LC/MS Profiling and Gold Nanoparticle Formulation of Major Metabolites from Origanum majorana as Antibacterial and Antioxidant Potentialities

Abstract

Origanum majoranum L. is a Lamiaceae medicinal plant with culinary and ethnomedical applications. Its biological and phytochemical profiles have been extensively researched. Accordingly, this study aimed to investigate the chemical composition and the antibacterial and antioxidant properties of O. majoranum high features, as well as to search for techniques for activity optimization. A metabolomics study of the crude extract of O. majoranum using liquid chromatography-high-resolution electrospray ionization mass spectrometry (LC ± HR ± ESI ± MS) was conducted. Five fractions (petroleum ether, dichloromethane, ethyl acetate, n-butanol, and aqueous) were derived from the total extract of the aerial parts. Different chromatographic methods and NMR analysis were utilized to purify and identify the isolated phenolics (high features). Moreover, the antimicrobial, antibiofilm, and antioxidant activity of phenolics were performed. Results showed that metabolomic profiling of the crude extract of O. majoranum aerial parts revealed the presence of a variety of phytochemicals, predominantly phenolics, resulting in the isolation and identification of seven high-feature compounds comprising two phenolic acids, rosmarinic and caffeic acids, one phenolic diterpene, 7-methoxyepirosmanol, in addition to four flavonoids, quercetin, hesperitin, hesperidin, and luteolin. On the other hand, 7-methoxyepirosmanol (OM₁) displayed the most antimicrobial and antioxidant potential. Such a phenolic principal activity improvement seems to be established after loading on gold nanoparticles.

Keywords: 7-methoxyepirosmanol; Origanum majoranum L.; antimicrobial; antioxidant potential; gold nanoparticles; high features; metabolomics.

Figure 1

Structures of high features of compounds (ranked by peak intensity) detected in hydromethanolic extract of OM after dereplication of their metabolomes.

Figure 2

In vitro antimicrobial activity. (A) Antibacterial activity of different purified compounds, compared to control (ciprofloxacin). (B) Antibacterial and antifungal activity of compound OM₁, compared with AuNPs and AuNPs-OM₁.

Figure 3

Surface plasmon bands of the compound OM₁ (a), AuNPs (b), and the AuNPs-OM₁ conjugate (c). Color change of the gold alone (d) and extract (e), when mixed together (f) and the formation of AuNPs-OM1 (g). Surface plasmon absorption bands (SPR).

Figure 4

TEM and SEM micrographs of the prepared AuNPs (a,c) and AuNPs-OM₁ (b,d).

Figure 5

The XRD of the prepared AuNPs.

Figure 6

FTIR spectra for compound OM₁ (a) and the prepared AuNPs-OM₁ (b).