REMPI and Double Resonance Spectroscopy of L -β-Homotryptophan in Gas Phase Hae Jun Jung, Jung Jin Kim, and Hyuk KANG Ajou University, Suwon , Korea 69 th International Symposium on Molecular Spectroscopy

Submicroscopic Histology Section the active part Use a natural chromophore or stain it Freeze it Illuminate it with laser in a vacuum chamber Directly observe the active conformations Directly observe the active molecular interaction

How to Distinguish Conformers w/ UV Conformer A Conformer B S0S0 S1S1 hν A0-0 hν B0-0 hν A0-0 < hν B kcal mol -1 (B3LYP/6-31G**) cis-meta-aminophenol trans-meta-aminophenol

S1S1 S0S0 hν burn c-3AP t-3AP UV-UV Double Resonance UV-UV Hole Burning hν probe Mass-Resolved Conformer-Specific UV Spectrum

L -β-homotryptophan L -tryptophan E. E. Baquero, W. H. James, III, S. H. Choi, S. H. Gellman, and T. S. Zwier, J. Am. Chem. Soc., 130, 4784 (2008). more flexible or easier to fold? β-Amino acids

L. C. Snoek, R. T. Kroemer, M. R. Hockridge and J. P. Simons, Phys. Chem. Chem. Phys., 3, 1819 (2001). Conformers of tryptophan

Experimental and Computational Thermal oven / laser desorption Supersonic expansion Frequency doubled pulsed dye laser Resonance-Enhanced Multiphoton Ionization (REMPI) TOF MS, MCP, DSO, PC Conformational search –Macromodel with Amber force field Geometry optimization –Gaussian09 at M05-2X/6-31G**

REMPI spectrum of laser-desorbed Trp T. R. Rizzo, Y. D. Park, L. A. Peteanu, and D. H. Levy, J. Chem. Phys. 84, 2534 (1986). Levy’s group Ours

REMPI spectrum of Trp and Trp-HCl R-NH Cl - R-NH 2 + HCl R-NH 3 + ·Cl -

REMPI spectrum of L -β-homotryptophan * *HCl salt

L -β-Homotryptophan and L -tryptophan *HCl salt

UV-UV HB spectra of L -β-hTrp * *

0.0 kJ/mol 3.66 kJ/mol 0.86 kJ/mol 3.64 kJ/mol (23% at 300 K) 4.76 kJ/mol 0.22 kJ/mol 0.28 kJ/mol 2.10 kJ/mol 5.66 kJ/mol (10% at 300K) 2.59 kJ/mol 1.82 kJ/mol (48% at 300 K) 2.61 kJ/mol 2.80 kJ/mol 4.36 kJ/mol 5.16 kJ/mol Stable conformers of L -β-homotryptophan M05-2X/6-31G**

Issues Short progression –Lower Franck-Condon activity than Trp? –Faster non-radiative process? Less conformers observed –Signal intensity ≠ population –Low barriers between conformers Conformer-specific non-radiative process? L -β-homotryptophan L -tryptophan

Conformer-specific IC M. Mališ, Y. Loquais, E. Gloaguen, C. Jouvet, V. Brenner, M. Mons, I. Ljubić and N. Došlić, Phys. Chem. Chem. Phys. 16, 2285 (2014).

Published in: Momir Mališ; Yohan Loquais; Eric Gloaguen; Himansu S. Biswal; François Piuzzi; Benjamin Tardivel; Valérie Brenner; Michel Broquier; Christophe Jouvet; Michel Mons; Nađa Došlić; Ivan Ljubić; J. Am. Chem. Soc. 2012, 134, DOI: /ja Copyright © 2012 American Chemical Society

Acknowledgements Hae Jun Jung Jung Jin Kim