Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

Quantification of the liquid window of deep eutectic solvents

Deep eutectic solvents (DESs) have been considered as a new class of green solvents with tunable physical properties based on the selective combination of their individual components. As the liquid window of a DES identifies the range of feasible applications, it is essential to determine, quantify, and predict their phase behavior. Phase diagrams were measured for systems consisting of tetrapentylammonium bromide and erythritol or succinic acid. Regular solution theory is applied to quantitatively describe the liquid window of DESs. The succinic acid mixture shows a larger deviation from ideal behavior, caused by the stronger hydrogen bond forming acid groups. The interaction parameter between the two DES components in regular solution theory could be determined directly from the eutectic temperature of the mixture and this enables quantification of the degree of non-ideality of DESs

Degradation of deep-eutectic solvents based on choline chloride and carboxylic acids

\u3cp\u3eMixtures of carboxylic acids and choline chloride are one of the most commonly used families of deep-eutectic solvents. The thermal and long-term stability of carboxylic acid-choline chloride (ChCl) deep-eutectic solvents was investigated. This family of DESs was found to degrade due to an esterification reaction, mainly between the carboxylic acid and the alcohol moiety of ChCl. The esterification reaction occurs even at room temperature over extended periods of time and is promoted at elevated temperatures. The esterification reaction takes place independently of the preparation method used. Moreover, the deep-eutectic solvent malonic acid-ChCl (x\u3csub\u3eChCl\u3c/sub\u3e = 0.50) was found to decompose into acetic acid and carbon dioxide when prepared via the heating method, or when heated after preparation at room temperature. Therefore, the applicability of carboxylic acid-ChCl-based solvents is compromised.\u3c/p\u3

Activity modelling of the solid-liquid equilibrium of deep eutectic solvents

\u3cp\u3eCompared to conventional solvents used in the chemical industry, deep eutectic solvents (DESs) are considered as promising potentially sustainable solvents. DESs are binary mixtures and the resulting liquid mixture is characterized by a large melting point depression with respect to the melting temperatures of its constituents. The relative melting point depression becomes larger as the two components have stronger attractive interactions, resulting in non-ideal behavior. The compositional range over which such binary mixtures are liquids is set by the location of the solid-liquid phase boundary. Here we present experimental phase diagrams of various recent and new DESs that vary in the degree of non-ideality. We investigate whether thermodynamic models are able to describe the solid-liquid equilibria and focus on relating the parameters of these models to the non-ideal behavior, including asymmetric behavior of the activity coefficients. It is shown that the orthogonal Redlich-Kister-like polynomial (OP) expansion, including an additional first order term, provides an accurate description. This theory can be considered as an extension of regular solution theory and enables physical interpretation of the fit parameters.\u3c/p\u3

Quantification of the liquid window of deep eutectic solvents

\u3cp\u3eDeep eutectic solvents (DESs) have been considered as a new class of green solvents with tunable physical properties based on the selective combination of their individual components. As the liquid window of a DES identifies the range of feasible applications, it is essential to determine, quantify, and predict their phase behavior. Phase diagrams were measured for systems consisting of tetrapentylammonium bromide and erythritol or succinic acid. Regular solution theory is applied to quantitatively describe the liquid window of DESs. The succinic acid mixture shows a larger deviation from ideal behavior, caused by the stronger hydrogen bond forming acid groups. The interaction parameter between the two DES components in regular solution theory could be determined directly from the eutectic temperature of the mixture and this enables quantification of the degree of non-ideality of DESs.\u3c/p\u3

A centrifuge method to determine the solid–liquid phase behavior of eutectic mixtures

The centrifuge method is a novel, equilibrium-based, analytical procedure that allows the construction of solid–liquid phase diagrams of binary eutectic mixtures. In this paper, the development, optimization, and successful verification of the centrifuge method are described. Contrary to common dynamic analysis techniques—differential scanning calorimetry and hot-stage microscopy—the studied mixtures are equilibrated at constant temperature. Therefore, the mixtures do not need to be recrystallized from the melt during analysis. This offers a great advantage for mixtures that exhibit strong supercooling behavior rather than direct crystallization. The centrifuge method was verified by reproducing the binary eutectic phase behavior of both the nearly ideal biphenyl–bibenzyl system and the strongly non-ideal deep eutectic solvent (DES) urea–choline chloride, which is prone to supercooling. Hence, the centrifuge method offers an alternative route to common dynamic analysis techniques for the quantification of the liquid range of DESs and other binary eutectic mixtures

From a eutectic mixture to a deep eutectic system via anion selection: Glutaric acid + tetraethylammonium halides

In pursuit of understanding structure-property relationships for the melting point depression of binary eutectic mixtures, the influence of the anion on the solid-liquid (S-L) phase behavior was explored for mixtures of glutaric acid + tetraethylammonium chloride, bromide, and iodide. A detailed experimental evaluation of the S-L phase behavior revealed that the eutectic point is shifted toward lower temperatures and higher salt contents upon decreasing the ionic radius. The salt fusion properties were experimentally inaccessible owing to thermal decomposition. The data were inter- and extrapolated using various models for the Gibbs energy of mixing fitted to the glutaric-acid rich side only, which allowed for the assessment of the eutectic point. Fitting the experimental data to a two-parameter Redlich-Kister expansion with Flory entropy, the eutectic depth could be related to the ionic radius of the anion. The anion type, and in particular its size, can therefore be viewed as an important design parameter for the liquid window of other acid and salt-based deep eutectic solvents/systems

Ionic liquids and deep eutectic solvents for lignocellulosic biomass fractionation

Lignocellulosic biomass has gained extensive research interest due to its potential as a renewable resource, which has the ability to overtake oil-based resources. However, this is only possible if the fractionation of lignocellulosic biomass into its constituents, cellulose, lignin and hemicellulose, can be conducted more efficiently than is possible with the current processes. This article summarizes the currently most commonly used processes and reviews the fractionation with innovative solvents, such as ionic liquids and deep eutectic solvents. In addition, future challenges for the use of these innovative solvents will be addressed

A centrifuge method to determine the solid–liquid phase behavior of eutectic mixtures

The centrifuge method is a novel, equilibrium-based, analytical procedure that allows the construction of solid–liquid phase diagrams of binary eutectic mixtures. In this paper, the development, optimization, and successful verification of the centrifuge method are described. Contrary to common dynamic analysis techniques—differential scanning calorimetry and hot-stage microscopy—the studied mixtures are equilibrated at constant temperature. Therefore, the mixtures do not need to be recrystallized from the melt during analysis. This offers a great advantage for mixtures that exhibit strong supercooling behavior rather than direct crystallization. The centrifuge method was verified by reproducing the binary eutectic phase behavior of both the nearly ideal biphenyl–bibenzyl system and the strongly non-ideal deep eutectic solvent (DES) urea–choline chloride, which is prone to supercooling. Hence, the centrifuge method offers an alternative route to common dynamic analysis techniques for the quantification of the liquid range of DESs and other binary eutectic mixtures