Elucidating Anion Effect on Nanostructural Organization of Dicationic Imidazolium-Based Ionic Liquids

Abstract

This work reports the influence of anion structure (Br -, NO 3 -, BF 4 -, and SCN -) in the aggregation process of ionic liquids (ILs), derived from 1,8-bis(3-methylimidazolium-1-yl)octane, in 4.75% ethanol-water solution (v/v). The aggregation behavior was investigated using small angle x-ray scattering (SAXS), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Spin-lattice relaxation times (T1), obtained by NMR, indicated that the molecular mobility of the ILs changed when aggregates are formed. 1 H-NMR showed distinct chemical shifts as a function of the concentration of [BisOct(MIM) 2 ][2X] (in which X = Br, NO 3 , SCN, and BF 4 ) in solution. This change was associated with different chemical environments experienced by the hydrogen atoms when the aggregation process occurs.This behavior was characterized by the different types of interactions in the aggregates, in accordance with the anion of the IL structure. The SAXS measurements demonstrated that the distance between two molecules, which function as scattering centers, was dependent on the anion hydrophobicity. Less hydrophobic anions resulted in shorter distances between scattering centers due to their better solvating ability. Due to the lower solvating ability of hydrophobic anions, a larger distance between two scattering centers was observed. Furthermore, ILs with more hydrophobic anions (e.g., BF 4 -) resulted in closely-packed aggregates.

Thermal Stability and Kinetic of Decomposition of Mono- and Dicationic Imidazolium-Based Ionic Liquids

“…1,2 Depending of the cation and anion combination, ILs may exhibit different physicochemical properties when compared with conventional electrolytes media or organic solvents. [3][4][5] Properties such as high thermal stability, tunable electrochemical window, low flammability, broad liquid range, and ability to dissolve and stabilize a wide range of materials allow ILs to be used in engineered materials synthesis. Imidazolium-based ILs are among the most studied classes of ILs.…”

Impact of Anions on the Partition Constant, Self-Diffusion, Thermal Stability, and Toxicity of Dicationic Ionic Liquids

“… 21 , 28 In a recent study published by our research group, it was observed that the anions (Br, NO 3 , SCN, and BF 4 ) of [BisOct(MIM) 2 ][2X] do not influence the hydrodynamic radius of the aggregates in a solution (determined by dynamic light scattering) at different concentrations (50, 300, and 500 mM). 31 …”

Heteroassembly Ability of Dicationic Ionic Liquids and Neutral Active Pharmaceutical Ingredients

“…Furthermore, it was found that alkyl chains are folded and cationic heads interact by CH···π at the aggregate surface. 23 We expect dicationic IL aggregates in an ethanol–water solution (1–1, v/v) to be organized in a similar way, including [BisOct(BnIM) 2 ][2Br]. Therewithal, it can be concluded that API molecules can strongly affect the interactions between cationic heads when compared with self-assembly, in which the head groups organize themselves to interact effectively with APIs.…”

“…21,22 Dicationic ILs consist of a doubly charged cation linked by a spacer chain. 23 These ILs with a long spacer chain (e.g., 8 and 10 carbons) possess excellent surface activity properties and are capable of forming aggregates in solution. 24,25 Because of such characteristics, this new class of ILs is comparable with traditional surfactants and can be used, with advantages, in the same applications as monocationic structures.…”

“…11,27 Furthermore, a broad range of studies on interactions between IL and APIs are carried out with ionic APIs, in which the association with ILs are mostly favored by ionic interactions. 10,11,16 Our research group has already verified the influence of the alkyl chain length 25 and the nature of the anions in the selfaggregation behavior of dicationic IL structures in solution, 23,24 in addition to evaluating thermodynamic properties of aggregation using [BisOct(MIM) 2 ][2Br] as a study model. 28 Thus, this study aims to assess if dicationic ILs can interact with APIs in solution by investigating the following: (i) a systematic study related to heteroassembly between IL + API in ethanol− water solution (1:1), (ii) thermodynamic differences in the aggregation behavior of the ILs with different structural changes in the presence and the absence of distinct APIs, (iii) association between these components by intermolecular interactions, and (iv) the strength of the interactions between IL and API.…”