TERAHERTZ SPECTROSCOPY OF BIOMOLECULES IN WATER: L-PROLINE IN REVERSE MICELLES NIST Colleagues:...
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Transcript of TERAHERTZ SPECTROSCOPY OF BIOMOLECULES IN WATER: L-PROLINE IN REVERSE MICELLES NIST Colleagues:...
TERAHERTZ SPECTROSCOPY OF BIOMOLECULESIN WATER: L-PROLINE IN REVERSE MICELLES
NIST Colleagues: Craig Brown, Alan Migdall, Jerry Fraser, David Plusquellic
NIST Postdocs: Andrea Markelz, Matt Beard, Tim Korter, Okan Esenturk, Larry Iwaki, Karen Siegrist, Catherine Cooksey, Ahmasi Harris
Summer Students: Ari Evans (Cornell), Mary Kutteruf (UVa), Brendon Scheinman (Wash. U.), Ben Greer (Carnegie Melon)
Collaborators: Rad Balu and Susan Gregurick (UMBC), Joe Melinger (NRL)
Project Support and Funding
NIST Competence Program, Office of Law Enforcement and Safety,NIST STRS, DARPA, NAVY, DHS
• E. J. Heilweil and D. F. Plusquellic, “Terahertz Spectroscopy of Biomolecules,” book chapter in “Terahertz Spectroscopy: Principles and Applications,” Taylor and Francis, CRC Press, Susan Dexheimer, editor. Chapter 7, pages 269-298 (2008).
• David F. Plusquellic, Karen Siegrist, Edwin J. Heilweil, and Okan Esenturk, “Applications of Terahertz Spectroscopy in Biosystems,” review paper for Chemical Physics Physical Chemistry 8, 2412-2431 (2007).
Homeland Security
THz Metrology
BiomolecularPhysics
Pharmaceuticals
IMAGING
MATERIALS CHARACTERIZATION TIME-RESOLVED
SPECTROSCOPY
MODELING/THEORY
NIST Terahertz Project Objectives(1998- present)
• Investigate low frequency vibrational spectra of biomolecules, model biosystems and materials:
“THz spectroscopy probes structure, large-amplitude “torsional” modes and local environment, thus allowing the
conformational landscape to be directly mapped…”
• Examine hydrogen-bonding and bio-system dynamics • Bring together complimentary low-frequency spectroscopies
(e.g., Infrared, Raman, Inelastic Neutron Scattering)• Compare experiments to molecular modeling & theory• Advance THz imaging methods for bio-molecular and
materials applications (wafers, tissue, tablets, etc.)
Other Groups’ Biomolecular THz Work …
• P. Jepsen (Denmark) – Spectroscopy and modeling of peptides, sugars, biomolecules
• P. Bolivar (Germany) – DNA hybridization/chips• M. Havenith (Germany) – Spectroscopy of sugars in water• C. Schmuttenmaer (Yale) – Molecular liquids, biomolecules• M. Ito (Japan) – Methods development, biomaterials
spectroscopy• P. Taday (Teraview, UK) – Spectroscopy of
Pharmaceuticals, Rapid-scanning THz imager for tissue, tablets, materials characterization
• A. Markelz (SUNY Buffalo) – Spectroscopy of proteins, DNAs, etc.
• T. Korter (Syracuse) – Spectroscopy and theory for small biomolecules and explosives
Modified Fourier-Transform Infrared Spectrometer
MODIFICATIONS:• Silicon-coated mylar broadband beam-splitter• DTGS room temperature detector with HDPE window• Sensitivity from ~ 50 – 700 cm-1
Nicolet Magna 550 FTIR
Biomolecular THz Spectroscopy in AqueousReverse Micelles
Catherine Cooksey, NIST/NRC Postdoctoral Associate
AOTn-Heptane
Approach: • Encapsulate room temperature amino acids, proteins, DNAs in reverse water-alkane micellar structures to control water content and eliminate strong bulk THz water absorption • Also used in NMR and single molecule studies . . .
H2O and D2O in AOT and Brij-30 MicellesH2O / AOT
D2O / AOT
H2O / Brij-30
• Water in AOT anionic surfactant exhibits decreasing intensity and frequency shifts with higher w or micelle water loading
• Water encapsulated in the non-ionic surfactant Brij-30 shows “minimal” change in THz spectrum as the size is changed…
w=1,2,3,5,10,15,20
D2O / Brij-30
w=2: ~100 waters, d ~4 nm
Pathlength 4.2 mm
L-Proline-Water Inverse AOT Micelles[Pro]max ~ 11 Mol/liter
Solid in PE
L-Proline-Water Inverse AOT Micelles and Solid-State Spectrum
• L-Proline in AOT surfactant exhibits clear THz absorptions that correspond closely to those observed in the solid-state
• There appears to be significant red and blue-shifting of band frequencies arising from solvation interactions (e.g., hydrogen-bonding and solvent exclusion…
• Low frequency phonon bands of the solid become a broadened water hydrogen-bonding band
L-Proline-D2O in AOT Micelles[Pro]max ~ 11 Mol/liter
50 150 250 350 450 550 650
Ab
sorp
tio
n (
OD
)
0.000
0.050
0.100
0.150
0.200
Fructose in Water Inverse AOT MicellesCatherine Cooksey & Ben Greer (SURF student)
Wavenumber (cm-1)
50 150 250 350 450 550 650
Ab
sorp
tio
n (
OD
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
5% Solidin PE
??~5 mole/lw = 10
Phonons?
Wavenumber (cm-1)
•P3HT = Poly(3-hexylthiophene-2,5-diyl)
Regio-regular structure, average Mw ~87,000 (Sigma-Aldrich)
< 200 nm thick CVD films
•Conductive polymer organic semi-conductor
•Scientific and industrial interest ..
High efficiency solar cells,
flexible electronics , displays
•Non-contact, All optical measurement
•THz carrier concentration and mobility
•Frequency-dependent mobility
THz Measurement of Carrier Mobility in Semiconductor Polymer Films
With Okan Esenturk and Joe Melinger (NRL)
erahertz Signals Carrier Mobility
= mobility, = photogeneration efficiency
T /To = differential transmission,
h = Plank constant, light frequency,
N = refractive index of substrate,
e = electric charge, F = Fluence,
Z0 = free space impedance
eF(1-e-d) Z0
|T/To| h (1+N) =
(Hegmann et al. J. Appl. Phys. 98, 033701, 2005)
-6 -4 -2 0 2 4 6
-10
-5
0
5
10
Sig
nal
(a.
u)
Time (ps)
Ref THz-TDS
5
-5 0 5 10 15-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
T/T
o (
%)
Relative Probe Time (ps)
Signal Comparison for P3HT versus PBTTT:PBTTT exhibits higher conductivity…
Esenturk, et. al. J. Phys. Chem. C (Letters), in press
-5 0 5 10 15 20 25 30 35 40 45
-60
-50
-40
-30
-20
-10
0
-2 0 2 4
Blend Ratios 75:25 50:50 45:55 20:80 0:100
T (
a.u
.)
Time Delay (ps)
10 15 20 25 30 35 40
40
50
60
70
80
Power dependence neat C60 film
Pea
k S
igna
l
Power (mW)
Blended Zn-Pthalocyanene/C60 Films
• ~ 1:1 blend has highest mobility
• Tightly bound excitons
• Peak ~t=0 is from C60
• Is dissociation intermolecular?
h
e-
Nano-layered ZnPthalocyanine/C60 Films
0 10 20 30 40
-70
-60
-50
-40
-30
-20
-10
0
T (
a.u
.)
Time Delay (ps)
40 nm 50:50 Blend 20 nm 10 nm 5 nm
Ratio exp calc -------- ----- ------5/10 2.0 2.05/20 4.1 4.15/40 8.8 8.7
10/20 2.0 2.010/40 4.4 4.3
20/40 2.2 2.1
Exp ratio = I1 / I2 at 30 psCalc ratio = nint1 / nint2 for tfilm = 440 nm• Tightly bound excitons -> free carriers
• Exciton diffusion length is ~nm in few ps • Thinner alternating layer structure -> higher mobility
Carrier Population Persists Beyond 0.5 ns
0 100 200 300 400 500
-60
-50
-40
-30
-20
-10
0
-5 0 5 10 15 20-1.0
-0.8
-0.6
-0.4
-0.2
0.0
10 nm
5 nm
Diffe
ren
tia
l T
ran
sm
issio
n (T/T
o,
a.u
.)
Time Delay (ps)
T/T
o (N
orm
aliz
ed)
• Amplitude ratio extends beyond 0.5 ns
• Similar carrier diffusion and recombination processes
0 10 20 30 40
0
5
10
15
2020 nm
295 K 78 K
T/T
o
Time Delay (ps)
0 10 20 30 40
0
5
10
15
20 C60
295 78
T/T
o
Time Delay (ps)
0 10 20 30 40
0
5
10
1540 nm
295 K 78 K
Lock
-in S
igna
l (V
)
Time Delay (ps)
0 10 20 30 40
0
5
10
15
20
255 nm
350 K 295 K 78 K
T/T
o (a
.u.)
Time Delay (ps)
Photoconductivity versus Temperature
Summary THz FTIR and TDS spectrometers can collect low-frequency vibrational spectra of biomolecular solids and as solutes in dispersed aqueous micelle samples
Low frequency THz aqueous spectra obtained for L-Proline and Fructose model species Novel Time-Resolved THz measurements of conducting nanometer
organic thin-films reveals carrier mobility and efficiencies forscreening materials for semiconductor device applications
Future Prospects:
THz methods will be useful for determining water-phase biomolecular structure and solvent interactions
Modeling and theoretical advances (e.g., modified potential functions; add anharmonicity?) are needed to identify spectral features of hydrogen-bonded systems
Try similar approach on peptides and small proteins…
THz Spectra of Water in AOT Micelles
Optical pathlength = 4.2 mm
(~100 waters; d~4 nm)