Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems

Abstract

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Ultralong-Chain Ionic Liquid Surfactants Derived from Natural Erucic Acid

“…Compared to other anionic ILSs, the current ULILSs exhibited some unique advantages. First, the present ULILSs possess very small cmc (μM-grade), far lower than those of all reported to date anionic ILSs, ,,− ,,,− significantly lowering the cost and potential harm to environment stemming from a high dose of usage. Second, the current ULILSs were derived from natural erucic acid, a leftover of rapeseed oil processing, rather than a nonrenewable fossil resource. ,, This not only enables the reuse of waste resource, but also lessens the consumption of the nonrenewable resource, complying the principle of green chemistry .…”

“…Various ILSs have been extensively reported, but the majority is confined to one type: cationic quaternary nitrogen linked with a relatively long alkyl chain (commonly no more than 16 carbon atoms) as the cation moiety and a (relatively small) halogen counterion. , A serious drawback, however, is that these ILSs are potentially hazardous to the environment (especially aquatic systems), because of their high toxicity and nonbiodegradable nature originating from the quaternary nitrogen cations, , or the potential release of corrosive HCl or HF from hydrolysis. − …”

Modification with Conventional Surfactants to Improve a Lipid-Based Ionic-Liquid-Associated Transcutaneous Anticancer Vaccine

“…The CLSM observation confirmed that the FITC-OVA nanoparticles moved freely in the IPM, and the particle size agreed well with the DLS observation ( Figure S2i,ii ). Because of the ionic properties of cationic and anionic cosurfactant-based formulations, interfacial-tension-reducing capability is significantly affected, leading to physical instability at room temperature (25 ± 1 °C) [ 31 ],and precipitation within 1 week, whereas nonionic cosurfactant-based formulations, apart from Brij-35- and PEG-based formulations, were stable ( Figure S1 ) [ 31 ]. The hydrophobic and hydrophilic structural groups of nonionic surfactants aid in correctly dispersing drug molecules in solution as emulsifiers or foaming agents, whereas ionic surfactants work in the reverse way, which leads formulation instability [ 32 ].…”

“…The hydrophobic and hydrophilic structural groups of nonionic surfactants aid in correctly dispersing drug molecules in solution as emulsifiers or foaming agents, whereas ionic surfactants work in the reverse way, which leads formulation instability [ 32 ]. Nonionic cosurfactants improved the phase stability with the IL and drug by forming covalent or weak van der Waals interactions in the oil phase, resulting in increased bioactivity and physiochemical stability for no-ionic ILNDFs [ 31 ]. Ionic surfactants can transfer their cationic or anionic charge to the surface of the nanoparticles in liquid formulation, which leads the nanoparticles to deteriorate and precipitate due to electrostatic forces; as a result, ionic surfactant-based formulations become unstable [ 33 ].…”

Impact of Surface Chemistry on Emulsion–Electrode Interactions and Electron-Transfer Kinetics in the Single-Entity Electrochemistry

“…To investigate the interaction between a droplet and an electrode surface, stabilized droplets and well-defined model systems are needed. Using room temperature ionic liquid (RTIL) as the surfactant is a good way to stabilize the emulsion since the cation and anion of RTIL could be adjustable for the required amphiphilicity and surfactancy, together with the biocompatibility and environmental friendliness. , The most studied droplets are emulsions in SEE. ,− Deng’s group suggested the shape changes of oil emulsions landing on the electrode and proposed four collision mechanisms by employing fast-scan cyclic voltammetry and monitoring the phase angle of the current. , It is known that the ET at the emulsion–electrode interface is coupled with ion transfer (IT) at the oil/water interface or oil/RTIL interface. The IT thermodynamics has also been revealed in Deng’s reports, , however, the ET kinetics, the dynamic emulsion–electrode interaction, and the relationship between the two still remain unknown.…”