Transcript Applications of High-Tc SQUID Magnetometers for Chemical

Biomedical & Biophysics Research at TcSUH:
Electromagnetic Properties of Biological Systems
John H. Miller, Jr.
Department of Physics and
Texas Center for Superconductivity
University of Houston
Summer 2005 Houston Quarknet Workshop
June 24, 2005
Fundamental Principles of biological systems
 Emergence:
Higher organizing principles emerge independently of the details of the
microscopic Hamiltonian. (Anderson, Laughlin, Pines).
 Information; Bioinformatics:
Biological systems carry, preserve, and replicate information. Information is
encoded via genetic code, sugar code, histone code, splicing code, gene
regulation code ...
 Convergent increase in complexity:
The information content in an organism is vastly greater than that of its
genome.
 Natural Selection; Evolution:
Similar principles may extend to non-biological systems (eg. language, music,
culture). In biology, evolution is partly driven by mutations.
TcSUH
2
Fundamental Principles (continued)
 Metabolism; Bioenergetics:
Living systems consume free energy: U – TS. The total energy is conserved
(Uin = Uout) so Sin << Sout. Organisms consume ‘negative entropy’: - S = k log
(1/Nstates). (Schrödinger “What is Life”.)
 Quantum Protectorate:
Quantum mechanics plays a crucial role in preserving information. Discrete
gaps between energy levels enable stability of molecules (DNA, proteins, etc.).
Lifetime of a molecule can be long: t ~ texp[D/kT], so at T ~ 300 K, if D ~ 1.8
eV, then t ~ 30,000 years.
 Biological systems are complex, dynamically evolving materials.
Condensed matter physics phenomena include: diamagnetism, charge
density waves, dielectric response, ferroelectricity, piezoelectricity,
quantum tunneling, excitons, and proposed biological
superconductivity.
TcSUH
3
Electromagnetic Interactions are vital to living systems.
 Electromagnetism is dominant in chemical and biological processes.
 Biological macromolecules (in water) are highly charged &/or have
strong electric dipole moments.
 Both repulsion and attraction (eg. in presence of Ca2+) can occur
between like charged polyelectrolytes.
 Electromagnetic interactions can be extended to long distances by
charge density waves, microtubules, etc.
 Live cells exhibit electromotility, especially outer hair cells.
TcSUH
4
Effects of an external electric field
 At low frequencies, most of the potential drop is across the plasma
membrane.
 Induced potential: Um(w,q) = 1.5 E0R cosq [1 + iwtm].
 5 V/cm field  Um ~ 15mV for a 20mm radius cell.
TcSUH
5
Oscillatory field affects membrane proteins.
 AC fields can actually drive cation transport in membrane pumps,
even in the absence of ATP (Tsong, Astumian, et al).
 Oscillatory fields also induce conformational changes.
 Resulting motion of electric dipoles and charges generates harmonics.
TcSUH
6
P-type ATPases
TcSUH
7
Nonlinear response: Measurement of induced harmonics
SQUID controller
SR 780 analyzer
SQUID
0-5 V
1-100 kHz
sample cell
(side view)
magnetic shield
1 cm
Au
pins
1.5 cm
N2(l)
dewar
sample cell
(top view)
cell suspension
 A sinusoidal electric field is applied to the cell suspension.
 At low frequencies (< 1 kHz) we use a SQUID to probe the currents.
 A spectrum of harmonics, induced by membrane pumps, is recorded.
(Nawarathna et al, APL
2004)
TcSUH
8
Probing membrane pumps in yeast cells
Variation of the third harmonic vs
Frequency
.8mM [VANADATE]
Yeast
Third harmonic a.u
250
200
3 V/cm
150
100
50
0
0
10
20
30
40
50
60
70
80
90
100
110
Frequency Hz
Variation of the harmonic vs Applied electrical
field
600
.8mM [VANADATE]
Cells
Third harmonic a.u
500
400
23 Hz
300
200
100
0
0
1
2
3
4
5
6
-100
Electrical field V/cm
TcSUH
9
Harmonic response of yeast after adding glucose
45 Hz
3 V/cm
TcSUH
10
Asymmetric Junction Model
AC voltage drives conformational changes & cation transport.
 Threshold voltages, V1 & V2, and time scales, t1 & t2.
TcSUH
11
Can probe internal organelles at kHz freqs.
ATP Synthase
TcSUH
12
Probing the mitochondrial electron transport chain
Nonlinear harmonic response
Budding yeast cells (S. cerevisiae)
ampl if ier c ircuit
biolo gical cells
test f ixtur e
I
R1
SR780 s ignal anal y zer
signal output
(single f requency )
Ch1
display
data out
uncoupled mitochondria
Peaks are suppressed by
adding potassium cyanide.
TcSUH
13
Electron Transfer via Quantum Tunneling
Pathway for ET from cytochrome c to active site of CcO
For a recent review see:
A. A. Stuchebrukhov, “Long-distance
electron tunneling in proteins,”
Theoretical Chem. Accounts, 110, 291
(2003).
Discovery of activationless ET:
DeVault & Chance (1966)
Theory of ET reactions: Rudolph
Marcus (Nobel Prize in Chem. 1992)
Pilet et al. (2004) PNAS 101, 16198
Analogy to Coulomb blockade
and time-correlated singleelectron tunneling.
Protein environment of the heme
rings a and a3. The dominant ET
pathway from heme a to a3 is
shown as a dotted line. (Tan et al.,
BPJ 86, 1813 (2004))
Iron atom in heme a = e- queing
point: feeds 4 e-s into an O2
molecule held at the Cu – Fe
active site at heme a3.
4e- + 4H+ + O2  2H2O
TcSUH
Section of a tunnel junction array from a CBT
sensor. The bright spots are tunnel junctions.
14
Probing the electron transport chain in chloroplasts
Nonlinear harmonic response in presence of light
Variation of the second harmonic vs frequency for cloroplasts
a mpl if ier c ircu it
R1
biolo gical cells
I
SR7 80 s ignal anal y zer
12
sign al ou tput
(sin gle f requ ency )
10
Ch1
d ispla y
Second Harmoinc mV
test f ixtur e
With out light
with light
8
6
4
2
0
0
data out
3
6
9
12
15
18
21
24
27
-2
Frequency kHz
30
30
With light
25
With Light
25
Light+K3FeCN2
Second Harmonic mV
Second Harmonic mV
Light+K3FeCN2
20
15
10
5
Light+K3FeCN2+NH4Cl
20
15
10
5
0
0
0
3
6
9
12
15
18
21
24
0
27
3
6
9
12
15
18
21
24
27
-5
-5
Frequency kHz
Frequency kHz
TcSUH
15
Photosynthetic electron transport chain
Absorption spectra of various chlorophylls
Frigaard et al. (1996), FEMS Microbiol. Ecol. 20: 69-77
Reaction center & light
harvesting complexes
of photosystem 2.
Theory:
Frenkel excitons in cylindrical aggregates
(Top view)
TcSUH
M. P. Bednarz, “Dynamics of Frenkel excitons in Jaggregates,” Ph.D. Thesis, Groningen, 2003.
16
Charge Density Waves
(A) Uncondensed and (B) condensed F-actin, mediated by charge-density wave of divalent cations.
T. E. Angelini, et al. PNAS 100, 8634 (2003).
Charge density waves also proposed to form in membranes.
TcSUH
17
Microtubules
Anisotropic diamagnetism reported for microtubules.
MTs also proposed to be ferroelectric.
a-b tubulin dimer
MT cytoskeleton
Very large dipole moment!
~ 1500 debye = 5 x 10-27 C m.
A microtubule may act as a ferroelectric with a “melting” temp. of ~57ºC.
Brown & Tuszynski, Phys. Rev. E 56, 5834 (1997).
TcSUH
18
Microtubules: Electrostatic Interactions
MTs radiating from centrosome
MT growth:
Analogy:
Electrostatic repulsion of hair.
1. During mitosis
Nanoscale electrostatics may play a
key role in prometaphase,
metaphase, and anaphase-A.
2. After depolymerization
(Moscow State University)
Intracellular pH peaks during mitosis.
Artificial mitotic spindle,
R. Heald, et al. (1996)
Nature 382, 420-425.
TcSUH
L. J. Gagliardi, J. Electrostatics 54, 219
(2002).
19
Live cells & proteins show dielectric responses
that decrease with frequency.
TcSUH
20
Tubulin dimer suspensions show strong dielectric response.
Free tubulin dimers become “frozen out” as they polymerize
(self-assemble) to form microtubules when T > 0º C.
 Reduced concentration of free dimers.
TcSUH
21
Tubulin dimer suspensions: conductivity vs. frequency.
TcSUH
22
Prestin:
A Membrane Protein Involved in OHC Electromotility
Has 12 transmembrane domains; may form a tetramer; high density (~1/(20nm2)) in membrane.
•
Mediates OHC length changes
to tune hearing frequencies
• has homology with sulfate transporters
• operates at microsecond rates up to 100kHz
• voltage-to-force converter
– Electromotility
– Cochlear amplifier
– Incomplete anion transporter
TcSUH
Zheng et al, Nature 405, 149 (2000).
23
P. Dallos & B. Fakler, 2002
Linear dielectric response:
Prestin-transfected yeast vs. control.
105
105
Control Yeast
104
εr
Prestin Yeast
104
εr
103
103
102
102
10
10
10
102
103
104
105
10
Frequency (Hz)
102
103
104
We see slight differences between S. cerevisiae
expressing prestin vs. control samples.
Miller et al., J. Biological Physics 2005.
105
Frequency (Hz)
D = ep(f)/ep(f=f0) - ec(f)/ec(f0).
Frequency range appears consistent w/ OHC piezoelectric resonances.
Rabbitt et al. 2004.
TcSUH
24
Other CMP Phenomena: Diamagnetism
High Field Magnet Lab – University of Nijmegen
Partly due to disipationless screening
currents in aromatic rings.
Anisotropic diamagnetism in
microtubules, actin, fibrin….
Lowest energy p orbital of an aromatic ring,
constructed from a superposition of pz-orbitals.
The p-electron moves freely in a torus
following the conjugation path of the molecule.
TcSUH
25
Biomedical Applications: Biomagnetism
 Magnetic fields produced by action potentials:
• Magnetoencephalography (MEG), MCG, MGG, MMG, MRG, etc.
Dr. George
Zouridakis prepares
a patient for MSI
epilepsy source
localization study at
Hermann Hospital,
Houston, Texas.
Examples of medial
temporal sources of
activity evoked
during a wordrecognition task.
TcSUH
26
Impedance Magnetocardiography (I-MCG)
•ECG measures the electrical potentials generated by bioelectric currents in the
heart.
•MCG measures the weak magnetic fields due to bioelectric currents resulting
from the propagating action potentials in the heart (eg. A. Brazdeikis)
•I-MCG measures changes in impedance during the cardiac cycle due, in part,
to changes in blood volume. Can probe cardiac ejection fraction and other
properties.
TcSUH
27
I-MCG Setup
Noise measurements inside
and outside the shield
1/2
field noise (nT/Hz )
1000
100
10
1
0.1
1
10
100
frequency (Hz)
TcSUH
28
ECG and I-MCG (a.u.)
I-MCG recording using High-Tc SQUID
1.0
0.5
0.0
-0.5
-1.0
1
2
3
time (seconds)
TcSUH
4
5
29
Simulated current density during the cardiac cycle
Atrial Systole
Diastole(I)
Current Density
j ( A/m2 )
1.620
1.466
1.313
1.159
1.005
0.852
0.698
0.544
0.391
0.237
0.083
Ventricular Systole
TcSUH
Diastole(II)
Current Density
j ( A/m2 )
1.620
1.466
1.313
1.159
1.005
0.852
0.698
0.544
0.391
0.237
0.083
30
Magnetic Resonance Imaging (MRI)
TcSUH
31
MRI: Twin-Horseshoe HTS 2-T Receiver Probe
(84.4 MHz, J. Wosik)
Patterned on a double sided
2” YBCO film on LaAlO3
The probe inside a plastic liquid
nitrogen cryostat
TcSUH
32
MRI: 2-Tesla MR Image of Rat
spinal-cord
4 dB gain
brain
TcSUH
33
Conclusions
• Physics concepts can contribute to understanding
of biological processes and lead to biomedical
applications.
• Experimental tools of condensed matter physics
and materials science can play an important role in
characterizing biological systems.
TcSUH
34
Acknowledgements
• University of Houston
– Jarek Wosik (MRI), Audrius Brazdeikis (MCG), D.
Nawarathna, Hugo Sanabria, Vijay Vajrala, James
Claycomb, Gustavo Cardenas, David Warmflash,
Jarek Wosik, William Widger, Jeffrey Gardner
• Baylor College of Medicine
– William Brownell, Fred Pereira
• Funding
– TcSUH, Welch Foundation,
– NASA-ISSO
TcSUH
35