Chemical Composition and Biological Activity of the Essential Oil of Viola diffusa
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CHEMICAL COMPOSITION AND BIOLOGICAL ACTIVITY OF THE ESSENTIAL OIL OF Viola diffusa
Bing-Cheng Liu,1 Ruo-Lan Wang,2 Lu-Na Yang,2 Peng-Xiang Lai,2 and Xiang Xing2*
Viola diffusa Ging., an annual herb of the Viola genus, belongs to the family Violaceae and is mainly distributed in southern China. In traditional Chinese medicine, V. diffusa is widely used for the treatment of snake bites, bruises, cough, ulcerative carbuncle, pleuritis, and hepatitis [1–3]. In the previous phytochemical investigation, several seco-ring-A-friedelanes3,4-lacones were isolated from V. diffusa and demonstrated to exhibit potent anti-hepatitis B virus (anti-HBV) activity [2–4]. To our knowledge, there is no previous study on the essential oil (EO) profile and bioactivity of V. diffusa essential oil. Therefore, the main objective of this research was to characterize the chemical constituents of the essential oil obtained from the aerial parts of V. diffusa and the antioxidant, antibacterial, and cytotoxic properties of the oil. The plant material was collected in July 2018 from Lishui in Zhejiang Province of China. A voucher specimen (No. 0170019) was deposited at the Laboratory of Botany of Marine College, Shandong University, China. The air-dried and ground aerial parts of V. diffusa (500 g) were hydrodistilled for 3 h using a Clevenger apparatus, and the essential oil was obtained in a yield of 0.08% (v/w) based on dry weight of the sample. The essential oil was analyzed by GC-FID and GC-MS methods using the analytical conditions described previously [5]. Identification of individual compounds was carried out by matching their mass spectra with the NIST 14 MS Search 2.2 Mass Spectral Database, as well as by comparison of their retention indices determined using mixtures of homologous series of n-alkanes (C7–C30) under the same experimental conditions with reference libraries [6–8]. The relative amounts of essential oil components were calculated by normalizing the GC-FID peak area without a correction factor. Thirty-two compounds accounting for 95.8% of the total essential oil were identified (Table 1). The predominant components of the obtained essential oil were 1-octen-3-ol (23.7%), neophytadiene (11.0%), linalool (10.4%), (E)-11-hexadecenol (5.4%), hexahydrofarnesyl acetone (5.3%), isophytol (3.6%), 2-tridecanone (3.6%), and neointermedeol (3.0%). The antioxidant activities of the essential oil were investigated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonate (ABTS) radical cation scavenging, and ferric reducing antioxidant power (FRAP) assays [9]. Trolox and BHT (butylated hydroxytoluene) were used as positive control. The results are presented in Table 2. It was observed that the V. diffusa essential oil exhibited moderate radical scavenging ability in both DPPH and ABTS tests with IC50 values of 0.56 and 0.14 mg/mL, and good ferric reducing power in the FRAP assay with a TEAC (Trolox equivalent antioxidant concentration) value of 106.30 μmol Trolox × g–1. Antimicrobi
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