Automated 2D IR Spectroscopy using a high

repetition rate laser system and mid IR pulse shaper

Sudipta MukherjeeZanni Group

Department of ChemistryUniversity of Wisconsin at Madison

2D IR Spectroscopy-The vibrational analogue of 2D NMR

• Molecular Structures-Vibrational frequency ,coupling, anharmonicity, transition dipole angles

• Ultrafast Dynamics-fast time resolution(fs/ps)• Environment-Lineshape analysis

2

Merits of 2D IR Spectroscopy

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)

j

ij

ijj

i

jiprobe

pu

mp

| 0 0 >

| i 0 >| 0 j >

| 2i 0>

| 0 2j>| i j >

0

Ei

Ej

2Ei iEi Ej ij

2Ej j

local modes normal modes(a) (b)

3

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

Nd:YVO4

CW laserTi:Sapphire

Oscillator

StretcherRegenerative Amplifier

CompressorNd

:YL

Fn

s la

ser -BBO based

OPA

DifferenceFrequency

Mixingw/ AgGaS2

800 nm, 88 MHz. 2 nJ/pulse

idlerGe AOM

PulseShaper

Tunable mid-IR3-10 m, 2-5 J/pulse

800 nm, 1kHz, 1mJ/pulse

signal

beam dump

optical chopper

k1

kpump-probe= k1+k1+k2

sample

k1+k1 k2

monochromatorMCT array

--+

--+

Our Experiment set-up: automatic 2D IR spectrometer

6

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

7

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

8

However….

9

• 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.

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 withnot much loss of power.

Summary:

10

•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.

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!