Hydrogen Bond Donor/Acceptor Cosolvent-Modified Choline Chloride-Based Deep Eutectic Solvents

Abstract

Deep eutectic solvents (DESs) have emerged as nontoxic and inexpensive alternatives not only to the common organic solvents but to the ionic liquids as well. Some of the common and popular, and perhaps the most investigated, DESs are the ones comprising an ammonium salt and an appropriate hydrogen bond (HB) donor in a predetermined mole ratio. The formation of the DES is attributed to the H-bonding interaction(s) present between the salt and the HB donor. Consequently, addition of a predominantly HB donor or a predominantly HB acceptor cosolvent to such DESs may result in intriguing features and properties. We present investigation of two DESs constituted of salt choline chloride along with HB donors urea and glycerol, respectively, in 1:2 mol ratio, named reline and glyceline as the cosolvent of very high HB donating acidity and no HB accepting basicity 2,2,2-trifluoroethanol (TFE) and of very high HB accepting basicity and no HB donating acidity hexamethylphosphoramide (HMPA), respectively, is added. TFE shows up to 0.25 mole fraction miscibility with both reline and glyceline. While up to 0.25 mole fraction HMPA in glyceline results in transparent mixtures, this cosolvent is found to be completely immiscible with reline. From the perspective of the solvatochromic absorbance and fluorescence probes, it is established that the cybotactic region dipolarity within up to 0.25 mole fraction TFE/HMPA-added DES strongly depends on the functionalities present on the solute. Fourier transform infrared absorbance and Raman spectroscopic investigations reveal no major shifts in vibrational transitions as TFE/HMPA is added to the DES; spectral band broadening, albeit small, is observed nonetheless. Excess molar volumes and excess logarithmic viscosities of the mixtures indicate that while TFE may interstitially accommodate itself within H-bonded network of reline, it does appear to form H-bonds with the constituents of the glyceline. Increase in overall net repulsive interactions as HMPA is added to glyceline is suggested by both positive excess molar volumes and excess logarithmic viscosities. The addition of HB donor/acceptor cosolvent appears to disturb the salt-HB donor equilibria within DES via complex interplay of interactions within the system.

Deep Eutectic Solvents formed by chiral components as chiral reaction media and studies of their structural properties

“…The same effect was observed and studied in literature with other DESs mixtures and it is proved to be responsible for the decrease of the melting points of the mixtures. [21,[51][52][53] Moreover, the differences observed between the +CSA/FR and +CSA/FS mixtures were in agreement with the data observed in 1 H-NMR titrations and in  DESs analysis, where differences in the portions involved in the electrostatic interactions were observed between the two DESs.…”

Determination of Binding Strengths of Host‐Guest Complexes in Deep Eutectic Solvents Using Spin Probe Methodology

“…The value of nitrogen splitting, a N =15.97 G, which depends on the polarity of the environment, is significantly smaller than that measured in water ( a N =16.69 G), as expected on the basis of the normalized empirical scale of solvent polarity E T N, which has been reported to be 0.81 for ChCl−U [15] . This E T N value corresponds to that measured in a methanol/water 80 : 20 (v : v) mixture [16] .…”

In vitro toxicity assessment and enhanced drug solubility profile of green deep eutectic solvent derivatives (DESDs) combined with theoretical validation

“…It has been noticed that the aqueous DESDs practically do not have an absorption band within the $300-600 nm wavelength range. 32 Thus, based on the inset gures, the absorption bands at around $302 nm and $313 nm depicted the presence of the LDC molecule. DESD 1 and DESD 2 showed absorption peaks around $302 nm for 25% DESDs + 75% water, which further shied to $305 nm besides an increase in intensity with increasing DESD concentration.…”