Search results for "calixarene"
showing 10 items of 149 documents
Cyclodextrin‐Calixarene Nanosponges as Potential Platforms for pH‐Dependent Delivery of Tetracycline
2019
Four mixed cyclodextrin-calixarene nanosponges were tested as possible Drug Delivery Systems, using Tetracycline antibiotic as a suitable model drug. The selected nanosponges featured a different composition ratio between the two host co-monomer components, and the possible presence of ionisable amine or carboxyl groups deriving from chemical post-modification. The pH-dependent absorption and release abilities of the materials were verified; in particular release kinetics showed the occurrence of a simple first-order profile. The antibacterial activity of nanosponge-tetracycline composites suitably prepared under sterile conditions was assayed towards both Gram-positive and Gram-negative ty…
Anionic tert-butyl-calix[4]arenes substituted at the narrow and wide rim by cobalt bis(dicarbollide)(1−) ions and CMPO-groups. Effect of stereochemis…
2013
Abstract Two ionic calix[4]arenes substituted at the narrow rim with an unpaired number ( n ) of cobalt bis(dicarbollide)(1−) anions ( 1 − ) ( n = 1 and 3) and (4 − n ) CMPO groups ( 3c , 4c ) have been synthesized via a three-step procedure based on nitrile substituted calix[4]arene precursors. Conjointly with them, the compound with a paired ratio of the groups, where n = 2 and the same substituents are located in mutually adjacent 1,2-positions, is reported ( 5c ). Another compound with the paired ratio, but from a wide rim series ( 6c ) ( n = 2) was successfully prepared starting from calix[4]arenes substituted with two nitro functions and two –OH sites available for further modific…
A calixarene-based chromoionophore for the larger alkali metals
1995
Abstract A bis(arylazo)calix[5]arene crown ether derivative displays large spectral changes upon complexation of cesium and rubidium salts, with good selectivity over the smaller alkali metals.
Crown ethers derived from bicyclocalix[4]arenes as chromoionophores
2001
The synthesis of calix[4]arenes in which opposite phenolic units are connected by a poly(oxyethylene) bridge at the narrow rim and a 2,6-dimethylene-4-nitrophenol bridge at the wide rim is reported. For two derivatives with tetra- (4) and penta(oxyethylene) (5) bridges UV-Vis spectrophotometric studies were carried out in buffered solution in the presence of alkali metal ions. Their complexation was associated with changes in their UV-Vis spectra, especially with an increase of the absorption band at 450 nm. For 4 and 5 this was most intense in the presence of potassium and caesium ions, respectively, indicating that the calixarene with the shorter crown ether bridge is selective towards po…
Effect of pH Variations on the Properties of Cyclodextrin‐Calixarene Nanosponges
2019
The pH-responsive properties of cyclodextrin-calixarene nanosponge co-polymeric materials have been investigated. In particular, ISE-H+ potentiometric titrations were carried out in order to evaluate the acid-base properties and the actual amount of ionizable sites present in the materials. Moreover, the relevant pH-dependent adsorption abilities were evaluated towards a set of selected model organic pollutant molecules by means of adsorption tests and by studying the corresponding adsorption isotherms. The latter ones could be suitably described by means of the Freundlich model. The whole of the experimental results enabled us to clarify some general aspects of the microscopic behavior of …
Structure of 5,17-dimethyl-11,23-dioctylcalix[4]arene
1991
The title compound C46O4H60 crystallizes in the triclinic space group, P¯1, witha=11.584(2),b=16.261(2),c=11.172(1) A,α=103.15(8),β=95.68(1),γ=96.85(1)°. The structure was solved by direct methods, and refined by weighted full-matrix least squares toR=0.097. This is the second calix[4]arene with two different alkyl substituents atpara positions of the phenolic rings. The macrocycle adopts the cone conformation. Interactions CH3-π are established between two calixarenes related by a center of symmetry. Comparisons are made between the conformation of this molecule and that of symmetrically substituted calix[4]arenes.
Mannich Reactions with Amino Alcohols
2000
The condensation of resorcarenes 1 with various amino alcohols and an excess of formaldehyde was studied. The tetrabenzoxazines 2a−e were found as the only products in the reaction with 6-aminohexan-1-ol, 4-aminobutan-1-ol, and 2-aminoethanol, while 3-aminopropan-1-ol forms the tetraoxazine 3 as the main product. In the case of aminoethanols substituted at the 2-position with alkyl groups, the tetraoxazolidines 4 are the preferred reaction products, while 1-methyl aminoethanol (1-amino-propan-2-ol) yields predominantly the tetrabenzoxazine 2f. The structures of all these compounds have been confirmed by NMR spectroscopy and additionally by single-crystal X-ray analysis in the case of 2a and…
Regioselective synthesis of calixcrowns derived from p-tert-butylcalix[5]arene
1993
Abstract Alkylation of p-tert-butylcalix[5]arene with oligoethylene glycol-ditosylates in the presence of CsF affords the 1,3-bridged calix[5]crowns 1a–c in 51 to 72% yield. In the case of hexaethylene glycol the isomeric 1,2-bridged calix[5]crown-7 2c was obtained additionally. The calixcrowns were further modified by alkylation of the remaining hydroxyl groups.
Diastereoselective Functionalization of a Spherand‐Type Calixarene
1994
Condensation of 5,5'-di-tert-butyl-2,2'-dihydroxybiphenyl (1) with formaldehyde yields a cyclic trimer 2 (and tetramer 3) having three (four) methylene groups less than a calix[6]arene (calix[8]arene). Alkylation of the (flexible) trimer with ethyl bromoacetate gives exclusively the stereoisomer 4 with C 2 symmetry, while the isomer with D 3 symmetry is not observed. Two isomers 6a and 6b (C 2 and C 1 symmetry) are obtained by treatment with tert-butyl bromoacetate which both are converted by transesterification with methanol into the same hexamethyl ester 5 having C 2 symmetry. These results are rationalized by restricted rotation around Ar-Ar bonds for larger O-alkyl groups also around Ar…
Cyclodextrin–calixarene co-polymers as a new class of nanosponges
2014
Hyper-reticulated co-polymers jointly formed by cyclodextrin and calixarene units, which can be considered as a new class of nanosponges, were easily obtained by means of a click chemistry approach. In particular, we succeeded in preparing our materials by exploiting the copper-catalyzed 1,3-dipolar cycloaddition (CuAAC) reaction between heptakis-(6-deoxy)-(6-azido)-beta-cyclodextrin and (5,11,17,23-tetra-tert-butyl)-(25,26,27,28-tetra-propargyloxy)-calix-[4]-arene, mixed in different proportions. These materials were fully characterized by means of combined FT-IR, thermogravimetric, C-13 {H-1} CP-MAS NMR and nitrogen adsorption/desorption techniques. In particular, C-13 {H-1} CP-MAS spectr…