Abstract
The negligible volatility and high tunable nature of ionic liquids (ILs) have been the main drivers of their investigation in a wide diversity of fields, among which is their application in areas involving pharmaceuticals. Although most literature dealing with ILs is still majorly devoted to hydrophobic ILs, evidence on the potential of hydrophilic ILs have been increasingly provided in the past decade, viz., ILs with improved therapeutic efficiency and bioavailability, ILs with the ability to increase drugs’ aqueous solubility, ILs with enhanced extraction performance for pharmaceuticals when employed in biphasic systems and other techniques, and ILs displaying low eco/cyto/toxicity and beneficial biological activities. Given their relevance, it is here overviewed the applications of hydrophilic ILs in fields involving pharmaceuticals, particularly focusing on achievements and advances witnessed during the last decade. The application of hydrophilic ILs within fields involving pharmaceuticals is here critically discussed according to four categories: (i) to improve pharmaceuticals solubility, envisioning improved bioavailability; (ii) as IL-based drug delivery systems; (iii) as pretreatment techniques to improve analytical methods performance dealing with pharmaceuticals, and (iv) in the recovery and purification of pharmaceuticals using IL-based systems. Key factors in the selection of appropriate ILs are identified. Insights and perspectives to bring renewed and effective solutions involving ILs able to compete with current commercial technologies are finally provided.
Highlights
The research on more environmentally safer solvents to replace hazardous volatile organic solvents (VOCs) is part of the “Twelve Principles of Green Chemistry” [1]
Shorter chain [Cn Car]Br (n ≤ 6) ionic liquids (ILs) are the least toxic compounds followed by [C4 C1 im]Br while remaining [Cn Car]Br ILs being as prone as the two reference surfactants to induce a cytotoxic effect [71]. These results underscore that, if properly designed, ILs are able to tackle the toxicity and efficiency challenges faced with typical hydrotropes and to overcome solubility restrictions associated with common surfactants
Given the lower degree of tunability and limited aptitude of hydrophobic ILs to extract polar compounds when compared to their hydrophilic counterparts, strategies enabling the use of hydrophilic ILs in solvent-based extraction should be pursued
Summary
The research on more environmentally safer solvents to replace hazardous volatile organic solvents (VOCs) is part of the “Twelve Principles of Green Chemistry” [1]. The discussed results clearly evidence the remarkable capability of ILs to act as hydrotropic agents, where both the IL cation and anion have a solute-dependent influence on their hydrotropic behavior This behavior will certainly allow one to use the hydrotropic effect to design proper ILs to improve the solubility of target APIs in aqueous media. Despite this hydrotrope concentration-dependent behavior, the best result was achieved when solubilizing ibuprofen in [N111(2OH) ][Sal] aqueous solutions at 15 mol/kg [70] Another example of naturally-derived ILs that can enhance the water solubility of sparingly soluble compounds are those bearing L-carnitine as the cation core. These results underscore that, if properly designed, ILs are able to tackle the toxicity and efficiency challenges faced with typical hydrotropes and to overcome solubility restrictions associated with common surfactants
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