Judul: Inhibitor Tirosinase Ekstrak Metanol Berbagai Bagian Pohon Jabon dan Mangium
Abstrak: Jabon and mangium are currently planted in community forest. The wastes resulted from the utilization of forest products can reach 75%, including leaves barks, and woods. One of the ways to increase value of those wastes can be done by utilizing the extractive compounds contained in wood waste as tyrosinase inhibitor. Parts of tree which were extracted consist of leaves, barks, sapwood, and heartwood. The extraction method used in this research was soxhletation using methanol for 12 hours. The yield of extracts was 0.89-13.02%, with the lowest yield from sapwood of mangium and the highest was resulted by jabon’s leaves. Mangium bark extract had the highest activity as inhibitors of tyrosinase, with the value of IC50 was 129.81 ppm for the monophenolase reaction or three times higher than kojic acid (38.45 ppm) and 240.88 ppm for the diphenolase reaction or two times higher than kojic acid (102.11 ppm). The compounds contained within mangium bark extracts were expected to be inhibitor of tyrosinase, which was classified to flavonoids.
Keyword: tyrosinase inhibitor, monophenolase, mangium, jabon, Diphenolase

Judul: Aktivitas Gabungan Ekstrak Bakau (Rhizophora apiculata), Alamanda (Allamanda schottii), dan Binahong (Anredera cordifolia) terhadap Enzim Tirosinase
Abstrak: The aim of this study was to determine the most active composition of mangrove, alamanda, and binahong extract as tyrosinase inhibitor and antioxidant. Stem of mangrove was extracted with methanol-water and fractionated to obtain flavonoid extract, leaves of alamanda were extracted with water, and leaves of binahong were extracted with ethanol. Each extracts were combined based on the extract weight using simplex centroid design, then tested its tyrosinase inhibitor and antioxidant activities (DPPH). Single extract of mangrove stem (IC50 monophenolase: 202 μg/mL; IC50 diphenolase: 419 μg/mL) had the best activity as tyrosinase inhibitor. The combined extract of mangrove:alamanda:binahong (2/3:1/6:1/6) had good inhibition activity on monophenolase stage (IC50 147 μg/mL). The extract and combination also showed good antioxidant activity (IC50 23 μg/mL and 50 μg/mL, respectively). Thin layer chromatography fingerprint pattern of single extract of mangrove eluted with diethyl ether:ethyl acetate (1:1) showed 4 spots, and the combined extract of mangrove:alamanda:binahong (2/3:1/6:1/6) showed the same spot with an Rf of 0.11.
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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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