Judul: Potensi Ekstrak Rhizophora sp. sebagai Inhibitor Tirosinase
Abstrak: Rhizophora sp. is one of plant type that has benefit as medicinal plants, for example, as whitening agent. The purpose of this study is to discover the parts and species of Rhizophora sp. which have best tyrosinase inhibitory activity. Leaves, stems, and roots of R. mucronata and R. stylosa were extracted with methanol and were tested their activities in order to obtain the best tyrosinase inhibitory activity. Based on the results, extracts of leaves, stems, and roots of R. mucronata from Tritih, Cilacap; Gebang, Cirebon; Eretan Kulon, Indramayu; Ujung Negoro Beach, Batang; Sigundu Beach, Batang; and Kapuk Beach, Jakarta were not potencial as tyrosinase inhibitor. Tyrosinase inhibitor activity from roots of R. mucronata from Samboja, East Kalimantan was higher than from its leaves and stems, especially for monophenolase with IC50 15.34 μg/ml. In perponderonce with, tyrosinase inhibitor activity from stems of R. stylosa from Samboja, East Kalimantan was also higher compared with stems of R. mucronata with IC50 38.02 μg/ml.
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Judul: Potensi bakau Rhizophora apiculata sebagai inhibitor tirosinade dan antioksidan
Abstrak: The purpose of this study was to screen the potency of crude extract, fractions from silica gel column chromatography, and fraction from preparative thin layer chromatography (TLC) of Rhizophora apiculata which has the best activity as tyrosinase inhibitors, and antioxidant. Stem, bark and roots of R. apiculata were extracted with n-hexane, ethylacetate and methanol. Each extracts were tested for tyrosinase inhibitors and antioxidant activities. Based on the tyrosinase inhibitors, methanol extracts of R. apiculata bark had the best potency as tyrosinase inhibitors (monophenolase: 78.79 μgmL-1; diphenolase: 1116.5 μgmL-1) and the best radical scavenging activity 1,1-diphenyl-picrylhidrazil (DPPH) and 2,2’- Azinobis(3-etilbenzatiazolin)-6-sulfonat acid (ABTS) with IC50: 3.81 μgmL-1 and 18.47 μgmL-1, respectively. Fractionation was performed on methanol extracts of R. apiculata bark using silica gel column chromatography and yielded 10 fractions (A to J). Fraction B from column chromatography had the best tyrosinase inhibitors with monophenolase (IC50: 1045.6 μgmL-1), diphenolase (IC50: 846.71 μgmL-1), and the best antioxidants activities with DPPH (IC50: 9.19 μgmL-1), ABTS (IC50: 7.73 μgmL-1). Fraction B was fractionated with preparative TLC resulted 9 fractions (B1 to B9). Fraction B1 had the best tyrosinase inhibitors with monophenolase (IC50: 1278 μgmL-1) and diphenolase (IC50: 1678.2 μgmL-1), dan the best antioxidants activity with DPPH (IC50: 5.75 μgmL-1), ABTS (IC50: 24.78 μgm/L). Fraction B1 further fractionated with preparative TLC resulted 2 fractions (B1.1 and B1.2). Fraction B1.1 had the best tyrosinase inhibitors with monophenolase (IC50: 1037.32 μgmL-1) and diphenolase (IC50: 1257.24 μgmL-1), and antioxidants activity with DPPH (IC50: 14.40 μgmL-1), ABTS (IC50: 40.67 μgmL-1). The result of phytochemical test and infrared spectroscopy on fraction B1.1 showed that the active compounds as tyrosinase inhibitors and antioxidant was an isoflavon compound.
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Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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