H 2 Predissociation Spectroscopy: Arron Wolk Yale University Infrared Predissociation Spectroscopy of H 2 -tagged Dicarboxylic Acid Anions

H 2 Predissociation Spectroscopy Surveying the energetics of extended systems: Assess the influence of intramolecular H-bonds and chain length on conformational dynamics Characterize the influence of the H 2 adduct on vibrational spectra

Exploring the Diacid family The neutral dodecanedioc acid molecule: What happens as we remove the protons? Linear versus Ring conformation or

Two Experimental Hurdles Low Vapor Pressure High energy content –Need to quench latent heat of large molecules Probing the Effects of Ring Strain Experiment Theory HO 2 C-(CH 2 ) n -CO 2 - L.S. Wang, JCPA, 2006

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 *

How does the Hydrogen condense? All structures optimized at B3LYP/ G(d,p) level 114 m/z +nH2+nH2 ?

A closer look at H 2 condensation Structure optimized at B3LYP/ G(d,p) level

Electrostatic Potential Confirmation Greater exposed chargeIncreased H 2 condensation

? ? ? ? Photon Energy, cm -1 H2H2 CH 2 sym CH 2 asym C=O asym C=O sym (a) (b) (c) (d) Carboxylic Acid Series Structures optimized at B3LYP/ G(d,p) level No –OH Photon Energy, cm -1 Predissociation Yield

Electrostatic Potential Surfaces

Future Work Deuteration for confident identification of shared proton transition Competitive base binding to open ring structures Chain length study to probe H 2 perturbation

Thanks to: Mark Johnson Mike Kamrath Chris Leavitt Etienne Garand Rachael Relph Helen Gerardi Krissy Breen Tim Guasco Andrew Deblase Joe Fournier

Photon Energy, cm -1 H2H2 CH 2 sym CH 2 asym C=O asym C=O sym (a) (b) (c) (d) Carboxylic Acid Series Structures optimized at B3LYP/ G(d,p) level Predissociation Yield

Track solvation effects to reveal subtleties overlooked in theoretical spectra A Well Understood Model Peptide: GlyGlyH + (H 2 ) 2 Optimization and frequency calculations at MP2/ G(d,p) Photon Energy, cm -1 Calculated Intensity Predissociation Yield H 2 stretch O–H stretch Protonated Amine N-H Region Amide Region Fingerprint Region

n = 1 Predissociation Yield Photon Energy, cm -1 GlyGlyH + ·(H 2 ) n n = 2 Optimization and frequency calculations at MP2/ G(d,p) Calculated Intensity n = 0 Sym. NH 2 stretch Asym. NH 2 stretch Amide N-H stretch O-H stretch

Simulating an Ion Trap SIMION 8.0 Collision gas modeling Without Collision Gas

With Collision Gas Simulating an Ion Trap Collision gas is crucial! Now on to the real system…