Simple preparation of broadband UV filters based on TiO2 coated with aqueous extracts of native trees from the Chaco region of Argentina.

The native forest of northwestern Argentina, as part of the Chaco region, is a rich and unexploited source of phytochemical compounds for medicinal/cosmetic applications. In the present study, fruit, leaf, branch, and bark organs of the native trees Sarcomphalus mistol (Mistol, M) and Schinopsis lorentzii (Quebracho Colorado santiagueño, QC) were harvested, and aqueous plant extracts (PE) were prepared. The spectroscopic (UV-Vis absorbance, diffuse reflectance, ATR-FTIR) and antioxidant (TEAC, Folin-Ciocalteu) properties of PE were characterized and used as TiO2 coating material to obtain a series of TiO2@PE nanocomposites. These materials showed almost null photocatalytic activity compared to aqueous suspensions of bare TiO2, displaying yellowish to brownish coloration and high long-term stability in both freshwater and seawater model solutions. The loss of photocatalytic activity in TiO2@PE was associated with the combination of the internal filter effect and the antioxidant/radical capacity exerted by the phytochemicals of the PE coating, with higher broadband photoprotection for the nanocomposites prepared with QC extracts. Thus, this study shows the potential capacity of the forest resources of the Chaco region of Argentina for the development of new cosmetic and/or sun protection formulations.

Photosensitization With Supramolecular Arrays for Enhanced Antimicrobial Photodynamic Treatments.

Microbial infections represent a silent threat to health that has worsened in recent decades due to microbial resistance to multiple drugs, preventing the fight against infectious diseases. Therefore, the current postantibiotic era forces the search for new microbial control strategies. In this regard, antimicrobial photodynamic therapy (aPDT) using supramolecular arrays with photosensitizing capabilities showed successful emerging applications. This exciting field makes it possible to combine applied aspects of molecular photochemistry and supramolecular chemistry, together with the development of nano- and biomaterials for the design of multifunctional or "smart" supramolecular photosensitizers (SPS). This minireview aims to collect the concepts of the photosensitization process and supramolecular chemistry applied to the development of efficient applications of aPDT, with a brief discussion of the most recent literature in the field.

Photocatalytic Efficiency Tuning by the Surface Roughness of TiO2 Coatings on Glass Prepared by the Doctor Blade Method.

A set of opaque films were prepared with Degussa P25® or Hombikat UV100® TiO2 powders by the doctor blade method on glass slides with different compositions of polyethylene glycol of 20 kDa (PEG20), and they were characterized by spectroscopy, microscopy and photochemical kinetics measurements. After annealing treatment at 450 °C, about 5-7% C atom was incorporated into the films, as a consequence of the degradation of the organic complexing agents, inducing a small reduction of the energy band gap of TiO2 (i.e. 3.02 ≤ Eg (eV) ≤ 3.08). All films were about 15 ± 2 µm thick but their micro-morphological characteristics depended on the content of PEG20, showing different patterns of cracks and aggregates that produce intense light scattering and retransmission phenomena with the result of a three-dimensional excitation of the TiO2 particles in the thick film. Back-face excitation with UVA light (365 ± 42 nm) of the opaque films in contact with an aqueous solution produced both surface-bound and free hydroxyl radicals (HO• ), as detected using a coumarin solution as a radical dosimeter. The photogeneration efficiency of HO• decreased with the surface roughness of the films, which varied between 135 and 439 nm depending on the film's composition.

Electrochemical and Spectrophotometric Methods for Polyphenol and Ascorbic Acid Determination in Fruit and Vegetable Extracts.

RESEARCH BACKGROUND: Fresh-cut fruits and vegetables are considered sources of antioxidant compounds. However, their shelf life is limited due to nutritional, quality and safety deterioration. Therefore, in recent decades, various methods have been reported for food processing and preservation, as well as for the determination of antioxidant compounds, due to their many benefits when consumed. The aim of the present work is to compare the performance of electrochemical and spectrophotometric methods in the analysis of the content of polyphenolic compounds and ascorbic acid in extracts from fruits (eggplant), edible roots (carrot) and leaves (rocket, lettuce and chard), and evaluate their capability to detect small changes in the antioxidant content in the eggplant extracts previously irradiated with different UV-C light intensities. EXPERIMENTAL APPROACH: Polyphenolic compounds and ascorbic acid were determined by electrochemical and spectrophotometric methods. An enzymatic biosensor and a nanocomposite sensor were used for polyphenolic compounds and ascorbic acid, respectively, in electrochemical measurements, while Folin-Ciocalteu and Kampfenkel methods were used for spectrophotometric measurements. RESULTS AND CONCLUSION: Results obtained through the different methodologies were comparable and consistent with each other. Both methods allowed determining the content of ascorbic acid and polyphenolic compounds in the fruit and vegetable extracts. Moreover, both techniques enable the detection of the analyte concentration changes in samples exposed to different UV-C intensities and storage days. Finally, it was observed that the antioxidant capacity depends on the type of food, treatment and storage period. NOVELTY AND SCIENTIFIC CONTRIBUTION: Both methodologies were suitable for the quantification of analytes; however, the electrochemical sensors provided higher specificity and selectivity, applicable to different fruit and vegetable matrices, obtaining results with higher precision, in shorter time and with a smaller sample volume, minimizing the economic costs because of the lower consumption of reagents.