Assessment of antibacterial and antioxidant activity of aqueous crude flower, leaf, and bark extracts of Ethiopian Hibiscus rosa-sinensis Linn: geographical effects and Co2Res2 /Glassy carbon electrode

Abstract

ABSTRACT Ethiopian Hibiscus rosa-sinensis Linn contains a variety of bioactive phytochemicals, which possess several biological activities. This study aims to analyze the antibacterial and antioxidant activity of aqueous crude flower, leaf, and bark extracts of Hibiscus rosa-sinensis, as well as to see the geographical effects and method development of Co2Res2/Glassy carbon electrode. The secondary metabolites of Hibiscus rosa-sinensis extracts were investigated by maceration techniques. Disc diffusion methods are used for antimicrobial activities against a total of four human pathogens bacteria such as E. coli, K. pneumonia, S. aureus, and S. epidermidis, respectively. Antioxidant activities were assessed using differential pulse voltammetry (DPV), whereas, the phytoconstituents of Hibiscus rosa-sinensis extracts were profiled using FTIR and UV-Vis analysis. The phytochemical investigations showed that phenols, flavonoids, and quinines were observed more exist in crude flower, whereas quinines and flavonoids moderately exist in leaf, but steroids, terpenoids, and cardiac glycosides have not existed in leaf and bark extracts of Hibiscus rosa-sinensis, respectively. The plant extracts showed a growth inhibitory effect against S. aureus and S. epidermidis in the range of 6.33 ± 0.33 to 11.50 ± 0.29 mm, whereas a growth inhibitory effect was recorded against K. pneumonia and E. coli in the range of 6.67 ± 0.33 to 13.00 ± .58 mm, respectively. The XRD analysis confirmed that Co(II) based MOF, Co2Res2 was a nanosize structure with an average crystal size of 27.17 nm. Furthermore, the DPV showed that the observed net modified current peaks and potentials were the most significant compared to the pure net current peaks and the potential of aqueous fresh flower, leaf, and bark extracted from Hibiscus rosa-sinensis. These extracts of Hibiscus rosa-sinensis have shown an improved potential source of natural antioxidants and as well as antibacterial activities. Chemically and thermally stable porous crystalline MOF, Co2Res2 serves as catalytic reactions to increase current and decrease potential in modified GCE, this might be due to the synergetic cumulative effect of the presence of bioactive ingredients and Co2Res2 catalyst. Abbreviations: ABS: Acetate buffer solution; ANOVA: Analysis of variance; ATR: Attenuated total reflectance; CFU/ml: Colony forming unit per milliliter: Co2Res2: Co(II) based metal-organic framework (ResH2: resorcinol); DPV: Differential plus voltammetry: FTIR; Fourier transforms infrared radiation; GCE: Glassy carbon electrode; JCPDS: A joint committee on power diffraction standards; MOF: Metal-organic framework; PBS: Phosphate buffer solution; SPSS: Statistical package for the social sciences; UV-Vis: Ultraviolet-visible spectroscopy; XRD: X-ray diffraction