From the multitude of materials currently available on the market that can be used in the development of microparticles, sodium alginate has become one of the most studied natural anionic polymers that can be included in controlled-release pharmaceutical systems alongside other polymers due to its low cost, low toxicity, biocompatibility, biodegradability and gelatinous die-forming capacity in the presence of Ca²⁺ ions. In this review, we have shown that through coacervation, the particulate systems for the dispensing of drugs consisting of natural polymers are nontoxic, allowing the repeated administration of medicinal substances and the protection of better the medicinal substances from degradation, which can increase the capture capacity of the drug and extend its release from the pharmaceutical form.

The main goal of this systematic review on the flavonol class secondary metabolite quercetin is to evaluate and summarize the existing research on quercetin’s potential health benefits, therapeutic properties, and effectiveness in disease prevention and treatment. In addition to evaluating quercetin’s potential for drug development with fewer side effects and lower toxicity, this type of review attempts to collect scientific evidence addressing quercetin’s roles as an antioxidant, anti-inflammatory, antibacterial, and anticancer agent. In the first part, we analyze various flavonoid compounds, focusing on their chemical structure, classification, and natural sources. We highlight their most recent biological activities as reported in the literature. Among these compounds, we pay special attention to quercetin, detailing its chemical structure, physicochemical properties, and process of biosynthesis in plants. We also present natural sources of quercetin and emphasize its health benefits, such as its antioxidant and anti-inflammatory effects. Additionally, we discuss methods to enhance its bioavailability, analyzing the latest and most effective delivery systems based on quercetin.

The aim of this study was to determine the potential pharmaceutical applications of quercetin—a natural flavonoid compound with a polyphenolic structure—following its encapsulation in polymeric microspheres resistant to degradation. The microspheres were prepared from natural polymeric compounds (chitosan and sodium alginate) via a complex coacervation method, with the goal of protecting quercetin from the degradation reactions that can affect its bioactivity. After the microspheres were prepared, they were characterized using various analytical methods. The encapsulation efficiency (EE (%)), swelling index (idxSWL%), roughness (measured using confocal laser scanning microscopy—CLSM), and surface morphology (measured using scanning electron microscopy—SEM) were all analyzed. In addition, the release capacity of quercetin from the microspheres (mQrel%) and the antimicrobial activity of the microspheres were evaluated in vitro. Finally, a multivariate statistical analysis (MANOVA, p = 0.05, PCA, and AHC) was conducted. This analysis showed that chitosan–sodium alginate–quercetin microspheres (CAQ-Ms) entrap 86.91 ± 1.10–93.11 ± 0.72% quercetin; in vitro, 71.46 ± 0.25–91.06 ± 0.15% quercetin was released, and the swelling index was higher (6701.29 ± 0.39–10,009.30 ± 1.11%) in the phosphate-buffered solution with a pH of 7.4. The CLSM and SEM analyses showed that the polymer concentration in CAQ-Ms was increased, and the roughness and smoothness of the microspheres were also increased. SEM also showed that the external layer of CAQ-Ms was formed from chitosan and the internal layer was formed from sodium alginate. Antimicrobial tests showed that CAQ-Ms had antibacterial and antifungal effects on the analyzed strains and produced larger inhibition zones between 15.3 and 14.4 mm on Escherichia coli and between 13.3 and 14.2 mm on Candida albicans, and smaller inhibition zones, between 12.4 and 13.6 mm, on Staphylococcus aureus. According to the obtained results, after the multivariate statistical analysis, it can be observed that the best performance was presented by samples P1, P2, and P3. In conclusion, the method used for the formulation of CAQ-Ms was efficient because it enabled an increase in the solubility of quercetin in water and its protection against external and internal degradation in the gastrointestinal tract. This system can be further used to produce new pills for oral administration that are able to reach the small intestine, where they can then release loaded active drugs.

Nowadays, choosing a corrosion inhibitor is not only based on efficiency, but must also consider the toxicity of the compound, the impact on the environment, and, obviously, the regulations in the field. In the last two decades, a special class of substances has begun to be studied, namely polyoxometalates (POMs). Their electronic properties and redox characteristics make the polyoxometalates potential candidates to be used in many electrochemical processes, and as potential corrosion inhibitors. Electrochemical methods such as a Tafel extrapolation plot, chronopotentiometry, or gravimetry have been used to establish the capacity of corrosion inhibition of S235 and SS304 steels in the presence of phosphovanadomolibdate acid (@PMoV) and phosphovanadotungstate acid (@PWV) in 0.5 M sulphuric acid solution. The inhibition efficiency for S235 steel is about 90.6% for @PMoV, and 69.5% for @PWV after 24 h of immersion. In the case of SS304 steel, polyoxometalates have similar effects: the inhibition degree, as a function of Flade potential, is 4.66 for @PMoV; better than 3.26 for @PWV, with both proving the passivant effect.

The objective of this study was to develop microspheres (Ms) from natural materials, chitosan (Ch) and sodium alginate (Na-Alg), that protect Ruta graveolens L. (RG) extract against temperature, pH, and the oxidative impact of degradation. The microspheres also masked the unpleasant taste by enclosing them in a biodegradable polymeric matrix. First, the total polyphenols, total flavonoid content, and antioxidant activity were quantified spectrophotometrically. Individual polyphenol contents were identified and quantified by high-performance liquid chromatography (HPLC) with UV detection. The RG extract was encapsulated in microspheres of chitosan–sodium alginate–Ruta graveolens L. extract (CARG-Ms) using two distinct procedures (method 1, in which the RG extract was added to the Ch solution and the Na-Alg solution was dripped into this mixture, and method 2, in which the RG extract was added to the Na-Alg solution and then dripped into the Ch solution) to determine which method was more advantageous. All microspheres were evaluated and characterized by confocal laser-scanning microscopy (CLSM), scanning electron microscopy (SEM), optical scanning, entrapping efficiency (EE%), swelling index (SWL%), and in vitro release (RGrel%), and all results underwent univariate and multivariate analysis using a regression model. Following these tests, it was observed that the extract had an appreciable flavonoid content of 37.98%, with antioxidant properties evidenced by the 54.25% inhibition of DPPH. Of the polyphenolic compounds identified in the extract by using the HPLC method, rutin was present in the highest amount, at 745.17 μg/mL. The microspheres prepared by method 2, which contained the highest concentration of chitosan, had several desirable properties, including a high degree of roughness, high entrapping efficiency (75%), a wrinkled appearance, a better in vitro release capacity, and a lower SWL%. On the other hand, CARG-Ms prepared by method 1, which contained a smaller concentration of Ch, had faster swelling and slower release of the extract due to the lower entrapping efficiency (35%). These results suggest that the concentration of wall material and the preparation method play important roles in the encapsulation process and final particle characteristics. According to the obtained results, after the multivariate statistical analysis, it can be observed that the microspheres prepared via method 2 of the complex coacervation process were the most efficient for encapsulating rue extract in microspheres, because the extract was protected against degradation from the gastrointestinal tract.

Five new complexes with metal cations (Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, and Cu²⁺) of monolacunary Keggin monovanado-deca-tungstophosphate, K₈[PVW₁₀O₃₉]·15H₂O, have been synthesised. The molar ratio of the combination between metal cations and K₈[PVW₁₀O₃₉]·15H₂O has been established to be 1:1, and its general molecular formulas were found to be: K_n[MPVW₁₀O₃₉(H₂O)]·xH₂O (n = 5 for M = Fe³⁺ and n = 6 for M = Mn²⁺, Co²⁺, Ni²⁺, and Cu²⁺). Optimal conditions for complexes’ synthesis (pH, temperature, and reaction time) have been determined. The characterisation of K₈[PVW₁₀O₃₉]·15H₂O and of its compounds K_n[MPVW₁₀O₃₉(H₂O)]·xH₂O have been performed using AAS, TG-DTA-DTG, UV-VIS, IR, Raman, and powder XRD methods. In UV spectra, two maximums of absorption were obtained, at 200 and 250 nm, characteristic of Keggin polycondensate compounds. The coordination of cations Ni²⁺, Co²⁺, and Cu²⁺ through oxygen atoms from K₈[PVW₁₀O₃₉]·15H₂O in an octahedron system has been reflected with VIS spectroscopy. All these methods have proved the compositions and structures of K₈[PVW₁₀O₃₉]·15H₂O and K_n[MPVW₁₀O₃₉(H₂O)]·xH₂O, their similarity with other vanadotungstophosphates, and their achievements in the Keggin class. Additionally, all analysis methods have shown an increase in the degree of structural symmetry and the thermal stability of a polyoxoanion complex after attaching metal cations compared to the monolacunary, K₈[PVW₁₀O₃₉]·15H₂O.