1. Proton Sponges: A Simple Organic Motif for Revealing the Quantum Structure of the Intramolecular Proton Bond H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Andrew F. DeBlase, Christopher M. Leavitt, Timothy L. Guasco, Michael T. Scerba, Thomas Lectka, and Mark A. Johnson June 23, 2011 Ohio State University International Symposium on Molecular Spectroscopy

2. Ar Predissociation Yield The Shared Proton Shared proton vibrational frequency well characterized by vibrational predissociation spectroscopy Roscioli et. al. Science 2007 1000 15002000250030003500 Photon Energy (cm -1 ) Stoyanov and Reed J. Phys. Chem. A 2006 Absorption

3. Applications of Shared Proton Bonds Fuel Cell Membranes - Imidazole wires for anhydrous membranes +

4. Applications of Shared Proton Bonds Fuel Cell Membranes Gerardi et. al. J. Chem. Phys. Lett. 2011

5. Applications of Shared Proton Bonds Fuel Cell Membranes Proposed increase in binding affinity of pharmaceuticals - Neutral H-bond: 15-fold increase - Charged H-bond: 3000-fold increase Enhancement of organic bases (proton sponges) - Destabilized base - Stabilized conjugate acid: intramolecular proton bond H+H+ “Smeared out” QM particle 1 8

6. What to Expect? “Universal Trend” For intermolecular A∙H + ∙B Gas Phase Dimers: Let’s start in easiest range to measure! F N Roscioli et. al. Science 2007 PA[(CH 3 ) 3 N] = 939.1 kJ·mol -1 PA[CH 3 F] = 631.8 kJ·mol -1 Parrillo et. Al. J. Am. Chem. Soc. 1993 Beauchamp Annu. Rev. Phys. Chem. 1971 ∆PA = 307.3 kJ·mol -1 ≈ 3200 cm -1

7. Experimental Setup Ion optics Electrospray Needle RF Only Quadrupoles Octopoles Pressure (Torr) 3D Quadrupole Ion Trap with Temperature Control to 8 K TOF to IR Spectrometer New Cryogenic Ion Source 3×10 -7 1×10 -5 1.5×10 -2 1.5760 Heated Capillary 90 ° Ion Bender Wiley- McLaren Extraction Region

8. 26002700280029003000310032003300340035003600 Photon Energy (cm -1 ) Loss D 2 Loss 2H 2 C–H Stretches N–H + ∙∙∙F Stretch Predissociation MP2/6-311+G** (NH Scaled: 0.943) (CH Scaled: 0.957) C–H Stretches N–H + stretchResults “The Lone Ranger”

9. 600800100012001400160026002800300032003400 Photon Energy (cm -1 ) Calculated Intensity Predissociation Yield N H 3 C H 3 C F H N–H + ∙∙∙F Stretch MP2/6-311+G** (NH Scaled: 0.943) (CH Scaled: 0.957) (Bending/Deformations: 0.977) Loss 2H 2 Loss D 2 CH and NH BendingResults

10. MP2/aug-cc-pVTZ N N Minimal energy PT path: (1)N-N contraction (2)Ammonium N-H elongation Asmis et. al. Angew. Chem. Int. Ed. 2007. Anharmonicities: N-H: 464 cm -1 calc. N-H + N-N = 743 cm -1 N-H + 2N-N = 1069 cm -1 N-H + 3N-N = 1440 cm -1 Potential Energy Surfaces

11. y = 0 x = 0 Jaroszewski, Lesyng, Tanner, McCammon Chem. Phys. Lett. 1990. R (Å) y (Å) x (Å) R

12. 0.40.60.81.01.21.41.61.82.02.2 -20 0 20 40 60 80 100 120 V(x) (kcal∙mol -1 ) x (Å) R 1 = (CH 3 ) 2 N, R 2 = F R 1 = (CH 3 ) 2 N, R 2 = OH x y R 1 = R 2 = (CH 3 ) 2 N Potential Energy Surfaces ∆E 1 ←0 : 797 cm -1 2744 cm -1 2897 cm -1

13. Future Work Get spectra! - Compounds in the fridge - Others being synthesized Substitution R1R1 R2R2 N(CH 3 ) 2 OH N(CH 3 ) 2 OMe N(CH 3 ) 2 OEt NH 2 OH NH 2 OMe NH 2 OEt N(CH 3 ) 2 OCF 3 NH 2 OCF 3 Question: When will shared proton couple to aromatic vibrations? Use motiffs that increase/decrease proton donor-acceptor distance e.g.

14. Acknowledgements Labmates: Especially Tim Guasco and Chris Leavitt Mark: New science, new hobbies! Tom Lectka’s group at JHU for making the molecules! Funding: National Science Foundation, Air Force

15. Supplemental Slides

16. Potential Energy Surfaces U(r) (kcal∙mol -1 ) r(N-H) Å R = 3.00 Å R = 2.87 Å R = 2.75 Å R = 2.50 Å Equilibrium: R ≈ 2.75 Å R = 2.75 Å Jaroszewski, Lesyng, Tanner, McCammon Chem. Phys. Lett. 1990. Image from: Foces-Foces, et. al. J. Mol. Struct. 1990.

17. Deviation from Universal Trend Breaks down if ∆ PA is small and ∆ μ is large Gardenier, Roscioli and Johnson J. Phys. Chem. A. 2008  PA = 88.2 kJ/mol  = 2.05 D Photon Energy (cm -1 ) 800120016002000 24002800 32003600800120016002000 24002800 32003600800120016002000 24002800 32003600800120016002000 24002800 32003600 x20 Predicted Shared-Proton Transition