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Gas Phase IR and UV Spectroscopy of Neutral Contact Ion Pairs
Sana Habka, Valérie Brenner, Michel Mons, Eric Gloaguen Biomolecular Structures Group, Saclay, France Solvent ? International Symposium on Molecular Spectroscopy - June 20-24, 2016
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International Symposium on Molecular Spectroscopy - June 20-24, 2016
Ion Pairing Ion pairing occurs between oppositely charged molecules or atoms. They play a crucial role in many biological processes such as membrane polarization for neuron function and muscle contraction. They remain difficult to evidence and characterize due to the coexistence of several types of pairing in solution. International Symposium on Molecular Spectroscopy - June 20-24, 2016
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Neutral Ion Pairs in The Gas Phase
All types of ion pairs are important to study in order to answer basic questions: How can they be characterized? What is the effect on the biomolecule structure? Find a reliable method to form cold contact ion pairs in the gas phase. Determine the effect of ion pairing on small model complexes. International Symposium on Molecular Spectroscopy - June 20-24, 2016
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Experimental approach
Vacuum Chamber Laser desorption: hot vapour containing the complex is formed with limited fragmentation. Cooling in a supersonic expansion (He/Ne): complexes are trapped in their most stable conformations. Conformational analysis of the conformationnal populations with IR and UV laser spectroscopy in the interaction region of a time-of- flight mass spectrometer. Pulsed valve Sample (Salt + graphite) International Symposium on Molecular Spectroscopy - June 20-24, 2016
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International Symposium on Molecular Spectroscopy - June 20-24, 2016
(Li+, PA-) ion pair IR2P-1C IR/UV double resonance spectroscopy spectroscopy: Quantum chemistry calculation: UV – R2PI spectrum: BSSE-corrected-full-CCSD(T)/dhf-TZVPP//RI-B97-D/dhf-TZVPP Corrected harmonic frequencies RI-B97-D3/dhf-TZVPP CO-2anti CO-2sym Bidentate (O-O) ∆G(300K) = 0 kJ mol-1 (O-O) (O-π) Bidentate (O-π) ∆G(300K) = 36 kJ mol-1 Wavenumber (cm-1) Wavenumber (cm-1) International Symposium on Molecular Spectroscopy - June 20-24, 2016
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UV spectroscopy: evidence of cation-π interaction
Electronic energies BSSE-corrected-full-CCSD(T)/ dhf-TZVPP//RI-B97-D3/dhf-TZVPP level of theory UV spectroscopy of the three ion pairs in the π-π* transition region (Li+, PA-) O-O S. Habka, V. Brenner, M. Mons, E. Gloaguen, J Phys Chem Lett 2016, 7, International Symposium on Molecular Spectroscopy - June 20-24, 2016
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IR spectroscopy of (Li+, PB-)
Corrected harmonic frequencies RI-B97-D3/dhf-TZVPP ? Wavenumber (cm-1) Wavenumber (cm-1) IR spectroscopy of B, C, D and E conformers were assigned to Bidentate O-O structures, each structure is different in the orientation of its carbon chain. Conformer A is assigned to a Tridentate O-O-π structure → IR and UV unique signatures of a cation-π interaction! S. Habka, V. Brenner, M. Mons, E. Gloaguen, J Phys Chem Lett 2016, 7, International Symposium on Molecular Spectroscopy - June 20-24, 2016
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International Symposium on Molecular Spectroscopy - June 20-24, 2016
Gas phase vs. Solution Rudolph, Fischer, Irmer, Dalt. Trans. (2014) Habka, Brenner, Mons, Gloaguen (to be published) Solution spectroscopy Gas phase spectroscopy Li 1444 Water bending Li CH3 Li CIP Wavenumbers (cm-1) Na 1414 CIP Na Na Wavenumbers (cm-1) SIP/SSIP Wavenumber (cm-1) The suprising agreement between solution and gas phase spectra in the case of lithium and sodium interacting with the carboxylate group raises questions on the attribution made in solution which should be reconsidered. Further experiments and theoretical studies are ongoing in order to prove this hypothesis. International Symposium on Molecular Spectroscopy - June 20-24, 2016
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International Symposium on Molecular Spectroscopy - June 20-24, 2016
Acknowledgements Researchers : Michel MONS Eric GLOAGUEN Valérie BRENNER Marie Géléoc Benjamin TARDIVEL Post-docs : Thibaut VERY Woon Yong SOHN PhD : Sana HABKA Intern : Sarah DE LIMA BARBOSA Alexandre CARLIER THANK YOU FOR YOUR ATTENTION!!! International Symposium on Molecular Spectroscopy - June 20-24, 2016
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