Automated 2 D IR Spectroscopy using a high

Automated 2 D IR Spectroscopy using a high repetition rate laser system and mid IR pulse shaper Sudipta Mukherjee Zanni Group Department of Chemistry University of Wisconsin at Madison

2 D IR Spectroscopy-The vibrational analogue of 2 D NMR Merits of 2 D IR Spectroscopy • • • Molecular Structures-Vibrational frequency , coupling, anharmonicity, transition dipole angles Ultrafast Dynamics-fast time resolution(fs/ps) Environment-Lineshape analysis Scientific Problems • Characterization of Transmembrane Proteins eg CD 3ξ(receptor in T cells) , Ovispirin(antibiotic polypeptide), M 2(ion channel)etc • Studying folding kinetics eg HIAPP(HUMAN ISLET AMYLOID POLYPEPTIDE) 2

Examples of FTIR and 2 D IR spectra of HIAPP-Human Islet Amyloid Polypeptide-Type 2 diabetes 3

Traditional ways of doing 2 D IR spectroscopy Hole Burning Method • Easier • time resolution –less Pulsed Photon Echo Method • Difficult • Better time resolution

Our Experiment set-up: automatic 2 D IR spectrometer Ti: Sapphire Oscillator Nd: YVO 4 CW laser Nd: YLF ns laser 800 nm, 88 MHz. 2 n. J/pulse Stretcher Regenerative Amplifier Compressor b-BBO based idler OPA signal Difference Frequency Mixing w/ Ag. Ga. S 2 800 nm, 1 k. Hz, 1 m. J/pulse t k 2 - k +k + 1 - 1 beam dump sam ple Ge AOM Pulse Shaper Tunable mid-IR 3 -10 mm, 2 -5 m. J/pulse k 1 kpump-probe= +k 1+k 2 - optical chopper MCT array monochromator

How to generate the double pulses-pulse shaper • Ge-AOM is used as a modulated grating • Phase and amplitude tailored by a 75 Mhz acoustic wave of bandwidth 50 Mhz 6

Advantages of the pulse shaping method • Easier alignment. • Little maintenance. • Fast data collection. • Absorptive spectra-no phasing needed! • Complicated pulse shapes, higher dimension. 7

However…. 8

30 Khz laser!! A complete laser system including oscillator, cryo cooled amplifier and pump lasers-KM LABS • Rep Rate: 50 KHz • Pulse Duration: 40 fs(expected) • Pulse Energy: 300 -500 u. J Cryo-cooling and Downchirped Pulse Amplification gives high rep rate with not much loss of power. Moving towards even faster data collection • More averaging over larger number of laser shots. S/N almost 6 times • Even faster data collection-0. 3 s • Even lower sample concentration to mimic physiological conditions. 9

Summary: • Hence programmable pulse generation in MID IR achieved. • Easier implementation of 2 D IR spectroscopy. • We expect to get even better structural resolution with our new laser system. • Understand the role of intermediates in HIAPP folding. 10

Acknowledgement • • • Dr Martin Zanni Sang-Hee Shim Dave Strasfeld Ann Woys Wei Xiong Emily Blanco Yun Ling Dr Chris Middleton Dr Prabudhdha Mukherjee Thanks for your attention!