Influence of Hofmeister Ions on the Structure of Proline-Based Peptide Models: A Combined Experimental and Molecular Modeling Study

Hydrogen Bonding and Solvation of a Proline-Based Peptide Model in Salt Solutions

The hydrogen bonding of water and water/salt mixtures around the proline-based tripeptide model glycyl-l-prolyl-glycinamide·HCl (GPG-NH2) is investigated here by multi-wavelength UV resonance Raman spectroscopy (UVRR) to clarify the role of ion-peptide interactions in affecting the conformational stability of this peptide. The unique sensitivity and selectivity of the UVRR technique allow us to efficiently probe the hydrogen bond interaction between water molecules and proline residues in different solvation conditions, along with its influence on trans to cis isomerism in the hydrated tripeptide. The spectroscopic data suggest a relevant role played by the cations in altering the solvation shell at the carbonyl site of proline., while the fluoride and chloride anions were found to promote the establishment of the strongest interactions on the C=O site of proline. This latter effect is reflected in the greater stabilization of the trans conformers of the tripeptide in the presence of these specific ions. The molecular view provided by UVRR experiments was complemented by the results of circular dichroism (CD) measurements that show a strong structural stabilizing effect on the β-turn motif of GPG-NH2 observed in the presence of KF as a co-solute.

The Role of Counter-Ions in Peptides-An Overview

Peptides and proteins constitute a large group of molecules that play multiple functions in living organisms. In conjunction with their important role in biological processes and advances in chemical approaches of synthesis, the interest in peptide-based drugs is still growing. As the side chains of amino acids can be basic, acidic, or neutral, the peptide drugs often occur in the form of salts with different counter-ions. This review focuses on the role of counter-ions in peptides. To date, over 60 peptide-based drugs have been approved by the FDA. Based on their area of application, biological activity, and results of preliminary tests they are characterized by different counter-ions. Moreover, the impact of counter-ions on structure, physicochemical properties, and drug formulation is analyzed. Additionally, the application of salts as mobile phase additives in chromatographic analyses and analytical techniques is highlighted.

Dynamic mechanism of halide salts on the phase transition of protein models, poly(N-isopropylacrylamide) and poly(N,N-diethylacrylamide)

The effects of salts on protein systems are not yet fully understood. We investigated the ionic dynamics of three halide salts (NaI, NaBr, and NaCl) with two protein models, namely poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-diethylacrylamide) (PDEA), using multinuclear NMR, dispersion corrected density functional theory (DFT-D) calculations and dynamic light scattering (DLS) methods. The variation in ionic line-widths and chemical shifts induced by the polymers clearly illustrates that anions rather than cations interact directly with the polymers. From the variable temperature measurements of the NMR transverse relaxation rates of anions, which characterize the polymer-anion interaction intensities, the evolution behaviors of Cl^-/Br^-/I^- during phase transitions are similar in each polymer system but differ between the two polymer systems. The NMR transverse relaxation rates of anions change synchronously with the phase transition of PNIPAM upon heating, but they drop rapidly and vanish about 3-4.5 °C before the phase transition of PDEA. By combining the DFT-D and DLS data, the relaxation results imply that anions escape from the interacting sites with PDEA prior to full polymer dehydration or collapse, which can be attributed to the lack of anion-NH interactions. The different dynamic evolutions of the anions in the PNIPAM and PDEA systems give us an important clue for understanding the micro-mechanism of protein folding in a complex salt aqueous solvent.

Evidence for cooperative Na+ and Cl− binding by strongly hydrated l-proline

Strongly hydrated l-proline cooperatively binds Na⁺ and Cl⁻ ions in aqueous solution.

NMR spectroscopic studies of a TAT-derived model peptide in imidazolium-based ILs: influence on chemical shifts and the cis/trans equilibrium state

The impact of ionic liquids on the chemical shifts and the cis/trans equilibrium state of a model peptide was systematically investigated by NMR spectroscopy.