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)

Experimental approach S0 S1 v=1 detected fragments Add animation UV IR

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)

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

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

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

[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

[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

[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

[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

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

[TyrAla + H]+ A B

[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

[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

[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

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

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

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.

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

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