Host–guest interactions between calixarenes and Cp2NbCl2

Abstract

The possible inclusion complexes of Cp2NbCl2 into calixarenes hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed by a combination of NMR, ab-initio calculations, thermogravimetric analysis, FTIR, Raman and PXRD. Ab-initio calculations, 1H NMR solution and solid state 13C CP MAS NMR results demonstrated that p-sulfonic calix[6]arene does form an inclusion complex with Cp2NbCl2. Raman spectroscopy showed, for the inclusion compound of p-sulfonic calix[6]arene-Cp2NbCl2, a band between 500–850 cm−1 characteristic of Nb-O vibration. This result suggests that Nb(V) may engage in coordination with the oxygen of the sulfonate group, as part of the host-guest interaction. However, it is important to mention that the niobocene dichloride (Cp2NbCl2) dissolves in water and undergoes oxidation and hydrolysis processes to yield Cp2NbCl2(OH) species. For that reason this band does not exclude that the Nb-O band belongs to Cp2NbCl2(OH). Solid State 13C CP MAS NMR and solution 1H NMR spectroscopies together with ab-initio results showed that Cp2NbCl2 is included in the p-sulfonic calix[6]arene cavity, with both Cp rings inside the cavity. In contrast, the solution 1H NMR results demonstrated that calix[6]arene does not form inclusion complex with Cp2NbCl2 in CDCl3 solution. Cp2NbCl2 is not included in the calix[6]arene cavity, possibly due to the lack of sulfonate heads which promote Nb-O interactions and assist the inclusion of Cp2NbCl2 into the cavity.

Calixarenes: Generalities and Their Role in Improving the Solubility, Biocompatibility, Stability, Bioavailability, Detection, and Transport of Biomolecules

“…Furthermore, as mentioned above, the calix[ n ]arenes can be functionalized at both rims, R and –OH (Figure 3) [51,52,53], producing a wide variety of compounds that can have different complexing properties. In particular, calix[ n ]arenes functionalized with a sulfonic group in the para position have been found to have several pharmaceutical applications, due to their potential for encapsulating drugs, increasing their solubility, bioavailability, oral absorption, and stability under heat, light, and acidic conditions [54,55,56].…”

Study on Complex Formation of Fluorescein-p-Sulfonatocalix[4]arene by Spectroscopic Methods

“…The formation constant of the p-Sulfonatocalix [4]arene with FL system has been performed by spectrophotometric and spectrofluometric titrations in water. It has been shown from NMR data that FL is inserted partially into the cavity of p-SCX4 due to favorable formation constant of π-π interactions with benzene rings and electrostatic interactions with the 3 …”

“…The present study investigate the formation for complexation of fluorecscein by water soluble p-Sulfonatocalix [4]arene and discuss about their interaction.…”

“…p-Sulfonic calix[n]arenes provided not only hydrophobic environment (benzene rings) with the above favorable properties, but also hydrophilic heads (sulfonates) and form water soluble encapsulated complexes [4]. Many researchers have studied inclusion properties of water soluble calixarenes with organic ions and neutral molecules [5]- [15].…”

Syntheses and reactivity of calixarenes functionalized at meso positions

“…Since the investigation of calixarenes dealing with their syntheses, reactivity and a large variety of applications is very intense, [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] only selected examples of considered compounds are described in this review.…”