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Sitafloxacin (STFX) is a new generation of broad-spectrum oral fluoroquinolones. STFX has significantly enhanced antibacterial activity than most similar drugs. Clinically, this drug is mainly used to treat respiratory and urinary tract infections and other serious bacterial infections. In this study, the interaction between sitafloxacin and human serum albumin (HSA) was investigated by spectroscopic methods and molecular simulations. Fluorescence quenching experiments showed that the interaction mechanism between STFX and HSA was static quenching, which was confirmed by time-resolved fluorescence. Thermodynamic parameters and docking results indicated that hydrophobic and electrostatic forces played a key role in this mechanism. Probe experiments and molecular docking results indicated that the major binding of STFX was at site I. 3D fluorescence showed that the insertion of STFX had minimal impact on the microenvironment. Analysis of the protein secondary structure showed that the insertion of STFX had little effect on the secondary structure of the protein. Hydrophobicity experiments showed the slight decrease in the overall hydrophobicity index of the system. Molecular dynamics simulations further validated the stability of the HSA-STFX complex. This study are useful for further drug development, in vivo toxicity studies, and can provide guidance for the clinical application of STFX to study its pharmacokinetic properties., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The interaction between trelagliptin and pepsin was probed through spectroscopy methods and molecular dynamics simulation. Results of fluorescence lifetime and fluorescence spectroscopy analysis showed that trelagliptin can spontaneously interact with pepsin through a static quenching. This interaction was mainly driven by hydrogen bonding and van der Waals, as evident from thermodynamic parameters and molecular dynamics simulation. The microenvironment of tyrosine residues and the secondary structure of pepsin were slightly influenced by trelagliptin based on synchronous fluorescence, three-dimensional fluorescence, and circular dichroism spectra. In addition, the activity of pepsin was hardly affected by the insertion of trelagliptin. Molecular dynamics simulations were used to further analyze the pepsin-trelagliptin complex. This study provides useful information for binding mechanisms of trelagliptin on pepsin. [ABSTRACT FROM AUTHOR]