Effects of Lysozyme on the Activity of Ionic of Fluoroquinolone Species.

Fluoroquinolones (FQs) constitute an important class of biologically active broad-spectrum antibacterial drugs that are which are in contact with many biological fluids under different acidity conditions. We studied the reactivity of ciprofloxacin (Cpx) and levofloxacin (Lev) and their interaction with lysozyme (Lyz) at different pH values, using UV-visible absorption, fluorescence, infrared spectroscopies supported by DFT calculation and docking. In addition, by antimicrobial assays, the biological consequences of the interaction were evaluated. DFT calculation predicted that the FQ cationic species present at acid pH have lower stabilization energies, with an electric charge rearrangement because of their interactions with solvent molecules. NBO and frontier orbital calculations evidenced the role of two charged centers, NH2⁺ and COO-, for interactions by electronic delocalization effects. Both FQs bind to Lyz via a static quenching with a higher interaction in neutral medium. The interaction induces a structural rearrangement in ß-sheet content while in basic pH a protective effect against the denaturation of Lyz was inferred. The analysis of thermodynamic parameters and docking showed that hydrophobic, electrostatic forces and hydrogen bond are the responsible of Cpx-Lyz and Lev-Lyz associations. Antimicrobial assays evidenced an antagonist effect of Lyz in acid medium while in neutral medium the FQs' activities were not modified by Lyz.

Configuration of carbonyl groups at the lipid interphases of different topological arrangements of lipid dispersions.

The purpose of this work is to analyze the conformation of the carbonyl groups of acyl phospholipids at the hydrocarbon-water interphase in different topological ensembles and phase states, such as micelles and bilayers. The separation of the band components in lipids dispersed in D(2)O is compared with that of PCs in a low hydrated state. When hydrated, the differences in the frequencies of the band components corresponding to the carbonyl groups identified as low hydrated and hydrated populations increase when dimyristoylphosphatidylcholine (DMPC) bilayers go from the lamellar gel to the ripple corrugated phase at the pretransition temperature. Below the pretransition, at which the membrane in the gel state is planar, the two components overlap making the deconvolution unreliable. A further analysis shows that the frequency of the highly hydrated population increases more noticeable than that corresponding to the low hydrated one following the sequence: micelles, fluid phase, ripple gel phase, and lamellar gel phase. This is confirmed by the increase in the separation of the band components when the liposomes are subjected to an osmotic dehydration suggesting that the hydrated population loses water and the dehydrated one partially hydrates. It is concluded that this behavior is a feature conferred by hydration of the different topological arrangements. The relevance of these results on the interphase properties of lipid membranes is discussed.