| Praxelis clematidea R.M. King & Robinson and Ageratum conyzoides L., native to South America, are common invasive weeds in south China at present. There is negative effects on Agriculture, Forestry, Animal husbandry and Biodiversity. The resource utilization is a research focus on the control of invasive plants currently. Our topic is the determination of extracts from Praxelis clematidea and Ageratum conyzoides on antimicrobial activity, the isolation and identification of active components and the process optimization of total flavonoids in Praxelis clematidea. The study not only provides reference for resource utilization but also benefit to the invasive weeds control. The main results are as following:(1)Study on the antimicrobial activity: The activity of the four solvents extracts on the 29 strains were determined by oxford cups method. The results indicated that the extracts from Praxelis clematidea had strong inhibitory activity on most strains with no effects on fungi and the extracts from Ageratum conyzoides showed weaker antimicrobial activity.(2)Study on the antibacterial activity sites: The inhibitory activity of the different sites and ethanol concentration extracts from Praxelis clematidea and Ageratum conyzoides on Staphylococcus aureus were determined. The result revealed that the active compounds existed in 70% ethanol extract of aerial part in Praxelis clematidea and 50% ethanol extract of leafs in Ageratum conyzoides.(3)Study on the stability of extracts and MIC / MBC: The 70% ethanol extract of aerial part in Praxelis clematidea and 50% ethanol extract of leafs in Ageratum conyzoides were treated by different temperature, UV and oxidation and then were used to determine the antibacterial activity. The results of stability determination indicated that the 70% extract of Praxelis clematidea and Ageratum conyzoides both had good stability on temperature, UV and oxidation. The MIC and MBC on Staphylococcus aureus were 0.78125 mg/mL, 3.125 mg/mL, 3.125 mg/mL and 25 mg/mL.(4)The isolation and identification of active components: The 70% ethanol extract of Praxelis clematidea was preliminarily separated into four phases and then tested their antibacterial activity. The results of antibacterial activity were ethyl acetate phase > normal butanol phase > water phase > petroleum ether phase. Three main antibacterial compounds were isolated from the ethyl acetate phase by Silica Gel Column Chromatography and gel filtration Sephadex LH-20, then identified by TLC / HPLC. The diameter of inhibition zone were 12.27 mm, 14.17 mm and 13.80 mm under the concentration of 2 mg/m L.The compounds were 5, 6, 7- trimethoxy- 2-(4-methoxyphenyl)- 4 H- chromen- 4- one(3.71g), 5- hydroxy- 2-(4-hydroxyphenyl)- 6, 7- dimethoxy- 4 H- chromen- 4- one(301 mg), and 5, 7- dihydroxy- 2-(4-hydroxyphenyl)- 6- methoxy- 4 H- chromen- 4-one(150 mg), which were identified by NMR and ESI-MS.(5)Optimization of total flavonoids using response surface methodology(RSM): The standard curve of measurement of flavonoids from Praxelis clematidea was established by colorimetric method. Based on the single factor test, we chose ethanol concentration, solid-liquid ratio and ultrasonic power as random factor to optimize the extraction yield of total flovanoids by RSM. The optimum extraction conditions were as follows: extraction temperature 60℃, extraction time 8 min, ethanol concentration 53.89%, liquid-solid ratio 26.27 and ultrasonic power 163.73 W. Under The optimum extraction conditions, the yield of total flovanoids was 2.385%. The relative error with the theoretical value was 0.02%. Thus the optimized process obtained from response surface method was reliable, stable, practical.In summary, Praxelis clematidea had remarkable antibacterial activity. The exploitation of the active components make waste to wealth. Moreover, the work will be benefit to the invasive weeds control. |
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