Ultraviolet and infrared spectroscopy of helical peptides and their water complexes Jaime A. Stearns, Monia Guidi, Caroline Seaiby, Natalia Nagornova Annette Svendsen, Oleg V. Boyarkin, and Thomas R. Rizzo Laboratoire de Chimie Physique Moléculaire Ecole Polytechnique Fédérale de Lausanne 3 January 2016

The Helix Hudgins, R. R. and M. F. Jarrold (1999). JACS 121: (% of ideal helix) Ac-Phe-(Ala) n -Lys-H + C 13 C 10 What is the detailed structure of the helix? How many conformations are there? Where do the first water molecules bind?

22-pole ion trap (6 K) Experimental setup UV S0S0 S1S1 fragments

Infrared-ultraviolet double resonance spectroscopy S0S0 S1S1 v=1 detected fragments UV IR fragmentation threshold UV only UV+IR IR Wavenumber /cm -1 A B

Ac-Phe-(Ala) 5 -Lys-H + UV spectrum A D C B

NH stretch spectra of Ac-Phe-(Ala) 5 -Lys-H + B3LYP/6-31G** (scaled 0.952) A B 3 kJ/mol 7 kJ/mol C 10 -C 10 -C 13 -C 13 C 10 -C 10 -C 10 -C 10 C 10 -C 13 -C 13 -C 13 A B 0 kJ/mol

B3LYP/6-31G** (scaled 0.952) C D 0 kJ/mol 4 kJ/mol NH stretch spectra of Ac-Phe-(Ala) 5 -Lys-H + C 10 -C 10 -C 10 -C 10 C 10 -C 13 -C 13 -C 13 C 10 -C 10 -C 10 -C 13

Low-energy conformations B3LYP/6-31G** gauche – (0 kJ/mol) gauche + (4 kJ/mol) gauche + (7 kJ/mol) gauche – (3 kJ/mol)

Where will a water molecule bind? Peripheral binding sites: COOH, free NH,  system Integrated binding sites: insertion into C=O H-N bonds We can create Ac-Phe-(Ala) 5 -Lys-H + (H 2 O) n in the ion source, and probe the details of the structure with IR and UV spectroscopy.

Creating water complexes in the ion source *impurity Ac-Phe-(Ala) 5 -Lys-H + (H 2 O) n

UV spectra of Ac-Phe-(Ala) 5 -Lys-H + (H 2 O) n

IR spectrum of Ac-Phe-(Ala) 5 -Lys-H + (H 2 O) 1 free OH monomer v=0 v=1 IR water complex

Isotopically labeled Ac-Phe-(Ala) 5 -Lys-H + 15 N-Ala anticipated red shift of 8 cm -1

Isotopically labeled Ac-Phe-(Ala) 5 -Lys-H + monomer Ala 2 Ala 6 Ala 4

AcFA 5 K-H + -(H 2 O) 1 isotopic substitution Ala 2 Ala 4 Ala 6

IR spectrum of Ac-Phe-(Ala) 5 -Lys-H + (H 2 O) 1 Ac-Phe-(Ala) 5 -Lys-H + conf B Ac-Phe-(Ala) 5 -Lys-H + conf C COOH bonded H 2 O Ala 2 Ala 4 Ala 6 Ala 4

Conclusions Ac-Phe-(Ala) 5 -Lys-H + is a helical peptide with four conformations at low temperature (10-15 K) We can create complexes between this peptide and more than 15 water molecules The UV spectra indicate the first four water molecules attach away from the chromophore, likely near the charge The fifth water molecule binds near the chromophore The first water molecule binds in a double-donor motif Both helical backbones are retained upon binding of the first water molecule

Acknowledgements Prof. Tom RizzoMonia GuidiCaroline SeaibyDr. Oleg Boyarkin Dr. Annette Svendsen Dr. Catherine Servis, Protein and Peptide Chemistry Facility George PapadopoulosUlrich Lorenz Natalia Nagornova FN S NF Funding: