Contributions to the selection of solvents in the extraction of phenolic acids

Naturally occurring phenolic acids are well-known and studied for their bioactive properties and wide distribution in plants, where they can be found in free form, or conjugated to other molecules. The study of the solubility of phenolic compounds in water and organic solvents is thus fundamental for the design of extraction, separation, crystallization and purification processes of great importance in the pharmaceutical, cosmetics and food industries. In this context, the main objective of this work is to measure the solubility of trans-cinnamic, p-coumaric and ferulic acids in water and in seven organic solvents (methanol, ethanol, 1-propanol, 2-propanol, 2-butanone, ethyl acetate and acetonitrile) at 298.2 K and 313.2 K and test the ability of the NRTL-SAC model, with or without the Reference Solvent Approach (RSA), and the Abraham solvation model to correlate, and preferably, predict the solubility data. To accomplish the objectives above the shake-flask method experimental method was combined with UV-Visible spectroscopy and gravimetric methods of analysis to perform the solubility measurements. In general, the results obtained were in close agreement with the very scarce information available in literature. After, the NRTL-SAC segment descriptors of each solute were fitted to solubility data in seven solvents, obtaining average relative errors (ARD) between 23% and 39%. The model was then applied to predict the solubility in other eight solvents, with ARD between 42% and 61%. The RSA was also applied, but no significant improvements were obtained relatively to the first approach. The optimization parameters of the Abraham solutes were also obtained by fitting the solubility data in six solvents for the trans-cinnamic and p-coumaric acids, and seven solvents for the ferulic acid, obtaining ARD between 7% and 24% for correlations and between 4% and 33% for the predictions in the remaining solvents. These values indicate Abraham's solvation model as the most suitable and very satisfactory model to predict the solubility of the selected solutes at 298.2 K.Os ácidos fenólicos de ocorrência natural são bem conhecidos e estudados por suas propriedades bioativas e ampla distribuição em plantas, onde podem ser encontrados na forma livre ou conjugados com outras moléculas. O estudo da solubilidade de compostos fenólicos em água e solventes orgânicos é fundamental para a conceção de seus processos de extração, separação, cristalização e purificação de grande importância nas indústrias farmacêutica, cosmética e alimentar. Nesse contexto, o principal objetivo deste trabalho é a medição de solubilidade dos ácidos trans-cinâmico, p-cumárico e ferúlico em água, e em diferentes solventes orgânicos (metanol, etanol, 1-propanol, 2-propanol, 2-butanona, acetato de etilo e acetonitrilo) a 298,2 K e 313,2 K e testar a capacidade dos modelos NRTL-SAC, combinado ou não com a metodologia do Solvente Referência (RSA), e do modelo de solvatação de Abraham para correlacionar e, preferencialmente prever, os dados de solubilidade. Para atingir esses objetivos, o método dos frascos agitados, combinado com os métodos de espectroscopia de UV-Visível e o gravimétrico, foram selecionados para efetuar as medições de solubilidade. Em geral, os resultados obtidos são bem consistentes com as escassas informações disponíveis na literatura. Finalmente, os descritores de segmentos do soluto NRTL-SAC foram obtidos através do ajuste de dados de solubilidade em sete solventes, obtendo-se um erro relativo médio (ARD) entre 23% e 39%. O modelo foi então avaliado quanto à sua capacidade para prever a solubilidade em oito solventes, obtendo-se um ARD entre 42% e 61%. Os parâmetros dos solutos no modelo de Abraham foram obtidos através do ajuste de dados de solubilidade em seis solventes para os ácidos trans-cinâmico e p-cumárico, e sete solventes para o ácido ferúlico, obtendo-se um ARD entre 7% e 24% para as correlações e entre 4% e 33% para as previsões em sete solventes. Esses valores indicam o modelo de solvatação de Abraham como o mais promissor para prever a solubilidade dos solutos estudados a 298,2 K.This work is a result of: Project “AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-FEDER-000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF); Associate Laboratory LSRE-LCM - UID/EQU/50020/2019 - funded by national funds through FCT/MCTES (PIDDAC); Project AllNat - POCI-01-0145-FEDER-030463, financed by COMPETE and Portugal2020 and national funds through FCT

Solvent and temperature effects on the solubility of syringic, vanillic or veratric acids: Experimental, modeling and solid phase studies

The solubility of syringic acid, vanillic acid and veratric acid was measured in pure water and eleven organic solvents (methanol, ethanol, 1-propanol, 2-propanol, 2-butanone, ethyl acetate, acetonitrile, dimethylformamide, 1,2-propanediol, 1,3-propanediol and 1,3-butanediol), at 298.2 K and 313.2 K. Besides the solubility data, the melting temperatures and enthalpies of the solutes were determined by differential scanning calorimetry, while powder and single X-ray diffractionwere used to resolve the solute solid structure, before and after the solubility studies. Formodeling purposes, theNRTL-SACmodel, also combinedwith the Reference Solvent Approach (RSA), and the Abraham solvation model were applied to describe the solid-liquid equilibria of the binary systems. A set of solvents was used to estimate the model parameters and afterwards, solubility predictions were carried out for binary systems not included in the correlation step. Better results were obtained using the Abraham solvation model with average relative deviations (ARD) of 15% for the correlation set and 26% for the predictions, which are more satisfactory than the results found with the NRTL-SAC model (33% for the correlation and 59% for the predictions) or the NRTL-SAC model combined with RSA (30% for the correlation and 59% for the predictions).We acknowledge the support of the project “AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-FEDER- 000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF); Associate Laboratory LSRE-LCM - UID/EQU/50020/2019 - funded by national funds through FCT/MCTES (PIDDAC); UID/CTM/50011/2019 (CICECO), financed by national funds through the FCT/MCTES; and project AllNat - POCI-01- 0145-FEDER-030463 (PTDC/EQU-EPQ/30463/2017), financed by FEDER funds through COMPETE and Portugal2020 and national funds through FCT - Fundação para a Ciência e a Tecnologia. The authors also thank FCT for financial support to S. M. Vilas-Boas grant (SFRH/BD/138149/2018) and V. Vieira grant (SFRH/BD/108487/ 2015).info:eu-repo/semantics/publishedVersio

Solid-liquid phase equilibrium of trans-cinnamic acid, p-coumaric acid and ferulic acid in water and organic solvents: Experimental and modelling studies

The solubility of the trans isomers of cinnamic acid, p-coumaric acid and ferulic acid was measured in water and seven organic solvents (methanol, ethanol, 1-propanol, 2-propanol, 2-butanone, ethyl acetate and acetonitrile), at 298.2 K and 313.2 K, using the analytical shake-flask technique. The melting temperatures and enthalpies of the solutes were studied by differential scanning calorimetry, while solute solid structures were identified by powder and single X-ray diffraction. The NRTL-SAC model was applied to calculate the solubility of trans-cinnamic acid and trans-ferulic acid in pure solvents. For trans-p-coumaric acid, the NRTL-SAC was combined with the Reference Solvent Approach, as the solute melting properties could not be determined. The global average relative deviations (ARD) were 32% and 41%, in the correlation and prediction stages, respectively. The Abraham solvation model was also applied. The global ARD were 20% for correlation and 29% for predictions, which can be considered very satisfactory results for these semi-predictive models.This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/ 50011/2020, and CIMO-Mountain Research Center, UIDB/00690/ 2020, both financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. We also acknowledge the support of the projects “AIProcMat@N2020 - Advanced Industrial Processes and Materials for a Sustainable Northern Region of Portugal 2020”, with the reference NORTE-01-0145-FEDER- 000006, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF); and project AllNat - POCI-01-0145-FEDER-030463, funded by the European Regional Development Fund (ERDF) through the Competitiveness and Internationalization Operational Program (COMPETE2020-POCI) and national funding from the Foundation for Science and Technology (FCT, Portugal). S. M. Vilas-Boas thanks the financial support provided by FCT PhD grant (SFRH/BD/138149/ 2018).info:eu-repo/semantics/publishedVersio

Educação Ambiental envolvendo o descarte de pilhas e baterias: uma ação do PIBID de Química na comunidade do Salobrinho

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Measurement of the cosmic ray spectrum above 4×10184{\times}10^{18} eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-\gamma}$ with index $\gamma=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.Comment: Replaced with published version. Added journal reference and DO

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.Comment: Replaced with published version. Added journal reference and DO

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.Comment: Replaced with published version. Added journal reference and DOI. Supplemental material in the ancillary file