Ceibinin, a new positional isomer of mangiferin from the inflorescence of Ceiba pentandra (Bombacaceae), elicits similar antioxidant effect but no anti-inflammatory potential compared to mangiferin

Ceiba pentandra (L.) Gaertn. (Bombacaceae) is popular for the quality of its wood. However, its leaf, stem bark and root bark have been popular in ethnomedicine and, apart from the inflorescence, have been subject of extensive phytochemical investigations. In this study, two compounds were isolated from the crude methanol extract of the inflorescence. Through data from UV, NMR, MS, electrochemical studies, differential scanning calorimetry, and thermogravimetric analysis, the structures were elucidated as 3-C-β-d-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone (1) and 2-C-β-d-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone (mangiferin, 2). They were assessed for antioxidant efficacy (DCFDA assay) and for anti-inflammatory efficacy using the lipopolysaccharide (LPS)-induced inflammation model in the RAW 264.7 macrophages (nitrite levels quantified, using Griess Assay, as surrogate for nitric oxide (NO)). Compound 1 (named ceibinin) was established as a novel positional isomer of mangiferin (2). While both 1 and 2 were antioxidant against basal and hydrogen peroxide (100 μM)-induced oxidative stress (6.25 μg/ml abrogated peroxide-induced oxidative stress), ceibinin (1) demonstrated no anti-inflammatory potential, unlike mangiferin (2) which, as previously reported, showed anti-inflammatory effect. Our work reports a positional isomer of mangiferin for the first time in C. pentandra and demonstrates how such isomerism could underlie differences in biological activities and thus the potential for development into therapeutics.

Sensitive Electrochemical Sensor Based On an Aminated MIL-101(Cr) MOF for the Detection of Tartrazine

The aminated metal-organic framework H₂N-MIL-101(Cr) was used as the carbon paste electrode (CPE) modifier for the determination of tartrazine (Tz) in soft drinks. The amino material was characterized by electrochemical impedance spectroscopy and showed significantly faster electron transfer with lower charge-transfer resistance (0.13 kΩ) compared to the electrode modified with the unfunctionalized MIL-101(Cr) material (1.1 kΩ). The H₂N-MIL-101(Cr)-modified CPE [H₂N-MIL-101(Cr)-CPE] was then characterized by cyclic voltammetry (CV) using [Fe(CN)₆]^3- and [Ru(NH₃)₆]³⁺ ions as the redox probes, showing good accumulation of [Fe(CN)₆]^3- ions on the electrode surface. A CV scan of Tz in Britton Robinson buffer solution revealed an irreversible system with an oxidation peak at +0.998 V versus Ag/AgCl/KCl. Using CV and differential pulse voltammetry, an electrochemical method for quantifying Tz in aqueous medium was then developed. Several parameters that affect the accumulation and detection steps were optimized. Optimal detection of Tz was achieved after 180 s of accumulation in Britton Robinson buffer solution (pH 2) using 2 mg of H₂N-MIL-101(Cr) material. Under optimal conditions, the sensor exhibited a linear response in the concentration range of 0.004-0.1 μM and good detection sensitivity (35.4 μA μM^-1), and the detection limit for Tz was found to be 1.77 nM (S/N = 3). Satisfactory repeatability, stability, and anti-interference performance were also achieved on H₂N-MIL-101(Cr)-CPE. The sensor was applied to commercial juices, and the results obtained were approximately similar to those given by UV-vis spectrophotometry.

A new sensor based on an amino-montmorillonite-modified inkjet-printed graphene electrode for the voltammetric determination of gentisic acid

An amperometric sensor based on an inkjet-printed graphene electrode (IPGE) modified with amine-functionalized montmorillonite (Mt-NH₂) for the electroanalysis and quantification of gentisic acid (GA) has been developed. The organoclay used as IPGE modifier was prepared and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, CHN elemental analysis, and thermogravimetry. The electrochemical features of the Mt-NH₂/IPGE sensor were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibited charge selectivity ability which was exploited for the electrochemical oxidation of GA. The GA amperometric response was high in acidic medium (Brinton-Robinson buffer, pH 2) due to favorable interactions between the protonated amine groups and the negatively charged GA. Kinetic studies were also performed by cyclic voltammetry, and the obtained electron transfer rate constant of 11.3 s^-1 indicated a fast direct electron transfer rate of GA to the electrode. An approach using differential pulse voltammetry was then developed for the determination of GA (at + 0.233 V vs. a pseudo Ag/Ag⁺ reference electrode), and under optimized conditions, the sensor showed high sensitivity, a wide working linear range from 1 to 21 μM (R² = 0.999), and a low detection limit of 0.33 μM (0.051 ± 0.01 mg L^-1). The proposed sensor was applied to quantify GA in a commercial red wine sample. The simple and rapid method developed using a cheap clay material could be employed for the determination of various phenolic acids.

Promoting Potato Seed Sprouting Using an Amphiphilic Nanocomposite

Most potato tubers were used as seeds and sprouted relatively slowly in soil, greatly influencing potato production. To solve this problem, an amphiphilic nanocomposite was fabricated by loading hydrophobic silica (H-SiO₂) in hydrophilic attapulgite nest-like and used as a nano presprouting agent (NPA). This technology could conveniently adjust the occupation area ratio of water and air (OARWA) on the potato surface. NPA could endow potatoes with an appropriate OARWA and, thus, effectively accelerate sprouting. Additionally, NPA greatly decreased soil bulk density, facilitated earthworm growth, promoted potato growth, and increased the yield by 14.1%. Besides, NPA did not pass through the potato skin and mainly existed on the surface of potatoes. Importantly, NPA showed tiny influence on the viability of fish and nematodes, demonstrating good biosafety. Therefore, this work provides a promising presprouting approach for potatoes, which may have a potential application prospect in ensuring food supply.