Sergio Antonio Rodriguez

The electro-oxidation of eugenol (EUG) natural antioxidant was studied by cyclic voltammetry in phosphate buffer solutions (PBS) of different pH at electrochemically partially reduced graphene oxide (GCE/ePRGO). The voltammetric responses were mainly controlled by adsorption at this modified electrode. Current values were higher at pH 2.0 PBS, therefore, this pH was chosen to perform all experiments. DFT calculations of pKa’s and standard potentials defined the possible pathways of eugenol and its oxidation products. These pathways were evaluated through the comparison of voltammetric simulations of adsorbed species with experiments at pH 2.0, which also allowed for the estimation of the values of the kinetic parameters involved in electrochemistry. Our findings suggest a multi-step redox process in which Eugenol is first oxidized to the radical species and then to a cationic product. At this stage, the pathways branch into to methylenquinone and a 4-allyl-1,2-diquinone molecules. 4-allyl-1,2-diquinone is finally reduced in single or double reversible electrochemical step to the hydroquinone species. The present physicochemical work allows for a deeper understanding of the eugenol oxidation mechanism, which was only partially proposed in previous studies.

Background: The rise in multidrug-resistant bacteria has intensified the search for new antibiotics, drawing attention to essential oils (EOs) for their antimicrobial properties. For this reason, this study focuses on the antimicrobial action of the EO obtained from Tagetes minuta and its impact on bacterial membranes. Methods: The EO was chemically characterized by chromatography–mass spectrometry, and its antimicrobial activity and its effects on surface and bacterial membrane were assessed by using Zeta potential, membrane transition temperature (Tm) determination; and fluorescence spectroscopy with Laurdan and Di-8 ANEPPS. Results: Twenty-seven compounds could be identified, with (E)-Tagetone, (Z)-Ocimenone, and β-pinene as the most abundant. Afterward, the EO was tested against Escherichia coli (MIC and MBC = 17 mg/mL) and Staphylococcus aureus (MIC = 8.5 mg/mL; MBC > 17 mg/mL), showing antimicrobial action in both bacteria, being more effective against E. coli. Mechanistic studies revealed that the EO interacts with bacterial membranes, increasing the Zeta potential by more than 9 mV and enhancing membrane permeability up to 90%. These effects were further confirmed using model lipid membranes, where the EO induced significant changes in membrane properties, including a reduction in dipole potential and transition temperature, suggesting that some EO components could be inserted into the lipid bilayer, disrupting membrane integrity. Conclusions: The EO from T. minuta demonstrates efficient antimicrobial activity by compromising bacterial membrane structure, highlighting its potential as a natural antimicrobial agent.

Electrochemical oxidation of butylated hydroxytoluene (BHT) was revisited in acetonitrile (ACN) using cyclic voltammetry, numerical simulations, and density functional theory (DFT) calculations. BHT exhibited a single irreversible anodic peak at ∼1 V vs Ag/AgNO₃, corresponding to its oxidation to a cationic radical (BHT ^.+ ), which subsequently undergoes a deprotonation and second electron transfer to form BHT ⁺ . DFT calculations defined the possible oxidation pathways evaluated through experiments and simulations. In ACN, a two-electron ECEC mechanism dominates, where the second electron transfer occurs at a lower standard potential than the first, resulting in a single anodic peak. In contrast, previous studies in aqueous media have shown two distinct voltammetric peaks, due to the first electron transfer being at a lower standard potential than the second redox reaction. Addition of potassium t-butoxide shifted the BHT/BHT ⁻ equilibrium toward the formation of BHT ⁻ , resulting in an additional redox process at negative potentials; this redox reaction was predicted from DFT calculations. Numerical simulations of the current response aligned with experimental data revealed faster electron transfer kinetics in ACN compared to water. The dimeric oxidation products were elucidated by NMR experiments. These results provide detailed insights into BHT oxidation mechanisms, emphasizing solvent effects and the formation of reactive intermediates.

Essential oils (EO) have the potential to control ectoparasites, being an alternative to the use of synthetic products. The essential oils of Baccharis trimera and Mimosa verrucosa were evaluated for lethality, residual efficacy, and repellence against the ectoparasite Ctenocephalides felis felis Bouché, and toxicity was using Saccharomyces cerevisiae eukaryote model. EOs were obtained by steam distillation and characterized by GC/FID/MS. Mortality at different immature stages and among adult fleas was measured through in vitro filter paper tests at different concentrations of EOs, as well as residual effect and repellent activity. The major compounds for B. trimera were carquejyl acetate (33.0%), carquejol (7.07%), and palustrol (6.99%), and for M. verrucosa, β-pinene (14.2%), (E)-caryophyllene (13.8%), and α-pinene (10.6%). Low toxicity was recorded for B. trimera and M. verrucosa EOs at 200 µg.mL^-1. EOs recorded 100% efficacy against adult fleas at 800 µg.cm^-2 (LC₅₀ = 369.22 µg.cm^-2) and residual effect for three days, B. trimera EO promoted 46.7% of mortality on the 3^rd day of the exposition, and M. verrucosa EO 20% of mortality on the 3^rd day of the exposition. The repellent activity was presented in the concentration of 40000 µg.mL^-1 for B. trimera EO (80% at 12h) and M. verrucosa EO (75% at 6h). The results show great potential for developing alternative products from the essentials of B. trimera and M. verrucosa in control against C. felis felis, which show low toxicity and high activity.

In the present work, the oxidation mechanism of di-t-butyl-hydroxytoluene (BHT) was studied in an aqueous medium through different approaches to have a thorough vision of the physical chemistry: experiments with cyclic voltammetry (CV), quantum chemical calculations, and simulations of CV. Calculations of thermodynamic parameters, such as pK _a and standard oxidation potential (E _ox°), were used to analyze and rationalize the CV experiments. Subsequently, different pathways of the mechanism were constructed, and the most thermodynamically favorable one was selected. Numerical simulations were then used to model this mechanism and compare it with the experimental data. The results show that the oxidation process is due to the coupled loss of an electron and a proton in the first instance, followed by an irreversible second electron-transfer process without loss of protons, mainly due to the adsorption of the products of the first oxidation on the electrode surface. The effect of different pH values on this oxidative mechanism was also analyzed, with alkaline pH of 12 as a medium where changes in reactivity were observed as the appearance of a new peak in the second voltammetric sweep, the interpretation of this peak is also provided.

The goal of this research was to create an antibacterial formulation from Scinus areira essential oil (EO) that could spread in water. To achieve this, we developed liposomal formulations of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) or DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) that encapsulated the EO. In addition, we utilized the EO as a reducing and stabilizing agent to synthesize silver nanoparticles (AgNPs). The nanoformulations were characterized by determining their size and zeta potential. In the case of liposomal formulations, chemical composition, and encapsulation efficiency were also determined. Furthermore, antimicrobial activity studies against Gram-positive and Gram-negative model bacteria were carried out for both kinds of formulations. The results obtained showed the successful encapsulation of the S. areira EO in multilamellar liposomes of phosphatidylcholine with high efficiency. DPPC liposomes have proven to be a better encapsulation system, retaining more monoterpenes from the EO and therefore presenting antimicrobial activity against S. aureus with an minimal inhibitory concentration (MIC) value of 3 mg/mL of EO. On the other hand, it was also possible to obtain AgNPs by using S. areira EO, which showed antimicrobial activity against S. aureus and E. coli at low concentrations of EO, with MIC values of 6.68 µg/mL and 3.4 µg/mL of silver, respectively. The data obtained will contribute to enhancing the biotechnological value of natural products derived from native plant species in Argentina. This will be achieved through the generation of novel formulations with antibacterial activity and potential bioavailability.