Structure and Photochemistry of <i>N</i>‑Salicylidene‑<i>p</i>‑carboxyaniline Isolated in Solid Argon

Infrared matrix isolation spectroscopy and DFT/B3LYP/6-311++G­(d,p) calculations have been used to characterize the conformational space of the enol-imine and keto-amine tautomers of <i>N</i>-salicylidene-<i>p</i>-carboxyaniline (SCA) in both their <i>E</i> and <i>Z</i> isomeric forms. Monomers of SCA were isolated in an argon matrix (15 K), which was shown to contain only the most stable conformer of the <i>E</i>-enol isomer of the compound. The matrix-isolated <i>E</i>-enol was then subjected to <i>in situ</i> UV irradiation (λ = 335; 345 nm, provided by a laser/MOPO system, or λ > 235 nm, provided by a Hg­(Xe) broad-band source), and the photoinduced processes probed by infrared spectroscopy. Two photoreaction channels were observed, with a branching ratio of ∼1:1, corresponding to <i>E</i>-enol → <i>Z</i>-enol isomerization and <i>E</i>-enol → <i>E</i>-keto tautomerization. Both processes were found to be rather effective, with practically complete consumption of the reactant after broad-band irradiation by 1 min only. Identification among the photoproduced species of the <i>Z</i>-enol conformer that differs from the reactant only by <i>E</i>-to-<i>Z</i> isomerization suggests the initial photoproduction of this conformer, which subsequently decays into the lowest energy <i>Z</i>-enol conformer (also identified experimentally). The <i>E</i>-enol → <i>E</i>-keto tautomerization requires an excited state intramolecular proton transfer and twisting about the exocyclic CC bond of the molecule. These processes most probably take place sequentially. However, in the present study the <i>Z</i>-keto isomer, which should act as intermediate in this sequence of processes, could not be detected, most probably due to its short lifetime under the used experimental conditions. On the contrary, the detailed structural and vibrational characterization of the photoproduced <i>E</i>-keto form was successfully achieved

3D Matrices for Enhanced Encapsulation and Controlled Release of Anti-Inflammatory Bioactive Compounds in Wound Healing

Current trends in the development of wound dressings are oriented towards the use of biopolymer-based materials, due to their unique properties such as non-toxicity, hydrophilicity, biocompatibility and biodegradability, properties that have advantageous therapeutic characteristics. In this regard, the present study aims to develop hydrogels based on cellulose and dextran (CD) and to reveal their anti-inflammatory performance. This purpose is achieved by incorporating plant bioactive polyphenols (PFs) in CD hydrogels. The assessments include establishing the structural characteristics using attenuated total reflection Fourier transformed infrared (ATR-FTIR) spectroscopy, the morphology by scanning electron microscopy (SEM), the swelling degree of hydrogels, the PFs incorporation/release kinetics and the hydrogels’ cytotoxicity, together with evaluation of the anti-inflammatory properties of PFs-loaded hydrogels. The results show that the presence of dextran has a positive impact on the hydrogel’s structure by decreasing the pore size at the same time as increasing the uniformity and interconnectivity of the pores. In addition, there is an increased degree of swelling and of the encapsulation capacity of PFs, with the increase of the dextran content in hydrogels. The kinetics of PFs released by hydrogels was studied according to the Korsmeyer–Peppas model, and it was observed that the transport mechanisms depend on hydrogels’ composition and morphology. Furthermore, CD hydrogels have been shown to promote cell proliferation without cytotoxicity, by successfully culturing fibroblasts and endothelial cells on CD hydrogels (over 80% viability). The anti-inflammatory tests performed in the presence of lipopolysaccharides demonstrate the anti-inflammatory properties of the PFs-loaded hydrogels. All these results provide conclusive evidence on the acceleration of wound healing by inhibiting the inflammation process and support the use of these hydrogels encapsulated with PFs in wound healing applications

Physical Hydrogels of Oxidized Polysaccharides and Poly(Vinyl Alcohol) for Wound Dressing Applications

Two natural polymers, i.e., cellulose and water soluble pullulan, have been selectively oxidized employing the TEMPO-mediated protocol, to allow the introduction of C6-OOH groups. Thereafter, the composite hydrogels of poly(vinyl alcohol) (PVA) and different content of the oxidized polysaccharides were prepared by the freezing/thawing method. The Fourier transform infrared spectroscopy (FTIR) has been used to discuss the degree of interaction between the hydrogels constituents into the physical network. The homogeneity of the prepared hydrogels as revealed by the SEM show an excellent distribution of the oxidized polysaccharides inside the PVA matrix. The samples exhibit self-healing features, since they quickly recover the initial structure after being subjected to a large deformation. The cell viability was performed for the selected hydrogels, all of them showing promising results. The samples are able to load L-arginine both by physical phenomena, such as diffusion, and also by chemical phenomena, when imine-type bonds are likely to be formed. The synergism between the two constituents, PVA and oxidized polysaccharides, into the physical network, propose these hydrogels for many other biomedical applications