SPIONCLUS — Structure, Dynamique et Spectroscopie de Clusters Ioniques. Synergie entre expériences IR-PD et simulations DFT-MD.

The proposed research is an effort to understand the role of non-covalent interactions in formation of secondary structures in biological systems, and the selective sequestration of ions. The focus will be on understanding how intermediate configurations, of higher energy, ultimately reach the ground state configuration, a process analogous to protein folding, going from a collapsed and/or denatured state to the native structure. This will be accomplished through by a combined experimental and theoretical investigation of ion-molecule complexes, partially hydrated, that exhibit a variety of structural conformers. Newly developed experimental methods, combining mass spectrometry and infrared laser spectroscopy, will be used to identify and characterize the molecular configurations of these systems. State-of-the-art theoretical methods, density functional theory combined with molecular dynamics (DFT-MD), will be applied to these systems to characterize the energy barriers between different configurations and the pathways over these barriers connecting them. Anharmonic vibrational spectra will be obtained from DFT-MD, compared to the experiments, and the band assignments will provide a detailed microscopic interpretation of the experimental features, and will provide final assessments of conformations experimentally probed. Initial studies will target solvated cations and anions in order to map out potential energy surfaces and to develop/refine the combined experimental/theoretical approach. Next, specific molecules of biological interest: n-methyl acetamide (a model for the protein backbone), amino-phenyl ethanol (a model neurotransmitter), and serotonin (a neurotransmitter) will be investigated. The selective sequestering of mono and divalent ions of biological interest, Na+, K+, Mg2+, and Ca2+, as well as environmental interest, Cs+, I-, and Sr2+, with specific ionophores in a hydrated environment will also be studied. More broadly, mono and divalent ions are ubiquitous in biological systems, they are involved in wide range of functions and play important roles in the structure of proteins, RNA and DNA. Environmental remediation is also of particular interest in light of safety concerns associated with nuclear facilities, world-wide. The experiment developed in the Lisy group is unique and brings a new possibility of detailed conformational mapping of clusters’s conformers and energy barriers, within the gas-phase community. By combining mass spectrometric methods with infrared laser spectroscopy, Prof. Lisy helped pioneer the field of ion cluster spectroscopy. Prof. Lisy’s insistence that cluster internal energy (or effective cluster temperature) is crucial to understanding cluster structure and conformation has changed the way the others in the field now approach these systems. The Gaigeot group brings originality in the emerging field of DFT-MD to the experimental facets of the research that desperately need accurate anharmonic vibrational frequencies, potential energy barrier heights and vibrational energy relaxation. The expertise of the group in theoretical spectroscopy using MD simulations and its coupling to action spectroscopy experiments is unique in Europe. The association between the two groups will bring novelty and excellence to the domain of vibrational spectroscopy of strongly anharmonic molecular ions. This proposal aims to develop a new cadre of young scientists, with the knowledge of experimental methods to probe fundamental issues in biological and environmental issues, and equipped with modern theoretical approaches that go beyond implementing computational software packages. The collaboration and exchange between the groups at the University of Illinois and the University of Evry will make this possible.