0000000000710450
AUTHOR
Rocco Ungaro
Cobalt bis(dicarbollides)(1-) covalently attached to the calyx[4]arene platform: the first combination of organic bowl-shaped matrices and inorganic metallaborane cluster anions
Various calix[4]arene and resorc[4]arene ionic compounds substituted by cobalt bis(dicarbollide) anions (1) have been prepared for the first time. From tBu-calix[4]arene (A) the complete series of mono-, di-, tri- and tetrasubstituted derivatives bearing one to four cluster anions on the lower rim (3-6) have been obtained in the form of their alkali-metal salts by O-alkylation with the 1-dioxane derivative [8-O(CH2CH2)2O(+)-1,2-C2B9H10)-(1',2'-C2B9H11)-3,3'-Co] (2), all of which are syn or cone isomers. In contrast, disubstitution of the dipropyl ether of tBu-calix[4]arene (B) led to a mixture of the cone and 1,3-alternate conformers 7a and 7b, respectively. Starting from tetrapropoxy-calix…
Dendrimer-coated magnetic particles for radionuclide separation
Magnetic particles were synthesised for radionuclide removal from nuclear wastes by magnetic separation. Dendrimers with terminal amino groups attached to the particle surface were used to bind chelating groups for lanthanides and actinides. This led to a 50–400-fold increase of the distribution coefficients for europium and americium in comparison to the reference particles without the dendrimers. Back-extraction studies have demonstrated the possibility of multiple particle recycling.
Calixarenes as Stoppers in Rotaxanes
The synthesis of the amide-based rotaxane 7a bearing calix[4]arene blocking groups is described for the first time. While rotaxane formation fails if a calix[4]arene is functionalized at the upper rim with only an amino or methylamino group lacking any spacer, the prolonged amine 5a works successfully as stopper unit preventing dethreading of the dimeric wheel 1a by its size. Rotaxane formation of 8b was observed only by MALDI-TOF mass spectrometry of the reaction mixture of the amine 5b, the axle 6 and 1a. With the larger trimeric wheel 1b no stable rotaxane could be obtained. It either does not act as a concave template or its opening is too wide, even for the bulky calixarene stoppers.
CMPO-substituted calix[6]- and calix[8]arene extractants for the separation of An3+/Ln3+ from radioactive waste
Abstract Three calix[6]arene derivatives ( 1a – c ) and two calix[8]arene derivatives ( 2a , b ), with six and eight CMPO residues, respectively, attached to the narrow/lower rim via ether links, were synthesised. Preliminary liquid–liquid extraction studies for Eu(III) and Am(III) from aqueous nitric acid to o -nitrophenylhexyl ether reveal remarkable properties with respect to efficiency and selectivity, especially for the tert -butylcalix[6]arene derivative with a –(CH 2 ) 3 – spacer.
Arginine clustering on calix[4]arene macrocycles for improved cell penetration and DNA delivery
Cell-penetrating peptides are widely used as molecular transporters for the internalization inside cells of various cargo, including proteins and nucleic acids. A special role is played by arginine-rich peptides and oligoarginines covalently linked or simply mixed with the cargo. Here we report cell-penetrating agents in which arginine units are clustered on a macrocyclic scaffold. Instead of using long peptides, four single arginine units were covalently attached to either the upper or lower rim of a calix[4]arene, kept in the cone conformation building a ‘parallel’ cyclic array. These new macrocyclic carriers show high efficiency in DNA delivery and transfection in a variety of cell lines.
Strontium complexes of calixarene amides in the solid state: structural dependence on the ligand size and on the counter ions
For the first time, crystal structures of three strontium complexes of calixarene amides have been determined. A p-tert-butylcalix[6]arene hexaamide forms a 1∶1 complex with Sr(Pic)2 (Pic = picrate), whereas p-tert-butylcalix[8]arene and p-methoxycalix[8]arene octaamides encapsulate two strontium cations each. The binding geometries of the metal cations depend on the ligand size and on the counter anion used (chloride or picrate).