The crescent evolution of a global pandemic COVID-19 and its respiratory syndrome (SARS-Cov-2) has been a constant concern (Ghosh 2021 ; Khan et al. 2021 ; Alazmi and Motwalli 2020 ; Vargas et al. 2020 ). The absence of a proven and effective medication has compelled all the scientific community to search for a new drug. The use of known drugs is a faster way to develop new therapies. Molecular docking is a powerful tool (Gao et al. J Mol Model 10: 44–54, 2004 ; Singh et al. J Mol Model 18: 39–51, 2012 ; Schulz-Gasch and Stahl J Mol Model 9:47–57, 2003 ) to study the interaction of potential drugs with SARS-CoV-2, Alsalme et al. ( 2020 ) and Sanders et al. ( 2020 ) spike protein as a consequence the main goal of this article is to present the result of the study of an interaction between ( R and S )-Linezolid with receptor-binding domain (RBD) of SARS-Cov-2 spike protein complexed with human Angiostensin-converting enzyme 2 (ACE2) (6vW1 - from PDB). The Linezolid enantiomers were optimized at B3LYP/6-311++G(2d,p) level of theory. Molecular docking of the system ( S )-Linezolid⋯ RBD ⋯ACE2 and ( R )-Linezolid⋯ RBD ⋯ACE2 was performed, the analysis was made using LigPlot+ and NCIplot software packages, to understand the intermolecular interactions. The UV-Vis and ECD of the complexes - ( R and S )-Linezolid⋯ RBD ⋯ACE2 were performed in two layers with DFT/6-311++G(3df,2p) and DFT/6-31G(d), respectively. The results showed that only the ( S )-Linezolid had a stable interaction with − 8.05 kcal.mol − 1 , whereas all the R -enantiomeric configurations had positive values of binding energy. The ( S )-Linezolid had the same interactions as in the ( S )-Linezolid ⋯ Haluarcula morismortui Ribosomal system, where it is well-known the fact that the latter has biological activity. A specific interaction on the fluorine ring justified an attenuation on the ECD signal, in comparison to isolated species. Therefore, some biological activity of ( S )-Linezolid with SARS-CoV-2 RBD was expected, indicated by the modification of its ECD signal and justified by a similar interaction in the S -Linezolid⋯ Haluarcula marismortui Ribosomal system. Supplementary information The online version contains supplementary material available at 10.1007/s00894-021-04828-8.

Fluorescence quenching is widely used to obtain association constants between proteins and ligands. This methodology is based on assumption that ground-state complex between protein and ligand is responsible for quenching. Here, we call the attention about the risk of using the temperature criterion for decision of applying or not fluorescence quenching data to measure association constants. We demonstrated that hydrophobic effect can be the major force involved in the interaction and, as such, superposes the well-established rationalization that host/guest com-

The incorporation of the phthalimide moiety into caffeic acid was decisive for its effectiveness as an NADPH oxidase inhibitor.

Rose Bengal (RB) is a xanthene dye used as a sensitizer to convert triplet (3O2) to singlet oxygen (1O2). This photophysical property makes it one of the most used dyes in photodynamic therapy. Thus, understanding its interaction with biomacromolecules can provide helpful information about its mode of action and application. The protein chosen for this study was human serum albumin (HSA), which has nine binding sites for fatty acids (FA), and at least three sites for interactions of drugs (DS). The complexation of HSA with RB caused a maximum bathochromic shift in its absorption. From this displacement and the application of the Benesi–Hildebrand model, the ligand–protein association constant (3.90 ± 0.08 × 105 M−1) was obtained. Applying the Job’s Plot method resulted in a 6:1 (ligand-protein) stoichiometry. The determination of preferred binding sites was performed by measuring the association constant in the presence of drugs for which their binding sites in HSA are already well established, such as warfarin (DS1), ibuprofen (DS2 and FA6), digitoxin (DS3), diazepam (DS2), and diflunisal (DS2 and FA6). From these studies, it was found that RB is able to bind at DS1, DS3, and FA6 sites but not at DS2. Subsequently, molecular docking studies using the 2BX8 and 2BXE crystallographic structures were performed and corroborated the experimental results. The lowest energy poses were −52.13, −58.79, and −67.55 kcal mol−1 at DS1, DS3, and FA6, respectively. Conversely, DS2 was the lower affinity binding site. In conclusion, HSA has a high affinity for RB, being able to bind up to six dye molecules.