The study of roselle flower (Hibiscus sabdariffa L.) antioxidants reactivity based on Frontier Molecular Orbital (FMO) theory

The roselle plant (Hibiscus sabdariffa L.) is one of the abundant plants in South-East Asia, especially Indonesia. The roselle flower petals, a resourceful part of the roselle plant, contain a lot of antioxidants such as Protocatechuic Acid (PCA), Quercetin, Ascorbic Acid (AA), Cyanidin-3-O-Sambubioside (C3OS), Cyanidin-3-O-Glucoside (C3OG), and Tannic Acid (TA). The COVID-19 pandemic nowadays increases the hygiene lifestyle for the majority of people in the world. The repetitive usage of hand sanitizer has now become familiar in this state. So, it is interesting to develop natural-based hand sanitizer or hygiene products that are friendlier and has a less invasive effect on the skin. Roselle flower contains several types of antioxidants which have high reactive rates that can be used to alternate the use of alcohol as an active agent in hygiene products. Therefore, this research tried to conduct a theoretical study to understand the highest reactive roselle flower antioxidants by analyzing the reaction possibility of each antioxidant to the singlet oxygen (¹O₂) and triplet oxygen (³O₂) with the help of Frontier Molecular Orbital (FMO) theory. One of the results shows that the PCA and AA have the highest reactive antioxidant rate to normalize ¹O₂ with values of 1.22 eV and 1.86 eV. The C3OG and TA are also reactive antioxidants that bind the ³O₂ to prevent oxidation reaction with values of 3.61 eV and 3.50 eV respectively. This result supports the idea that the PCA and AA in roselle flower as antioxidants and natural acids can cause the inactivation of COVID-19 by breaking the protein membrane of the viral. This happens due to massive electron transfer and pH effect which dispose of the hydrogen bonds that preserve the viral structure.