Understanding the behaviour of carnosine in aqueous solution: an experimental and quantum-based computational investigation on acid–base properties and complexation mechanisms with Ca2+ and Mg2+

A thorough investigation on the acid–base properties of carnosine, and its potential interactions with the two essential metal cations Ca2+ and Mg2+, is here reported. The thermodynamic parameters of protonation and complexes formation are identified at different values of ionic strength and temperature, based on experiments employing potentiometric, spectrophotometric and 1H NMR spectroscopic techniques. The involvement of the diverse functional groups in the protonation steps and complex formation equilibria with Ca2+ and Mg2+ are also investigated by means of Density Functional Theory and state-of-the-art ab initio molecular dynamics (AIMD) approaches, respectively. Among other things, AIMD simulations elucidate, for the first time, the complexation mechanisms of Ca2+ and Mg2+ to carnosine by explicitly treating, at the quantum level, the role of the water solvation. Since the biochemical behaviour of carnosine is ruled by the subtle interactions it establishes with metal cations such as Ca2+ and Mg2+, this study provides unprecedented fundamental insights into the mechanisms of action of this dipeptide and, hence, paves the way towards the development of potential therapeutic applications of carnosine.