Characterization of Ion-Driven Conformations in Diphenylacetylene Molecular Switches Arron Wolk Johnson Lab Yale University

Hydrogen Bonding in Supramolecular Complexes Infrared predissociation of cryogenically cooled ions Accessing the vibrational transitions of amide functionalities in supramolecular complexes Catalytic Cycles Host-Guest Interactions Protein Folding Solvent Interactions Electospray Ionization Andersen, Biopolymers, 2006 N-H O=C Bonds Hydrogen Bond Linkages Electrostatic Interactions C-O Na + Rizzo, JACS, 2011

Cryogenic Mass Spectrometry: H 2 -Tagging in a Quadrupole Ion Trap Wiley-McLaren extraction region Ion optics To time-of-flight and 2-D infrared analysis Electrospray needle Heated capillary 90°ion bender RF onlyquadrupolesH 2 /He filled 3-Dquadrupole ion trap with temperature control to 8 K Einzel Octopoles 1 st skimmer 2 nd skimmer Differential aperture 50 K heat shield 1x x x10 -7 Pressure (Torr) Adapted from Lai-Sheng Wang’s H 2 tagging instrument Paul trap interfaced to our standard TOF experiment. Molecular H 2 tag, analogous to Ar tag in previous predissociation experiments. We have interfaced our Ar tagging, TOF instrument to a new electrospray ionization source

Trapping, Cooling, and Tagging He/H 2 buffer gas RF Pulsed valve Ions in Ions out Paul Trap at 10K 100’s of collisions for translational cooling 1,000-10,000’s of collisions for internal energy cooling Time of Flight (  s) 30 ms 50 ms 40 ms 20 ms 10 ms doubly-charged parent a) b) c) d) e) trap residence time: Signal Intensity (arbitrary units) hydrogen adduct formation *

The Diphenylacetylene Scaffold Rigid scaffold limits conformational complexity Creates specific acceptor- donor interactions An ideal molecular switch backbone that responds with a conformation switch ? Urea Amide Lactone Cl -

Sodium Complex ν ester C=O ν ν CH ν free C=O Free NH Donor NH Photon Energy, cm Carbonyl RegionNH Region Na + B3LYP/6-31+G(d,p)

A Neutral Analog B3LYP/6-31+G(d,p) Na + Complex Free NH Urea NHs TMA + Complex Photon Energy, cm -1 AcceptorPossible Donors Acceptor redshifts Two donors redshift Remaining carbonyls largely unaffected

Donor NH Perturbation Photon Energy (cm -1 ) N-H C=O ν NH free Larger Shift Acceptor Responds!

Electrostatic Potential: Positive Counterions + - Na + Complex TMA + Complex Na + TMA +

A Story of Electrostatics CationsAnions Na + TMA + Cl - I-I- Charge Solvation vs. Double H-bond Steric effects versus double H-bond Three cation solvators

The Chloride Anion Photon Energy (cm -1 ) ester ν CH Free NH Conformation Switch Donor NHs ν amide ν urea Only one neutral NH h- bond donor Acceptor blueshifts, losing a hydrogen bond Spectator C=O’s blueshift B3LYP/6-31+G(d,p) TMA + Cl -

Surveying Charge Solvation + - Na + TMA + Cl -

Photon Energy, cm -1 Switch * Cl - SwitchCl - SwitchBr - SwitchI - Halide Series Donor acidity drops Acceptor Proton Affinity drops

Conclusions Gained microscopic picture of an amide-based molecular switch accommodating a charge center Observed conformation switch in gas-phase Future studies: Anion-Dependent Switching Cl - Molecular Switch Dynamics Versatile Hydrogen Bond Framework pH-Dependent Switching Oxidation-Dependent Switching Fluorescence Studies: Materials Mimic Hydrogen-Bonded Scaffold Mimic H+H+ e-e- hv

Thank You Ian Jones and Andrew Hamilton Etienne Garand, Mike Kamrath, Chris Leavitt, and Mark Johnson

Comparison to FTIR