Heterogeneity in hydrophobic deep eutectic solvents: SAXS prepeak and local environments

Abstract

The observation of the prepeak in the simulated total X-ray scattering structure function (S(q)) reveals the presence of intermediate-range structural heterogeneity in hydrophobic deep eutectic solvents.

Effect of Water on a Hydrophobic Deep Eutectic Solvent

“…Because the chloride ions avoid the low-polarity hydrocarbon regions, the hydrocarbon chains of DecA tend to be associated with each other even in the dry solvent ( Figures 4 a and S33 ), as also recently suggested for another hydrophobic DES. 64 , 65 However, in dry DES, the components (TBAC and DecA) are well mixed but already a low water content brings about enhanced separation into larger dynamic TBAC-rich and DecA-rich nanophases ( Figure 4 ). We attribute the nanophase formation to the interplay between the van der Waals interactions of the chains and the weakening Cl···HOOC hydrogen bonding, which makes the association of the hydrocarbon chains thermodynamically more favorable ( Figure 4 d; all parts of the chain behaved similarly, Figure S34 ).…”

On the nanoscopic structural heterogeneity of liquid n-alkyl carboxylic acids

“…Such a feature and corresponding behaviour as a function of chain length are uncommon in simple organic liquids, which are usually homogeneous at mid-long scales, presenting flat SAXS patterns below 1 Å À1 . Nevertheless, the pre-peak has been reported in markedly amphiphilic systems such as n-alcohols, [27][28][29][30] and n-aldehydes, 31,32 and also in more complex systems like ionic liquids, [33][34][35][36] deep eutectic solvents, 37 and pseudo-ionic liquids. [38][39][40] The trend of the pre-peak position as a function of the alkyl tail length is shown in Fig.…”

Hydrogen Bonding and Vaporization Thermodynamics in Hexafluoroisopropanol‐Acetone and ‐Methanol Mixtures. A Joined Cluster Analysis and Molecular Dynamic Study

“…It is formed by the combination of two non‐ionic moieties which establish a strong hydrogen bond network, and has been proven to be more sustainable than traditional organic solvents [8] . In recent works, hydrophobic DES formed by menthol with different organic acids have been proved to present a strong hydrogen bond between the two components, stronger than the hydrogen bond network in the neat system [9,10] . Different hydrogen bond donors and acceptors have been investigated as components of hydrophobic or Type V DESs, [8] such as decanoic acid and lidocaine, [11] menthol with different natural acids, [12] and 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) with betaine and L‐carnitine [13] .…”

“… [8] In recent works, hydrophobic DES formed by menthol with different organic acids have been proved to present a strong hydrogen bond between the two components, stronger than the hydrogen bond network in the neat system. [ 9 , 10 ] Different hydrogen bond donors and acceptors have been investigated as components of hydrophobic or Type V DESs, [8] such as decanoic acid and lidocaine, [11] menthol with different natural acids, [12] and 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) with betaine and L‐carnitine. [13] HFIP in particular is an extraordinary solvent used in many different applications, including the activation of organic functionalities such as the intramolecular Schmidt reaction using a Lewis acid in HFIP, [14] the activation of carbonyl and epoxide substrates,[ 15 , 16 ] or the activation of hydrogen peroxide in the Baeyer−Villiger oxidation reaction.…”