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

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

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

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

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

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] = kJ·mol -1 PA[CH 3 F] = kJ·mol -1 Parrillo et. Al. J. Am. Chem. Soc Beauchamp Annu. Rev. Phys. Chem ∆PA = kJ·mol -1 ≈ 3200 cm -1

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× × × Heated Capillary 90 ° Ion Bender Wiley- McLaren Extraction Region

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”

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

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 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

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

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 cm cm -1

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.

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

Supplemental Slides

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 Image from: Foces-Foces, et. al. J. Mol. Struct

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