Browsing by Author "Romero, Romina"

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    Chemiluminescence emission in fenton reaction driven by 1,2-dihydroxybenzenes: Mechanistic approaches using 4-substituted ligands
    (2021) Romero, Romina; Marquéz, Katherine; Benítez Olivares, Francisca Javiera; Toro Labbé, Alejandro Miguel; Cornejo Ponce, Lorena; Melín, Victoria; Contreras, David
    Fenton (F) and Fenton-like (FL) reactions can be amplified by dihydroxybenzenes (DHBs). These compounds chelate and reduce Fe(III), promoting the hydroxyl radical production ((OH)-O-center dot). The products or intermediaries of F and FL reactions driven by DHBs can produce chemiluminescence (CL) with different profiles, depending on the type of DHB involved. In this work, CL produced by F and FL systems driven by different -para substituted DHBs was measured and compared with the reactivity of each system and with the structural parameters of each DHB. CL emission was not related to the reactivity of each studied system but was favored by DHBs substituents with -NHR and -OH groups combined in the branching (NHR-DHBs). PLS multivariate regression models were constructed using computational parameters for each DHB, quinone (Q) and semiquinone (SQ(center dot)) to find the influence of structural and electronic parameters over CL emission. Analysis showed that in NHR-DHBs, the higher CL exhibited could be explained by cycling ability of these compounds. In DHBs with an electron-donor group (EDG) the CL emission would depend only on the stability of the intermediary species generated by DHB and (OH)-O-center dot reaction. While DHBs with electron-withdrawing groups (EWG) showed that CL will increase depending on the stability of the intermediaries by resonance, and by the acidity of the hydroxyl protons of the ring. PLS-SQ(center dot) showed that spin densities were strongly correlated with an increase in CL emission. DHBs with substituents that favor the delocalization of charge in the SQ(center dot) to the ramification would enhance CL emission. Meanwhile, when the delocalization is promoted over the DHB-ring, these systems become more reactive, and the CL emission is disadvantaged by quinone formation.
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    Organic radicals stabilization in natural rubber: Discerning the influence of thermo-oxidation using chemically modified or unmodified lignin as antioxidant
    (2024) Troncoso-Ortega, Eduardo; Castano-Rivera, Patricia; Romero, Romina; Henriquez, Adolfo; Mendez, Camila; Schott, Eduardo; Contreras, David
    We have implemented a lignin compatibilization strategy through silylation and elaborated NR compounds with lignin and silylated lignin. Then, the lignin's contribution to the preservation of physico-mechanical properties and stability of the materials obtained against thermo-oxidation was studied. Thus, our work considered the indirect study of the antioxidant activity on NR compounds by determining the physico-mechanical properties before and after accelerated thermo-oxidative aging, which allowed us to determine that the increase in crosslinking density during the initial hours of accelerated aging was the main observed cause associated with a higher tensile strength retention rate (TSRR: 13.4 %) in NR compound with 5 phr of lignin (CL5) versus a TSRR: 4.7 % for the compound with 5 phr of silylated lignin (CL5Si1). On the other hand, the direct study of the antioxidant capacity by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) using oxygen atmosphere indicated greater thermal stability in NR compounds when lignin is not silylated. The maximum degradation temperature for the CL5 compound was 341.6 degrees C, while for the CL5Si1 compound it was 328.6 degrees C. The oxidation induction temperature (OITtemp) in the CL5 compound was 190.9 degrees C with a peak at 221.0 degrees C, while for CL5Si1 it was 170.3 degrees C with a peak at 194.1 degrees C, indicating again that unsilylated lignin is more suitable as an antioxidant. Finally, through Electron Paramagnetic Resonance (EPR), we determined that the radical quenching effect due to the presence of lignin was significant as the lignin content increases, with a reduction in radical presence close to 50 % compared to a reference compound without lignin.
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    Stress Dependent Biofilm Formation and Bioactive Melanin Pigment Production by a Thermophilic Bacillus Species from Chilean Hot Spring
    (2022) Marin-Sanhueza, Cathalina; Echeverria-Vega, Alex; Gomez, Aleydis; Cabrera-Barjas, Gustavo; Romero, Romina; Banerjee, Aparna
    Thermophilic bacteria able to survive extreme temperature stress are of great biotechnological interest due to their extracellular production of bioactive molecules as a part of a survival strategy, or by intracellular modifications. In the present study, thermophilic Bacillus haynesii CamB6, isolated from a Chilean hot spring, was studied for the formation of different stress response molecules. The polymeric pigment produced by the bacterial strain was characterized by different physicochemical techniques. On exposure to ranges of temperature (50-60 degrees C), pH (5.0-7.0), and sources of nitrogen and carbon (1-5 g center dot L-1), the bacteria responded with a biofilm network formation in a hydrophobic polystyrene surface. Biofilm formation under fed-batch conditions was also statistically validated. The bacteria showed a planktonic pellicle network formation in the presence of induced hypoxia and salinity stress (19.45 g center dot L-1) under static conditions. Salinity stress also resulted in the intracellular response of brown pigment production. The pigment was structurally and functionally characterized by UV-Vis absorbance and the presence of different characteristic peaks via FTIR analysis (bacterial pyomelanin fingerprints) were assessed. A high thermal stability and TGA profile indicated the brown pigment was a probable pyomelanin candidate. Micropyrolysis (Py-GC/MS) showed that isoprene, pyrrole, benzene, pyridine, and their derivatives were the major components detected. In addition, acetic acid, indole, phenol, and its derivatives were observed. The absence of sulfocompounds in the pyrolyzed products agreed with those reported in the literature for pyomelanin. The pigment surface morphology was analyzed via SEM, and the elemental composition via EDS also demonstrated the similarity of the brown pigment to that of the melanin family. The pyomelanin pigment was observed to be bioactive with promising antioxidant capacity (H2O2, Fe2+) compared to the standard antioxidant molecules. In conclusion, B. haynesii CamB6 demonstrated the formation of several biomolecules as a stress response mechanism that is bioactive, showing its probable biotechnological applications in future.