## 3 Results and Discussion
### Physicochemical Characterisation
Furthermore, the FTIR spectrum of the biosynthesized ZnO NPs showed a sharp and intense band at 546 cm\({}^{-1}\), indicating the existence of Zn-O vibrations [52]. The FTIR results demonstrated that phenol and flavonoid compounds were abundant in the prepared extract and ZnO NPs. In addition, according to the GC-MS technique and Table 1, the most important compounds in the extract were carbonyl acids, ethers, and phenolic compounds. There are many advantages of applying natural plants in NP synthesis, including coating NPs with different pharmacological species (such as phenolic and polyphenolic compounds) on the metal oxide layer, which facilitates the bonding of NPs with the receivers on bacterial membranes. The _S. ebulus_ extract is rich in such compounds, which are responsible for enhancing the antibacterial properties of ZnO NPs. The possible mechanism for the formation of ZnO NPs using the plant extract could be related to the flavonoid/phenolic molecules reacting with Zn\({}^{2+}\) ions through the donor-acceptor mechanism. Oxygen or hydroxyl compounds present in the plant extract tend to donate an electron to electrophile Zn complexes resulting in oxidation of OH groups and reduction of electron deficient zinc ions to zinc atoms (Figure 1). The synthesized NPs were investigated by XPS surface analysis; Figure 3 depicts a full survey scan in the range 0-1100 eV. Two intense peaks located at \(\sim\)1024 and 1044 eV were observed, which are attributed to the Zn \(2p_{3/2}\) and Zn \(2p_{1/2}\), respectively, corresponding to Zn-O bonding within the hexagonal wurtzite-type structure [53; 54]. The O1s peak was also present in the spectrum at \(\sim\)529-530 eV, corresponding to Zn-O bonds in the intrinsic sites of the ZnO matrix, which is in good agreement with the FTIR spectrum of the biosynthesized ZnO NPs (sharp and intense band at 546 cm\({}^{-1}\), which indicates the existence of Zn-O vibrations). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & \begin{tabular}{c} **Retention** \\ **Time (min)** \\ \end{tabular} & **\%** & **Compound** & \
\begin{tabular}{c} **Retention** \\ **Time (min)** \\ \end{tabular} & **\%** \\ \hline Acetic acid & 5.50 & 1.20 &
\begin{tabular}{c} 14-methyl-Pentadecanoic acid, \\ methyl ester \\ \end{tabular} & 41.12 & 0.67 \\ \hline
1,3-dimethoxy- Propane & 5.60 & 0.17 & n-Hexadecanoic acid & 41.81 & 9.3 \\ \hline
1-Butanol & 6.41 & 2.38 & Hexadecanoic acid, ethyl ester & 42.43 & 0.33 \\ \hline
1,1-diethyl-2-Propanone & 11.68 & 0.66 & \
\begin{tabular}{c} 9Z,12Z-Octadecanionic acid, \\ methyl ester \\ \end{tabular} & 44.39 & 0.36 \\ \hline Isovaleric acid & 12.01 & 3.52 &
\begin{tabular}{c} 9Z,12Z,15Z-Octadecatrienoic \\ acid, methyl ester \\ \end{tabular} & 44.52 & 1.2 \\ \hline
4-vinylphenol & 24.27 & 1.6 & Phytol & 44.74 & 3.08 \\ \hline D(-)-Quinic acid & 34.76 & 0.32 & \(\alpha\)-Linilenic acid & 45.21 & 8.2 \\ \hline Pentanoic acid & 36.22 & 0.28 & Octadecanoic acid & 45.52 & 2.62 \\ \hline (-)-Loliolide & 41.03 & 0.42 &
\begin{tabular}{c} 9Z,12Z,15Z-Octadecatrienoic \\ acid, ethyl ester, \\ \end{tabular} & 44.52 & 0.9 \\ \hline Neophyadiene & 39.421 & 1.02 & Mono(2-ethylhexyl) phthalate & 52.02 & 51.41 \\ \hline
9-Methyl-3,4-dihydro-2H- & 39.76 & 2.50 & Octadecanoic acid (stearic acid) & 45.52 & 2.57 \\ pyrido(1,2-a)pyrimidin-2-one & & & & \\ \hline
14-methyl-Pentadecanoic acid, methyl ester & 41.12 & 0.80 & D-alpha-Tocopherol(Vitamin E) & 64.15 & 0.69 \\ \hline Lignocaine & 41.03 & 0.42 & 22,23 -dihydro Stigmasterol & 71.65 & 3.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Compounds contained in the alcoholic extract of _S. ebulus._