An outbreak of a cluster of viral pneumonia cases, subsequently identified as coronavirus disease 2019 , due to a novel SARS-CoV-2 necessitates an urgent need for a vaccine to prevent infection or an approved medication for a cure. In our in silico molecular docking study, a total of 173 compounds, including FDA-approved antiviral drugs, with good ADME descriptors, and some other nucleotide analogues were screened. The results show that these compounds demonstrate strong binding affinity for the residues at the active sites of RNA-dependent RNA-polymerase (RdRp) modelled structures and Chymotrypsin-like cysteine protease (3CLpro) of the HCoV proteins. Free energies (ΔG's) of binding for SARS-CoV-2 and SARS-CoV RdRp range from -5.4 to -8.8 kcal/mol and -4.9 to -8.7 kcal/mol, respectively. Also, SARS-CoV-2 and SARS-CoV 3CLpro gave ΔG values ranging from − 5.1 to − 8.4 kcal/mol and − 5.5 to − 8.6 kcal/mol, respectively. Interesting results are obtained for ivermectin, an antiparasitic agent with broad spectrum activity, which gave the highest binding energy value (− 8.8 kcal/mol) against the 3CLpro of SARS-CoV-2 and RdRps of both SARS-CoV and SARS-CoV-2. The reason for such high binding energy values is probably due to the presence of hydroxy, methoxy and sugar moieties in its structure. The stability of the protein-ligand complexes of polymerase inhibitors considered in this investigation, such as Sofosbuvir, Remdesivir, Tenofovir, Ribavirin, Galidesivir, 5c3, 5h1 and 7a1, show strong to moderate hydrogen bonding and hydrophobic interactions (π-π stacked, π-π T-shaped, π-sigma and π-alkyl). The stability provided from such interactions translate into greater antiviral activity or inhibitory effect of the ligands. Assessment of the average free energies of binding of the FDA approved drugs are highly comparable for conformers of a particular inhibitor, indicating similar modes of binding within the pockets.
Anacardium occidentale gum exudate was analyzed for physicochemical, spectroscopic and rheological characteristics. Physicochemical analysis revealed that the gum is mildly acidic, ionic, extremely rich in carbohydrate and calcium. GCMS spectrum revealed the presence of some carboxylic acids, ketone and alkanes. The FTIR spectrum of the gum closely resembled those of other polysaccharides. Scanning electron micrograph revealed the presence of pores containing particles with irregular shapes. The average value of intrinsic viscosity of the gum was 3.28 dL/g, which compared favourably with those obtained for some plant gums. From the Huggins, Kraemer and Power law models, it was deduced that there is absence of molecular association and that the conformation of the gum is more rod like. Viscosity of the studied gum was found to be greatly influenced by the presence of urea, K+, Ca2+ and Al2+. Anarcadium occidentale gum exhibited a non-Newtonian property with characteristics dilatant and shears thickening properties.
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