title: XANES Reveals the Flexible Nature of Hydrated Strontium in Aqueous Solution.
abstract: X-ray absorption near-edge structure (XANES) spectroscopy has been used to determine the structure of the hydrated strontium in aqueous solution. The XANES analysis has been carried out using solid [Sr(H2O)8](OH)2 as reference model. Classical and Car-Parrinello molecular dynamics (MD) simulations have been carried out and in the former case two different sets of Lennard-Jones parameters have been used for the Sr(2+) ion. The best performing theoretical approach has been chosen on the basis of the experimental results. XANES spectra have been calculated starting from MD trajectories, without carrying out any minimization of the structural parameters. This procedure allowed us to properly account for thermal and structural fluctuations occurring in the aqueous solution in the analysis of the experimental spectrum. A deconvolution procedure has been applied to the raw absorption data thus increasing the sensitivity of XANES spectroscopy. One of the classical MD simulations has been found to provide a XANES theoretical spectrum in better agreement with the experimental data. An 8-fold hydration complex with a Sr-O distance of 2.60 Å has been found to be compatible with the XANES data, in agreement with previous findings. However, the hydration shells of the strontium ions have been found to have a flexible nature with a fast ligand exchange rate between the first and second hydration shell occurring in the picosecond time scale.
authors.affiliation: Dipartimento di Chimica, "La Sapienza" Università di Roma , P. le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: D'Angelo
authors.affiliation: Dipartimento di Chimica, "La Sapienza" Università di Roma , P. le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Migliorati
authors.affiliation: Dipartimento di Chimica, "La Sapienza" Università di Roma , P. le Aldo Moro 5, 00185 Rome, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Sessa
authors.affiliation: Scuola Normale Superiore , Piazza dei Cavalieri 7, 56126 Pisa, Italy.
authors.forename: Giordano
authors.initials: G
authors.lastname: Mancini
authors.affiliation: Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences (SLU) , SE-750 07 Uppsala, Sweden.
authors.forename: Ingmar
authors.initials: I
authors.lastname: Persson