Isothermal titration calorimetry (ITC), circular dichroism (CD) spectroscopy, and molecular dynamics simulations were applied to describe interactions between lipopeptides and decavanadate ions ([V₁₀O₂₈]⁶⁻). The selected lipopeptides are conjugates of the amide of the KR12 peptide, the smallest antimicrobial peptide derived from human cathelicidin LL-37, with lauric acid (C12-KR12) and myristic acid (C14-KR12). The smaller sizes of C12-KR12 and C14-KR12 compared to proteins allow for the rigorous characterization of their non-covalent interactions with highly negatively charged [V₁₀O₂₈]⁶⁻ ions. The stoichiometry of the resulting decavanadate–peptide complexes and the thermodynamic parameters (ΔG, ΔH, and TΔS) of the interactions were determined. The ITC results, supported by the MD simulation, showed that the binding of cationic lipopeptides for decavanadate is rather non-specific and is driven by enthalpic contributions resulting from electrostatic interactions between the positively charged residues of the peptides and the anionic decavanadate. Furthermore, the influence of temperature and the interactions with decavanadate ions on the stability of the α-helical structure of the lipopeptides were assessed based on CD spectra. Under the experimental conditions (50 mM sodium cacodylate buffer, pH 5), the peptides adopt an α-helical conformation, with C14-KR12 showing greater thermal stability. The interactions with vanadium species disrupt the α-helical structure and reduce its thermal stability.

The objective of this study was to examine the interactions between anionic surfactants, specifically 1-alkylsulfonates (KXS) and 1-alkylsulfates (SXS) ions, with human serum albumin (HSA). A combination of experimental techniques, including isothermal titration calorimetry (ITC), steady-state fluorescence spectroscopy (SF), and molecular dynamics-based approaches was employed to gain a comprehensive understanding of these processes. It has been demonstrated that the subtle variations in the charge distribution on the anionic surfactant headgroups have a significant impact on the number of binding sites, the stoichiometry of the resulting complexes, and the strength of the interactions between the surfactants and the protein. Additionally, we established that the affinity of the investigated ligands to specific regions on the protein surface is governed by both the charge of the surfactant headgroup and the length of the aliphatic hydrocarbon chain. In summary, the findings highlight the crucial role of charge distribution on surfactant functional groups in the binding mode and the thermodynamic stability of surfactant–protein complexes.

In this article, the binding interactions of lysozyme with hexacyanoferrate(III)/(II), i.e., [Fe(CN)₆]³⁻ and [Fe(CN)₆]⁴⁻ ions, have been characterised using steady-state fluorescence spectroscopy (SF), isothermal titration calorimetry (ITC), circular dichroism spectroscopy (CD), cyclic voltammetry (CV), and molecular-dynamics-based computational approaches. Studies have shown that under experimental conditions (10 mM cacodylate buffer, pH 7, 298.15 K), complexes with a 1:1 stoichiometry are formed. Four distinct regions on the lysozyme surface patches with the potential to bind hexacyanoferrate(III)/(II) were identified and described. Thermodynamic parameters revealed that the interactions are predominantly governed by electrostatic and van der Waals forces. These interactions enhance the electron transfer kinetics of the [Fe(CN)₆]^3−/4− system. The secondary structure of the protein is not affected by these interactions. Enzyme activity studies demonstrated that the affinity of lysozyme for the substrate remained unchanged regardless of whether free lysozyme or the lysozyme-[Fe(CN)₆]^3−/4− complex was present in the test sample. Finally, biological tests performed on both Gram-positive (B. subtilis, S. aureus) and Gram-negative (E. coli, P. aeruginosa) bacteria confirmed the results of the biochemical analysis, indicating that [Fe(CN)₆]^3−/4− ions do not block the active site of the enzyme and do not interfere with its activity.