Tetra-CMPO-derivatives of calix[4]arenes fixed in the 1,3-alternate conformation

Calix[4]arene derivatives fixed in the 1,3-alternate conformation and substituted at one side by four carbamoylmethylphosphine oxide (CMPO) residues were synthesised. Two CMPO groups are directly attached to the wide rim, while the second pair is bound to the narrow rim via a tri- or tetramethylene spacer. Similar compounds, in which two CMPO groups at the wide rim are combined with two picolinamide groups or two ionisable carboxylic groups at the narrow rim, were also prepared. Some of these calixarene derivatives were studied as extractants for lanthanides (La³⁺, Eu³⁺, Yb³⁺) and thorium (Th⁴⁺) from acidic solution into methylene chloride. For selected samples, stability constants in methanol were determined by spectrophotometric titrations. Three compounds (1b′, 13, 17) in the 1,3-alternate conformation and one intermediate in the cone conformation (18) were confirmed by a crystal structure.     

Liquid crystalline properties of dissymmetric molecules part X: The effect of a terminal nitro group on molecular arrangement in smectic phases in three aromatic ring systems with two ester groups

The smectic A (SmA) layer structure has been examined by X-ray diffraction for four isomeric systems: 4-nitrophenyl 4-(4-alkoxybenzoyloxy)benzoates 1, 4-alkoxyphenyl 4-(4-nitrobenzoyloxy)benzoates 2, 4-(4-alkoxybenzoyloxy)phenyl 4-nitrobenzoates 3, and 4-alkoxyphenyl 4-nitrophenyl terephthalates 4. The phase transition behaviour and layer structure of the SmA phases are notably influenced by the relative orientation of the two ester groups to the terminal groups, by alkoxy chain length, and by temperature. The SmA phase for compounds 1 and 3 has a mainly ‘monolayer’ arrangement, where the layer spacing is 2-5 Å longer than the molecular length. The SmA phase for compounds 2 and 4 consists of a mixed layer structure having monolayer, bilayer, and partially bilayer arrangements, the distribution depending on the relative orientation of the ester groups, the alkoxy chain length, and temperature. It is supposed that the diversity of the SmA phase is related to the polar interaction around the nitro or the nitrobenzene moieties through the smectic layers and reversal of the ester groups causes a subtle change in the entire molecular shape.     

New Azothiacalix[4]arenes Containing Biheterocyclic Subunits: Extraction and Complexation Properties

New thiacalix[4]arenes 2a, 3a, 4 and 5 functionalized with biheterocyclic and azophenyl groups at the lower rim and the upper rim of the macrocycle, respectively, were synthesized and their extraction properties towards Cu²⁺, Ag⁺, Ni²⁺ and Pb²⁺ studied. The complexation properties of the bithiazolyl receptors 2a, 4 and the bipyridyl receptors 3a, 5 were investigated by fluorescence and UV–visible titrations, respectively. The stoichiometries of the complexes were determined. A stoichiometry of 1:1 was found for the Cu-2a, Ag-3a complexes and 2:1 for the Cu₂-4, Ag₂-5 complexes as a function of the number of grafted bithiazolyl groups. The association constants for the 1:1 complexes were calculated using the Benesi–Hildebrand plot and by linear regression analysis.     

Synthesis and Characterization of Calix[4]arene Functionalized Poly(ethylene glycol) Derivatives

Calix[4]arenes with both ligating and methoxy poly(ethylene glycol) groups appended have been synthesized using several approaches, involving the formation of sulfonyl ester groups on the wide rim, Schiff base derivatives on the narrow rim, and thioether groups on both the wide and narrow rims. These new derivatives have been characterized by a combination of infrared and ¹H NMR spectroscopy. Compounds 10 and 11 are insoluble in both water and aqueous poly(ethylene glycol), but the other new compounds are soluble.     

Complexation of M3+ Lanthanide Cations by Calix[4]arene-CMPO Ligands: A Molecular Dynamics Study in Methanol Solution and at a Water/Chloroform Interface

Abstract

We report a molecular dynamics study on the 1:1 M³⁺ lanthanide (La³⁺, Eu³⁺ and Yb³⁺) inclusion complexes of an important extractant molecule L: a calix[4]arene-tetraalkyl ether substituted at the wide rim by four NH-C(O)-CH₂-P(O)Ph₂ arms. The M(NO₃)₃ and MCl₃ complexes of L are compared in methanol solution and at a water / chloroform interface. In the different environments the coordination sphere of M³⁺ involves the four phosphoryl oxygens and three to four loosely bound carbonyl oxygens of the CMPO-like arms. Based on free energy simulations, we address the question of ion binding selectivity in pure liquid phases and at the liquid-liquid interface where L and the complexes are found to adsorb. According to the simulations, the enhancement of M³⁺ cation extraction in the presence of the calixarene platform, examined by comparing L to the (CMPO)₄ “ligand” at the interface, is related to the fact that (i) the (CMPO)₄Eu(NO₃)₃ complex is more hydrophilic than the LEu(NO₃) one and (ii) the free CMPO ligands spread at the interface, and are therefore less organized for cation capture than L.     

Calix[4]arenes with carboxamide and sulfonamide groups and their complexation with transition metal salts

Calix[4]arene derivatives functionalized by ester and carboxamide groups on the lower rim and sulfonamide groups on the upper rim were synthesized, and their complexing properties toward transition metal salts (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺) were studied by extraction in chloroform-water system. The presence of carboxamide and sulfonamide fragments in the ligand was shown to considerably enhance binding of transition metal cations.     

Metal ion complexation in acetonitrile by cone,di-ionised calix[4]arene-1,2-crown ethers with two pendant dansyl fluorophores

Four cone calix[4]arene-1,2-crown ethers each with two ionisable side arms containing dansyl groups are synthesised. The crown ether ring on the lower rim is varied from crown-4 to crown-5 with hydrogen or tert-butyl groups on the para position of the upper rim. Di(tetramethylammonium) salts of the di-ionised ligands are utilised for spectrofluorimetric titration experiments in MeCN. The influence of alkali metal, alkaline earth metal and selected transition and heavy metal (Co²⁺, Fe²⁺, Hg²⁺, Mn²⁺, Pb²⁺, Zn²⁺ and Fe³⁺) cations on the spectroscopic properties of the two dansyl groups linked to the lower rim of the conformationally locked, di-ionised calix[4]arene-1,2-crown ether frameworks is investigated by emission spectrophotometry. All of the metal cations induce red shifts in the emission spectra of the di-ionised ligands. The metal cations produce enhancement or quenching of the fluorescence emissions. Changes in the fluorescence emission as a function of the metal cation identity, the lower rim crown ether ring size and the absence or presence of upper rim tert-butyl groups are investigated.     

Complexation and extraction of non-ferrous metals by calix[n]arene phosphine oxides

The extraction of non-ferrous metal (M²⁺) nitrates by the calix[4,6]arenes (L), bearing four or six phosphine oxide donor groups at the upper or at the lower rim, was quantitatively described in the form of [M_n(NO₃)_2nL] (n = 1, 2) complexes. The extraction constants (Zn²⁺ > Cu²⁺ > Co²⁺ > Ni²⁺) for the both types of L coincide with Irving-Williams sequence. Calix[4]arenes, phosphorylated at the lower (narrow) rim, provide better stability of ML complexes because of the best spatial fitting of M²⁺ by the donor groups. For the upper (wide) rim phosphorylated calix[4]arenes M₂L and ML₂ complexes are more stable. Unusual zwitterionic [Co₂(NO₃)₄L] complex of the lower rim tetraphosphorylated calix[4]arene 1 was determined by X-ray structural analysis.     

Synthesis and C70 complexation studies of a fluorescent 5,5’-bi-p-tert-butylcalix[4]arene scaffold

Abstract

In this paper, we report the synthesis and C70 complexation studies of a new fluorescent 5,5′-bi-p-tert-butylcalix[4]arene capsule with an extended hydrophobic cavity. The synthetic route required development of a series of selective protection and de-protection reactions, such as esterification and ester cleavage, as well as a cross-coupling reaction at the lower rim. The resulting 5,5′-bi-p-tert-butylcalixarene was fully characterised, including by X-ray crystallography. In the solid state, the compound exists in an ‘open-capsule’ orientation, with a perfectly planar bridging biphenylene unit resulting in high fluorescence with a maximum emission peak at 390 nm. Preliminary fluorescence-based complexation experiments with C70 fullerene did not provide conclusive evidence for formation of inclusion complexes.     

AN EXCELLENT APPROACH TOWARDS THE DESIGNING OF A SCHIFF-BASE TYPE OLIGOCALIX[4]ARENE,SELECTIVE for THE TOXIC METAL IONS

ABSTRACT

A new Schiff-base type oligocalix[4]arene containing two nitrile ligating sites at narrow rim was synthesized via a simple condensation reaction through a wide rim of the calixarene moiety. The extraction ability of the oligomer with selected alkali and transition metals is compared with its monomeric analogous. It has been observed that the oligomer 6 is not selective as compared to its analogae 2 and 3, but shows a remarkable high affinity towards toxic metal cations such as Cu²⁺, Hg²⁺ and Pb²⁺.     

Rearrangement of 3-Acyl Derivatives of L-Ascorbic Acid

Abstract

Evidence of rearrangement of 3-acyl derivatives of ascorbic acid to 2-acyl derivatives has been found for carbon and phosphorus acyl groups. The observations are consistent with intramolecular rearrangement through a cyclic intermediate in which the acyl group is bonded to both the 2- and 3-oxygen atoms of ascorbic acid. A rate of rearrangement has been measured for the 3-diphenylphosphinate ester. Calculated results indicate an increase in negative atomic charge at O-2 in the 3-acyl esters but a decrease in the charge of O-3 in the 2-acyl esters.     

Versatile Inclusion Behaviour of a Dinitrocalix[4]arene Having Two Ester Pendants – Preparation and X-ray Crystal Structures of Complexes

An upper-rim dinitro-substituted calix[4]arene possessing two lower-rim ethyl ester pendant groups (1) has been shown to form solid inclusion compounds with acetone (1:1) (1a), DMF (1:1) (1b), DMSO (1:1) (1c) and n-BuOH (2:1) (1d). X-ray crystal structures of the four complexes 1a–d are reported and comparatively discussed, including isostructurality calculations. Although the solid-state conformation of the dinitrocalix[4]arene moiety, stabilized by two intramolecular O–H…O bonds, is maintained in the four inclusion compounds, and all four co-crystals have similar unit cell dimensions and identical space group symmetries, only three of them (1a–c) are homostructural. Depending on the nature of the guest molecule, either the upper or the lower rim site of the calixarene is involved in the complexation, demonstrating either cavitate- or clathrate-type of supramolecular interactions, respectively. Moreover, due to the different guest recognition modes, the calixarene host in 1d is rotated through a non-crystallographic virtual rotation of 180° within the unit cell, in relation to the host molecules in each of the other three homostructural compounds 1a–c, thus giving rise to supramolecular morphotropism – to our knowledge the first case ever described.     

Theoretical study on the structure and conformational features of distally dibromo-dipropoxythiacalix[4]arene derivatives and their Zn<Superscript>2+</Superscript> complexes

A comparative DFT study of distally dibromo-dipropoxythiacalix[4]arene and dipropoxythiacalix[4]arene was performed. The hydrogen bonds OH O at the lower rim play an important role in stabilizing all the conformers, and cone is predicted to be the most stable. The structure and energetic ordering of the conformers are not affected by the bromination at upper rim. The inclusion of the solvent effect keeps the energetic orderings unchanged, but leads to a reduction in the energy gaps between conformers. Concerning the 1:1 neutral Zn²⁺ complexes, only one binding mode was found which presented the metal ion coordinated to four oxygen atoms at lower rim. This is in good agreement with our previous study on the Zn²⁺ complex with thiacalix[4]arene carrying opposite phenolate groups. The results thus support the idea that the position of the phenolate groups at lower rim is crucial to define the structural binding mode pattern of metal complexes.     

Liquid crystalline properties of dissymmetric molecules IV. The substituent effect on thermal properties of nematic and smectic A phases in three aromatic ring systems with ester linkages

This paper describes the effect of substituent and ester linkage on smectic properties for some derivatives of 4-R -phenyl 4-(4-octyloxybenzoyloxy)benzoates (1), 4-octyloxyphenyl 4-(4-R-benzyloxy)benzoates (2), 4-(4-octyloxybenzoyloxy)phenyl 4- R -benzoates (3), and 4-R-phenyl 4-octyloxyphenyl terephthalates (4) where R = OCH₃, CH₃, OC₈H₁₇, C8H17, halogens, CF₃, OCF₃, CN, NO2, etc. The thermal properties are discussed in terms of the electrostatic nature of the substituents and the relative orientation of the ester groups with respect to both terminal substituents. The substituent effect on the layer structure of the smectic A phase is also examined by means of a small angle X-ray analysis.     

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.     

Wide- and narrow-rim functionalised calix[4]arenes: synthesis and characterisation

Functionalisation of calix[4]arene at both the wide and narrow rims leads to the formation of compounds containing bipyridyl, via an amide linkage, at the wide rim and having either a butyl chain, a benzyl group or an alkyl ester functionality at the narrow rim. All compounds were characterised using ¹H and ¹³C NMR spectroscopies. Initial binding studies with Ru(bipy)₂Cl₂ are reported.     

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.     

Two‐ and Three‐Component Reactions Leading to New Enamines Derived from 2,3‐Dicyanobut‐2‐enoates

The three‐component reactions of 1‐azabicyclo[1.1.0]butanes 1 , dicyanofumarates (E)‐ 5 , and MeOH or morpholine yielded azetidine enamines 8 and 9 with the cis‐orientation of the ester groups at the C?C bond ((E)‐configuration; Schemes 3 and 4). The structures of 8a and 9d were confirmed by X‐ray crystallography. The formation of the products is explained via the nucleophilic addition of 1 onto (E)‐ 5 , leading to a zwitterion of type 7 (Scheme 2), which is subsequently trapped by MeOH or morpholine ( 10a ), followed by elimination of HCN. Similarly, two‐component reactions between secondary amines 10a – 10c and (E)‐ 5 gave products 12 with an (E)‐enamine structure and (Z)‐oriented ester groups. On the other hand, two‐component reactions involving primary amines 10d – 10f or NH₃ led to the formation of the corresponding (Z)‐enamines, in which the (E)‐orientation of ester groups was established.     

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.     

Structure of poly(methyl methacrylate) chains adsorbed on sapphire probed using infrared-visible sum frequency generation spectroscopy

We have studied the orientation of the train segments of a poly(methyl methacrylate) (PMMA) adsorbed layer at the CCl4-sapphire interface using surface-sensitive IR-visible sum frequency generation (SFG) spectroscopy. The SFG spectra of PMMA chains adsorbed on sapphire indicate ordered ester methyl groups. In comparison, we did not observe any significant contributions from the backbone methylene and alpha methyl groups, suggesting that these groups are disordered. No change in the structure of the adsorbed layer is observed upon cooling the solvent below the theta temperature; this is consistent with the picture of flat adsorbed chains on the surface. Interestingly, the orientation of the ester methyl groups of a spin-coated PMMA film at the PMMA-sapphire interface is similar to that of the same groups in the chains adsorbed from solution.