Thermodynamic and 1H NMR study of proton complex formation of histidine-containing cyclodipeptides in aqueous solution
Abstract
A thermodynamic and 1H NMR study of proton complex formation in aqueous solution of some L-histidine-containing cyclic L-dipeptides has been carried out. The enthalpic and entropic changes associated with protonation of the cyclodipeptides, obtained by potentiometric and calorimetric measurements, together with the 1H NMR data and NOESY experiments, enable the role played by non-covalent interactions in proton complex formation to be assessed. In addition, a comparison with c(Glys–His) permits the influence of side-chain residues on the conformation of protonated species to be observed.