Judul: Evaluasi Keberadaan dan Posisi Gugus Prenil pada Aktivitas Antioksidan Kuersetin di Cincin A Berdasarkan Teori Fungsional Rapatan B3LYP.
Abstrak: Kuersetin merupakan anggota flavonoid golongan flavonol yang memiliki beberapa aktivitas hayati, salah satunya ialah aktivitas antioksidan. Pada penelitian ini, aktivitas antioksidan kuersetin dan kuersetin berprenil di posisi 6 dan posisi 8 diperkirakan menggunakan 3 parameter, yaitu energi pemutusan ikatan (EPI), potensial ionisasi (PI), dan selisih energi orbital molekul (Egap) pada tingkat B3LYP/6-31G(d). Mekanisme antioksidan yang dikaji adalah pemutusan ikatan antara atom hidrogen dan oksigen pada gugus fenolik baik secara homolitik maupun heterolitik, sehingga perhitungan EPI dan PI memenuhi asumsi tersebut. Secara keseluruhan, keberadaan gugus prenil di posisi 8 pada kuersetin meningkatkan aktivitas antioksidan dengan menurunnya nilai EPI, nilai PI, dan nilai Egap terhadap kuersetin..
Keyword: antioksidan, Egap, EPI, kuersetin, PI, prenil

Judul: Analysis of Antioxidant Activity of Three Flavonoid Compounds from Lime Fruit Using Density Functional Theory
Abstrak: Radikal bebas tubuh dapat diklasifikasikan dari 2 jenis berdasarkan sumbernya, yaitu radikal bebas endogen dan eksogen. Radikal bebas endogen adalah radikal bebas yang berasal dari dalam tubuh sendiri seperti autoksidasi, oksidasi enzimatik dan respiratory burst, sedangkan radikal bebas eksogen adalah radikal bebas yang berasal dari luar tubuh seperti polusi udara, radiasi UV, sinarX, pestisida dan asap rokok. Menghadapi hal ini dibutuhkan antioksidan alami yang meningkatkan imunitas tubuh dengan mengikat radikal bebas. Ketersediaan andtioksidan alami sangat banyak ditemukan pada tanaman lokal seperti jeruk nipis dengan kandungan flavonoid seperti hesperetin, kuersetin, dan naringenin. Diperlukan analisis sifat antioksidan senyawa – senyawa tersebut untuk mengetahui kereaktifan molekul dalam menangkal radikal bebas. Melalui DFT dengan exchange-correlation B3LYP dan basis sets def2/SVP, penulis menganalisis sifat antioksidan hesperetin, kuersetin, dan naringenin. Perhitungan yang dilakukan dengan DFT adalah optimasi molekul, frekuensi vibrasi, dan single point energy. Analisis sifat antioksidan yang diinginkan dengan memperoleh nilai dari parameter BDE rendah, IP rendah, PDE rendah, PA rendah, dan ETE rendah melalui tiga mekanisme HAT, SPLET, dan SET-PT. Selanjutnya dianalisis dengan parameter nilai reaktivitas global yang dipengaruhi oleh nilai energi HOMO dan energi LUMO. Antioksidan yang baik diperoleh dengan nilai parameter reaktivitas global yaitu energi gap kecil, elektronegativitas besar, potensial kimia lebih positif, hardness kecil, softness besar, electrophilicity besar, nucleophilicity kecil, energi ionisasi kecil, dan afinitas elektron besar., Free radicals can be classified into 2 types based on their source, namely endogenous and exogenous free radicals. Endogenous free radicals are free radicals originating from within the body itself such as autoxidation, enzymatic oxidation and respiratory burst, while exogenous free radicals are free radicals originating from outside the body such as air pollution, UV radiation, X-rays, pesticides and cigarette smoke. In dealing with this condition, natural antioxidants are needed to enhance human body’s immune system by scavenging free radicals. Natural antoxidant are abundantly found in local plants such as lime fruits, which contain flavonoids like hesperetin, quercetin, and naringenin. The analysis of the antioxidant properties of these compounds is necessary to understand their molecular reactivity in neutralizing free radicals. Using DFT with the B3LYP exchange-correlation functional and def2/SVP basis sets, the author analyzed the antioxidant properties of hesperetin, quercetin, and naringenin. The DFT calculations involved molecular optimization, vibrational frequency analysis, and single-point energy calculation. The analysis aimed to identify desirable antioxidant properties, characterized by low BDE, low IP, low PDE, low PA, and low ETE, through three mechanisms: HAT, SPLET, and SET-PT. Additionally, the global reactivity values were analyzed, influenced by the HOMO energy and LUMO energy. Excellent antioxidants were identified by having small gap energy, high electronegativity, most positive value of chemical potential, low hardness, high softness, high electrophilicity, low nucleophilicity, low ionization energy, and high electron affinity
Keyword: DFT, Antioxidant, Hesperetin, Quercetin, Naringenin

Judul: Characteristic of Overshooting Top (OT) Based on  Himawari  8  Satellite  as  a  Convective  Cloud  Feature  that  Generates  Extreme Weather in the Java Island Region
Abstrak: Overshooting Top (OT) is a feature at the top of a convective cloud that is associated with extreme weather. Research on OT in tropical Indonesia is still very limited. The existence of geostationary satellites with wide area coverage and fast frequency observations is useful for observing the fast dynamics of the OT life cycle. Therefore, this study intends to analyze the relationship between OT and extreme weather, updraft and thermodynamic conditions of OT when extreme weather occurs, the best objective method for detecting OT in the day time and night time, and the spatiotemporal distribution of OT in the tropical region of Java Island during the 2018-2021 period. Based on visual analysis using visible channel and Himawari 8 sandwich products, 87% of extreme weather events in Java were accompanied by the appearance of OT. It indicates that the presence of the OT pattern is a convection cloud pattern or feature that is closely related to extreme weather events for the Java Island region. The existence of a time lag between the appearance of OT and extreme weather events on Java Island indicates that the OT of convection cloud can be used as a precursor or nowcasting for the appearance of extreme weather. Most of the convective cloud OT features during extreme weather events on Java Island have altitude that were only able to exceed the altitude of the equilibrium level and few were able to exceed the tropopause level of 9 km – 16 km. The difference in atmospheric conditions during extreme weather events on Java Island, which is in the tropics and subtropics, is a strong and unstable convective energy condition characterized by a larger CAPE, as well as unstable KI, LI, SI and TTI values. It is offset by kinematic factors in the form of a weak vertical wind shear (bulk wind shear 0-6 km) and a higher freezing point height. The difference between extreme weather events in the Java Island region and other tropical regions compared to subtropical regions is the strong updraft speed of convection clouds. The IRW Texture COMB algorithm based on the IRW-Texture Gradient modification and the COMB algorithm shows a significant increase in quality for detecting OT and non-OT pixels in Java. Rainy days with rainfall > 50 mm/day are very common in areas with an altitude of > 500 m. On the other hand, the level of convection activity which is indicated by the presence of OT and lightning is significantly reduced in this area. OT of convective clouds appear more frequently during the DJF season and less frequently during the JJA season. OT often appears during the day time and rarely at night time. Most OTs appear in the central part, away from the south and north coasts of Java Island during the day, while OTs that appear near the south and north coasts of Java Island can appear in the morning or afternoon.
Keyword: convective clouds, extreme weather, Overshooting Tops, Himawari 8 Satellite