The Gelling Ability of Some Diimidazolium Salts: Effect of Isomeric Substitution of the Cation and Anion

Abstract

The gelling ability of some geminal imidazolium salts was investigated both in organic solvents and in water solution. Organic salts differing either in the cation or anion structure were taken into account. In particular, the effects on the gel‐phase formation of isomeric substitution on the cation or anion as well as of the use of mono‐ or dianions were evaluated. As far as the cation structure is concerned, isomeric cations, such as 3,3′‐di‐n‐octyl‐1,1′‐(1,4‐phenylenedimethylene)diimidazolium and 3,3′‐di‐n‐octyl‐1,1′‐(1,3‐phenylenedimethylene)diimidazolium, were used. On the other hand, in addition to the bromide anion, isomeric dianions, such as the 1,5‐ and 2,6‐naphthalenedisulfonate anions, were also examined. After preliminary gelation tests, different factors affecting the obtained gel phases, such as the nature of the solvent, organogelator concentrations, and action of external stimuli, were analyzed. The gel‐phase formation was also studied as a function of time, by using resonance light scattering measurements. Gel morphologies were analyzed by scanning electron microscopy. To further support the understanding of the different behavior shown by the isomeric cations, some representative ion pairs were analyzed by DFT‐based investigations. The collected data underline the significant role played by isomeric substitution of both cation and anion structures in determining the gelling capability of the investigated salts, as well as the properties of the gel phases. Finally, DFT investigations were helpful in the identification of the structural features affecting the self‐assembly.

Organic salts and aromatic substrates in two-component gel phase formation: the study of properties and release processes

“…35 Indeed, for both organic salts, this gelator concentration falls in the plateau region where thermal stability does not depend on concentration. The gelator concentration was chosen on the grounds of experimental trend previously obtained for thermal stability of pure gels in 1-propanol.…”

“…Gel phase formation was studied using RLS measurements as a function of time. 35 These differences in the gelation mechanism seem to persist also when [NDS] salts are involved in two-component gels formation (see Fig. 46 To carry out RLS measurements, we kept constant the gelator concentration (8%, w/w) and the guest/gelator molar ratio (5/1).…”

“…7,8,12 In this case, the use of supramolecular gels responsive to different pH and temperature conditions or enzymatic action could favour the release of active molecules within the target organ. 32,33,35 In particular, we took into account organic salts showed in Scheme 1, namely 3,3'-di-n-octyl-1,1'-(1,4phenylenedimethylene)diimidazolium 1,5-naphthalenedisulfonate ([p-Xyl-(oim) 2 ][1,5-NDS]) and 3,3'-di-n-octyl-1,1'-(1,4phenylenedimethylene)diimidazolium 2,6-naphthalenedisulfonate ([p-Xyl-(oim) 2 ] [2,). 14,16 The whole of above statements highlights the need to collect information on the effect exerted on a given gel phase by a guest or second component.…”

“…Furthermore, gels are also used in pollution recovery, because of their porosity that allows absorbing of both inorganic and organic waste. 35 Aiming to practical applications of the above gel phases as reaction media or soft materials for organic pollutants removal, we thought it could be interesting to investigate the effects of several organic guest molecules on the formation and properties of some gels. This could allow optimizing its applications.…”

Solution and thermal behaviour of novel dicationic imidazolium ionic liquids

“…50 In the optimised geometry the anion is embedded in a kind of close cage formed by two aromatic rings of the cation. The sulfonate group of the anion interacts simultaneously through hydrogen bonds with two imidazolium rings belonging to different cations.…”