A giant coordination cage based on sulfonylcalix[4]arenes

A strategy for building coordination cages by a [6 + 8] condensation of M(II)(4)-calix SBUs and rigid ancillary ligands was successfully applied to a cobalt-sulfonylcalix[4]arene system. A giant cage obtained with BTE ligands has an overall periphery diameter of 5.0 nm and an internal spherical cavity of 2.3 nm.     

Bilayers, corrugated bilayers, and coordination polymers of p-sulfonatocalix[6]arene

Exploration into the host-guest supramolecular chemistry of p-sulfonatocalix[6]arene with pyridine N-oxide and 4,4'-dipyridine N,N'-dioxide has resulted in the characterization of three new structural motifs with the calixarene in the "up-down" double partial cone conformation. Two are hydrogen-bonded network structures formed with pyridine N-oxide and either nickel or lanthanide metal counterions (1 and 2, respectively). Complex 1 displays host-guest interactions between pyridine N-oxide and the calixarene in the presence of hexaaquanickel(II) counterions. Complex 2 demonstrates selective coordination modes for different lanthanides involving the calixarene and pyridine N-oxide. The third structure, 3, is a coordination polymer which is formed with 4,4'-dipyridine N,N'-dioxide molecules which span a hydrophilic layer and join lanthanide/p-sulfonatocalix[6]arene fragments. Although complexes 1-3 all have the calixarene in the "up-down" double partial cone conformation, 1 and 3 form bilayer arrangements within the extended structures while 2 forms a previously unseen corrugated bilayer arrangement.     

Anion receptors based on ureido-substituted thiacalix[4]arenes and calix[4]arenes

The regioselective nitration of 25,27-dipropoxythiacalix[4]arene was carried out as a key step in the synthesis of thiacalix[4]arene derivative bearing two arylureido functions on the upper rim. The preorganisation of ureido units using the thiacalix[4]arene/calix[4]arene moieties as a molecular scaffold gave novel anion receptors. These compounds, albeit based on hydrogen bonding interactions, show good complexation ability even in highly HB-competitive solvent, such as DMSO. Direct comparison of otherwise identical structures 6a and 7a revealed remarkable dominance of the thiacalix[4]arene derivative over its classical analogue in anion binding.     

Scandium triflate-catalyzed cyclocondensation of 1,3-dialkoxybenzenes with 1,3,5-trioxane. Formation of resorcin[4]arenes and confused resorcin[4]arenes

The cyclocondensation of 1,3-dialkoxybenzenes with 1,3,5-trioxane was catalyzed by Sc(OTf)₃ to produce resorcin[4]arene octaalkyl ethers as the major products. In addition, ‘confused’ resorcin[4]arene octaalkyl ethers bearing one alkoxy group at the intra-annular position were obtained as the minor products. The variable temperature ¹H NMR spectroscopy showed that the alkoxy group at the intra-annular position cannot pass through the macrocyclic annulus, indicating a rigid molecular framework. The structure of the ethoxy derivative of the confused resorcin[4]arene was determined by X-ray crystallography.     

Study on the inclusion interaction of p-sulfonatocalix[n]arenes with norfloxacin

The inclusion complexes of norfloxacin (NFX) with p-sulfonatocalix[n]arenes (SCXn) were studied. The characteristics of host–guest (HG) complexation between p-sulfonatocalix[n]arenes with NFX were investigated by fluorescence spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). Stoichiometry and association constants (K) of the inclusion complexes were determined by the non-linear fitting method. An interesting 1:1 stochiometric of HG complexes were formed at different pH values (pH = 3.00, 6.00, 8.00) The inclusion mode of NFX with p-sulfonatocalix[n]arenes was confirmed by NMR spectroscopy.     

Fourfold [2]rotaxanes based on calix[4]arenes

Tetraurea calix[4]arenes with four loops form exclusively heterodimers with open-chain urea calix[4]arenes when they are dissolved in aprotic solvents. These assemblies can be considered as pseudorotaxanes. If open-chain tetraureas ending with maleic imide functions are used, their Diels-Alder reaction with 1,4,5,8-tetrapentoxyanthracene leads to tetra[2]rotaxanes which cannot be split into the single calixarene parts by hydrogen bond breaking solvents.     

Anion receptors based on ureido-thiacalix[4]arenes

The regioselective ipso-nitration of tert-butylthiacalix[4]arene-tetrasulfone was used for the construction of thiacalixarene derivatives bearing one or two arylureido functions on the upper rim. The preorganization of ureido units using the thiacalix[4]arene moiety as a molecular scaffold leads to novel anion receptors with good complexation ability toward selected anions of various geometry (halides, carboxylates, HSO₄⁻, H₂PO₄⁻, NO₃⁻, CN⁻) in organic solvents.     

'Molecular capsules' based on p-sulfonatocalix[6]arene shrouding two tetraphenylphosphonium cations

p-Sulfonatocalix[6]arene in the double cone conformation forms a molecular capsule-like arrangement confining two tetraphenylphosphonium cations, as part of an extended structure involving layers of additional tetraphenylphosphonium cations, aquated lanthanide ions and a large array of water molecules.     

Reorientational dynamics of p-sulfonatocalix[4]arene and of its La(III) complex in water

The reorientational dynamics of p-sulfonatocalix[4]arene and of its La(III) complex in deuterated water were studied by 1H NMR longitudinal relaxation rates. It is shown that the relaxation is purely dipolar in the non-extreme narrowing regime. The distance between the geminal protons could be determined from the NMR data, giving good agreement with the values generally used in correlation time calculations. The correlation times show an Arrhenius behaviour in good agreement with previously reported data from 13C measurements for a similar uncomplexed calixarene. The Arrhenius energies of activation are identical for the uncomplexed and the complexed calixarenes, suggesting a reorientational motion strongly dependent on the structure of the water cage around the complex. This is also in agreement with a complexation of the La(III) cation in the second sphere of solvation of the sulfonate groups, as shown by molecular dynamics simulations.     

Site specific Co(III) sarcophagine binding in multi-component phosphonium and p-sulfonatocalix[4]arene systems

Co(III) sarcophagine-type cage molecules, [Co(diCLsar)](3+) or [Co(HONOsar)](3+), form either 1 : 1 or 1 : 2 host-guest inclusion complexes with mono-phosphonium cations and sodium p-sulfonatocalix[4]arene in the solid state yielding complex I [p-sulfonatocalix[4]arene·Co(diCLsar)·2{benzyltriphenylphosphonium}], complex II [2{p-sulfonatocalix[4]arene}·Co(diCLsar)·3{tetraphenylphosphonium}] and complex III [p-sulfonatocalix[4]arene·Co(HONOsar)·tetraphenylphosphonium]. The diversity of the structural types of these multi-component systems, including the orientation of the Co(III) molecules in the cavities of the calixarenes, depends on the nature of their terminal functional groups. The secondary coordination interactions binding between the Co(III) molecules and p-sulfonatocalix[4]arene have also been investigated in water using NMR techniques.     

Photoactive Eu(III) and Tb(III) complexes of calix[4]arenes with pyridine-N-oxide pendant groups

Two calix[4]arenes with four 2-pyridyhnethyl-l-oxide pendant groups at the lower rim have been synthesized, and their Tb(III) and Eu(III) complexes are fluorescent upon UV light excitation at 312 nm. The complexes are not stable in aqueous solution, completely losing their luminescent properties.     

Porphyrin-Calix[4]arenes

The review deals with the synthesis, chemical modification, and complexing properties of a new class of molecular receptors, porphyrin-calix[4]arene conjugates.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 6, 2005, pp. 807–826.Original Russian Text Copyright © 2005 by Mamardashvili, Koifman.     

Guest exchange in dimeric capsules formed by tetra-urea calix[4]arenes

Ten tetra-urea calix[4]arene derivatives with different ether residues (methyl, pentyl, benzyl, all combinations of methyl and pentyl, 1,3-dibenzyl-2,4-dipentyl), including also the tetrahydroxy compound and the 1,3-dipentyl ether, were synthesised. Their urea groups were substituted with a lipophilic residue to ensure sufficient solubility in cyclohexane. Thus, kinetics for the exchange of the included guest (benzene) against the solvent (cyclohexane) could be followed by 1H NMR spectroscopy. The apparent first order rate constants decrease with increasing size of the ether residues from methyl to benzyl by more than three orders of magnitude. This can be understood by a decreasing flexibility/mobility of the calixarene skeleton. In line with this explanation is the rather slow exchange for the tetrahydroxy compound, where the cone conformation is stabilised by a cyclic array of intramolecular OH...OH hydrogen bonds.     

Synthesis of novel calix[4]arenes containing organosilicon groups

Metalation of (RSiMe₂)₃CH (1a R = H, 1b R = Me, 1c R = Ph) with lithium diisopropylamide (LDA) or methyllithium in THF gave organolithium reagents (RSiMe₂)₃CLi, which reacted with the formylated calixarene (2), to give the corresponding 5,17-bis[2,2-bis(organosilyl)-1-ethenyl]-25,26,27,28-tetrapropoxycalix[4]arenes (3a, 3b and 3c) via the Peterson olefination. The compounds (RSiMe₂)₃CLi were treated with 25,26,27,28-tetrakis(4-bromobutoxy)calix[4]arene (4) to give 25,26,27,28-tetrakis[4-(tris(dimethylsilyl)methyl)butoxy] calix[4]arene (5a) and 25,26,27,28-tetrakis[4-(tris(trimethylsilyl)methyl)butoxy] calix[4]arene (5b) via nucleophilic substitution reactions. However the compound 25,26,27,28-tetrakis[4-(tris(dimethylphenylsilyl)methyl)butoxy] calix[4]arene (5c) was not obtained, presumably because (PhSiMe₂)₃C- is highly sterically hindered and the reactivity of its derivatives is low. The compound 5a has potential as a core for dendrimers.     

Synthesis of new calix[4]arenes containing nucleoside bases

A family of novel calix[4]arene derivatives containing nucleoside bases were designed and synthesized. Coupling reaction between para mono- or bis-amino calix[4]arenes 5, 6 or 7 and thymin-1-ylacetic acid in the presence of DCC afforded mono- or bis-thymine-substituted calix[4]arenes 8, 9 or 10 in over 70% yield. Owing to the low solubility of adenine-N⁹-ylacetic acid in DMF and DMSO and the weak nucleophilicity of aminocalix[4]arene derivatives, alternatively, the substitution reaction of bromoacetylated aminocalix[4]arenes derivatives 11, 12, 13 with adenine in the presence of sodium hydride was carried out to synthesize mono- or bis-adenine-substituted calix[4]arenes. Two kinds of isomers 15 and 16 or 17 and 18 were obtained due to the non-regiospecific alkylation of adenine, and their structures have been confirmed by ¹³C NMR and ¹H NMR spectra.     

Synthesis of （p-Formylphenyl）azo Calix[4]arenes

Five novel azo calix[4]arenes were reported. The p-aminobenzaldehyde was diazotized with sodium nitrite in aqueous hydrochloride solution. Mono-, bis-, tris- and tetrakis(p-formylphenyl)azo calix[4]arenes (including proximal and distal isomers) were obtained respectively by diazo-coupling in different molar ratio to calix[4]arene(1) under pH=7.5--8.5 at 0-5℃. All (p-formylphenyl)azo calix[4]arenes were characterized by ^1H NMR, ^13C NMR, IR, MS (ESIMS) spectroscopies and elemental analysis.     

Recognition-mediated contrasting fluorescence behaviour of 4′,6-diamidino-2-phenylindole (DAPI): probing the pKa of p-sulfonatocalix[4/6]arenes

Abstract

The interaction between a biologically important dye, 4′,6-diamidino-2-phenylindole (DAPI) and a macrocyclic host, p-sulfonatocalix[6]arene (SCX6) has been investigated using ground-state absorption, steady-state as well as time-resolved fluorescence measurements at two preset pH conditions: 2.5 and 6. Acknowledging the complexation with SCX6 at both the pHs with strong binding, DAPI shows spectral shifts in the absorption and emission spectra; however, strikingly, the fluorescence intensity behaviour is seen contrastingly opposite. At lower pH (~2.5), DAPI displays six-fold intensity, whereas drastic quenching in the fluorescence intensity is recorded at pH 6. Detailed spectroscopic analysis revealed that the SCX6 with phenolate ion stabilised at the lower rim, prevailing at pH 6, efficiently quench the excited state of DAPI, presumably through an electron transfer process, whereas at pH 2.5, the undissociated phenolic groups extend the dye a favourable encapsulation to prevent the excited-state protonation process resulting in remarkable enhancement in the fluorescence. This interesting host–guided fluorescence response with pH is worth as fluorescence on-off switch at lower pH conditions as well as the DAPI system offers a good optical probe for the easy determination of the pK_a of p-sulfonatocalixarenes by visible fluorescence measurements.     

Lanthanide-induced helical arrays of [{Co(III) sepulchrate} intersection {p-sulfonatocalix[4]arene}] supermolecules

In the presence of lanthanide ions, a Co(III) sepulchrate cation [Co(diHOsar)]3+ and sodium p-sulfonatocalix[4]arene form a 1:1 host-guest complex which is self-assembled into a zeolite-like lattice network comprised of parallel, single stranded helices.     

Thermodynamic origins of selective binding affinity between p-sulfonatocalix[4,5]arenes with biguanidiniums

The binding geometries, abilities and thermodynamic parameters for the intermolecular complexation of two water-soluble calixarenes, p-sulfonatocalix[4]arene (SC4A) and p-sulfonatocalix[5]arene (SC5A), with biguanidinium guests, metformin (MFM) and phenformin (PFM), were investigated by (1)H and 2D NMR spectroscopy, X-ray crystallography, and isothermal titration calorimetry (ITC). The obtained results show that biguanidinium guests are captured by calixarenes with the alkyl or aromatic portion immersed into the cavities and the guanidinium portion fixed at the upper-rims. At both acidic and neutral conditions, SC4A always presents stronger binding affinities to biguanidinium guests than SC5A. Moreover, SC4A prefers to include MFM rather than PFM. As a result, the binding selectivity of MFM is up to 44.7 times for the SC4A/SC5A hosts. The intrinsic relationship between binding structures and selectivities were comprehensively analyzed and discussed from the viewpoint of thermodynamics. Finally, the ITC measurements were further performed in phosphate buffer instead of aqueous solution, to examine the buffer effects, counterion effect, and the differences between thermodynamic and apparent association constants.