Percorrer por autor "Ribeiro-Claro, Paulo J.A."
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- Effect of the cation on the interactions between alkyl methyl imidazolium chloride ionic liquids and waterPublication . Khan, Imran; Taha, Mohamed; Ribeiro-Claro, Paulo J.A.; Pinho, Simão; Coutinho, João A.P.A systematic study of the interactions between water and alkyl methyl imidazolium chloride ionic liquids at 298.2 K, based on activity coefficients estimated from water activity measurements in the entire solubility range, is presented. The results show that the activity coefficients of water in the studied ILs are controlled by the hydrophilicity of the cation and the cation-anion interaction. To achieve a deeper understanding on the interactions between water and the ILs, COSMO-RS and FTIR spectroscopy were also applied. COSMO-RS was used to predict the activity coefficient of water in the studied ionic liquids along with the excess enthalpies, suggesting the formation of complexes between three molecules of water and one IL molecule. On the basis of quantum-chemical calculations, it is found that cation-anion interaction plays an important role upon the ability of the IL anion to interact with water. The changes in the peak positions/band areas of OH vibrational modes of water as a function of IL concentration were investigated, and the impact of the cation on the hydrogen-bonding network of water is identified and discussed.
- Using Molecular Conformers in COSMO-RS to Predict Drug Solubility in Mixed SolventsPublication . Cordova, Isabella Weber; Teixeira, Gabriel; Ribeiro-Claro, Paulo J.A.; Abranches, Dinis O.; Pinho, Simão; Ferreira, Olga; Coutinho, João A.P.This work explores the impact of solute conformers on the conductor-like screening model for real solvents (COSMO-RS) solubility predictions of vanillin and ethyl vanillin in water, short alcohols, and their mixed solvents. Two major conformers of these solutes and changes with solvent polarity were experimentally established by Raman spectroscopy and further confirmed by density functional theory calculations. The COSMO-RS predictions using the individual conformers show a poor description of the solubilities. Estimation with the COSMO-RS default conformer distribution gave better predictions and an intermediate behavior between the predictions obtained using each individual conformer. To further improve the description of the solubilities, the weight of each conformer was fitted to the experimental solid-liquid equilibrium data of the solute in a pure solvent at different temperatures. Better solubility predictions in ternary systems describing solubility maxima were found, suggesting a semipredictive approach to COSMO-RS. This method can predict the liquid-liquid oiling-out effect in the studied binary and ternary systems.
- What a difference a methyl group makes-probing choline-urea molecular interactions through urea structure modificationPublication . Silva, Liliana P.; Araújo, Catarina; Abranches, Dinis O.; Melle-Franco, Manuel; Martins, Mónia A.R.; Nolasco, Mariela M.; Ribeiro-Claro, Paulo J.A.; Pinho, Simão; Coutinho, João A.P.There is a lack of fundamental knowledge on deep eutectic solvents, even for the most extensively studied mixtures, such as the mixture of cholinium chloride and urea, which prevents a judicious choice of components to prepare new solvents. The objective of this work is to study and understand the fundamental interactions between cholinium chloride and urea that lead to the experimentally observed melting temperature depression. To do so, the structure of urea was strategically and progressively modified, in order to block certain interaction centres, and the solid–liquid equilibrium data of each new binary system was experimentally measured. Using this approach, it was concluded that the most important interaction between cholinium chloride and urea occurs through hydrogen bonding between the chloride anion and the amine groups. Any blockage of these groups severely hampers the melting point depression effect. Raman spectroscopy and DFT calculations were utilized to study in more detail this hydrogen bonding and its nuances.