Contents lists available at ScienceDirect Biophysical Chemistry journal homepage: www.elsevier.com/locate/biophyschem Study of Al 3+ interaction with AMP, ADP and ATP in aqueous solution Paola Cardiano, Claudia Foti, Fausta Giacobello, Ottavia Giuffrè ⁎ , Silvio Sammartano Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Università di Messina, Viale F. Stagno d'Alcontres 31, 98166 Messina, Italy HIGHLIGHTS • Study of Al 3+ -nucleotide interaction in NaCl at different ionic strengths • ΔH values of Al 3+ -ATP species de- termined by titration calorimetry • Stability and speciation model of Al 3+ -ATP system confirmed by 1 H NMR titrations • Sequestering ability of different nu- cleotides towards Al 3+ at different pH values GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Al 3+ complexes Nucleotides, aqueous solutions Thermodynamic parameters Sequestration ABSTRACT The interaction of Al 3+ and nucleotide ligands, namely adenosine-5′-monophosphate, (AMP), adenosine-5′-di- phosphate, (ADP), adenosine-5′-triphosphate, (ATP), has been studied in aqueous solution at T = 298.15 K and I = 0.15 mol L -1 in NaCl (only for Al 3+ -ATP system at I = 0.1 mol L -1 ). Formation constants and speciation models for the species formed are discussed on the basis of potentiometric results. The speciation models found for the three systems include ML and ML 2 species in all the cases, and for Al 3+ -ADP and ATP systems, MLH, MLOH and ML 2 OH species as well. The formation constant value for ML species shows the trend, AMP < ADP < ATP. 1 H NMR spectroscopy was also employed for the study of Al 3+ -ATP system. The 1 H NMR results are in agreement with the speciation model obtained from analysis of potentiometric titration data, confirming the stabilities of the main species. Enthalpy change values were obtained by titration calorimetry; for the main Al 3+ -ATP species (at T = 298.15 K and I = 0.1 mol L -1 in NaCl), they resulted always higher than zero, as typical for hard-hard interactions. The dependence of formation constants on ionic strength over the range I = 0.1 to 1 mol L -1 in NaCl is also reported for Al 3+ -ATP system. The sequestering ability of the nucleotides under study towards Al 3+ was also evaluated by the empirical parameter pL 0.5 . 1. Introduction Nucleotides are building block of nucleic acids, such as DNA and RNA, essential for living organisms. AMP, ADP and ATP are nucleotides formed by an adenine, a ribose and a mono-, di- or triphosphate unit (Fig. 1). ATP is an important biological molecule in living organisms, widely known as a primary energy substrate. ADP or AMP can be generated from ATP by breaking the high-energy phosphate bond with release a large amount of energy [1]. The biological importance is due mainly to their function of chemical energy carriers in cells and to the involvement in several enzymatic reactions [2,3]. Depending on the system, various biological reactions require specific metal cations or, conversely, their presence can inhibit them. For this reason, the accu- rate assessment of the nucleotide protonation constants and metal https://doi.org/10.1016/j.bpc.2018.01.003 Received 9 January 2018; Received in revised form 22 January 2018; Accepted 22 January 2018 ⁎ Corresponding author. E-mail address: ogiuffre@unime.it (O. Giuffrè). Biophysical Chemistry 234 (2018) 42–50 0301-4622/ © 2018 Elsevier B.V. All rights reserved. T