Degradation of caffeic acid in subcritical water and online HPLC-DPPH assay of degradation products

Boric acid functionalized Fe3O4@CeO2/Tb-MOF as a luminescent nanozyme for fluorescence detection and degradation of caffeic acid

Caffeic acid (CA) is a natural polyphenol that can have various positive effects on human health. However, its extraction and processing can cause significant ecological issues. Therefore, it is crucial to detect and degrade CA effectively in the environment. In this study, we have developed a multifunctional magnetic luminescent nanozyme, Fe3O4@CeO2/Tb-MOF, which combines peroxidase activity to detect and degrade CA. The fluorescence of the nanozyme was significantly attenuated due to the specific nucleophilic reaction between its boronic acid moiety and the o-diphenol hydroxyl group of CA, energy competition absorption and photo-induced electron transfer (PET) effect. This nanozyme demonstrates a linear detection range from 50 nM to 500 μM and an exceptionally low detection limit of 18.9 nM, along with remarkable selectivity and stability. Moreover, the synergistic catalysis of Fe3O4 and CeO2 within Fe3O4@CeO2/Tb-MOF fosters peroxidase activity, leading to the generation of substantial free radicals catalyzed by H2O2, which ensures the efficient degradation of CA (∼95%). The superparamagnetic property of Fe3O4 further enables the efficient reuse and recycling of the nanozyme. This research provides a novel approach for the concurrent detection and remediation of environmental contaminants.

Caffeic acid accelerated the Fe(II) reinvention in Fe(III)/PMS system for bisphenol A degradation: Oxidation intermediates and inherent mechanism

Fe(II)-catalyzed PMS process was widely used in the degradation of refractory pollutants in wastewater, while its performance was restricted by the slow regeneration efficiency of Fe(II). Herein, caffeic acid (CFA), a representative of hydroxycinnamic acids, was introduced into Fe(III)/PMS system to accelerate the transformation of Fe(III) to Fe(II) and promote the removal of bisphenol A (BPA). Under optimum condition of 0.1 mM CFA, 0.05 mM Fe(III), and 0.5 mM PMS, almost complete removal of BPA can be achieved within 20 min, which was roughly 6.2 times higher than that in Fe(III)/PMS system. As the addition of CFA into Fe(III)/PMS system, pH application range was widened from acidic to alkaline conditions. The reduction and chelation of CFA expedited the Fe(III)/Fe(II) cycle by forming CFA-Fe chelate, thereby facilitating the PMS activation. Based on LC-MS analysis and DFT calculation, the intermediate products of CFA were found to play a decisive role in boosting the regeneration of Fe(II), and the toxicity of these intermediates towards organisms was evaluated by ECOSAR. The alcohol-scavenging and chemical probe tests certified that hydroxyl radical (•OH), sulfate radical (SO4•-), and Fe(IV) coexisted in Fe(III)/CFA/PMS system, and the second-order reaction rate constants of •OH and SO4•- reacted with CFA were calculated to be 3.16✕109 and 2.30✕1010 M-1 s-1, respectively. Two major degradation pathways of BPA, •OH addition and SO4•- induced hydroxylation reaction, were proposed. This work presented a novel green phenolic compound that expedited the Fe(II)-catalyzed PMS activation process for the treatment of organic contaminants.

A facile synthesis of CuBi2O4 hierarchical dumbbell-shaped nanorod cluster: a promising photocatalyst for the degradation of caffeic acid

The present study reports on the synthesis of Cu-bismuth oxide (CuBi2O4)-based nanorods by using a simple co-precipitation method for the photocatalytic degradation of caffeic acid (CA). The incorporation of Cu metal ions during the synthesis of CuBi2O4 nanorods might be advantageous to avoid the aggregation and control the leach out of metal ions. The calculated bandgap values of ~ 1.04, 1.02, and 0.94 eV were observed for CuBi2O4 with different amounts of Cu 1.0, 0.50, and 0.25 g, respectively. Varying the quantity of Cu metal ions easily tuned the bandgap value within the CuBi2O4-based nanorods. However, a further decrease in the bandgap value increased the recombination rate, and the less photocatalyst performance was observed. The CA degradation could be explained based on the species distribution. The CA pKa was mainly located between pKa1 and pKa2 of 4.43 and 8.6, respectively. The Cu within the CuBi2O4-based nanorods changed the electronic properties and the antibacterial ability. Therefore, the synthesized CuBi2O4-based nanorod cluster might be a promising material for the photocatalytic degradation of CA.

Ultrasound-, subcritical water- and ultrasound assisted subcritical water-derived Tartary buckwheat polyphenols show superior antioxidant activity and cytotoxicity in human liver carcinoma cells

The effects of ultrasound-assisted (UAE), subcritical water (SWE) and ultrasound assisted-subcritical water (UA-SWE) treatments on tartary buckwheat polyphenol yield, composition, antioxidant activity and cytotoxicity in human liver carcinoma cells were studied. Folin Ciocalteu assay was used to measure total free phenol content (TFPC), and ABTS, DPPH, FRAP and TEAC assays were used to measure antioxidant activity (AA). Polyphenol characterization was done by LC-MS and cell antioxidant activity (CAA) and cytotoxicity were done using the 2,2'-Azobis-(2-amidinopropane) dihydrochloride [ABAP] and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide [MTT] assays respectively. The highest polyphenol yield was obtained by SWE (53.3 mg g^-1), followed by UA-SWE (31.8 mg g^-1), UAE (19.3 mg g^-1) and HWE (4.2 mg g^-1). Also, SWE had the highest TFPC (7.9 mgGAE/gdw). UAE and UA-SWE showed no differences with TFPC being 6.6 and 6.8 mgGAE/gdw, respectively. The control method (HWE) had the largest number of phenolic compounds identified (25), followed by UAE, SWE and UA-SWE which had 20, 13 and 11 phenolics respectively. Beside phenolic acids, all treatments extracted a number of flavonoids such as flavan-3-ols (catechin-7-O-glucoside, epigallocatechin-3-gallate, epigallocatechin, epicatechin), flavonols (kaempferol-3-O-glucoside, kaempferol, kaempferol-3-rutinoside, rutin, quercetin, quercetin-3-O-glucuronide hyperin), flavones (vitexin, isovitexin, orientin, isoorientin) and anthocyanins (cyanidin-3-O-rutinoside, Cyanidin 3-O-galactoside, cyanidin-3-O-glucoside). SWE gave the highest AA for all tests. However, the AA of those obtained by UAE and UA-SWE did not vary (P < 0.05), but were higher than HWE. Different extracts had best AA at different concentrations (HWE, 300; UAE, 250; SWE, 150; UA-SWE, 200 μg/mL). The IC₅₀ of AA were 270.8 ± 21.3, 198.1 ± 16.0, 97.9 ± 13.5, and 150.4 ± 12.8 μg/mL, respectively for HWE, UAE, SWE and UA-SWE. Generally, SWE and UA-SWE showed the highest cytotoxic activities, followed by UAE, with HWE being the lowest. IC₅₀ of cytotoxicity were 76.1 ± 3.3, 79.5 ± 7.0 and 92.6 ± 4.9 µg/mL for SWE, UA-SWE and UAE, respectively. SWE is a promising method for polyphenol extraction and its combination with ultrasound should be optimized for high yield and conservation of bioactivity.

One injection to profile the chemical composition and dual-antioxidation activities of Rosa chinensis Jacq

An on-line high-performance liquid chromatography-diode-array-detector-electrospray ionization-ion-trap-time-of-flight-mass spectrometry-total antioxidant capacity detection (HPLC-DAD-ESI-IT-TOF-MS-TACD) system was applied for the identification and evaluation of antioxidants in Rosa chinensis Jacq., an edible flower in food industry and a widely used traditional Chinese medicine. With the help of this platform, the HPLC fingerprint, mass fragmentations, and sample activity profiles against 1,1-diphenylpicryl-2-hydrazyl radical (DPPH•) and ferric reducing antioxidant power (FRAP) were recorded after one injection. Using this technique, 80 compounds were separated and identified by their LC/MS behaviors with the assistance of standard compounds. In addition, 11 different Rosa chinensis Jacq. samples were profiled and then quantified for their DPPH• and FRAP activities. Interestingly, a total of 52 compounds showed antioxidative effects against DPPH• and 61 were active against FRAP. The results demonstrated that the on-line system is a powerful technique for antioxidant discovery in Rosa chinensis Jacq. and other food resources.

Electrochemical treatment of aqueous solutions of organic pollutants by electro-Fenton with natural heterogeneous catalysts under pressure using Ti/IrO2-Ta2O5 or BDD anodes

The treatment of toxic organic pollutants by electro-Fenton (EF) presents some drawbacks such as the necessity to work at low pH and the low solubility of oxygen in water contacted with air or oxygen at room pressure that results often in slow and relatively low abatements. Here, the coupled adoption of natural heterogeneous catalysts and of relatively high pressure was proposed in order to improve the performances of EF for the treatment of organic pollutants. Caffeic acid (CA) and 3-chlorophenol were used as model resistant organic pollutants. EF process was performed using both conventional homogeneous FeSO₄ and natural heterogeneous catalysts (pyrite, chalcopyrite, Fe₂O₃ and Fe₃O₄) as iron catalysts and oxygen at various pressures in the absence or in the presence of BDD anode. The effect of the nature of the catalyst, the oxygen pressure, the current density and the catalyst load was widely investigated in order to optimize the process. It was shown that the coupled utilization of a natural heterogeneous catalyst such as chalcopyrite and a relatively high pressure allows to obtain the total removal of CA and a high removal of the TOC (about 75%) in short times (2 h) with relatively high current efficiencies using an Iridium based anode. In the case of 3-chlorophenol, the utilization of a BDD anode was necessary to achieve a high removal of the pollutant and the TOC. It was shown that the removal of 3-chlorophenol can be effectively performed in different water bodies and with different initial concentrations of 3-chlorophenol.

Enhancement of Phenolic Production and Antioxidant Activity from Buckwheat Leaves by Subcritical Water Extraction

To enhance the production of phenolic compounds with high antioxidant activity and reduce the level of phototoxic fagopyrin, buckwheat leaves were extracted with subcritical water (SW) at 100~220°C for 10~50 min. The major phenolic compounds were quercetin, gallic acid, and protocatechuic acid. The cumulative amount of individual phenolic compounds increased with increasing extraction temperature from 100°C to 180°C and did not change significantly at 200°C and 220°C. The highest yield of individual phenolic compounds was 1,632.2 μg/g dry sample at 180°C, which was 4.7-fold higher than that (348.4 μg/g dry sample) at 100°C. Total phenolic content and total flavonoid content increased with increasing extraction temperature and decreased with increasing extraction time, and peaked at 41.1 mg gallic acid equivalents/g and 26.9 mg quercetin equivalents/g at 180°C/10 min, respectively. 2,2-Diphenyl-1-picrylhydrazyl free radical scavenging activity and ferric reducing ability of plasma reached 46.4 mg ascorbic acid equivalents/g and 72.3 mmol Fe²⁺/100 g at 180°C/10 min, respectively. The fagopyrin contents were reduced by 92.5~95.7%. Color values L* and b* decreased, and a* increased with increasing extraction temperature. SW extraction enhanced the yield of phenolic compounds with high antioxidant activity and reduced the fagopyrin content from buckwheat leaves.

Degradation kinetics of passion fruit pectin in subcritical water

The degradation of passion fruit pectin by subcritical water treatment in a continuous flow-type reactor was investigated in the temperature range of 80−160 °C at a constant pressure of 5 MPa. Changes in the degree of polymerization and reducing end formation were monitored and modeled by applying the Emsley equation and zeroth-order kinetics, respectively. The results showed that both the pectin degradation rate constant and the change in the amount of reducing end were enhanced by temperature, and that the temperature dependence of these parameters obeyed the Arrhenius relationship. The activation energies for pectin degradation and reducing end formation were 62.8 and 86.9 kJ/mol, respectively. The non-linear relationship between the ratio of broken galacturonic acid units to the total galacturonic acid units and the change in the amount of reducing end indicated that pectin cleavage became easier as hydrolysis progressed.

Hydrothermal Degradation of Rutin: Identification of Degradation Products and Kinetics Study

The model glycoside compound quercetin-3-O-rutinoside (rutin) was subjected to subcritical water within the temperature range of 120-220 °C, and the hydrothermal degradation products were analyzed. Two kinetic models describing the degradation of this compound in two different atmospheres (N₂ and CO₂), used for pressure establishment in the reactor, have been developed and compared. Reaction was considered a successive one with three irreversible steps. We confirmed that rutin degradation to quercetin follows first-order kinetics. At higher temperatures quercetin is further degraded in two degradation steps. Formations of 3,4-dihydroxybenzoic acid and catechol were described with the zero-order kinetic models. Reaction rate constants for hydrolysis of glycoside to aglycone in a CO₂ atmosphere are higher compared to those in a N₂ atmosphere, whereas at higher temperatures reaction rate constants for further two successive reactions of aglycone degradation are slightly lower in the presence of CO₂. The difference in reaction activation energies is practically negligible for both gases. Furthermore, degradation products of sugar moieties, that is, 5-hydroxymethylfurfural and 5-methylfurfural, were also detected and analyzed.