Abstrak: Antioksidan merupakan senyawa yang menghambat atau menunda reaksi oksidasi molekul dengan cara menghambat proses inisiasi atau propagasi reaksi oksidasi berantai . Struktur kimiawi antioksidan, sumber radikal bebas, dan sifat fisiko-kimia sediaan sampel yang berbeda dapat memberikan hasil uji aktivitas antioksidan yang beragam. Oleh karena itu, diperlukan suatu metode analisa aktivitas antioksidan yang selektif untuk suatu jenis sampel tertentu. Studi perbandingan metode uji aktivitas antioksidan DPPH, FRAP, dan FIC telah dilakukan terhadap asam askorbat (AA), asam galat (AG), dan kuersetin. Ketiga metode uji antioksidan dibedakan berdasarkan pada jenis mekanisme reaksinya, sedangkan sampel standar antioksidan dipilih berdasarkan struktur polihidroksi atau polifenol yang umumnya mewakili dasar struktur antioksidan bahan alam. Metode uji aktivitas antioksidan terhadap radikal DPPH ditemukan paling efektif dan efisien diantara ketiga metode uji yang digunakan dengan nilai IC 50 berturut-turut 1,27; 2,44; dan 2,77 mg/L untuk AG, kuersetin dan AA. Adapun metode FIC terbukti paling tidak efektif dan efisien karena sensitivitasnya yang sangat rendah dan daya kelatnya lebih kecil dari 20%. Korelasi antara metode uji untuk semua standar antioksidan terbukti sangat tinggi (R>0,98), khususnya antara FRAP dan DPPH. Hal ini mengindikasikan adanya keterkaitan sangat kuat antara daya hambat radikal bebas dengan potensial reduksi senyawa polihidroksi (polifenol) terhadap ion besi. Secara umum kedua metode ini sangat dimungkinkan bisa saling menggantikan satu sama lain.Abstract: Antioxidants are compounds that prevent or postpone oxidation reaction of a molecule by inhibiting initiation or propagation process of the chain oxidation reaction. The chemical structure of antioxidants, free radical sources, and physico-chemical properties of different sample preparations can provide various antioxidant activity test results. Therefore, selectivity of an antioxidant activity analysis method for a particular sample type is compulsary. The comparative study of antioxidant activity assays (DPPH, FRAP, and FIC) against ascorbic acid (AA), gallic acid (GA), and quercetin was accomplished. The three antioxidant activity assays were distinguished based on their typical reaction mechanism, while the samples of antioxidant standard were selected on the polyhydroxy or polyphenol based-structure, which are commonly available as the basic skeleton of the natural antioxidants compounds. The antioxidant assay against a radical of DPPH was found to be the most effective and efficient among the three assays with IC 50 1. 27, 2.44, and 2.77 mg/L for GA, quercetin and AA, respectively. In contrast, FIC method was proven to be the least one due to its poor sensitivity and low chelating capability (<20%). The correlation between the antioxidant assay methods was found to be really high (R>0,98), particularly between the FRAP and DPPH assay. This result indicated that the radical inhibition has strong correlation with the reduction power of t...
Silver oxide (Ag2O) nanoparticles have been successfully synthesized through several methods, namely sol-gel, sonochemical, and biological methods. X-ray diffraction studies revealed that the sonochemical method produces silver oxide with high phase purity, then the sol-gel method produces another phase, namely silver crystals, while the biological method produces Ag3PO4 phase from the precursor media. The research showed that the sol-gel method had the smallest crystallite and particle sizes of 9.5 and 232.7 nm, respectively, compared to sonochemical and biological methods. It is known that the specific surface area of the sol-gel method has the largest value, namely 60.09 m2/g, compared to the sonochemical and biosynthetic methods, which are 51.78 and 24.77 m2/g, respectively. Scanning electron microscopy study showed homogeneous spherical nanoparticles of silver oxide in the sol-gel and sonochemical methods, however, the biological method resulted in the formation of non-spherical silver oxide nanoparticles in the form like flakes. HIGHLIGHTS Synthesis of silver oxide by chemical method produces pure silver oxide crystals, smaller crystallite size, larger specific area, and more homogeneous particle size than biological methods The sol-gel method for the synthesis of silver oxide produces the smallest particle size than the sonochemical and biological methods The sonochemical method produces the highest crystallinity and size homogeneity compared to the sol-gel and biological methods GRAPHICAL ABSTRACT
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