1. Infrared-ultraviolet double resonance spectroscopy of cold biomolecular ions in the gas phase
Jaime A. Stearns, Monia Guidi, Sébastien Mercier,
Oleg V. Boiarkine, and Thomas R. Rizzo
Laboratoire de chimie physique moléculaire
Ecole Polytechnique Fédérale de Lausanne (EPFL)

2. Experimental approachS0 S1
v=1
detected
fragments
Add animation UV IR

3. Conformational landscapes
tryptophan
6 conformers
(Rizzo, Park & Levy JCP 85,6945,1986)
tyrosine
8 conformers
(de Vries et al JPCA 104, 6351, 2000)
NATMA
3 conformers
(Zwier et al, JCP 118, 2696, 2003)
Tyrosine-based protonated peptides
effect of charge
spectral complexity
secondary structure
Ac-Ala-Phe-Ala-NH2
1 conformer
(Mons et al, PCCP 8, 1033, 2006)

4. TyrosineH+ kcal/mol, B3LYP/6-31++G** ZPE-corrected 0.00 0.03 0.66 0.79
only structures under 4 kcal/mol
know A and B are different because of different mass spectra A B

5. TyrosineH+ 0.00 0.03 0.66 0.79 free N+H phenol OH COOH
can’t distinguish between OH-flips
0.03
0.66
0.79

6. [AlaTyr + H]+
simple spectrum, red shifted already indicating strong NH3-ring interaction

7. [AlaTyr + H]+ families kcal/mol, B3LYP/6-31++G** ZPE-corrected C5C5
0.00
C5 anti
0.05
families of structures found by macromodel/DFT (under 5 kcal/mol).
C5 anti
0.93 C8
2.74

8. [AlaTyr + H]+ C5-C5 C5 anti C5 anti C8
first, bound NH region eliminates C5 anti structures. Amide NH region says it’s C5C5.
C5 anti C8

9. [AlaTyr + H]+ 0.00 1.46 2.63 4.17 free N+H COOH bound N+H amide NH
phenol OH
0.00
1.46
There are 4 C5C5 structures with different OH and COOH orientations, but they are very different energetically! assume we see only the first one.
2.63
4.17

10. [AlaTyr + H]+ UV spectrum Holeburning on amide NH
seems to verify one structure, although some of the intensities aren’t quite right ... we intend to look into this.
Holeburning on amide NH

11. [TyrAla + H]+ monitor m/z 136 B monitor m/z 147 A
remind about YA having two conformers like tyrosine.

12. [TyrAla + H]+ A B

13. [TyrAla + H]+ families kcal/mol, B3LYP/6-31++G** ZPE-corrected C5 perp
1.31
C5C5
0.00
C5 anti perp
2.80
families of structures. within each OH, COOH, phi,psi can vary. C8
4.41
C5C5 anti
3.24

14. [TyrAla + H]+ C5C5 C5 perp C5 anti perp C5C5 anti C8 amide NH
bound N+H
free N+H
amide NH
COOH
phenol OH
C5C5
C5 perp
C5 anti perp
eliminate two on the basis of bound NH region, other NH region makes it C5C5.
C5C5 anti C8

15. [TyrAla + H]+
0.00
add #35 when it finishes! add the picture of either 35 or the other. again, can’t distinguish OH flips.
0.02
0.95
0.99

16. Conformer comparison
TyrH+
[AlaTyr + H]+
[TyrAla + H]+

17. Conformer-specific fragmentation revisited
TyrH+ B
NH3 loss,
loss of
side chain
both YA (A) and Tyr (B) show more fragmentation channels that aren’t consistent with the typical mass spec fragmentation. what is it about that particular structure that induces fast excited state reaction???
TyrH+ A
[TyrAla + H]+ B
[TyrAla + H]+ A
NH3 loss
ground state
dissociation
ground state
dissociation

18. Conclusions
Conformation-specific infrared spectra were recorded for TyrH+, [AlaTyr + H]+, and [TyrAla + H]+.
TyrH+ and [TyrAla + H]+ each showed at least two conformations, but further distinction on the basis of IR was not possible.
[AlaTyr + H]+ showed a single conformation. Elimination of similar conformers was done on the basis of energetics.
Both dipeptides were present in extended C5-C5 backbone conformations rather than more folded structures.
Analagous structures of TyrH+ and [TyrAla + H]+ showed similar fragmentation behavior, indicating conformer-specific excited state dissociation.

19. Acknowledgements Funding:
Prof. Tom Rizzo
Monia Guidi
Caroline Seaiby
Dr. Oleg Boiarkine
Sébastien Mercier
Dr. Anthi Kamariotis
FNSNF
Funding:

20. Free NH stretch region
I don’t really understand this!