Browsing by Author "Shimizu, Seishi"
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- Glycerol ethers as hydrotropes and their use to enhance the solubility of phenolic acids in waterPublication . Soares, Bruna de Paula; Abranches, Dinis O.; Sintra, Tânia E.; Leal-Duaso, Alejandro; García, José Ignacio; Pires, Elísabet; Shimizu, Seishi; Pinho, Simão; Coutinho, João A.P.The use of glycerol ethers (with alkyl side chain ranging from one to six methyl groups) as hydrotropes to enhance the solubility of gallic and syringic acids in water was here studied. These compounds were selected due to their biological and industrial applications and for serving as model molecules for lignin solubilization. The results obtained were compared against traditional co-solvents, demonstrating the exceptional hydrotropic ability of glycerol ethers. Setschenow constants show that the hydrophobicities of both solute and hydrotrope play an important role in the solubility enhancement by hydrotropy, shedding light into its molecular mechanism. The solubility curves of gallic acid and syringic acid in the aqueous glycerol ether solutions were fitted using a recently proposed statistical thermodynamics-based model. This allowed the estimation of solute recovery from hydrotropic solution by using water as antisolvent. Unlike what is usually claimed it is here shown that in some conditions it is impossible to recover the solute by simply adding water. This analysis paves the way for a rational design and selection of hydrotropes, in which both solubility enhancement and solute recovery are critical parameters to be taken into account.
- The impact of size and shape in the performance of hydrotropes: a case-study of alkanediolsPublication . Abranches, Dinis O.; Soares, Bruna de Paula; Ferreira, Ana M.; Shimizu, Seishi; Pinho, Simão; Coutinho, João A.P.Inspired by the recently proposed cooperative mechanism of hydrotropy, where water molecules mediate the aggregation of hydrotrope around the solute, this work studies the impact of apolar volume and polar group position on the performance of hydrotropes. To do so, the ability of two different families of alkanediols (1,2-alkanediols and 1,n-alkanediols) to increase the aqueous solubility of syringic acid is initially investigated. Interestingly, it is observed that in the dilute region (low hydrotrope concentration), the relative position of the hydroxyl groups of the alkanediols does not impact their performance. Instead, their ability to increase the solubility of syringic acid correlates remarkably well with the size of their alkyl chains. However, this is not the case for larger hydrotrope concentrations, where 1,2-alkanediols are found to perform, in general, better than 1,n-alkanediols. These seemingly contradictory findings are reconciled using theoretical and experimental techniques, namely the cooperative model of hydrotropy and chemical environment probes (Kamlet–Taft and pyrene polarity scales). It is found that the number of hydrotropes aggregated around a solute molecule does not increase linearly with the apolar volume of the former, reaching a maximum instead. This maximum is discussed in terms of competing solute–hydrotrope and hydrotrope–hydrotrope interactions. The results suggest that hydrotrope self-aggregation is more prevalent in 1,n-alkanediols, which negatively impacts their performance as hydrotropes. The results reported in this work support the cooperative model of hydrotropy and, from an application perspective, show that hydrotropes should be designed taking into consideration not only their apolar volume but also their ability to stabilize their selfaggregation in water, which negatively impacts their performance as solubility enhancers.
- Unveiling the mechanism of hydrotropy: Evidence for water-mediated aggregation of hydrotropes around the solutePublication . Abranches, Dinis O.; Benfica, Jordana; Soares, Bruna de Paula; Leal-Duaso, Alejandro; Sintra, Tânia E.; Pires, Elísabet; Pinho, Simão; Shimizu, Seishi; Coutinho, João A.P.A recent proposal attributes the origin of hydrotropy to the water-mediated aggregation of hydrotrope molecules around the solute. Experimental evidence for this phenomenon is reported for the first time in this work, using 1H-NMR. A new computational technique to quantify apolarity is introduced and is used to show that apolarity of both solute and hydrotrope is the driving force of hydrotropy. This journal is