Probing the dynamics of biomolecules in liquid water by terahertz spectroscopy

Transcription

1 Probing the dynamics of biomolecules in liquid water by terahertz spectroscopy Nguyen Quang Vinh Institute for Terahertz Science and technology Physics Department, UC Santa Barbara

2 Spectroscopy probes structure and dynamics Terahertz Near infrared UV-Visible

3 Terahertz: Conformational flexibility Domain 1 Domain 2 ~ 5 nm T4 Lysozyme De Groot et al Proteins: Struct. Funct. Gen. 31:

4 Theoretical calculations for Lysozyme Normal mode analysis and Monte Carlo simulations Hen Egg White Lysozyme Normal Mode Density a.u Levitt 1985 van Vlijmen 1999 Markelz 2002 Normal Mode Molecular Dynamics Molecular Dynamics Frequency THz

5 Previous work: Dry/Moist Limited Terahertz Absorption Measurements Limited to Dry Protein Measurement Markelz et al Phys. Med. Biol. 47: Molar Extinction 10 3 cm -1 M Frequency THz

6 Water absorption Data collection from literature 10 6 Wavelength μm Absorption coefficient cm THz radio infra frequency THz red VIS UV soft X-ray Frequency GHz J. D. Jackson, Classical Electrodynamics, Third edition, 1999, p.315

7 Water absorption: challenge 1mm water ~ attenuation 800 Extinction cm Precision Measurements Frequency THz Xu, Plaxco, Allen, J. Chem. Phys., 124: , 2006

8 Terahertz absorption: previous data Molar Extinction 10 3 cm -1 M Experiment Frequency THz Molar Extinction 10 3 cm -1 M -1 Levitt et al J. Mol. Biol., 181: Frequency THz

9 Fundamental optical phenomena A glass without and with water showing how light is refracted through water

10

11 Absorption and Refraction of water Data collection from literature 10 6 Wavelength μm Absorption coefficient cm THz Index of refraction radio infra frequency THz red VIS UV soft X-ray Frequency GHz 1 J. D. Jackson, Classical Electrodynamics, Third edition, 1999, p.315

12 Related fundamental quantities Complex index of refraction Refractive index Extinction coefficient * sol * sol v ik n n ν ν ν = + = v c K π α 4 = Energy stored per unit volume Energy dissipated per unit volume " sol ' sol * sol ν ν ν i + = Complex dielectric function = = 2, " sol 2 2 ' sol ν ν ν ν ν ν Κ n Κ n v K v n + = + + = 2 / ' " ' 2 / ' " ' ; " ' v Κ v n v v

13 What can we learn from ν? Charge dynamics Charge density Electronic relaxation times Frequencies of classical or quantum oscillations... Detailed comparison with microscopic theory

14 Outline GHz-THz spectroscopy setup Absorption of protein in liquid water Effective medium theory for the dynamics of biomolecules in liquid water Conclusions

15 UCSB GHz vector spectroscopy Vector Network Analyzer 10 MHz-43 GHz Frequency extenders GHz Virginia Diodes, Inc. + Thomas Keating, Ltd.

16 Frequency multipliers, mixers, horns

17 x12 RF source from VNA port 1 Freq Sour1 = 1 12 fb eg: f = 30 GHz Mixer x 12 eg: fb = 360 GHz REF f=279mhz sample to VNA MEAS f=279 MHz Mixer x 12 LO source from VNA port Freq Sour3 = fb eg: /12 GHz Frequency extension No. Freq. band Freq. Range Freq. factor Horn dia. Length GHz mm mm #1 WR x #2 WR x #3 WR x #4 WR x #5 WR x #6 WR x

18 Spectra linear scale 2 WR1.5 div 10 Power uw 1 Power mw G 600G 700G VNA / 10 WR10 WR6.5 WR5.1 WR3.4 WR2.2 WR G 400.0G 600.0G 800.0G Frequency GHz

19 db dynamic range Dynamic range db VNA 70 GHz to 700 GHz VNA WR10 WR6.5 WR5.1 WR3.4 WR2.2 WR1.5 0 Vapour absorption line 0 100G 200G 300G 400G 500G 600G 700G 800G Frequency Hz

20 Variable path length sample cell Precise measurement of attenuation and phase shift Water, water, water 1mm water ~ attenuation 800 I = I e αz 0 Extinction cm Precision Measurements Frequency THz Δ A = Δ Ln I α Δl Opaque wall Transparent windows Translation stage transmitted Variable Path Length Sample Cell Following C. Schmuttenmaer

21 Liquid measurements Absorption Phase shift THz 0.15 THz 0.30 THz 0.45 THz 1500 Intensity W THz THz 0.60 THz THz Unwrapped phase degree Path-length mm Path-length mm 0

22 Complex dielectric constant - water Absorption coefficient cm -1 Refractive index Kindt Thane Hasted Afsar Hasted Vij EvansVij simpson Robertson Free-electron laser Vinh NQ et al Kindt Thrane Hasted Simpson Vinh NQ et al Frequency GHz

23 Complex dielectric constant - water 100 Dielectric spectrum Water T= K ' ν '' ν Frequency GHz Wave number cm -1

24 Conclusions - Sensitive spectroscopy from GHz High resolution and dynamic range up to 140 db Large range of protein concentrations Real and imaginary response - Use Bruggeman EMT to extract dielectric constant Dielectric spectroscopy of protein in water - Water hydration level 5 e' - Dynamics of Lysozyme at GHz Multiple harmonic oscillations, with a cut-off frequency of 300 GHz e" mm 7.75 mm mm Fitting curves Frequency GHz

25 Acknowledgements Prof. Jim Allen, Dr Louis-Claude Brunel, Devin Edwards, Jerry Ramian, Prof. Mark Sherwin, Institute for Terahertz Science and Technology Department of Physics, University of California, Santa Barbara Prof. Song-i Han, Prof. Kevin Plaxco, Dr. Takanori Uzawa, Dr. Alexis Vallée-Bélisle Department of Chemistry, University of California, Santa Barbara W. M. Kerk foundation for support