One of potential inhibitors which is widely used for the clinical treatment of COVID-19 in comorbid patients is Angiostensin Converting Enzyme-1 (ACE1) inhibitor. A safer peptide-based ACE1 inhibitor derived from salmon skin collagen, that is considered as the by-product of the fish processing industry have been investigated in this study. The inhibitory activity against ACE1 was examined using in vitro and in silico methods. In vitro analysis includes the extraction of acid-soluble collagen, characterization using FTIR, Raman, UV–Vis, XRD, cytotoxicity assay, and determination of inhibition against ACE1. In silico method visualizes binding affinity, molecular interaction, and inhibition type of intact collagen and active peptides derived from collagen against ACE1 using molecular docking. The results of FTIR spectra detected amide functional groups (A, B, I, II, III) and imine proline/hydroxyproline, while the results of Raman displayed peak absorption of amide I, amide III, proline/hydroxyproline ring, phenylalanine, and protein backbone. Furthermore, UV–Vis spectra showed typical collagen absorption at 230 nm and based on XRD data, the chain types in the samples were α-helix. ACE1 inhibition activity was obtained in a concentration-dependent manner where the highest was 82.83% and 85.84% at concentrations of 1000, and 2000 µg/mL, respectively, and showed very low cytotoxicity at the concentration less than 1000 µg/mL. In silico study showed an interaction between ACE1 and collagen outside the active site with the affinity of − 213.89 kcal/mol. Furthermore, the active peptides of collagen displayed greater affinity compared to lisinopril, namely HF (His-Phe), WYT (Trp-Tyr-Thr), and WF (Trp-Phe) of − 11.52; − 10.22; − 9.58 kcal/mol, respectively. The salmon skin-derived collagen demonstrated ACE1 inhibition activity with a non-competitive inhibition mechanism. In contrast, the active peptides were predicted as potent competitive inhibitors against ACE1. This study indicated that valorization of fish by-product can lead to the production of a promising bioactive compound to treat COVID-19 patient with diabetic comorbid. Graphical Abstract

The purpose of this study was to determine the effect of silver nanoparticles (AgNPs) from different green synthesis medium and their various particle sizes on antibacterial activity. The article review method compares the results of 11 studies obtained from the PubMed database, Web of Science, and ScienceDirect indexed by Scopus in the last five years. The search was conducted based on the phrases nanoparticles, antibacterial, Green synthesis, and AgNPs. Green synthesis of AgNPs with various plant extracts produces different sizes of nanoparticles. The smallest size AgNPs were obtained in the range of 5-15 nm and an average of 13 nm extracted using the leaves of the Pacific Yew tree (Taxus brevifolia). Meanwhile, AgNPs with the best antibacterial effectiveness were obtained from the Blume flower extract (Wedelia urticifolia) measuring less than 30 nm providing a zone of inhibition for S. aureus, K. pneumoniae, E. coli, and P. aeruginosa bacteria.

Pyridine is a heterocyclic compound that is widely used as an ingredient in medicines, vitamins, food flavors, pesticides, dyes, adhesives, and others. Currently, pyridine synthesis is carried out with coal tar as a raw material, which is a non-renewable natural resource. In this research, a theoretical study was carried out to evaluate the synthesis process of pyridine using pyrylium salt as an alternative raw material to displace coal tar. This study also aims to simulate the pyridine synthesis and the energy required or released in the process. Density Functional Theory (DFT) method was employed to calculate some thermodynamic properties of the species involved in the reaction such as enthalpy, entropy, and Gibbs free energy in a vacuum and solvated model in order to study the progress of the reaction and mechanism. Based on the calculation results, the lowest value of enthalpy, entropy, and free energy Gibbs is obtained when the reaction takes place in a vacuum. The change of entropy and free Gibbs energy of the reaction was not predominantly affected by the degree of polarity of the solvent. Meanwhile, the enthalpy of reaction simulated in water solvent is higher than in the ethanol solvent. The synthesis reaction of pyridine from pyrylium salt is exothermic and exergonic because it has a negative value of enthalpy change and Gibbs free energy at 298.15 K, which is potential to be done at room temperature without extreme condition control.