Understanding the structural and dynamic properties of the Mg(II) ion would represent an important step forward towards the mechanistic comprehension of relevant biological and technological processes. Mg(II) plays in fact vital roles in all forms of life, many of which are not understood as yet, activating enzymes and nucleic acids and promoting their conformational transitions. Further, rechargeable Mg-ion batteries, where common electrolytes such as acetonitrile are employed, are gaining considerable interest as promising candidates for future energy storage systems.
X-ray Absorption Spectroscopy (XAS) is by far the most accurate spectroscopic technique for the determination of the local structure of ions in liquid systems. However, to date, the use of XAS to probe the structural and electronic properties of the Mg(II) ion in aqueous and non-aqueous solutions has been severely hampered by the requirement of soft X-rays, that need tailored beamline experimental set-ups (such as vacuum conditions and windowless beamlines) and special systems of detection.
In this project, we will address the need of innovative methods that may uncover the solvation properties of the Mg(II) ion through the use of X-rays. Specifically, by combining operando near edge X-ray absorption fine structure at ambient pressure with multivariate curve resolution, Density Functional Theory and Molecular Dynamics analyses, we will monitor in real time the chemical changes that take place at the surface of a Mg-containing solid system upon exposure to a series of solvating media, such as water, methanol and acetonitrile, and retrieve quantitative structural and electronic information for the reversibly dissolved Mg(II) ions in each of the investigated solvents.
We believe our results will pave the way for the application of operando soft XAS to access the often elusive properties of low-Z number metal ions involved in processes of chemical and biological interest.
The most significant and innovative results of this project would be the unambiguous and quantitative determination through XAS of the structural solvation interfacial properties of the Mg(II) ion in water, methanol and acetonitrile. This project has the potential to apply XAS for the first time, to the best of our knowledge, to tackle the structural problem of Mg(II) hydration and solvation at the interphase. Such desirable results would be appealing both from the point of view of ¿pure¿ research, by assessing an innovative methodology for the determination of molecular structures in solution, as well as by providing improved understanding of Mg(II) behavior in systems of biological and technological interest.
In fact, obtaining quantitative structural and electronic knowledge of the coordination geometry of Mg(II) in acetonitrile would allow one to establish relevant structure¿function relationships towards an improved use of Rechargeable Mg-ion batteries. Conversely, studying the hydration properties of the Mg(II) ion through our combined experimental and theoretical technique will pave the way for the investigation of future structure-function relations with biological implications for alkaline and alkaline-earth MI systems through interdisciplinary efforts rooted in soft-XAS.
Specifically, we expect that the presented approach will enable to add to the comprehension of the solvation properties of the Mg(II) ion by:
- Measuring for the first time AP-NEXAFS spectra relative to a system where the Mg(II) ion is dissolved at the interphase in water, methanol, acetonitrile and quantitatively characterizing the geometry of the associated clusters;
- Providing a convincing and definitive answer to the existing question on whether the Mg(II) ion is coordinated in a tetrahedral or octahedral geometry in acetonitrile, by applying an extensive theoretical analysis of the MCR-extracted AP-NEXAFS data;
- Providing a new method to investigate the reversible interfacial hydration properties of low-Z number elements of biological interest (such as Na+ and K+) by employing soft operando AP-NEXAFS together with theoretical support
We do believe that the proposed interdisciplinary strategy will prove to be essential to tackle the complexity of the problem of quantitatively unveiling the hydration and solvation properties of the Mg(II) ion.
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