Abstract
The design of environmentally friendlier solvents has gained increasing relevance in the last decade. Deep eutectic solvents (DES) have recently emerged, with advantages like low-cost and putative lower environmental impact. However, information about DES toxicity is still scarce. This work aims to contribute to profiling the ecotoxicity of DES based on cholinium chloride ([Chol]Cl). Six DES were addressed, combining [Chol]Cl (as hydrogen bond acceptor – HBA) with ethylene glycol, glycerol, 1,2-propanediol, propionic acid, 1-propanol, and urea as hydrogen bond donors (HBD), in different molar ratios. The Microtox® Acute Toxicity Test, was used for assessing their toxicity towards the marine bacteria Allivibrio fischeri . Because the dissociation of DES in water is expected, analysis appraising the mixtures toxicity theory should be considered, which is a step forward in this field. This analysis suggested that [Chol]Cl and all HBD with the exception of propionic acid:[Chol]Cl 1:2 and 4:1 behave antagonistically, which is contrary to what has been suggested previously. The most extreme cases are Urea:[Chol]Cl and 1-Propanol:[Chol]Cl, with EC50 values higher than their starting materials dosed singly, configuring very promising and biocompatible alternative solvents. Toxicity was found to be dependent on DES composition, as well as on molar proportions of the starting materials.
Highlights
The concept of “Green Chemistry” was introduced in the early 1990's with the propose of designing and applying chemical products and processes in order to reduce, or preferentially eliminate, the use and generation of hazardous substances (Anastas and Warner, 1998)
Deep eutectic solvents (DES) emerged in this context. They are simple to prepare and do not need purification, have low-cost production due to the low cost of starting materials, and have been showing good biocompatibility (Hayyan et al, 2013b; Jhong et al, 2009; Singh et al, 2012). These solvents were first developed combining urea with cholinium chloride (Abbott et al, 2003), but DES can be prepared through the mixing of two or three different components belonging to different chemical families, forming an eutectic mixture based on hydrogen bonding interactions between the components, with a melting point much lower than either of the individual components (Dai et al, 2013; Ruß and König, 2012; Zhang et al, 2012)
A comparative analysis of estimated 30 min-EC50 regarding the luminescence of A. fischeri was carried out, both considering the starting materials and series combining them in different proportions to establish different DES
Summary
The concept of “Green Chemistry” was introduced in the early 1990's with the propose of designing and applying chemical products and processes in order to reduce, or preferentially eliminate, the use and generation of hazardous substances (Anastas and Warner, 1998). Deep eutectic solvents (DES) emerged in this context They are simple to prepare and do not need purification, have low-cost production due to the low cost of starting materials, and have been showing good biocompatibility (Hayyan et al, 2013b; Jhong et al, 2009; Singh et al, 2012). These solvents were first developed combining urea with cholinium chloride (Abbott et al, 2003), but DES can be prepared through the mixing of two or three different components belonging to different chemical families (e.g., quaternary ammonium salts, amides, organic acids, polyalcohols), forming an eutectic mixture based on hydrogen bonding interactions between the components, with a melting point much lower than either of the individual components (Dai et al, 2013; Ruß and König, 2012; Zhang et al, 2012). Recent studies using ab initio molecular dynamic simulations were developed to gain insights on the charge spreading in the liquid state and casted strong doubts on this hypothesis (Zahn et al, 2016)
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