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Direct O-alkylation of p-tert-butyldihomooxacalix[4]arene (1) with N-(bromopropyl)- or N-(bromoethyl)phthalimides and K2CO3 in acetonitrile was conducted under conventional heating (reflux) and using microwave irradiation and ball milling methodologies. The reactions afforded mono- and mainly distal di-substituted derivatives in the cone conformation, in a total of eight compounds. They were isolated by column chromatography, and their conformations and the substitution patterns were established by NMR spectroscopy (1H, 13C, COSY and NOESY experiments). The X-ray structures of four dihomooxacalix[4]arene phthalimide derivatives (2a, 3a, 3b and 5a) are reported, as well as their photophysical properties. The microwave (MW)-assisted alkylations drastically reduced the reaction times (from days to less than 45 min) and produced higher yields of both 1,3-di-substituted phthalimides (3a and 6a) with higher selectivity. Ball milling did not reveal to be a good method for this kind of reaction.

The conformational changes of the homooxa adamantyl ketones 1 and 2, as well as of the calix[4]arene analogue derivative 3, all in the cone conformation, upon Pb2+ complexation were investigated by 1H, 13C, 207Pb NMR and proton spin-lattice relaxation times (T1) experiments. The X-ray crystal structures of ketones 1 and 3 were determined. The inclusion of an acetonitrile molecule in the hydrophobic cavity of the ligands was observed in the solid state. In solution, inclusion was observed only in the case of Pb2+ ⊂ ketone 3 complex. DFT calculations were also performed to complement the NMR conformational analysis and to bring further insights to the cation complexation. The data confirmed the formation of 1:1 complexes between Pb2+ and the ligands, and that the cation is located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. In general, the ligand conformations became closer to a regular cone upon complexation, with the binding models found for the three ketones through the NMR studies corroborated by the DFT calculations.

The intrinsic electronic absorption and fluorescence properties of several multifluorophoric dihomooxacalix[4]arenes are studied. The contributions of phenyl and/or benzyl groups (lower rim) and p-tert-butylphenyl ethers (upper rim) to the absorption and fluorescence are established. Fluorescence titrations were undertaken to investigate the calixarene complexes with nitrate and hydrogen sulfate. A comparison with UV-Vis titrations in the same concentration range showed that similar values for the association constants are obtained by both techniques. Fluorescence is thus demonstrated to be a good method for the determination of calixarene–anion association constants.

International audience; Lanthanide cation binding by tetraketone derivatives of p-tert-butyldihomooxacalix[4]arene (methyl 1a, tert-butyl 1b, adamantyl 1c and phenyl 1d) and of p-tert-butylcalix[4]arene (methyl 2a, adamantyl 2c and phenyl 2d), in the cone conformation, was investigated. These properties were assessed by extraction experiments of the metal picrates from water to dichloromethane and by stability constant measurements in acetonitrile by UV-vis absorption spectrophotometry. Proton NMR titrations with La3+, Eu3+ and Yb3+ cations were also performed to obtain information on the binding sites. Molecular dynamics (MD) simulations and potential of mean force (PMF) free energy calculations were carried out for ligands 1d and 2d in pure solvents and at a CH2Cl2/water interface to add further information on the complexation and extraction processes. Comparison between dihomooxacalix[4]arene and calix[4]arene ketone derivatives showed that the former are better extractants, displaying the highest percentages of extraction for Gd3+ and Yb3+ cations. Concerning complexation, all ligands studied presented high affinities for the lanthanide ions. Ligands 1b and 1d showed preference for the light La3+, while 2d displayed the strongest affinity for the heavy and smaller Yb3+. These results were also corroborated by MD simulations, which revealed specificities of ligands 1d and 2d in the binding of lanthanide cations.

Thermally activated delayed fluorescence (TADF) of 12C70 and 13C70 was observed up to 140 °C in a p-tert-butyldihomooxacalix[4]arene solid matrix, a temperature range significantly higher than that of previous TADF quantitative studies. An effective singlet-triplet energy gap of 29 kJ/mol and triplet formation quantum yields of 0.97 and 0.99 were measured for 12C70 and 13C70, respectively. The photophysical properties of the two fullerenes in this new matrix are comparable to those obtained in polystyrene at a lower temperature range. Calixarenes are proposed to be suitable matrices for high temperature TADF studies and applications.

The conformationally mobile tetramethoxy-dihomooxacalix[4]arene 1c is able to interact with linear and branched alkylammonium guests through an induced-fit process mainly driven by H-bonds and cation–π interactions. Although free 1c adopts a 1,4-alternate conformation in solution, in the presence of linear nBuNH3+ and branched sBuNH3+ and iPrNH3+ guests, it preferentially forms endo-complexes in a cone conformation through adaptive structural change in response to the presence of the ammonium guests. In accordance with previous results, the DFT-optimized structures of the complexes indicate that they are mainly stabilized by H-bonding interactions between the guest ammonium group and the host CH2OCH2 ethereal bridge.

Thiacalixarenes are members of the calixarene family in which sulfur has replaced one or more of the methylene bridges between the phenolic moieties of the macrocycles. Oxidation of the thiacalixarenes leads to sulfinyl and sulfonyl homologs. The incorporation of sulfur affects the metal-binding affinities of these calixarenes over their all-carbon analogs through the abilities of the heteroatoms both to bind directly and to influence lower rim phenolic binding. Other binding motifs are possible for the oxidized thiacalixarenes leading to a vast array of complexes with metal cations. This chapter covers the literature concerning thiacalixarenes containing free OH groups at the lower rim since they were first reported. Their coordination chemistry toward alkali, alkaline earth, transition, heavy, lanthanide, and actinide metals is discussed. Examples of crystal structures of these metal complexes are given, as well as brief descriptions of their applications in fields such as catalysis, transition-metal extraction, and cation transport. Keywords: thiacalixarenes; metal phenolates; coordination chemistry; metal complexes; alkali and alkaline earth metals; transition and heavy metals; lanthanide and actinide metals

Three new bidentate ureidodihomooxacalix[4]arene derivatives (phenyl 5a, n-propyl 5b, and tert-butyl 5c) were synthesized in four steps from the parent compound p-tert-butyldihomooxacalix[4]arene and obtained in the cone conformation, as shown by NMR studies. The binding ability of these neutral receptors toward spherical, linear, trigonal planar, and tetrahedrical anions was assessed by (1)H NMR and UV-vis titrations. The structures and complexation energies of some complexes were also studied by DFT methods. The data showed that the association constants are strongly dependent on the nature of the substituent (aryl/alkyl) at the urea moiety. In general, for all the receptors, the association constants decrease with decrease of anion basicity. Ph-urea 5a is the best anion receptor, showing the strongest complexation for F(-) (log K(assoc) = 3.10 in CDCl3) and also high binding affinity for the carboxylates AcO(-) and BzO(-). Similar results were obtained by UV-vis studies and were also corroborated by DFT calculations.

The binding of representative alkali, alkaline earth, transition and heavy metal cations by 2-pyridylmethoxy derivatives (1b, in cone and partial cone conformations) of p-tert-butylhexahomotrioxacalix[3]arene (1a) was assessed by spectrophotometry, microcalorimetry, proton NMR spectrometry and density functional theory methods.

Heteracalixarenes are members of the calixarene family in which heteroatoms such as oxygen, nitrogen, sulfur, selenium, or silicon are inserted between the methylene bridges or replace them entirely. The incorporation of heteroatoms affects the metal binding affinities of these calixarenes over their all-carbon analogues, through the abilities of the heteroatoms both to bind directly and to influence lower rim phenolic binding. This chapter covers the literature concerning phenolic homooxa- and homoazacalixarene-metal complexes mainly for the last two decades (1994–2014). The syntheses of homooxa- and homoazacalixarenes containing free OH groups at the lower rim are described and their coordination chemistry towards alkali, alkaline earth, transition, heavy, lanthanide and actinide metals is discussed. Examples of crystal structures of these metal complexes are given, as well as brief descriptions of their applications in fields such as catalysis, and metal cation extraction and transport. Keywords: alkali and alkaline earth metals; coordination chemistry; homoazacalixarenes; homooxacalixarenes; lanthanide and actinide metals; metal phenolates; metal complexes; transition and heavy metals

Competition between hydrogen bonding and proton transfer reactions was studied for systems composed of electrogenerated dianionic species from dinitrobenzene isomers and substituted dihomooxacalix[4]arene bidentate urea derivatives. To analyze this competition, a second-order ErCrCi mechanism was considered where the binding process is succeeded by proton transfer and the voltammetric responses depend on two dimensionless parameters: the first related to hydrogen bonding reactions, and the second one to proton transfer processes. Experimental results indicated that, upon an increase in the concentration of phenyl-substituted dihomooxacalix[4]arene bidentate urea, voltammetric responses evolve from diffusion-controlled waves (where the binding process is at chemical equilibrium) into irreversible kinetic responses associated with proton transfer. In particular, the 1,3-dinitrobenzene isomer showed a higher proton transfer rate constant (∼25 M(-1) s(-1)) compared to that of the 1,2-dinitrobenzene (∼5 M(-1) s(-1)), whereas the 1,4-dinitrobenzene did not show any proton transfer effect in the experimental conditions employed.

Homooxacalixarenes are calixarene analogues in which the CH2 bridges are partly or completely replaced by CH2OCH2 groups. The insertion of dimethyleneoxa bridges and the resulting higher conformational flexibility affect the host–guest properties of these compounds compared to classical calixarenes. The functionalization and ion binding properties of hexahomotrioxacalix[3]arenes, dihomooxacalix[4]arenes and tetrahomodioxacalix[4]arenes are reviewed in this chapter, covering the literature from 2000 to 2015. The use of these macrocycles in other applications, such as ion-selective electrodes and chemosensors, is also reported.

How big should a calixarene macrocycle be for endo-cavity complexation to occur or to allow through-the-annulus threading? To answer these questions, a complete study on the complexation of primary and secondary (di)alkylammonium cations by 18-membered p-tert-butyldihomooxacalix[4]arene macroring has been performed in the presence of the "superweak" TFPB counterion. Thus, it was found that this macrocycle is currently the smallest calixarene able to host linear and branched alkylammonium guests inside its aromatic cavity. Molecular mechanics calculations revealed that this recognition event is mainly driven by a H-bonding interaction between the guest ammonium group and the host CH(2)OCH(2) bridge. The endo-cavity complexation of chiral s-BuNH(3)(+) guest results in an asymmetric complex in the NMR time scale. The chirality transfer from guest to host is likely due to a restricted guest motion inside the tight cavity. The complexation study with secondary di-n-alkylammonium·TFPB salts revealed that the 18-membered dihomooxacalix[4]arene macroring cannot give the through-the-annulus threading with them because of its small dimension. However, the macrocycle is able to complex such ions, which can only be accommodated in an hook-like conformation characterized by two unfavorable gauche interactions around the CH(2)-NH(2)(+) bonds. The strain generated by this unfavorable folding is very likely compensated by stronger H-bonds and more favorable CH/π interactions between guest and host.

Hexahomotrioxacalix[3]arenes, commonly called oxacalix[3]arenes, were first reported in 1962. Since then, their chemistry has been expanded to include numerous derivatives and complexes. This review describes the syntheses of the parent compounds, their derivatives, and their complexation behaviour towards cations. Extraction data are presented, as are crystal structures of the macrocycles and their complexes with guest species. Applications in fields as diverse as ion selective electrode modifiers, fluorescence sensors, fullerene separations and biomimetic chemistry are described.

The binding properties of two homooxacalixarene diethylamides (1b and 2b) derived from p-tert-butyldihomooxacalix[4]arene and p-tert-butylhexahomotrioxacalix[3]arene, respectively, in the cone conformation, for lanthanide cations, were investigated. These properties were assessed by extraction studies of the metal picrates from water into dichloromethane and stability constant measurements in methanol, using spectrophotometric and potentiometric techniques. Microcalorimetric studies of La3+, Pr3+, Eu3+ and Gd3+ complexes in the same solvent were also performed. Proton NMR titrations with the representative lanthanides La3+, Eu3+ and Yb3+ were also carried out to establish the sites of interaction of the ligands with the cations. The analogous derivative (3b) of p-tert-butylcalix[4]arene was also studied and the results of the three compounds are compared. Diethylamide 1b is the strongest binder, showing some preference for the light lanthanides in extraction, but exhibiting practically no selectivity in c...

p-tert-Butylhexahomotrioxacalix[3]arene tri(adamantyl)ketone (1b) was synthesized for the first time. Compound 1b was obtained in a cone conformation in solution at room temperature, as established by NMR spectroscopy (H-1 and C-13). The binding properties of ligand 1b for alkali, alkaline earth, transition, heavy metal and lanthanide cations have been assessed by phase transfer and proton NMR titration experiments. Molecular mechanics and ab initio techniques were also employed to complement the NMR data. The results are compared to those obtained with other closely related homooxacalixarene derivatives. Although triketone 1b is a weak extractant, it shows a strong peak selectivity for Na+ and also some preference for Ag+. Proton NMR titrations indicate the formation of 1:1 complexes between 1b and the cations Studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Although the molecular mechanics results show little correlation with the NMR data, a good agreement was obtained with the ab initio models. (C) 2008 Elsevier Ltd. All rights reserved.

In this contribution, polyurethane foams are proposed as new polymeric phases for stir bar sorptive extraction (SBSE). Assays performed for polyurethane synthesis demonstrated that four series of formulations (P1 ,P 2 ,P 3 and P4) present remarkable stability and excellent mechanical resistance to organic solvents. For polymer clean-up treatment, acetonitrile proved to be the best solvent under sonification, ensuring the reduction of the contamination and interferences. SBSE assays performed on these polyurethane polymers followed by liquid desorption and high-performance liquid chromatography-diode array detection (LD–HPLC-DAD) or large volume injection-capillary gas chromatography–mass spectrometry (LD–LVI-GC–MS), showed that P2 presents the best recovery yields for atrazine, 2,3,4,5-tetrachlorophenol and fluorene, used as model compounds in water samples at a trace level. SBSE(P2) assays performed on this polymer mixed up with several adsorbent materials, i.e. activated carbon, a mesoporous material and a calixarene, did not bring any advantages in relation with the polymeric matrix alone. The comparison between assays performed by SBSE(P2) and by the conventional SBSE(PDMS) showed much better performance for the former phase on aqueous samples spiked with atrazine, 2,3,4,5-tetrachlorophenol and fluorene, in which the foremost two analytes present recovery values 3- and 10-fold higher, respectively. The polyurethanes proposed as new polymeric phases for SBSE provided powerful capabilities for the enrichment of organic compounds from aqueous matrices, showing to be indicated mainly in the case of the more polar analytes. © 2007 Elsevier B.V. All rights reserved.

The iteroselective "all-but-one" carbamatation methodology has been successfully extended to homooxacalixarenes and used for the selective and controlled synthesis of homooxacalixarene-monoquinones and calixarene-monoquinones. These moquinone derivatives constitute interesting molecular platforms that, until now, were inaccessible through any efficient means.

Electron transfer controlled hydrogen bonding was studied for a series of nitrobenzene derivative radical anions, working as large guest anions, and substituted ureas, including dihomooxacalix[4]arene bidentate urea derivatives, in order to estimate binding constants (Kb) for the hydrogen-bonding process. Results showed enhanced Kb values for the interaction with phenyl-substituted bidentate urea, which is significantly larger than for the remaining compounds, e.g., in the case of 4-methoxynitrobenzene a 28-fold larger Kb value was obtained for the urea bearing a phenyl (Kb ∼ 6888) vs tert-butyl (Kb ∼ 247) moieties. The respective nucleophilic and electrophilic characters of the participant anion radical and urea hosts were parametrized with global and local electrodonating (ω(-)) and electroaccepting (ω(+)) powers, derived from DFT calculations. ω(-) data were useful for describing trends in structure–activity relationships when comparing nitrobenzene radical anions. However, ω(+) for the host urea structures lead to unreliable explanations of the experimental data. For the latter case, local descriptors ωk(+)(r) were estimated for the atoms within the urea region in the hosts [∑kωk(+)(r)]. By compiling all the theoretical and experimental data, a Kb-predictive contour plot was built considering ω(-) for the studied anion radicals and ∑kωk(+)(r) which affords good estimations.

Ion-pair recognition-complexation of monoamine neurotransmitters and trace amine hydrochlorides takes place - with outstanding efficiency and selectivity - within the π-rich cavity and the pocket formed at the lower rim by the two ureido moieties of the tailor-made dihomooxacalixarene receptors 1 and 2. The solid-state structure of 1 is also reported.

1,3-Dimethoxy- p - tert -butyldihomooxacalix[4]arene-crown-6 ( 4 ) was synthesized for the first time. 4 was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements ( 1 H, 13 C, COSY and NOESY). Conformational behaviour of 4 and p - tert -butyldihomooxacalix[4]-crown-5 ( 2 ) and crown-6 ( 3 ) was studied by dynamic 1 H NMR and by MD/MM calculations. Two-phase (water/CH 2 Cl 2 ) picrate extraction studies and transport experiments with the same salts through a CH 2 Cl 2 membrane were performed to evaluate the binding properties of these ligands towards alkali and alkaline earth metal cations. 2 and 3 are poor phase transfer agents for all cations, while 4 is a reasonable extractant for the alkali cations, showing preference for Cs + . However, all three calixcrowns are good carriers for the alkali cations and display a very selective transport for Ba 2+ .

The binding properties of two phenylketones (2a and 3a) and two ethylesters (2b and {3b) derived from p-tert-butyldihomooxacalix[4]arene or from p-tert-butylcalix[4]arene, in the cone conformation, towards transition (Ag+, Ni2+, Cu2+, Co2+, Zn2+, Fe2+ and Mn2+) and heavy (Cd2+, Hg2+ and Pb2+) metal cations have been determined by extraction studies with metal picrates and liquid membrane transport experiments with the same salts. The affinity of these ligands for Ag+ has also been investigated by 1H NMR spectroscopy. Both ketones are better extractants than the esters, and show a strong preference for Ag+, while Cu2+ is the most extracted cation with the esters. 1H NMR titrations with AgSO3CF3 indicate 1 : 1 complexes for all ligands, those with ketones are more stable, on the NMR time scale, than those with esters. Both esters are good carriers for Ag+, and 2b exhibits the highest transport rate (4.7 μmol h-1) found until now with dihomooxacalix[4]arene derivatives.

Functionalization of the lower rim of p-tert-butyldihomooxacalix[4]arene with two (thio)ureido moieties provided new diurea (n-propyl 5a, tert-butyl 5b and phenyl 5c) and dithiourea (phenyl 5d) derivatives, all in the cone conformation, as shown by NMR studies. The X-ray crystal structure of 5c is reported. The binding ability of these neutral receptors towards a large variety of anions was assessed by 1H NMR titrations. The structures and complexation energies of some complexes were also studied using DFT methods. The data showed that, in general, the association constants decrease with decrease of anion basicity and they are strongly dependent on the nature of the substituent at the urea moiety. Phenyl-(thio)urea derivatives 5c and 5d are the best anion receptors, showing the strongest complexation for F− (log Kass=2.70 and 2.75, respectively) and also for the oxoanions AcO−, BzO− and H 2 PO 4 − . These results were corroborated by DFT calculations.

The synthesis of the inherently chiral triethyl ester monomethyl ether of p-tert-butyldihomooxacalix[4]arene (3) is reported. A distorted cone conformation in solution at room temperature has been established for triester 3 by NMR measurements (1H, 13C, NOE 1D and 2D). The extracting and complexing properties of 3 towards the entire alkali and alkaline earth cation series have been assessed by picrate extraction and stability constant determinations. Transport experiments with metal picrates through a CH2Cl2 membrane have also been performed. Comparison is made with tetraethyl ester of p-tert-butylcalix[4]arene (4) described in literature and also studied by us. 3 is a poor phase transfer agent and binder. In contrast, it is a good carrier, mainly for the alkali cations and displays a selective transport for Ba2+.

The tetraphenyl ketone of p-tert-butyldihomooxacalix[4]arene (2) was synthesized for the first time. This derivative possesses the cone conformation in solution at room temperature, which was confirmed by NMR measurements (1H, 13C and NOE 1D). Extraction studies with metal picrates from neutral aqueous solution into dichloromethane, transport experiments with metal picrates through a dichloromethane membrane and stability constant measurements by UV absorption spectroscopy in methanol and acetonitrile were performed to evaluate the binding ability of ketone 2 towards alkali and alkaline earth metal cations. The tetraphenylketone of p-tert-butylcalix[4]arene (3) was also studied, and the results for the two derivatives were compared. Compound 2 shows a preference for K+ and Ba2+ cations, being selective only in the alkaline earth metal cation series. Compound 3 is a stronger binder than 2, but is a weaker extractant. Both show transport rates that are not proportional to complex stability or to extraction efficiency. Ketone 2 can be characterized as a selective receptor. Copyright © 1999 John Wiley & Sons, Ltd.

In the present paper we have performed a conformational analysis of the tetrabenzyl ether of the p-tert- butyldihomooxacalix[4]arene by molecular mechanics/molecular dynamics simulations. These calculations indicate that among the six studied conformations, the 1,3-alternate is the thermodynamically most stable conformation, followed by the partial cone A, while the cone is the least stable conformation. Analysis of the energy components of the potential energy shows that these preferences are mainly due to coulombic repulsion interactions between the oxygen atoms as well as to non-bonded steric hinderance between the bulky groups. Molecular dynamics results also indicate that, although all the six conformations are flexible with the phenol rings twisting around from inward to outward pointing, they lie in geometries close to the starting ones and no conformational interconversions were detected.

The crystal structures of four derivatives of the p-tert-butyldihomooxacalix [4] arenes are reported. These four compounds are obtained by substitution of the four phenolic hydrogens by CH3 or CH2CH3 or CH2 [sbnd] CH = CH2 or groups. The four calixarenes exhibit a 1,2 alternate conformation; the geometry of the dimethyleneoxa group is studied for the different compounds.

Four tetraethers (methyl, ethyl, allyl and benzyl) of p - tert -butyldihomooxacalix[4]arene were synthesized and their conformational behaviour studied by means of variable temperature 1 H NMR, including the determination of coalescence temperatures and ΔG + . It was shown that the methyl ether still has some conformational monility at −100 °C, the ethyl ether displays a fixed conformation at −20 °C and the other two derivatives are conformationally rigid at room temperature. The conformations obtained are the 1,2-alternate B and cone, depending on the derivative formed.

The tetramethyl (2) and tetraethyl (3) ethers, and the tetraacetate (4) derivatives of the p-tert-butyldihomooxacalix[4]arene were prepared. The mobility of these compounds studied by temperature-dependent 1H NMR spectroscopy. For the tetraacetate derivative, at room temperature, 1,2- or 1,3-alternate conformations are suggested. Those conformations were confirmed by NOE difference and COSY spectra for the tetraethyl ether derivative in CDCl3 at -20°C.

The diethyl amides of p-tert-butyldihomooxacalix[4]arene (1), p-tert-butylhexahomotrioxacalix[3]arene (2) and p-tert-butylcalix[4]arene (3) were used as active materials in ion-selective membrane electrodes to check the detection of different kinds of cations (Na+, K+, Cs+, Mg2 + , Ca2 + , Mn2 + , Cu2 + , Zn2 + , Cd2 + , Pb2 + and tetramethylammonium cation). The electrode characteristics and selectivity coefficients were determined and compared. Optimisation of the PVC membrane composition was achieved using three different plasticisers (bis(2-ethylhexyl) adipate, o-nitrophenyl octyl ether and bis(2-butylpentyl) adipate). Amide 3 shows selectivity for Na+, whereas compounds 1 and 2 exhibit the highest selectivity for Pb2 + among all the studied cations. The X-ray crystal structure of dihomooxacalix[4]arene tetra(diethyl)amide (1) was determined, revealing it to be in the cone conformation.

1,3-Diethoxy-p-tert-butyldihomooxacalix[4]arene-crown-6 (3) was synthesised for the first time. Compound 3 was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements (1H, 13C and NOESY). The assignment of both proton and carbon NMR spectra was achieved by a combination of COSY and HSQCTOCSY experiments. The binding affinities of ligand 3 for alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. Compound 3 is a reasonable extractant for the alkali cations and also for Ag+, showing preference for Cs+. Ligand 3 forms 1:1 complexes with K+, Ca2+, Ag+ and Pb2+, as determined by proton NMR titrations, which also indicated that these cations should be encapsulated into the cavity defined by the crown ether unit, the ethoxy group and the inverted aryl ring. A new dihomooxacalix[4]crown-6 (3) was synthesised and isolated in a partial cone A conformation in solution at room temperature, as established by NMR (1H, 13C and NOESY). The binding properties of 3 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with calixcrowns 1 and 2.[image omitted].

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The binding of alkali, alkaline earth, transition (Mn2 + , Fe2 + , Co2 + , Ni2 + , Cu2 + and Zn2 + ) and heavy metal (Ag+, Cd2 + , Hg2 + and Pb2 + ) cations by cone p-tert-butylhexahomotrioxacalix[3]arene tri(diethyl)amide (1b) has been assessed by extraction studies of metal picrates from water to dichloromethane and proton NMR titration experiments. Molecular modelling techniques were also employed to complement the NMR data. The results are compared to those obtained with the dihomooxacalix[4]arene (2b) and calix[4]arene (3b) derivative analogues. Triamide 1b displays a high extracting ability towards Na+, Ba2 + , Ni2 + , Co2 + , Ag+ and mainly Pb2 + (80% E). However, these values are lower than those obtained with tetraamides 2b and 3b, presumably due to the higher conformational flexibility of 1b. 1H NMR titrations indicate the formation of 1:1 complexes between 1b and all the cations studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms.

The binding properties of three p-tert-butyldihomooxacalix[4]arene tetraketone derivatives (tert-butyl 2b, adamantyl 2c and phenyl 2d) in the cone conformation and one derivative (methyl 2a) in a partial cone conformation, towards alkali and alkaline earth metal cations have been established by extraction studies of metal picrates from water into dichloromethane, stability constant measurements in methanol and acetonitrile, and by H-1 NMR spectrometry. Transport experiments of metal picrates through a dichloromethane membrane were also performed. The results are compared to those obtained with closely-related calix[n]arene derivatives (n = 4 and 5) and discussed in terms of the substituents, size and conformational effects. Methylketone 2a is a poor binder for all the cations studied, due to its partial cone conformation. Ketones 2b, 2c and 2d show high extraction and complexation levels for the alkali cations, with similar profiles and preference for K+ and Na+ (plateau selectivity). Towards alkaline earth cations, these ketones show a strong peak selectivity for Ba2+ in extraction, but a plateau selectivity for Ca2+, Sr2+ and Ba2+ in complexation. The nature of the substituent attached to the ketone function has some influence on their binding properties, with phenylketone 2d being a slightly weaker binder than ketones 2b and 2c. H-1 NMR titrations confirm the formation of 1:1 complexes between the ketones and the cations studied, also indicating that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Ketones 2b, 2c and 2d show transport rates that do not follow, in general, the same trends observed in extraction and complexation.

1,3-Di(2-pyridymethoxy)-p-tert-butyldihomooxacalix[4]arene-crown-6 (2) was synthesized for the first time. 2 was isolated in a cone conformation in solution at room temperature, as established by NMR spectroscopy (H-1, C-13 and NOESY). Complete assignment of both proton and carbon NMR spectra wits achieved by a combination of COSY, HSQC and HMBC experiments. The binding properties of ligand 2 towards alkali, alkaline earth, transition and heavy metal cations have been assessed by phase transfer and proton NMR titration experiments. The results are compared to those obtained with other dihomooxacalix[4]arene-crowns-6 and closely-related calix[4]arene-crowns-6 derivatives. 2 shows a preference for the soft heavy metal cations (except for Cd2+), with it very strong affinity for Ag+. Some transition metal cations are also well extracted. 2 Forms 1: 1 complexes with K+, C2+ and Ag+, and H-1 NMR titrations indicate that they should be encapsulated into the cavity defined by the crown ether unit and by the two pyridyl pendant arms. A 1:2 (ML2) complex is formed with Zn2+ and two species, probably 1: 1 and 1:2 complexes, are obtained with Ph (c) 2006 Elsevier Ltd. All rights reserved.