Four 4-[[(4-nitrophenyl)methylene]imino]phenols (2a-d) were synthesized. After deprotonation in solution, they formed the solvatochromic phenolates 3a-d, which revealed a reversal in solvatochromism. Their UV-vis spectroscopic behavior was explained on the basis of the interaction of the dyes with the medium through combined effects, such as nonspecific solute-solvent interactions and hydrogen bonding between the solvents and the nitro and phenolate groups. Dyes 3a-c were used as probes to investigate binary solvent mixtures, and the synergistic behavior observed was attributed to solvent-solvent and solute-solvent interactions. A very unusual UV-vis spectroscopic behavior occurred with dye 3d, which has in its molecular structure two nitro substituents as acceptor groups and two phenyl groups on the phenolate moiety. In alcohol/water mixtures, the E(T)(3d) values increase from pure alcohol (methanol, ethanol, and propan-2-ol) until the addition of up to 80-96% water. Subsequently, the addition of a small amount of water causes a very sharp reduction in the E(T)(3d) value (for methanol, this corresponds to a bathochromic shift from 543 to 732 nm). This represents the first example of a solvatochromic switch triggered by a subtle change in the polarity of the medium, the color of the solutions being easily reversed by adding small amounts of the required cosolvent.
4-(4-Nitrobenzylideneamine)phenol was used in two strategies allowing the highly selective detection of F -and CN -. Firstly, the compound in acetonitrile acts as a chromogenic chemosensor based on the idea that more basic anions cause its deprotonation (colorless solution), generating a colored solution containing phenolate. The discrimination of CN -over F -was obtained by adding 1.4% water to acetonitrile: water preferentially solvates F -, leaving the CN -free to deprotonate the compound. Another strategy involved an assay comprised of the competition between phenolate dye and the analyte for calix [4]pyrrole in acetonitrile, a receptor highly selective for F -. Phenolate and calix[4]pyrrole form a hydrogen-bonded complex, which changes the color of the medium. On the addition of various anions, only F -was able to restore the original color corresponding to phenolate in solution due to the fact that the anion dislodges phenolate from the complexation site.
Films of three polymers, based on ethyl(hydroxyethyl)cellulose functionalized with protonated perichromic dyes, were used for anion sensing. The polymer functionalized with protonated Brooker's merocyanine acts as a chromogenic/fluorogenic system for the selective detection of cyanide in water. An increase of >28 times was verified for the fluorescence lifetime of the sensing units in the polymer in comparison with protonated Brooker's merocyanine in water. Moreover, an increase in the pK values was verified for the sensing units in the polymers. Data suggest that the hydrocarbonic polymeric chains provide an adequate microenvironment to protect the sensing unit from bulk water. The other polymer, functionalized with an iminophenol, also showed high selectivity for cyanide (detection limit=9.36×10molL and quantification limit=3.12×10molL). The polymer functionalized with azophenol units is unable for the detection of cyanide, due to the low pK value verified for its chromogenic units.
4-(4-Nitrobenzylideneamine)-2,6-diphenylphenol 3a was synthesized and studied as an anionic chromogenic chemosensor. Solutions of 3a in acetonitrile are colorless but turn blue under deprotonation. From the various anions added to the solutions of 3a only CN-, F-, and with less intensity CH 3 COOand H 2 PO 4-, led to colored solutions. With the addition of up to 2.4% (v/v) of water, of all the anions used only CNwas able to act as a base and cause a change in the color of the solution. A model was used to explain the results, based on two 3a:anion stoichiometries, 1:1 and 1:2.
Biodegradable nanoparticles (NPs) have received considerable attention because of their possible use in the development of strategies for the topical delivery of oils and therapeutic drugs, particularly when drug penetration in dermis is desired. Zein is a prolamine and is a promising material for the design of drug delivery systems. In this study, NPs were prepared with zein and were used to encapsulate and release terpinen-4-ol, which is a therapeutic agent for the treatment of melanoma. The results show that the zein NPs are promising nanostructured systems for the prolonged delivery of T4OL with potential applications in anti-melanoma therapy.
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