Outer-Sphere Association of p-Sulfonatothiacalix[4]arene and Tetrasulfonatomethylated Calix[4]resorcinarene with Cobalt(III) Tris(dipyridyl): The Effect on the Spectral and Electrochemical Properties of the Latter

P-Sulfocalix[6]arene as Nanocarrier for Controlled Delivery of Doxorubicin

Given the high toxicity of the anthracycline antibiotic doxorubicin (DOX), it is relevant to search for nanocarriers that decrease the side effects of the drug and are able to transport it towards a therapeutic target Here, the encapsulation of DOX by p-sulfocalix[6]arene (calix) has been studied. The interaction of DOX with the macrocycle, as well as with DNA, has been investigated and the equilibrium constant for each binding process estimated. The results showed that the binding constant of DOX to DNA, K_DNA , is three orders of magnitude higher than that to calix, K_calix . The ability of calixarenes to encapsulate DOX molecules, as well as the capability of the DOX molecules included into the inner cavity of the macrocycle to bind with DNA have been examined. Cytotoxicity measurements were done in different cancer and normal cell lines to probe the decrease in the toxicity of the encapsulated DOX. The low toxicity of calixarenes has also been demonstrated for different cell lines.

Binding of Ru(NH3)5pz2+ to 4-sulfocalix[4]arene sodium salt. Effects of the host-guest interaction on electron transfer processes

The reactions [Ru(NH3)5pz]2++S2O8(2-) and [Ru(NH3)5pz]2++[Co(C2O4)3]3- have been studied in solutions of 4-sulfocalix[4]arene sodium salt. Results show a binding of the ruthenium complex to the calixarene with a 2:1 stoichiometry; that is, a ruthenium molecule binds to two calixarene molecules. This stoichiometry changes when NaCl is added to the medium. Thus, a mixture of 1:1 and 2:1 adducts is found in the presence of 0.1 mol dm(-3) NaCl and only 1:1 adducts when the salt concentration is increased up to 0.3 mol dm(-3). Results show that the binding of the ruthenium complex to the calixarene is due to electrostatic and nonelectrostatic interactions. Kinetic data are interpreted by using the pseudophase model and taking into account the stoichiometry of the ruthenium binding to calixarene. The presence of a supporting electrolyte in the medium produces ion pair formation which exerts an influence on the kinetic rate constants.

Cooperative and noncooperative binding of *Ru(bpy)3(2+) to DNA and SB4.5G dendrimers

The process *Ru(bpy)(3)(2+) + S(2)O(8)(2-) in two different reaction media, the SB4.5G dendrimer and DNA solutions, was studied. In both media, the receptors have anionic characteristics. This fact will produce a binding of the ruthenium complex to the two receptors by attractive electrostatic interactions. On the contrary, the peroxodisulfate ions will be preferentially located in the aqueous solution due to electrostatic repulsions with the receptors. Despite the similarities of the receptors, some differences are observed in these two reaction media. These differences arise from the fact that the binding of the *Ru(bpy)(3)(2+) complex to DNA shows a negative cooperativity, whereas the binding to the dendrimer is noncooperative in character. The anticooperative character of the binding that happens in DNA solutions becomes noncooperative when an electrolyte, NaNO(3), is added to the medium. This is related to a condensation of the salt's counterions on the surface of the DNA which produces a decrease of the equilibrium constant corresponding to the binding of the complex to the receptor. Therefore, it is shown that the ionic strength of the reaction medium exerts a great influence on the cooperative nature of the ligand/receptor binding. This also explains the different behavior observed in DNA and dendrimer solutions.

Novel highly charged silica-coated Tb(III) nanoparticles with fluorescent properties sensitive to ion exchange and energy transfer processes in aqueous dispersions

Novel silica-coated Tb(III) nanoparticles with high luminecsence were synthesized using the reverse microemulsion procedure. The quenching of luminescent properties of these nanoparticles can be achieved by ion exchange and energy transfer mechanisms. The quenching through the ion exchange of Tb(III) by H+ or La(III) is time dependent, indicating that the ion exchange is probably diffusion controlled. The quenching by Co(III) complex cations is achieved by the energy transfer mechanism and thus is not time dependent. The analysis of quenching data in Stern-Volmer cooordinates reveal the negative charge of the silica-coated Tb(III)-TCAS nanoparticles and several types of luminophoric species, located within the core and close to the surface of silica nanoparticles.

Rigidity and/or Flexibility of Calixarenes. Effect of the p-Sulfonatocalix[n]arenes (n = 4, 6, and 8) on the Electron Transfer Process [Ru(NH3)5pz]2+ + Co(C2O4)33-

The reaction [Ru(NH3)5pz]2+ + Co(C2O4)33- has been studied in aqueous solutions of p-sulfonatocalix[n]arene (n = 4, 6, and 8). The results are interpreted by using the pseudophase model. Results show that the rigidity and/or flexibility of the assembled rings have a great effect on the thermodynamics of inclusion of the guest into the host and, therefore, on the kinetics of the electron transfer processes that take place in these media. The obtained results are discussed from the viewpoint of two types of interactions: electrostatic and nonelectrostatic. From surface potential measurements, the guest-host interactions have been demonstrated to be mainly due to nonelectrostatic interactions, although the species are charged. So, the nonelectrostatic contribution to the equilibrium constant in all the calixarenes studied is 1 order of magnitude higher than the electrostatic one (Knel = 144 and 884 mol-1 dm3 for p-sulfonatocalix[n]arene (n = 4 and 6, respectively) and Kel approximately 10 mol-1 dm3). Electrostatic interactions also affect the kinetic results.

Montreal Medal Award Lecture — Coordination chemistry of molecular bowls: Ligands and their complexes derived from resorcinarenes

A review is given of the design, synthesis, structures, and properties of octadentate or tetradentate ligands and their coordination compounds, based on the bowl-like resorcinarene skeleton.Key words: resorcinarene, coordination, phosphine, thiophosphinate, polymer.

Lanthanide-induced helical arrays of [{Co(iii) sepulchrate} ∩ {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.