Ultraviolet and infrared spectroscopy of helical peptides and

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 10/3/2020

The Helix Ac-Phe-(Ala)n-Lys-H+ (% of ideal helix) C 13 C 10 • What is the detailed structure of the helix? • How many conformations are there? • Where do the first water molecules bind? Hudgins, R. R. and M. F. Jarrold (1999). JACS 121: 3494 -3501.

Experimental setup 22 -pole ion trap (6 K) S 1 fragments UV S 0

Infrared-ultraviolet double resonance spectroscopy B A S 1 detected fragments fragmentation threshold UV v=1 UV only UV+IR IR S 0 IR Wavenumber /cm-1

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

NH stretch spectra of Ac-Phe-(Ala)5 -Lys-H+ A 7 k. J/mol B 3 k. J/mol 0 k. J/mol C 10 -C 13 -C 13 C 10 -C 10 C 10 -C 13 -C 13 B 3 LYP/6 -31 G** (scaled 0. 952) A B

NH stretch spectra of Ac-Phe-(Ala)5 -Lys-H+ 4 k. J/mol 0 k. J/mol C 10 -C 13 C 10 -C 10 C 10 -C 13 -C 13 B 3 LYP/6 -31 G** (scaled 0. 952) C D

Low-energy conformations B 3 LYP/6 -31 G** gauche – (0 k. J/mol) gauche + (4 k. J/mol) gauche – (3 k. J/mol) gauche + (7 k. J/mol)

Where will a water molecule bind? • Peripheral binding sites: COOH, free NH, p 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 Ac-Phe-(Ala)5 -Lys-H+ • (H 2 O)n *impurity

UV spectra of 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 v=1 IR monomer v=0 water complex free OH

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 4 Ala 6 Ala 2

Ac. FA 5 K-H+-(H 2 O)1 isotopic substitution Ala 4 Ala 6 Ala 4 Ala 2

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

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 Rizzo Dr. Oleg Boyarkin Dr. Annette Svendsen Dr. Catherine Servis, Protein and Peptide Chemistry Facility Ulrich Lorenz Monia Guidi George Papadopoulos Funding: FN Caroline Seaiby Natalia Nagornova SNF