Phytochemistry of Centaurea saligna: silver nanoparticle synthesis, quantification of natural compounds, antioxidant and antibacterial activityDownload PDF Download PDF ArticleOpen accessPublished: 20 July 2025Esma Nur Gecer ORCID: orcid.org/0000-0002-0095-079X1 Scientific Reports volume 15, Article number: 26307 (2025) Cite this articleSubjectsBiochemistryBiotechnologyChemical biologyChemistryNanoscience and technologyAbstractCentaurea species contain medicinally bioactive compounds. The capping, stabilization, and reduction of silver ions by the bioactive compounds in Centaurea saligna are crucial for the formation of silver nanoparticles. Nanotechnology, with its wide-ranging applications, is a significant discipline in science. Due to the widespread application of nanoparticles, many studies have been conducted. Herein, silver nanoparticles (AgNPs@cs) were produced via leaves of Centaurea saligna, and quantification of phenolics existing in leaves was established by LC–MS/MS. Furthermore, antioxidant and antibacterial activities were conducted for both the extract and the nanoparticles. The analytical techniques, including FTIR, UV–VIS, XRD, and TEM, were employed to elucidate the structure. Moreover, stability was determined by measuring the zeta potential. Scutellarin (8.67 mg/g extract), shikimic acid (3.97), and chrysin (2.67) were found as major compounds by LC–MS/MS. In DPPH radical scavenging activity, AgNPs@cs displayed an excellent effect (IC50, μg/mL, 9.27 ± 0.14) in association to BHT (12.45 ± 0.41, IC50, μg/mL). In addition, AgNPs@cs showed good activity against the tested bacteria. The absorption in UV–Vis analysis at 441 nm displayed nanoparticle formation. The size of the nanoparticle was calculated using TEM and XRD measurements, which were 16.2 nm and 18.5 nm, respectively. The zeta potential measurement confirmed the stability. It may be possible to use Centaurea saligna in the production of foods and medications.IntroductionNanotechnology has been known as the most popular research area lately1. Nanoparticles of noble metals are of interest due to their biocompatibility. They are effectively used in areas such as medicine, food, agriculture, pharmacy, and water treatment2. Physical and chemical methods have been employed to obtain metal nanoparticles. A significant amount of energy is spent, and a large amount of toxic chemicals are produced for nanomaterials obtained by traditional methods. Therefore, there is a widespread trend worldwide to obtain environmentally friendly, non-toxic, and affordable nanoparticles that adhere to the principles of “green chemistry.”Different natural materials can be used to synthesize nanoparticles biologically. Plants are essential because they contain bioactive compounds that act as reducing agents in nanoparticle fabrication3. Natural products show effective biological action because of their presence of bioactive compounds. The use of natural products in food and medicine is as old as human history4,5,6. Due to the side effects of chemical products, there is a growing tendency to use natural products instead of chemicals in food and medicinal products7. Additionally, the natural product-mediated synthesis of nanoparticles could be an effective material for use in nutrition and pharmaceuticals. In this context, Centaurea saligna-mediated nanoparticles could be a crucial material for biotechnology and food applications.The Centaurea genus, which belongs to the Asteraceae family, comprises 700 species distributed across Asia, Africa, the Americas, and Europe. Centaurea species grow widely in Turkey8. The Centaurea species exhibits significant biological effects, including anticancer, anti-ulcerogenic, anti-inflammatory, and antioxidant properties. The research on this plant yielded the separation of fascinating compound classes, including flavonoids, terpenes, steroids, phenolics, and alkaloids. Centaurea species are used as folk remedies for various diseases such as urethritis, abscesses, hemorrhoids, peptic ulcers, and colds9. The usage of Centaurea saligna for the synthesis of silver nanoparticles is significant for biological activity. Since this plant includes significant bioactive compounds that act as reducing, capping, and stabilizing agents.Reactive oxygen species (ROS) are molecules that damage the human body10. These molecules are by-products of cellular metabolism, particularly during aerobic respiration. They include non-radical molecules such as hydrogen peroxide, free radicals such as superoxide, and radicals11. Due to their unpaired electrons, ROS efficiently react with proteins and DNA. High levels of ROS can result in oxidative stress, which damages cellular components and contributes to aging, as well as diseases like cancer, neurodegenerative disorders, and cardiovascular diseases12. Antioxidants neutralize ROS by donating electrons to them. Both endogenous and dietary antioxidants play a key role in oxidative damage13.It is essential to develop new antibacterial drugs against drug resistance. Inorganic materials in the form of silver nanoparticles can be alternative drugs to control pathogenic microbial infections. Silver nanoparticles have been determined to have antibacterial effects14,15. Silver nanoparticles affect different parts of bacteria and inhibit their growth. Nanoparticles also cause membrane damage, leakage of cell components, and inhibition of crucial proteins, thus stopping microbial growth. AgNPs are responsible for killing and inhibiting microorganisms16.Herein, phytochemical analysis of Centaurea saligna, including quantitative analysis of phenolics with antioxidant and antimicrobial activity, was carried out. To our knowledge, this is the first study on this subject.Results and discussionSynthesis and UV–Vis analysisAgNPs@cs were synthesized from the leaves of Centaurea saligna using green approaches, which are cost-effective, efficient, scalable, and environmentally friendly. The bioactive compounds found in the leaves of C. saligna act as reducing agents. Because the Centaurea species contains significant biologically active compounds, silver nanoparticles synthesized from this plant are expected to exhibit high biological activity. UV–Vis analysis revealed a maximum absorption at 441 nm, indicating the formation of silver nanoparticles (Fig. 1). The absorption at 400–450 nm confirms the synthesis of silver nanoparticles. The signal observed at this wavelength is well-documented for a variety of metal nanoparticles with sizes ranging from 2 to 100 nm due to surface plasmon resonance17.Fig. 1UV–Vis spectrum of AgNPs@cs. The maximum absorption was observed at 441 nm.Full size imageSince scutellarin was the primary compound in C. saligna, the mechanism was shown with this molecule (Fig. 2).Fig. 2Proposed reaction mechanism for the formation of AgNPs@cs.Full size imageFourier transform infrared spectroscopy (FTIR) analysisThe responsible molecules for reducing agents were determined by FTIR analysis. The signal at 3261 cm−1 and 2921 cm−1 may be due to the hydroxyl stretching and C-H stretching of the alkane, respectively. The absorption peaks at 1594 cm−1 and 1381 cm−1 could be attributed to the N–H bending of amine and the OH bending, respectively. The stretching of the ether peak and C-F stretching signal were observed at 1243 cm−1 and 1009 cm−1, respectively (Fig. 3). The FTIR values obtained in this study are consistent with those in previous studies. Silver nanoparticles were synthesized using the walnut leaf18, and the OH bending signal was observed at 3258 cm−1. Silver nanoparticles were produced using Tagetes erecta leaves19, and the OH signal was observed at 3305 cm−1, CH stretching signals of alkanes occurred at 2973 cm−1 and 2885 cm−1. The interaction of silver ions with flavonoids, terpenoids, and phenolics created the colloidal suspension. Therefore, the reduction of silver ions by comparable natural components was ascertained using an FTIR20.Fig. 3FTIR spectrum of AgNPs@cs.Full size imageX-ray diffraction (XRD) measurementXRD measurement presented the particle size of nanoparticles as well as crystal structures. X’Pert HighScore Plus software was used to calculate particle size. The signal (2θ) observed at 38.12°, 44.26°, 64.53°, 77.47°, and 81.51° degrees corresponded to the crystal planes [1 1 1, 2 0 0, 2 2 0, 3 1 1, and 2 2 2] (ICDD, no:96-500-0219), verifying the structure as face-centered cubic21 (Fig. 4). The dimension of the particle was calculated as 18.49 nm using the Scherrer Equation (Eq. (1)).$${\text{D}} = \, 0.{9 }\lambda \, / \, \beta {\text{ cos }}\theta$$(1)Fig. 4XRD spectrum and full width at half maximum values of AgNPs@cs. Average particle size was calculated as 18.49 nm.Full size imageTransmission electron microscopy (TEM) analysisTEM analysis determined the morphology and size of green synthesized nanoparticles (Fig. 5). The particle size was 16.2 nm. Due to the different physical and chemical properties of nanoparticles, their sizes and shapes are significant. The TEM image revealed the homogeneously distributed monodisperse AgNPs@cs with a spherical shape. The monodispersity could be due to the capping of bioactive compounds.Fig. 5TEM images and particle size distribution of AgNPs@cs.Full size imageThe intense signals observed at 3.3 keV in the EDX spectrum confirmed the formation of AgNPs@cs (Fig. 6). This characteristic signal at 3.0–3.3 keV is attributed to the surface plasmon resonance of silver nanoparticles22. Elemental analysis exhibited remarkable yield (79.13%).Fig. 6EDX spectrum and elemental analysis of nanostructure. The silver nanoparticles were synthesized in high yield (79.13%).Full size imageZeta potential analysisThe surface charge of particles in suspension is determined by zeta potential measurement, which provides insight the stability since zeta potential is an indicator of electrostatic interactions between particles. A high zeta potential (positive or negative) generally reveals good dispersion and stability as particles repel each other and resist aggregation. A low zeta potential indicates that particles are more likely to aggregate, leading to instability. The values of zeta potential between the 30 mV and 60 mV show the good stability of nanoparticles23. The zeta potential of AgNPs@cs was calculated as − 20.3 mV, indicating moderate stability (Fig. 7).Fig. 7Zeta potential of AgNPs@cs. The zeta potential (−20.3 mV) reveals the stability.Full size imageQuantitative analysis of natural compoundsQuantitative analysis is essential for the synthesis of AgNPs, as it indicates natural compounds that reduce, stabilize, and cap the nanoparticles. The analysis of bioactive compounds in Centaurea saligna water extract was determined by LC–MS/MS and scutellarin (8.67 mg/g extract), shikimic acid (3.97 mg/g extract), chrysin (2.67 mg/g extract), and chlorogenic acid (0.55 mg/g extract) were found as major compounds by LC–MS/MS (Table 1). Quantification of phenolics found in Robinia pseudoacacia leaves and flowers was executed. Syringic acid (24.78 µg/g extract) was found as a major compound in leaves and rutin (199.74 µg/g extract) was found in flowers24. In another study, chlorogenic acid (250.171 µg/g extract) was found as a major product of Silybum marianum flowers25. Phytochemical analysis of phenolic compounds in Hypericum heterophyllum flowers resulted in the determination of chlorogenic acid as a major compound26. Syringa vulgaris was reported to contain hesperidin as an major compound27. The activity may be due to the corresponding bioactive compounds. These studies are essential in terms of the isolation of bioactive compounds from plants, the determination of their structures, and revealing their biological activities.Table 1 Quantitative analysis of phenolic compounds in Centaurea saligna leaf extract by HL-MS/MS.Full size tableAntioxidant activityThe antioxidant activity of the extract and AgNPs@cs was evaluated using the DPPH, ABTS, and FRAP assays. In DPPH free radical scavenging activity, nanoparticles displayed significant activity with the value of 9.27 ± 0.14 (IC50, µg/mL), and the activity of the extract was determined as 10.47 ± 0.31 (IC50, µg/mL). However, the effect of standard BHT was calculated as 12.45 ± 0.41 (IC50, µg/mL). In the ABTS radical cation scavenging effect, the same trend was observed. AgNPs@cs displayed a better effect (7.43 ± 0.15, IC50, µg/mL) than that of the extract (9.44 ± 0.35, IC50, µg/mL) and standard BHT (8.13 ± 0.09, IC50, µg/mL). In FRAP activity, nanoparticles displayed higher activity (5.4 ± 0.35, µmol TE/mg extract) than that of the extract (4.78 ± 0.15, µmol TE/mg extract) but lower activity than standard BHT (6.29 ± 0.13, µmol TE/mg extract) (Fig. 8). In Fig. 8, the different letters (a, b, c) reveal the statistical differences between each group. It was reported that the silver nanoparticles were synthesized using the plants. The walnut leaves were used for the synthesis of silver nanoparticles, which showed high activity against the L929, MCF-7, and H1299 cell lines28. Another study reported that Lactuca anatolica root aqueous extract was used for the synthesis of AgNPs that displayed good antioxidant, antibacterial, and enzyme inhibition activities29.Fig. 8Antioxidant activity of the extract and nanoparticles. The different letters (a, b, c) indicate the statistical differences in the sample activity. One-way ANOVA followed by Tukey’s multiple comparison test was used to compare the activities of each sample. A level of probability of