Theoretical Calculation of the Thermodynamic Properties of 20 Amino Acid Ionic Liquids

Complexation of Amino Acids with Cadmium and Their Application for Cadmium-Contaminated Soil Remediation

The interaction of amino acids with toxic heavy metals influences their immobilization and bioavailability in soils. However, the complexation ability of amino acids with Cd has not been well studied. The complexes of amino acids and cadmium were investigated by density functional theory (DFT) calculations and Fourier transform infrared spectrometry (FTIR) analyses. The complex structures were found to be [COc, COc] for fatty amino-cadmium and PheCd2+, [COc, COc, COs] for GluCd2+ and ThrCd2+, respectively. The complex energy of these conformers followed the order PheCd2+> AlaCd2+ > LeuCd2+ > GluCd2+ > GlyCd2+ > ThrCd2+. Importantly, all of the complex energy values were less than zero, indicating that these complexes could be easily dissolved in water. The Cd2+ concentration decreased with increasing amino acid concentration in aqueous solution. The complex stability constants (logβ) followed the order PheCd2+> AlaCd2+ > LeuCd2+ > GluCd2+ > GlyCd2+ > ThrCd2+, consistent with the order of the calculated complex energy values. The Cd removal efficiencies by Thr, Glu, Gly, Ala, Leu, and Phe were 38.88%, 37.47%, 35.5%, 34.72%, 34.04%, and 31.99%, respectively. In soil batch tests, the total Cd concentration in soil decreased in the presence of amino acids, while the Cd concentration in water increased from 231.97 μg/L to 652.94~793.51 μg/L. The results of sequential extraction showed that the acid-extractable fraction and the reducible fraction of Cd sharply decreased. Consequently, the significant features of amino acids along with their biocompatibility make them potentially applicable chelators in Cd-contaminated soil remediation processes.

Ionic liquids as a useful tool for tailoring active pharmaceutical ingredients

Ionic liquids (ILs) have been widely used in biomedical and pharmaceutical fields as solvents or permeation enhancers. Recently, more and more researchers focused on optimizing the physicochemical properties of active pharmaceutical ingredient (API) by ILs technology. Converting APIs into ILs (API-ILs) has shown great potential for drug delivery by eliminating polymorphism, tailoring solubility, improving thermal stability, increasing dissolution, controlling drug release, modulating the surfactant properties, enhancing permeability of APIs and modulating cytotoxicity on tumor cells. In addition, API-ILs are also used in various formulations as active ingredients, such as solutions, emulsions, even tablets or nanoparticles. This paper aims to review current status of API-ILs, including the rational and design, preparation and characterization, the improvement on the physicochemical characteristics of APIs, the compatibility of API-ILs with various formulations, and the future prospects of API-ILs in biomedical and pharmaceutical fields.

Thermal Stability and Decomposition Kinetics of 1-Alkyl-2,3-Dimethylimidazolium Nitrate Ionic Liquids: TGA and DFT Study

The thermal stability and decomposition kinetics analysis of 1-alkyl-2,3-dimethylimidazole nitrate ionic liquids with different alkyl chains (ethyl, butyl, hexyl, octyl and decyl) were investigated by using isothermal and nonisothermal thermogravimetric analysis combined with thermoanalytical kinetics calculations (Kissinger, Friedman and Flynn-Wall-Ozawa) and density functional theory (DFT) calculations. Isothermal experiments were performed in a nitrogen atmosphere at 240, 250, 260 and 270 °C. In addition, the nonisothermal experiments were carried out in nitrogen and air atmospheres from 30 to 600 °C with heating rates of 5, 10, 15, 20 and 25 °C/min. The results of two heating modes, three activation energy calculations and density functional theory calculations consistently showed that the thermal stability of 1-alkyl-2,3-dimethylimidazolium nitrate ionic liquids decreases with the increasing length of the alkyl chain of the substituent on the cation, and then the thermal hazard increases. This study could provide some guidance for the safety design and use of imidazolium nitrate ionic liquids for engineering.