Isolating Flavonoids in Japanese Honeysuckle Using Capillary Electrophoresis

Scientists from Henan University in Kaifeng, China recently combined capillary electrophoresis (CE) and magnetic solid-phase extraction (MSPE) to isolate flavonoid compounds from the leaves of Lonicera japonica Thunb. Their findings were published in the Journal of Chromatography A (1).

Rainy Day Honeysuckle | Image Credit: © Kenneth Keifer - stock.adobe.com

Flavonoids are bioactive components that are typically found in plant products, including teas and vegetables (1,2). They are noted for having anti-inflammatory, antibacterial, antioxidant, and cardiovascular protective properties. However, due to these samples being complex and having low content of these components, scientists in medical and food science still find it challenging to develop rapid and sensitive methods for isolating and extracting flavonoids.

In this study, a 4-formylphenylboronic acid functionalized magnetic Fe₃O₄ nanomaterial (Fe₃O₄@FPBA) was synthesized and applied as a sorbent of magnetic solid-phase extraction (MSPE) to covalently extract flavonoids from leaves of Lonicera japonica Thunb. Better known as the Japanese honeysuckle, this fast-growing vine has been reported to be invasive throughout both U.S. coasts, with scattered growth in the Southwest (3). It is widely known for its invasive nature, its ability to grow in various types of habitats, including forest floors, canopies, roadsides, wetlands, and disturbed areas (4). Further, Lonicera japonica is typically planted throughout the United States for decoration, erosion control, and as part of wildlife habitats.

Using six flavonoids as model compounds, the covalent adsorption properties were researched by combining magnetic solid-phase extraction (MSPE) with capillary electrophoresis (CE). From there, both methods were applied to the selective cis-dihydroxy compounds in the leaves of Lonicera japonica Thunb. The structure, morphology, and magnetic properties of Fe₃O₄@FPBA particles were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and scanning electron microscope (SEM) technologies. Luteoloside, luteolin, lonicerin, hyperoside, quercetin and rutin were used as model compounds, Fe₃O₄@FPBA was used as a sorbent, and the flavonoids were detected using a newly developed and optimized method combining MSPE with CE.

Adsorption kinetics showed that this process is in line with the Quasi-second-order model, which is controlled by chemisorption mechanism, with the equilibrium adsorption capacity ranging from 3.66 to 6.16 mg/g. Isothermal adsorption models show that adsorption is more consistent with Freundlich isotherm equation, and the exponent n is around 1. Further, the material was applied to the leaves of Lonicera japonica Thunb. extract. Four types of flavonoids and three fellow o-hydroxyl compounds were covalently extracted and magnetically separated. The material can also successfully maintain high adsorption properties after being recycled 5 times. The material possesses strong magnetism and boric acid ligands, which can realize rapid and high-capacity separation and enrichment of flavonoids in liquid samples.

The established method proved simple and controllable to operate. Moreover, the scientists could only complete separation and enrichment without damaging the molecular structure of the analyte and the boronic acid group by regulating the system’s pH value. Overall, this strategy enables a new method for extracting and purifying flavonoids from complex natural plants, all while providing a research basis for discovering new medicinal compounds based on natural products.

References

(1) Yuan, Y.; Wang, X.; Zhu, J.; et al. Phenylboronic Acid Functionalized Magnetic Ferroferric Oxide Nanoparticles and Capillary Electrophoresis for Efficient Isolation of Flavonoid Compounds from Leaves of Lonicera japonica Thunb. J. Chromatogr. A 2025, 1744, 465729. DOI: 10.1016/j.chroma.2025.465729

(2) Hatanaka, M. What Are Flavonoids? Everything You Need to Know. Healthline 2023. https://www.healthline.com/health/what-are-flavonoids-everything-you-need-to-know (accessed 2025-2-19)

(3) Japanese Honeysuckle. Invasive.org 2010. https://www.invasive.org/alien/pubs/midatlantic/loja.htm (accessed 2025-2-19)

(4) Japanese Honeysuckle (Lonicera japonica Thunb.) Invasive.org 2018. https://www.invasive.org/browse/subinfo.cfm?sub=3039 (accessed 2025-2-19)