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.
Keyword: 

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.
Keyword: 

Judul: A Continuous Vaccination Strategy in the SVIR Epidemic Model
Abstrak: Vaccination is conducted to minimize the spread of a disease. The vaccination is usually done several times within a fixed time interval. In the SVIR model, it is assumed that individuals do not get immediate immunity following a vaccination program. So according to process of vaccination on SVIR model, there are two strategies, i.e. the continuous vaccination strategy (CVS) and the pulse vaccination strategy (PVS). In this study, only the CVS strategy in epidemic model SVIR is considered. Results of the study indicate that dynamics of the CVS system depends on the basic reproductive number. If the basic reproductive number is less than one, then the disease-free fixed point is asymptotically stable. It means that the disease will eventually disappear from the population. Conversely, if the basic reproductive number is greater than one, then the endemic fixed point is asymptotically stable, which means that the disease will remain exist in the population. Simulation result shows that the vaccination would minimize the spread of disease by reducing the basic reproductive number. If the time for the vaccinated recipients to obtain the immunity, as well as a possibility of vaccinated recipients to be infected are neglected, then the disease will be eradicated. This condition is called an over-evaluating effect of vaccination.
Keyword: