cone conformation with approximate C_3v symmetry, and that a methanol molecule is enclosed in its hydrophobic cavity and stabilized by multi hydrogen bonds.     

Synthesis and Conformational Studies of Lower Rim Cyanomethyl Substituted Calix[4]arenes

The conformational inversion characteristics of calix[4]arenes carrying cyanomethyl groups on the lower rim have been investigated. Complete conversion from a 1,3-alternate to a partial cone conformation was observed for the 1,3-dicyanomethyl ether of calix[4]arene at room temperature, while at higher temperatures further inversion to a 1:1 mixture of partial cone and cone conformers occurred.