## 5 Using DES to Extract Bioactive Compounds from Other Natural Sources
[42] to carry out the deterpencation (separation between terpen and terpenoids) of citrus essential oil intensified by in situ formation of a DES between a quaternary ammonium salt and the compound of interest. With this aim, seven HBAs were thoroughly evaluated including ChCl, tetraethylammonium chloride (TEAC), tetrapropylammonium chloride (TPrAC), tetrapropylammonium bromide (TPrAB), tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB), tetrapentylammonium chloride (TPeAC), and tetrapentylammonium bromide (TPeAB). As indicated in Figure 2, in which the deterpencation mechanism based on the formation of a new DES composed of the ammonium salt and terpenoids is shown, terpenoid can act as weak HBDs in the presence of strong ammonium salt HBAs, whereas terpene is not able to develop interactions that involve the obtention of new DESs with the ammonium salt. This aspect allows the in-situ formation of a DESs between terpenoid and ammonium quaternary salts and, consequently, deterpencation process. Finally, the introduction of a strong HBD allows breaking the interaction previously established and, subsequently, the release of the terpenoid for its determination using a gas chromatographer. Besides, in order to simplify the HBAs comparison and selection, a quantum chemistry-based statistical thermodynamics approach using COSMOS-RS software was applied for calculating interactions among solvents and solutes. COSMOS-RS results indicated that Van der walls interactions were dominant for salt cations, increasing with the length of the alkyl chain, whereas hydrogen bonds were for salt ions of the HBAs, stronger for Cl\({}^{-}\) than for Br\({}^{-}\). Thus, TPeAC should have been the best HBAs to reach the aim of this work. However, experimental studies of model citrus essential oil with the selected HBAs showed that solid-liquid phases were formed with almost all HBAs, while for TBAC two liquid phases resulted, which favors the separation of terpenoids and terpenes by the developed strategy. Therefore, TBAC was selected as the most suitable HBA. Terpeneless product evaluation with a linalool purity of 98.76% demonstrated the success and efficiency of the approach to carry out the deterepation of citrus essential oil using NADESs. As it was demonstrated by [PERSON] et al. [42], the application of computational calculation such as COSMOS-RS software provides numerous advantages to understand the interaction established between DESs and analytes and DES formation, which considerably simplifies the research study and reduces the experimental work and consequently the cost and time consumption associated. Following the discussion about DESs applied in this area, it should be highlighted the work developed by [PERSON] et al. [10], in which a terpene-based NADES was applied for the extraction of astaxanthin from brown crab, shrimp shells and \(H\). _pluvialis_ prior to determination by HPLC-UV and the development of different bioactivity studies including cytotoxicity, antiproliferative and antimicrobial studies. Taking into account the advantages provided by these kinds of NADESs due to their higher volatility and the similarity with target compounds when terpenoids are the aim of the study, it is strangethat these kinds of DESs had not been more frequently applied. In this case, the authors investigated diverse combinations such as perilyl alcohol: camphor, DL-menthol: perilyl alcohol, DL-menthol: camphor, DL-menthol: eucalypt and compared the extraction performance with conventional soxhlet method. The results indicated that menthol:myristic acid (8:1) were able to match or even increase until 657 times the astaxanthin yield obtained by a Soxhlet extraction with acetone, which demonstrated the suitability of this NADES as an alternative solvent for the extraction of terpenoids from biomass. Regarding extraction procedures, both SLE and LLE, depending on the nature of the sample, were carried out with or without assistance.