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Vibrational Signatures of Solvent-Mediated Core Ion Deformation in Size-Selected [MgSO4Mg(H2O)n=4-11]2+ Clusters Patrick Kelleher, Joseph DePalma, Christopher Johnson, Joseph Fournier, and Mark Johnson 70th International Symposium on Molecular Spectroscopy June 22, 2015
![Vibrational Signatures of Solvent-Mediated Core Ion Deformation in Size-Selected [MgSO4Mg(H2O)n=4-11]2+ Clusters](http://slideplayer.com./slide/14463778/90/images/1/Vibrational+Signatures+of+Solvent-Mediated+Core+Ion+Deformation+in+Size-Selected+%5BMgSO4Mg%28H2O%29n%3D4-11%5D2%2B+Clusters.jpg "Patrick Kelleher, Joseph DePalma, Christopher Johnson, Joseph Fournier, and Mark Johnson. 70th International Symposium on Molecular Spectroscopy. June 22,")
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Center for Aerosol Impacts on Climate and the Environment
Mg2+ inhibits production of ClNO2 Allen group, J. Phys. Chem. A, 2013, 117, 13412−13418
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Center for Aerosol Impacts on Climate and the Environment
[Mg(Palmitate-)(Palmitic)2]+ FT-ICR MS Mg2+ inhibits production of ClNO2
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Ternary Salt Complex [MgSO4Mg]2+
D2 tag +2 m/z Start simple: MgSO4. Very soluble salt, electrosprays well and readily generates hydrated clusters How do water molecules bind to a “salt bridge” ternary ion core?
![Ternary Salt Complex [MgSO4Mg]2+](http://slideplayer.com./slide/14463778/90/images/4/Ternary+Salt+Complex+%5BMgSO4Mg%5D2%2B.jpg "D2 tag. +2 m/z. Start simple: MgSO4. Very soluble salt, electrosprays well and readily generates hydrated clusters. How do water molecules bind to a salt bridge ternary ion core")
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Cryogenic Ion Vibrational Predissociation (CIVP) Spectroscopy
A‾ · Tagm + hn → A‾ · Tagn + (m-n) Tag Generate Ions and Condense Tag Isolate One Mass Excite With Laser Detect Fragmentation and Generate Spectrum hn kIVR kevap a) b) c) d) mass mass
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CIVP Experimental Setup
2-4 kV Dry Air mM Solution 1st Skimmer Capillary ESI Needle H2O/D2O P Pressure 1st Diff. Stage
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Survey of MgSO4Mg(H2O)n2+ Spectra
asym (E) SO4 asym (B2) OH Stretch H2O bend Hydrogen Bond νs νas n=4 n=5 n=6 D2 Predissociation Yield n=7 n=8 n=9 n=10 n=11 1000 1200 1400 1600 3000 3200 3400 3600 3800 Photon Energy (cm-1)
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Survey of MgSO4Mg(H2O)n2+ Spectra
asym (E) SO4 asym (B2) OH Stretch H2O bend Hydrogen Bond νs νas n=4 n=5 n=6 D2 Predissociation Yield n=7 n=8 n=9 n=10 n=11 1000 1200 1400 1600 3000 3200 3400 3600 3800 Photon Energy (cm-1)
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Expected Symmetry of Salt Ion Core
SO4 asym (B2) Calculated Intensity Photon Energy (cm-1) SO4 asymmetric stretch (triply degenerate F2) SO2 asym (doubly degenerate E) θ O-S-O = 109.5° E O-S-O = 101° θ B2
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Observation of Symmetrical Hydration
Calculated Intensity/D2 Predissociation Yield 1000 1200 1400 1600 3400 3500 3600 3700 3800 B3LYP/ G(d,p) Photon Energy (cm-1) H2O bend SO4 asym νs νas SO2 MgSO4Mg(H2O)42+ (2:2) arrangement lies 8.33 kcal/mol and 39.6 kcal/mol lower than (3:1) and (4:0) arrangements, respectively
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Observation of Symmetrical Hydration
Tag induced splitting Calculated Intensity/D2 Predissociation Yield 1000 1200 1400 1600 3400 3500 3600 3700 3800 B3LYP/ G(d,p) Photon Energy (cm-1) H2O bend SO4 asym νs νas SO2 MgSO4Mg(H2O)42+ (2:2) arrangement lies 8.33 kcal/mol and 39.6 kcal/mol lower than (3:1) and (4:0) arrangements, respectively
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Differential Hydration Further Reduces Symmetry
SO2 asym (E) SO4 asym (B2) 2 + 2 H2O bend 1000 1200 1400 1600 1800 Mg2+ n=4 Mg2+ 3 + 2 SO42¯ n=5 3 + 3 D2 Predissociation Yield n=6 4 + 3 n=7 Photon Energy (cm-1)
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Bifurcated Motif in n = 4-7 Clusters
θ n = 4 n = 5 n = 7 Solvation of Mg2+ ions weakens the interaction between the constituents of the ion core
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Survey of MgSO4Mg(H2O)n2+ Spectra
asym (E) SO4 asym (B2) OH Stretch H2O bend Hydrogen Bond νs νas n=4 n=5 n=6 D2 Predissociation Yield n=7 n=8 n=9 n=10 n=11 1000 1200 1400 1600 3000 3200 3400 3600 3800 Photon Energy (cm-1)
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Survey of MgSO4Mg(H2O)n2+ Spectra
asym (E) SO4 asym (B2) OH Stretch H2O bend Hydrogen Bond νs νas n=4 n=5 n=6 D2 Predissociation Yield n=7 n=8 n=9 n=10 n=11 1000 1200 1400 1600 3000 3200 3400 3600 3800 Photon Energy (cm-1)
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New Binding Motif: Onset of Hydrogen Bonding
Calculated Intensity/D2 Predissociation Yield 1000 1200 1400 1600 3400 3500 3600 3700 3800 B3LYP/ G(d,p) Photon Energy (cm-1) H2O bend SO4 asym νs νas SO2 MgSO4Mg(H2O)42+ Bifurcated motif dictates the geometry of the n = 4-7 clusters
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New Binding Motif: Onset of Hydrogen Bonding
A n = 9 n = 10 D2 Predissociation Yield H2O bend SO2 asym A B νas IHB OH stretch SO4 νs n = 8 n = 9 n = 10 1000 1200 1400 1600 3000 3200 3400 3600 3800 Photon Energy (cm-1)
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Survey of MgSO4Mg(H2O)n2+ Spectra
asym (E) SO4 asym (B2) OH Stretch H2O bend Hydrogen Bond νs νas n=4 n=5 n=6 D2 Predissociation Yield n=7 n=8 n=9 n=10 n=11 1000 1200 1400 1600 3000 3200 3400 3600 3800 Photon Energy (cm-1)
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Survey of MgSO4Mg(H2O)n2+ Spectra
asym (E) SO4 asym (B2) OH Stretch H2O bend Hydrogen Bond νs νas n=4 n=5 n=6 D2 Predissociation Yield n=7 n=8 n=9 n=10 n=11 1000 1200 1400 1600 3000 3200 3400 3600 3800 Photon Energy (cm-1)
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Solvent Separated Ion Pair
Add a water to the n = 10 cluster? X-Ray Crystal Structure of MgSO4(H2O)6 Batsanov, Acta Crystallographica C, 2000 Hexahydrite mineral Calculated Structure of MgSO4Mg(H2O)112+ SSIP SSIP has never before been observed in cluster ion spectroscopy! 3.12 kcal/mol above global minimum structure
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SSIP vs. Second Hydration Shell Configuration
Free OH IHB OH stretch νs νas IRMPD Spectrum Solvent Separated Ion Pair x10 IRMPD/Calculated Intensity νD Second Hydration Shell νD-as νD-s 2700 3000 3300 3600 3900 Wavenumber (cm-1)
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Acknowledgments Johnson Lab Prof. Mark A. Johnson Prof. Gary H. Weddle
Dr. Fabian Menges Dr. Joe DePalma Joseph Fournier Conrad Wolke Olga Gorlova Stephanie Craig Chinh Duong Joanna Denton
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[Mg(Palmitate-)(Palmitic)2]+
What’s next? Continue to search for the elusive solvent separated ion pair! Continue CAICE collaboration by incorporate organic acids and alcohols to mimic chemistry taking place at the surface of the ocean [Mg(Palmitate-)(Palmitic)2]+ FT-ICR MS
![[Mg(Palmitate-)(Palmitic)2]+](http://slideplayer.com./slide/14463778/90/images/23/%5BMg%28Palmitate-%29%28Palmitic%292%5D%2B.jpg "What’s next Continue to search for the elusive solvent separated ion pair! Continue CAICE collaboration by incorporate organic acids and alcohols to mimic chemistry taking place at the surface of the ocean. [Mg(Palmitate-)(Palmitic)2]+ FT-ICR MS.")
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