REMPI and Double Resonance Spectroscopy of

L-β-Homotryptophan in Gas Phase

Hae Jun Jung, Jung Jin Kim, and Hyuk KANGAjou University, Suwon 443-749, Korea

69th 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

S0

S1

hνA0-0 hνB0-0hνA0-0 < hνB0-0

0.319 kcal mol-1 (B3LYP/6-31G**)

cis-meta-aminophenol

trans-meta-aminophenol

S1

S0

hνburn

c-3AP

t-3AP

UV-UV Double ResonanceUV-UV Hole Burning

hνprobe

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**

LinearTOF

MCP

DiffusionPump

DiffusionPump

TurboPump

IG

NY-61 Nd:YAGLaser (532nm)

ND-60 TunableDye Laser Autotracker(BBO)

PVSkimmer

SC

DM

34800 34900 35000 35100 35200

Sig

na

l (A

.U)

Wavenumber (cm-1)

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-NH3+ + Cl-

R-NH2 + HCl

R-NH3+·Cl-

34860 34880 34900 34920

Sig

nal (

A.U

.)

Wavenumber (cm-1)

Trp Trp HCl

22 24 26 28 30 32 34-0.18

-0.16

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

Mas

s S

igna

l (m

V)

Flight time (us)

Trp Trp HCl

34600 34700 34800 34900 35000 35100 35200 35300 35400

Ion S

ignal (A

.U.)

Wavenumber (cm-1)

34750 34800 34850 34900 34950 35000 35050

Ion

Sig

nal (

A.U

.)

Wavenumber (cm-1)

REMPI spectrum of L-β-homotryptophan*

*HCl salt

34600 34700 34800 34900 35000 35100 35200 35300 35400

34600 34700 34800 34900 35000 35100 35200 35300 35400

Ion S

ignal (A

.U.)

Wavenumber (cm-1)

L-β-Homotryptophan and L-tryptophan

*HCl salt

UV-UV HB spectra of L-β-hTrp

34800 34850 34900 34950 35000 35050

Sig

nal (

A.U

.)

Wavenumber / cm-1

H.B. at 34980 cm-1

H.B. at 34950 cm-1

REMPI

*

*

0

1

2

3

4

5

6

Re

lativ

e e

ne

rgy

(kJ/

mo

l)

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/mol2.80 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-homotryptophanL-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, 20340-20351.DOI: 10.1021/ja3054942Copyright © 2012 American Chemical Society

Acknowledgements

• Hae Jun Jung• Jung Jin Kim