Judul: Isolation of Phenolic Active Compounds as Antioxidant from Dandang Gendis (Clinachantus nutans) Leaves.
Abstrak: Daun dandang gendis (Clinacanthus nutans) merupakan salah satu tanaman obat yang berpotensi sebagai antioksidan. Tujuan penelitian ini ialah mengisolasi senyawa bioaktif dari tanaman yang termasuk famili Acantaceae untuk mendapatkan komponen aktif senyawa fenolik dengan aktivitas antioksidan yang tinggi. Aktivitas antioksidan ditentukan dengan metode penggaitan radikal bebas 1,1-difenil-2-pikrilhidrazil. Dari hasil fraksinasi menggunakan kromatografi lapis tipis preparatif dengan eluen n-butanol:air:asam asetat (4:5:1) diperoleh 3 fraksi. Fraksi teraktif ialah fraksi 2 dengan nilai konsentrasi hambat 50% (IC50) 89.50 mg L-1, sedangkan IC50 untuk senyawa kontrol, hidroksi toluena terbutilasi (BHT) sebesar 6.87 mg L-1. Hasil ini menyimpulkan bahwa aktivitas antioksidan fraksi 2 jauh lebih rendah bila dibandingkan dengan aktivitas BHT. Uji senyawa fenolik dilakukan dengan kromatografi gas‒spektrometer massa dan diduga terdapat 3 senyawa fenolik, yaitu p-isopropenilfenol, o-hidroksiasetofenon, dan p-hidroksiasetofenon.
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Judul: Isolasi senyawa golongan flavonoid sebagai antioksidan dari daun dandang gendis (Clinacanthus nutans)
Abstrak: The leaves of dandang gendis (Clinacanthus nutans) exhibit antioxidant activity. The objective of this study is to investigate the highest antioxidant activity from flavonoid extract of the leaves. Antioxidant activities were determined by radical scavenging assay using 1,1-diphenyl-1-pycryl-hydrazyl radical. The result showed that ethyl acetate extract had antioxidant activity with IC50 value of 178.40 mg L-1. The ethyl acetate extract was fractionated further using preparative thin layer chromatography with eluent of n-buthanol:acetic acid: water (4:1:5) and produced 3 fractions. The most active fraction was fraction 2 with IC50 value of 52.93 mg L-1, which was lower than that of butylated hydroxy toluene (IC50 16.71 mg L-1). Flavonoid assay of fraction 2 showed that it contained flavonol and flavon. The ultraviolet-visible spectrum of fraction 2 in methanol solvent showed a maximum absorption at 332 in band 1 and 274 nm in band 2. In MeOH+MeONa and MeOH+AlCl3-HCl solvents there was a bathochromic shift, indicated the presence of 4'-OH and 5-OH. The new peak at 326.5 nm showed the presence of 7-OH substituent.
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Judul: Approximation of the Median of Poisson Distribution Using the Relation of Poisson-Gamma Distribution
Abstrak: A major drawback of median is that median cannot usually be defined in closed form, even in the cases where their distribution functions are known. This study gives an approximation of the closed form for the median of the Poisson distribution by using the relation of Poisson-Gamma distribution. The approximation uses elementary techniques based on the monotonicity of certain sequences involving tail probabilities of the Poisson distribution and the Central Limit Theorem. Furthermore, a closed form expression for the mean absolute deviation 􀜧|􀜰􀰒 􀵆 􀜯􀝁􀝀􁈺􀜰􀰒􁈻| is also studied. The median is relevant because of the fact that it minimizes the mean absolute deviation of a Poisson random variable (􀜰􀰒􁈻 by considering median as central tendency.
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