Solution NMR studies of supramolecular complexes of [60]- and [70]fullerenes with mono O-substituted calix[6]arene

Supramolecular complexation of [60]- and [70]fullerenes with 37-allyl-38,39,40,41,42-pentahydroxy-5,11,17,23,29,35-hexa(4-tert butyl)calix[6]arene (I) has been studied in CCl(4) medium by NMR spectrometric method. All of the complexes are found to be stable with 1:1 stoichiometry. Formation constants (K) of the above supramolecular complexes have been determined from systematic variation of NMR chemical shifts of specific protons of I in the presence of [60]- and [70]fullerenes. Trends in the K value suggest that [70]fullerene binds more strongly with I relative to [60]fullerene. Both PM3 and ab initio calculations reveal that the intermolecular interaction in the [70]fullerene/I complex proceeds through quite deep energy minima.     

Supramolecular interactions of [60]- and [70]fullerenes with calix[n]arenes

[60]- and [70]fullerenes have been shown to form 1:1 supramolecular complexes with (i) 24,26-dimethoxy-25,27-dihydroxy-5,11,17,23-tetra(4-tert-butyl)calix[4]arene (1) and (ii) 37,39,41-trimethoxy-38,40,42-trihydroxy-5,11,17,23,29,35-hexa(4-tert-butyl)calix[6]arene (2) in CCl(4) medium by absorption spectroscopy. Charge transfer absorption bands of the complexes have been located in each of the cases (except [70]fullerene-2 complex) studied from which the vertical ionisation potential of 1 has been obtained. Formation constants of the complexes have been determined at four different temperatures from which the enthalpies and entropies of formation of the complexes have been obtained. Moreover, the formation constant of [70]fullerene-2 complex is higher than that of the [60]fullerene-1 and [60]fullerene-2 complexes at all the four temperatures studied. This has been accounted in terms of greater cavity size of 2 which is a calix[6]arene compared to 1 which is a calix[4]arene and also by the fact that a high degree of preorganisation takes place in case of 2 through intramolecular H-bonding at its lower rim.     

Spectrophotometric study of the supramolecular complexes of [60]- and [70]Fullerenes with biscalix[6]arene and crown[4]calix[6]arene

[60]- and [70]Fullerenes have been shown to form 1:1 supramolecular complexes with bis[2-(5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41-pentahydroxycalix[6]arenyl-oxy ethyl ether) (1) and 5,11,17,23,29,35-hexa-tert-butyl-37,38,40,41-tetra hydroxyl-39,42-(crown-4)calix[6]arene (2) in CHCl3 medium by electronic absorption spectroscopy. Formation constants (K) of the complexes of [60]- and [70]fullerenes with 1 and 2 have been determined at room temperature from which free energy of formation values of the complexes have been estimated. The very high formation constant value of [60]fullerene/1 complex (5900 dm3 mol-1) in indicative of formation of inclusion complex. Moreover, PM3 calculations reveal that intermolecular interaction between [60]fullerene and 1 proceeds through quite deep energy molecular orbital.     

Fullerene encapsulation with calix[5]arenes

This paper presents the synthesis of the fullerene hosts based on the calix[5]arenes and their binding properties. Calix[5]arenes 1a, 2, 3a bind C₆₀ or C₇₀ in organic solvents. The solvent effect of the fullerene complexation was clearly observed; the association constant decreases in a solvent with high solubility for C₆₀. Covalently linked double-calix[5]arenes 4-6 were also investigated on their binding properties for fullerenes in organic solvents. Their binding abilities for both C₆₀ and C₇₀ are extremely high in toluene solution. Higher binding selectivity toward C₇₀ is observed by all the double-calix[5]arenes. The selectivity of 5a toward C₇₀/C₆₀ is highest in toluene with a value of 10. The structures of the supramolecular complexes of the calix[5]arene hosts and C₆₀ or C₇₀ were investigated by using ¹H and ¹³C NMR studies. The molecular mechanics calculation and X-ray structure reveal that the interior of the calix[5]arene is complementary to the exterior of C₆₀ molecule. In contrast, the host-guest complexes of C₇₀ with the simple calix[5]arenes take many conformational options due to its less symmetric shape. The molecular mechanics calculation and our chemical shift simulation nicely worked to estimate the reliable structures; the calix[5]arene cavity takes up C₇₀ molecule, and the C₇₀ molecule tilts significantly from the C5 axis of the calix[5]arene. In the case of the host-guest complex of C₇₀ with the double-calix[5]arene, the molecular dynamics simulation of the host-guest complex represented the realistic movement of the bound C₇₀ inside the cavity. The combination of the molecular dynamics simulation and the chemical shift simulation of the host-guest complex suggested that the C₇₀ molecule rapidly moves inside the cavity.     

A paradigm shift in the construction of heterobimetallic complexes: synthesis of group 2 & 4 metal-calix[6]arene complexes

Deprotonation of calix[6]arenes with barium in methanol followed by the addition of [Ti(OPr(i))(4)] or [Zr(OBu(n))(4)] is effective in the formation of novel dimeric 2:1 barium-titanium(IV)/zirconium(IV) calix[6]arene complexes. In these complexes a central Ti(IV)/Zr(IV) coordinated in the exo-position connects the two calix[6]arenes in the 1,3-alternate conformation, each with an endo-barium sharing common phenolate groups with the titanium/zirconium centre and participating in cation-pi interactions. A homometallic barium calix[6]arene dimer was also prepared wherein the calix[6]arenes are in the 1,3-alternate conformation with each coordinating one endo- and one exo-barium centre. The exo-barium cations connect the two calix[6]arenes through bridging methanol ligands. In this and the heterometallic complexes, cation-pi complexation of the Ba(2+) ion within the 1,3 alternate conformation of calix[6]arene facilitates the formation of the dimeric complexes in methanol. In contrast, the smaller Sr(2+) ion did not form similar complexes in methanol, and the formation of an analogous 2:1 strontium-titanium calixarene complex required the use of the more sterically demanding donor alcohol, isopropanol, the resulting complex being devoid of cation-pi interaction. The results show (i) that a subtle interplay of solvation strength, coordination array type and cavity/cation size influences the accessibility of heterobimetallic complexes based on calix[6]arenes, and (ii) a synergistic endo-exo binding behaviour.     

Selective and Efficient Iodination of the p-Positions of Calix[4]arene Derivatives

Selective and very convenient methods of iodination of calix[4]arenes using ICl or NIS have been demonstrated, preparing mono(p-iodo) and 1,3-di(p-iodo) derivatives of calix[4]arenecrown-4 and -5, as well as mono(p-iodo) derivative of tris(O-propyl)calix[4]arene in good yields.     

Synthesis and crystal structure of uranium(IV) complexes with calix[n]arenes (n = 4, 6 and 8): mononuclear, polynuclear and 1D polymeric species

Reactions of UCl4 with calix[n]arenes (n = 4, 6) in THF gave the mononuclear [UCl2(calix[4]arene - 2H)(THF)2].2THF (.2THF) and the bis-dinuclear [U2Cl2(calix[6]arene - 6H)(THF)3]2.6THF (.6THF) complexes, respectively, while the mono-, di- and trinuclear compounds [Hpy]2[UCl3(calix[4]arene - 3H)].py (.py), [Hpy](4)[U2Cl6(calix[6]arene - 6H)].3py (.3py), [Hpy]3[U2Cl5(calix[6]arene - 6H)(py)].py (.py) and [Hpy]6[U3Cl11(calix[8]arene - 7H)].3py (.3py) were obtained by treatment of UCl4 with calix[n]arenes (n = 4, 6, 8) in pyridine. The sodium salt of calix[8]arene reacted with UCl4 to give the pentanuclear complex [U{U2Cl3(calix[8]arene - 7H)(py)5}2].8py (.8py). Reaction of U(acac)4 (acac = MeCOCHCOMe) with calix[4]arene in pyridine afforded the mononuclear complex [U(acac)2(calix[4]arene - 2H)].4py (.4py) and its treatment with the sodium salt of calix[8]arene led to the formation of the 1D polymer [U2(acac)6(calix[8]arene - 6H)(py)4Na4]n. The sandwich complex [Hpy]2[U(calix[4]arene - 3H)2][OTf].4py (.4py) was obtained by treatment of U(OTf)4 (OTf = OSO2CF3) with calix[4]arene in pyridine. All the complexes have been characterized by X-ray diffraction analysis.     

Synthesis of Macrocyclic Lactones Building on Double Calix[4]arenes

Naturalmacrocycliclactonesandlactamsastheionophoreshaveabsorbedextensiveinterestsbecauseoftheirveryhighselectiverecognitionforalkalimetals.rorexample,nactinslandvalinomycin'havethehighestselectivityforpotassiumamongalltheionopohores.Artificialmacrocycliclactonesalsoshowedselectivityforcanons,althoughthebindingstrengthwaslowerthanthatofcommoncrownethers3.Calixareneswereaveryimportantkindofartificialreceptors,whosederivativeshaveshowedthehighestselectivityforNa ,K andCs amongthesynthesizedmacro…     

Calix[4]arene stabilized Transition Metal Imido Complexes

The usage of calix[n]arenes as ancillary poly(phenolate) ligands is a rapidly developing area in coordination chemistry. This article focuses on the synthesis, structure and reactivity of calix[4]arene‐ and calix[4]arene ether‐stabilized imido complexes of group 4 — 6 transition metals as well as on the comparison of calix[4]arene dialkyl ethers in particular with other widely employed related ligand systems such as salenes, porphyrins and tetraazaannulenes. Contrary to these nitrogen containing systems, it is much easier to control the charge of the ligand system through the degree of alkylation of the calixarene's lower rim without a major change in the geometry of the resulting metal complex. This could lead to isoelectronic and structurally closely related transition metal complex fragments for metals in neighboring groups of the periodic table or for metals in different oxidation states. The “intrinsic” reactivity of metal imido linkages might therefore be explored using calix[4]arenes and calix[4]arene ethers and first results are summarized in this research report.     

Synthesis and reactivity of functionalized bridged m-xylylenedioxycalix[6]arenes

The synthesis of A,D-m-xylylene-bridged calix[6]arenes 1-8 functionalized at position 5 of the spacer arm is described. The cone conformation of the new bridged calix[6]arenes has been established by (1)H and (13)C NMR. The X-ray structure of compound 6 confirmed the cone conformation also in the solid state. Compounds 9 and 10, which are branched-like structures, were obtained by reductive amination of 5-amino-A,D-m-xylylene-bridged-B,C,E,F-tetra-O-ethylcalix[6]arene 7 with diformyl calix[4]arene and CTV derivatives 22 and 24, respectively.     

Synthesis and structures of an unusual germanium(II) calix[4]arene complex and the first germanium(II) calix[8]arene complex and their reactivity with diiron nonacarbonyl

The protonolysis reaction of the germanium(II) amide Ge[N(SiMe3)2]2 with calix[4]arene and calix[8]arene furnishes the two germanium(II) calixarene complexes {calix[4]}Ge2 and {calix[8]}Ge4, respectively, which have been crystallographically characterized. The calix[4]arene complex contains a Ge2O2 rhombus at the center of the molecule and is one of the only four germanium(II) calix[4]arenes that have been structurally characterized. The calix[8]arene species is the first reported germanium calix[8]arene complex, and it exhibits an overall bowl-shaped structure which contains two Ge2O2 fragments. The latter complex reacts with Fe2(CO)9 to yield an octairon compound, which has also been structurally characterized and contains four GeFe2 triangles arranged around the macrocyclic ring. The germanium(II) centers are oxidized to germanium(IV) in this process, with concomitant reduction of the neutral diiron species to Fe2(CO)(8)2- anions.     

新型偶氮杯[4]芳烃的合成与构象研究

使用相应的w-硫醚羧酸酰氯与杯[4]芳烃或者偶氮杯[4]芳烃酰化合成了一类新型的杯[4]芳烃衍生物。分离得到六个新化合物4a-4c和5a-5c，并使用MALDI, EA, ¹H和¹³C NMR进行了表征。NMR图谱表明偶氮杯[4]芳烃衍生物 5a-5c均为1,3-转换构型，而4a-4c则均为锥式构型。对偶氮杯[4]芳烃衍生物5a-5c的红外和紫外性质也进行了研究。     

A polymerized calix[6]arene monolayer having gas permeation selectivity that exceeds Knudsen diffusion

A polymerized monolayer of 5,11,17,23,29,35-hexamercaptomethyl-37,38,40,41,42-hexakis-(1-n hexadecyloxy)calix[6]arene (1) has been synthesized on the surface of an ca. 15 mum-thick film derived from poly[1-(trimethylsilyl)-1-propyne] (PTMSP). This monolayer exhibits a permeation selectivity toward He and SF6 that exceeds Knudsen diffusion. Analogous membranes made from a calix[6]arene that contains amidoxime headgroups (i.e., 2) showed Knudsen diffusion characteristics.     

Physicochemical Characterization of Hydrated 4-Sulphonato-Calix[n]arenes: Thermal,Structural, and Sorption Properties

In this study, the thermal behavior of three hydrated water-soluble 4-sulphonato calix[n]arenes was investigated. The melting points, heats of fusion, and heats of solution of the calix[4]arene, calix[6]arene and calix[8]arene were 277, 262, and 270°C; 192, 242 and 351 kJ/mol; and 30, 58 and 63 kJ/mol, respectively. Lower heat of fusion, smaller increase in entropy and smaller heat of solution of the calix[4]arene compared to the calix[6]arene and calix[8]arene showed that less heat was required to break up the crystal lattice of the smaller macromolecule. This apparent anomaly is rationalized in terms of smaller cooperativity of interaction between the molecules of calix[4]arene in the crystal lattice, although the strength of the individual interactions is stronger as evidenced by the higher melting point. TGA analysis indicated that about 17–20% of water was associated with the calix[n]arenes. Both TGA and hot stage microscopy results indicated that upon heating these molecules underwent stepwise water loss. TGA kinetics showed that the 4-sulphonato-calix[8]arene lost water easier than the other two calixarenes. The moisture adsorption behavior of all calixarenes followed type II isotherms. For the same amount of material, the calix[6]arene adsorbed more moisture than the calix[4]arene and the calix[8]arene. Moreover, dehydrated less crystalline 4-sulphonic-calix[n]arenes powders are hydroscopic.

     

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.     

Para-acylcalix[6]arenes: their synthesis, per-O-functionalisation, solid-state structures and interfacial assembly properties

The para-acylcalix[6]arenes bearing butanoyl, hexanoyl and octanoyl chains have been synthesized by Friedel–Crafts acylation of the parent calixarene. Persubstitution at the phenolic face was achieved to yield the methoxy-diethoxy, ethoxycarbonylmethoxy, methoxycarboxylic acid and butoxysulphonate derivatives. In the case of the derivatives, 5,11,17,23,29,35-hexa-octanoyl-37,38,39,40,41,42-hexa-methoxy-diethoxy-calix[6]arene, 5,11,17,23,29,35-hexa-butanoyl-37,38,39,40,41,42-hexaethoxycarbonyl methoxy-calix[6]arene and 5,11,17,23,29,35-hexa-octanoyl-37,38,39,40,41,42-hexaethoxycarbonyl methoxy-calix[6]arene the solid state structures were determined and show inclusion of two ester groups in the cavity. While for the para-acylcalix[6]arenes no stable monolayers can be formed at the air–water interface, stable monolayers are formed with the methoxy-diethoxy, ethoxycarbonylmethoxy, methoxycarboxylato compounds which show apparent molecular areas in the range 150–200 Å² depending on the length of the acyl chains.     

Silver(I) N-heterocyclic carbene-bridged calix[4]arene analogues as efficient [60]fullerene receptors

Two silver(I) N-heterocyclic carbene-bridged calix[4]arene analogues 4 and 5 were synthesized by a fragment-coupling approach; the preliminary inclusion properties of 5 with [60]fullerene shows that it is a novel efficient [60]fullerene fluorescent sensor.     

Evaluation and solubility improvement of Carvedilol: PSC[n]arene inclusion complexes with acute oral toxicity studies

The aqua phobic molecules that are practically insoluble in aqueous media demonstrate a staggeringly slow intrinsic dissolution rate. In this work, we exemplify the utility of calixarenes as a tool to form inclusion complexes with Carvedilol (CDL). It is poorly water soluble drug. CDL is a Biopharmaceutical Classification System (BCS) Class II drug and it is a nonselective β-adrenegenic blocking agent with α1-blocking activity. It is mainly used in the management of hypertension. The maximum complexation of the drug was accomplished after 48?h of stirring with para sulphonato calix[4]arene (PSC[4]arene) and para sulphonato calix[6]arene (PSC[6]arene) in water and evaporation of water to acquire solid complexes. The study includes characterisation of both the complexes—physical mixtures of drug and PSC[4]arene and PSC[6]arenes by different methods like Fourier-transform infra red spectroscopy, differential scanning calorimetry and powder X-ray diffraction, proton nuclear magnetic resonance. This studies shows that there is electrostatic interaction between drug and PSC[n]arenes. The complexation was determined by phase solubility study. The prepared complexes exhibited improved in vitro dissolution profile and decreased in vivo acute oral toxicity compared to the pure drug.     

Absorption spectrophotometric study of supramolecular complexation of [60]- and [70]fullerenes with 24,26-dimethoxy-25,27-dihydroxy calix[4]arene

Supramolecular interactions of 24,26-dimethoxy-25,27-dihydroxy calix[4]arene (1) with [60]- and [70]fullerenes have been studied in only chloroform and in a ternary solvent mixture comprising of chloroform, ethyl alcohol and toluene by UV-vis absorption spectrophotometric method. The experimental results are explained using the model that takes into account the interaction between electronic subsystems of 1 and fullerene. The most interesting feature is the preference of [60]fullerene over [70]fullerene for 1 in ternary solvent mixture as revealed by higher value of formation constant of [60]fullerene/1 complex. The selectivity towards [60]fullerene opens up the way toward self-assembling systems and new separation and purification methods for fullerenes.