Anca Ruxandra Leonties

The potential of zein gels as functional delivery platforms for resveratrol (RESV), a natural polyphenol with antiamyloidogenic action but low systemic bioavailability, is explored by a combination of spectroscopic (circular dichroism, infrared, fluorescence, UV–Vis), calorimetric (differential scanning microcalorimetry) and rheological methods. Molecular docking is also applied for mapping the interaction sites and forces between native zein and RESV. Zein–RESV interactions in solution are systematically evaluated to understand the structural changes from a soluble protein–polyphenol system to a gel network. The concentration-dependent effect of RESV on the structural and thermal stability of zein is investigated in relation to the mechanical and functional properties of zein–RESV gels. It is shown that RESV acts as a promoter of zein aggregation, with a more pronounced effect obtained at a RESV:zein 1:1 molar ratio. By increasing the α-helix content, RESV induces a more ordered zein secondary structure in solution. In gel, the three-dimensional zein network is disrupted by hydrophobic and hydrogen-bonding interactions with RESV. Fluorescence spectra of zein gels point to conformational changes upon interaction that are confirmed by infrared spectroscopy. A significant viscoelastic deformation of the gel occurs when the RESV:zein molar ratio increases to 4:1. The RESV:zein 1:1 gel network demonstrates optimal viscoelastic properties for the release of RESV, following a biphasic transition from diffusion to matrix-controlled release. The findings of this study contribute to the structural design of zein-based systems for encapsulating and delivering bioactive compounds.

Ionotropic alginate-based hydrogelation by divalent metal interaction has been employed to study the effect that different types of ions might have on gel formation. In this regard, EPR and IR spectroscopies, as well as rheology techniques, have been used to evaluate the influence of divalent cations on gel formation, and at the same time to assess host–guest interactions. Alginate was functionalized with TEMPO moieties; therefore, TEMPO-alginate system was taken as a reference. The novelty of this study consists of using a mixture of adamantyl-TEMPO-functionalized alginate and β-cyclodextrin linked through 1,3-diaminopropane to assess the host–guest interactions in functionalized gels. The properties of divalent cations considered in this study (Ba²⁺, Ca²⁺, Sr²⁺, Zn²⁺) were proven by changes in spectral parameters of paramagnetic moieties, while the viscoelastic moduli as functions of shear strain and frequency were evaluated through rheology measurements. Overall, the information obtained from these investigations has shown that the properties of the alginate gels are influenced both by the type of divalent cation used for complexation and by the host–guest interactions. The results show that the type of the cation significantly affects gel strength; therefore, Ba²⁺ forms the strongest gel, while Zn²⁺ the least resistant. Additionally, a high immobilization of the spin-labeled probes has been obtained by the addition of tosylated β-cyclodextrin in the alginate gel network containing Ba²⁺ ions.

The study investigated the impact of three prevalent polyphenols—quercetin, ferulic acid, and caffeic acid—on catalase activity. It was determined that all three polyphenols are capable of binding to catalase, resulting in the formation of a stable complex. This finding was corroborated through fluorescence quenching studies and kinetic modeling. At low concentrations, each polyphenol exhibited an activation effect on catalase; however, at concentrations exceeding 100 μM, they began to function as inhibitors. Notably, caffeic acid and ferulic acid were observed to protect the enzyme from operational inactivation, whereas quercetin did not demonstrate this protective effect. The association constants derived from kinetic modeling were compared with those obtained from docking simulations. The results suggest that polyphenols may exert both beneficial and potentially detrimental effects on cellular antioxidant systems, contingent upon their concentration and specific molecular interactions. This highlights the necessity for careful consideration of dosage in any prospective therapeutic applications.

We report a systematic investigation on the physicochemical properties of polymer systems consisting of polyvinyl alcohol (PVA) and hyaluronic acid (HA) mixed in various volume ratios (1/4, 2/3, 1/1, 3/2, and 4/1). At PVA/HA ratios above 1/1, in the presence of glutaraldehyde and divinyl sulfone as crosslinking agents, hydrogels are formed. Their swelling behavior is dependent on the polymer ratio, with the highest water uptake determined for PVA/HA 4/1. The in situ generation of reactive oxygen species (HO^• radicals) under UV-A irradiation, in the presence of riboflavin as a photoinitiator, is evidenced by electron paramagnetic resonance (EPR) spectroscopy. The diffusion of small paramagnetic molecules across the interface of two PVA/HA 4/1 gel pieces placed in direct contact reveals the occurrence of molecular exchange, which could indicate some degree of self-repair of the hydrogel network. When the paramagnetic moiety is attached to the HA polymer by spin labeling, the absence of diffusion demonstrates the stability of the crosslinked HA chains within the PVA/HA network. The structural modifications induced by crosslinking, by the presence of riboflavin, and by exposure to UV-A light, and the resulting alterations in the mechanical behavior of the hydrogels are monitored by infrared spectroscopy and rheology. Only a slight decrease in the viscoelastic moduli values is noted, indicating that the formation of HO^• radicals has minimal impact on the macroscopic properties of the hydrogels.

For decades, royal jelly achieved notoriety and became an ultra-rich ingredient with numerous pharmacological properties especially for its use in production of topical ointments and creams. A novel formulation enriched with 2% royal jelly has been developed and characterized. Rheological results highlight a gel-like behavior of the product in the packaging, as it does not flow from the costumer’s hand after application and behaves like a liquid, spreading evenly onto clean skin. A clear comparison in size distribution of pure and cream samples was noticed by dynamic light scattering analysis and completed further by Fourier transform infrared spectroscopy (FTIR-ATR) which showed off shift changes in the gel sample as compared to pure compounds. MTT assays were conducted in quintuplicate on murine fibroblasts cell line (NCTC L-929) for testing the biocompatibility of the product in the range of 50–1000 μg/mL over 24, 48 and 72 h. The designed formulation is typically intended to deliver active compounds to the skin surface and potentially into deeper layers. A molecular docking study was performed for binding mode prediction of P-gp protein residues with two ligands, quercetin and myricetin, in order to investigate their role in the internal modulation of drug transport across cell membranes within the skin.

The comonomer bisphenol A (BPA) finds applications in the plastics industry, where it is used in the production of polycarbonates, plastics, PVC, thermal paper, epoxy and vinyl ester resins, and polyurethane. The water, with which many of these materials come into contact, is one of the main sources of human exposure to BPA. When ingested or touched, BPA can damage organs, disrupt the endocrine and immune systems, generate inflammatory responses, and be involved in genotoxic processes. Therefore, the need to develop effective techniques for removing BPA from aqueous environments is imperative. This paper provides a comprehensive review regarding the effective removal of BPA from water, focusing on the performance and adsorption mechanisms of various adsorbents based on chitosan and chitosan composites. The chemical and physical factors, adsorption kinetics and models governing the adsorption process of BPA in chitosan materials are also examined. This review outlines that, despite considerable progress in the absorption of bisphenol using chitosan gels, further research is necessary to assess the efficacy of these adsorbents in treating real wastewater and in large-scale manufacture.

The effect of resveratrol (RESV) on α-lactalbumin (α-LA) thermal stability was evaluated using differential scanning calorimetry (DSC), circular dichroism (CD) and dynamic light scattering (DLS) measurements. Complementary information offered by molecular docking served to identify the binding site of the ligand on the native structure of protein and the type of interacting forces. DSC thermograms revealed a double-endotherm pattern with partial overlapping of the two components. The most relevant effect of RESV is manifested in the narrowing of the protein thermal fingerprint: the first process (peak temperature T₁) is shifted to higher temperatures while the second one (peak temperature T₂) to lower values. The CD data indicated partial conformational changes in the protein non-α-helix domain at T₁, resulting in a β-sheet richer intermediate (BSRI) with an unaffected, native-like α-helix backbone. The RESV influence on this process may be defined as slightly demoting, at least within DSC conditions (linear heating rate of 1 K min⁻¹). On further heating, unfolding of the α-helix domain takes place at T₂, with RESV acting as a promoter of the process. Long time incubation at 333 K produced the same type of BSRI: no significant effect of RESV on the secondary structure content was detected by CD spectroscopy. Nevertheless, the size distribution of the protein population obtained from DLS measurements revealed the free (non-bound) RESV action manifested in the developing of larger size aggregates.

The removal of pharmaceutical contaminants from wastewater has gained considerable attention in recent years, particularly in the advancements of hydrogel-based adsorbents as a green solution for their ease of use, ease of modification, biodegradability, non-toxicity, environmental friendliness, and cost-effectiveness. This study focuses on the design of an efficient adsorbent hydrogel based on 1% chitosan, 40% polyethylene glycol 4000 (PEG4000), and 4% xanthan gum (referred to as CPX) for the removal of diclofenac sodium (DCF) from water. The interaction between positively charged chitosan and negatively charged xanthan gum and PEG4000 leads to strengthening of the hydrogel structure. The obtained CPX hydrogel, prepared by a green, simple, easy, low-cost, and ecological method, has a higher viscosity due to the three-dimensional polymer network and mechanical stability. The physical, chemical, rheological, and pharmacotechnical parameters of the synthesized hydrogel were determined. Swelling analysis demonstrated that the new synthetized hydrogel is not pH-dependent. The obtained adsorbent hydrogel reached the adsorption capacity (172.41 mg/g) at the highest adsorbent amount (200 mg) after 350 min. In addition, the adsorption kinetics were calculated using a pseudo first-order model and Langmuir and Freundlich isotherm parameters. The results demonstrate that CPX hydrogel can be used as an efficient option to remove DCF as a pharmaceutical contaminant from wastewater.

In this study, the effect of gamma irradiation (10 kGy) on proteins extracted from animal hide, scales, and wool was evidenced by calorimetric (μDSC) and spectroscopic (IR, circular dichroism, and EPR) methods. Keratin was obtained from sheep wool, collagen and bovine gelatin from bovine hide, and fish gelatin from fish scales. The μDSC experiments evidenced that gamma irradiation influences the thermal stability of these proteins differently. The thermal stability of keratin decreases, while a resistance to thermal denaturation was noticed for collagen and gelatins after gamma irradiation. The analysis of the IR spectra demonstrated that gamma irradiation determines changes in the vibrational modes of the amide groups that are associated with protein denaturation, most meaningfully in the case of keratin. As evidenced by circular dichroism for all proteins considered, exposure to gamma radiation produces changes in the secondary structure that are more significant than those produced by UV irradiation. Riboflavin has different effects on the secondary structure of the investigated proteins, a stabilizing effect for keratin and fish gelatin and a destabilizing effect for bovine gelatin, observed in both irradiated and non-irradiated samples. The EPR spectroscopy evidences the presence, in the gamma-irradiated samples, of free radicals centered on oxygen, and the increase in their EPR signals over time due to the presence of riboflavin.