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- Exploring the role of temperature on hydrotropyPublication . Abranches, Dinis O.; Soares, Bruna P.; Cordova, Isabella Weber; Benfica, Jordana; Ferreira, Olga; Pinho, Simão; Coutinho, João A.P.Aqueous solubility can be enhanced through hydrotropy, where an amphiphilic molecule (the hydrotrope) ag-gregates around the solute, boosting its solubility. To understand the impact of temperature on this phenomenon, the solubility of syringic acid was measured in aqueous solutions of different bio-based hydrotropes. Solubility curves were modelled using Gaussian processes, a powerful class of machine learning interpolators. This allowed for a thermodynamic analysis of excess solvation properties that was complemented using the COSMO-RS model. As expected, the absolute solubility of syringic acid increased with temperature. However, at low hydrotrope concentrations, this increase was not driven by interactions in the liquid phase. Thus, the solubility enhancement of syringic acid was found to be independent of temperature. Conversely, at high hydrotrope concentrations, increasing the temperature significantly decreased the solubility enhancement of the solute. These effects were interpreted considering different solubilization mechanisms, namely hydrotropy (low hydrotrope concentrations) and co-solvency (high hydrotrope concentrations).
- Extraction of phenolic compounds from Juglans regia L. leaves using aqueous solutions of eutectic solventsPublication . Cordova, Isabella Weber; Oludemi, Taofiq; Vieira, Vanessa; Pires, Tânia C.S.P.; Pinho, Simão; Barros, Lillian; Ferreira, OlgaThe leaves of Juglans regia L. (walnut tree) are a rich source of bioactive phenolic compounds, particularly flavonoids and phenolic acids, which can be used in cosmetic applications due to their antioxidant properties. Conventionally, these compounds are extracted using volatile organic solvents. This study focuses on a more sustainable approach by designing a heat-assisted extraction process using aqueous solutions of eutectic solvents (ES) composed of cosmetic-compatible ingredients aiming for direct incorporation into cream formulations. In this context, aqueous solutions of the ES betaine + urea and betaine + 1,3-propanediol (PPD) were selected, considering their potential as cosmetic ingredients. The screening process targeted the maximum extraction yield of phenolic compounds (phenolic acids and flavonoids), quantified by HPLC-DAD. The selected variables were water content (25, 50 and 75 % in weight) and the molar proportion of the ES components. For comparison purposes, pure water was used as a reference solvent. The total phenolic content ranged between 5.5 and 14.6 mg/g of dry plant. Betaine:urea (2:1), betaine:PPD (1:2), betaine, and PPD, all with 50 % water mass percentage, were among those resulting in higher extraction yields and were further selected for bioactivity analysis. The system containing betaine presented the best antioxidant capacity, analysed through ferric reducing power, DPPH radical scavenging, and TBARS assays. The extracts obtained with PPD presented the highest antimicrobial activity against gram-positive and gram-negative bacteria, and yeast. The results show the potential of using binary aqueous mixtures of betaine, or 1,3-propanediol, which are simple ingredients in cosmetics formulations, to efficiently extract phenolic compounds from a natural matrix. Moreover, the bioactivity results, particularly in the antioxidant dimension, support using J. regia leaves as a source of natural antioxidants.
- 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.
- Infinite dilution activity coefficients in the smectic and isotropic phases of Tetrafluoroborate-based ionic liquidsPublication . Martins, Mónia A.R.; Vilas-Boas, Sérgio M.; Cordova, Isabella Weber; Carvalho, Pedro J.; Domańska, Urszula; Ferreira, Olga; Coutinho, João A.P.; Pinho, SimãoInverse gas chromatography was used to obtain the activity coefficients at infinite dilution (γ13∞) of several organic solutes and water in the thermotropic ionic liquid crystal phases of both [C12mim][BF4] and [C14mim][BF4] and their isotropic phases. In the smectic to isotropic transition, a change in the linear representation of the natural logarithm of γ13∞ with the reciprocal temperature was observed for [C14mim][BF4], and was more evident for alkanes, alkylbenzenes, esters, and alcohols, that can be related to structural modifications of the stationary phase. Results are interpreted in terms of the enthalpic and entropic contributions of solute-IL interactions. Selectivities and capacities of important separation problems, such as octane/benzene and cyclohexane/benzene, were calculated and compared with literature values for separating agents such as N-methyl-2-pyrrolidinone, sulfolane, and ionic liquids presenting the [BF4]- anion combined with several imidazolium-based cations. It is shown that to achieve maximum separation efficiency, imidazolium cations with short alkyl chain lengths such as [C2mim][BF4] should be used, whereas high capacities require larger alkyl chain lengths.
- Partition coefficients of phenolic compounds in biphasic organic solvent systemsPublication . Cordova, Isabella Weber; Ferreira, Olga; Pinho, Simão; Leite, Priscilla dos Santos Gaschi; Coutinho, João Manuel Costa Araújo PereiraFirst of all, I would like to express my sincere gratitude to the supervisors from IPB, professors Olga Ferreira and Simão Pinho, whose guidance, dedication and support has been so meaningful throughout this work. I also want to thank the professors Priscilla Leite and Juliana Pietrobelli for support and encouragement for participating in the Double Degree Program. I am very grateful for having provided me with this incredible experience. I would like to thank all my friends and colleagues that I made during this time, especially to Sérgio Vilas-Boas, for all the help, guidance and patience during this work. I am also very grateful for my family and friends, for all the encouragement, especially for my parents Carlos and Julieta, for all the love, support and education. Finally, many thanks to everyone that took part in the study and enabled this dissertation to be possible.
- Modeling the solubility of monoterpenoids with hybrid and predictive thermodynamic toolsPublication . Vilas-Boas, Sérgio M.; Cordova, Isabella Weber; Abranches, Dinis O.; Coutinho, João A.P.; Ferreira, Olga; Pinho, SimãoThe Abraham and NRTL-SAC semipredictive models were employed to represent the solubility of (-)-borneol, (1R)-(+)-camphor, L-(-)-menthol, and thymol in water and organic solvents, using data measured in this work and collected from the literature. A reduced set of solubility data was used to estimate the model parameters of the solutes, and global average relative deviations (ARDs) of 27% for the Abraham model and 15% for the NRTL-SAC model were obtained. The predictive capability of these models was tested by estimating the solubilities in solvents not included in the correlation step. Global ARDs of 8% (Abraham model) and 14% (NRTL-SAC model) were obtained. Finally, the predictive COSMO-RS model was used to describe the solubility data in organic solvents, with ARD of 16%. These results show the overall better performance of NRTL-SAC in a hybrid correlation/prediction approach, while COSMO-RS can produce very satisfactory predictions even in the absence of any experimental data.
- Comparison of two computational methods for solvent screening in countercurrent and centrifugal partition chromatographyPublication . Vilas-Boas, Sérgio M.; Cordova, Isabella Weber; Kurnia, Kiki A.; Almeida, Heloísa H.S.; Gaschi, Priscilla S.; Coutinho, João A.P.; Pinho, Simão; Ferreira, OlgaCountercurrent and centrifugal partition chromatography are techniques applied in the separation and isolation of compounds from natural extracts. One of the key design parameters of these processes is the selection of the biphasic solvent system that provides for the adequate partitioning of the solutes. To address this challenging task, the fully predictive Conductor-like Screening Model for Real Solvents (COSMO-RS) and the semi-predictive Non-Random Two-Liquid Segment Activity Coefficient (NRTL-SAC) model were applied to estimate the partition coefficients ( K ) of four model phenolic compounds (vanillin, ferulic acid, ( S )-hesperetin and quercetin) in different solvent systems. Complementing the experimental data collected in the literature, partition coefficients of each solute in binary, or quaternary, solvent sys- tems were measured at 298.2 K. Higher deviations from the experimental data were obtained using the predictive COSMO-RS model, with an average RMSD (root-mean-square deviation) in log( K ) of 1.17 of all four solutes (61 data points), providing a satisfactory quantitative description only for the systems containing vanillin (RSMD = 0.57). For the NRTL-SAC model, the molecular parameters of the solutes were initially calculated by correlating a set of K and solubility ( x , in mole fraction) data (16 partition coefficients and 44 solubility data points), for which average RMSD values of 0.07 and 0.41 were obtained in log( K ) and log( x ) , respectively. The predictions of the remaining log( K ) data (45 partition coefficients) resulted in an average RMSD of 0.43, suggesting that the NRTL-SAC model was a more reliable quantitative solvent screening tool. Depending on the amount of available solubility and partition data, both models can be valuable alternatives in the preliminary stages of solvent screening destined to select the optimal mobile and stationary phases for a given separation.