Colloidal Nature of Cationic Calix[6]arene Aqueous Solutions

Abstract

The study of the aqueous solutions of the cationic hexameric calixarene 5,11,17,23,29,38,39,40,41,42hexametoxycalix[6]arene hexachloride demonstrates their colloidal nature. Within the concentration range from 1 × 10 −5 to 0.01 M, this compound forms positively charged aggregates of a much larger size as compared with those of tetrameric cationic calix[4]arene previously studied by us. The aggregation was confirmed both by DLS and TEM experiments; the last method revealed that the 10 2 to 10 3 nm sized particles consist of smaller primary aggregates. These aggregates manifest themselves in displaying alteration of absorption spectra and marked shifts of apparent ionization constants of common acid−base indicators. These shifts resemble those registered in micellar solutions of cationic surfactants and cationic polyelectrolyte brushes. The pCl measurements also confirm the formation of calixarene aggregates. The dye associations with the calixarene are governed rather by interactions with the aggregates of the macrocycles than by expected inclusion of the guest into the hosts cavity. Hence, on using ionic calixarenes in aqueous media, not only inclusion phenomena but also micellar effects should be taken into account.

Colloidal properties and behaviors of 3 nm primary particles of detonation nanodiamonds in aqueous media

“…The observed 6 to 23 nm bathochromic shifts of the bands of the double charged anions of bromophenol blue, bromocresol green, bromocresol purple, fluorescein, sulfonefluorescein, aminofluorescein, and rose Bengal B (see ESI †) may be taken as a strong support for the positive interfacial charge of the colloidal species, because the same shifts are typical for these dyes in the presence of cationic surfactant micelles and aggregates of cationic dendrimers and calixarenes. 55,56 By contrast, the absorption band of the cationic dye pseudoisocyanine displays no shift in the presence of the ND particles; only small alteration of intensity is registered. These results support the significant role of the ND charge for adsorption of organic species such as fluorescent ions 21,27 and daunorubicin.…”

Encapsulation of Drug Molecules into Calix[n]arene Nanobaskets. Role of Aminocalix[n]arenes in Biopharmaceutical Field

“…36 For CA 56 consisting of six phenyl units and bearing methyl at the lower rim, the ability to form aggregates with 60-200 nm in diameter in water solutions was observed even at lower concentration. 35 Attempts have also been made to synthesize and study CAs with amino groups attached to the lower rim. In particular, Martin et al 27 analyzed the self-aggregation of amphiphilic aminoCA 35 with a highly fluorinated upper rim and a lower rim functionalized with long moieties each containing an amido-and amino group.…”

Assembling features of calixarene-based amphiphiles and supra-amphiphiles

“…Mchedlov-Petrossyan and co-workers found that the CAC of 64 decreased (4-0.12 mM) with increasing concentration of NaCl as well. 73 Similarly, the pH value could change the protonation states of hydrophilic heads, influencing charge interactions, resulting in a CAC change. Fujii and co-workers synthesized a new amphiphilic calix [4]arene 91 with hydrophilic amino end groups.…”