Automated 2D 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

2D IR Spectroscopy-The vibrational analogue of 2D NMR Merits of 2D 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 CD3ξ(receptor in T cells) ,Ovispirin(antibiotic polypeptide),M2(ion channel)etc Studying folding kinetics eg HIAPP(HUMAN ISLET AMYLOID POLYPEPTIDE)

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

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

Regenerative Amplifier Our Experiment set-up: automatic 2D IR spectrometer Nd:YVO4 CW laser Ti:Sapphire Oscillator Stretcher Regenerative Amplifier Compressor Nd:YLF ns laser b-BBO based OPA Difference Frequency Mixing w/ AgGaS2 800 nm, 88 MHz. 2 nJ/pulse idler Ge AOM Pulse Shaper Tunable mid-IR 3-10 mm, 2-5 mJ/pulse 800 nm, 1kHz, 1mJ/pulse signal beam dump optical chopper k1 kpump-probe= k1+k1+k2 t sample k1+k1 k2 monochromator MCT array - +

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

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

However….

Moving towards even faster data collection 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 uJ 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.

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

Thanks for your attention! 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!