1 Proteins: “ dopable - PowerPoint Presentation

Slide1

1

Slide2

Proteins:

“

dopable Solid-State Electronic Transport Materials

e

-

Slide3

“Traditional” methods to measure electron transfer in proteins

Flash-

quench

Pulse-

radiolysis

Electrochemistry

(ML on electrode)

Spectroscopy

(in solution)

Cyclic

Voltammetry

Chrono

-

amperometry

All these measure the

Electron transfer

r

ate

(s

-1

)

Slide4

From

electron transfer

to “solid-state”

electron transport

Goal:Understand how electron transport (ETp) via proteins in a 'dry'

configuration occurs and what influences it.Common approaches to measure solid state ETp:

CP-AFM

STM

Slide5

Protein layer

400 nm

150 nm

Slide6

Protein layer

IR

UV-Vis

Cytochrome

C

CD

CH-stretches

Slide7

Proteins survive partial

Dehydration



Suitable

…Proteins

are rather efficient solid-state transport medium

Co-factor is central 

proteins can be doped

Amide

backbone maybe

involved

in

elastic

transport

Functional and

dopable



★★★

Ultimate scientific goal:

Control & predict

electron

transport

across

proteins

Proteins as Electronic Transport Medium?

Slide8

Proteins on Today’s Menu

Natural electron transfer proteins

Azurin

Cytochrome

C

Not

an electron

transfer protein

Serum Albumin

Slide9

Our main experimental approach

Substrate – Smooth!

Protein layer – Dense, usually linked by a short linker

Top electrode – Suitable to contact soft matter

Conductive substrate

Electrical top contact

Idealized

Cartoon!

Slide10

Substrate

Highly doped Si

, Al(ox), Au

Controllable growth of thin oxide layer on SiLinker layer (“glue”)

<100> p

++-Si (< 0.001 Ω.cm)

SiO2

9-10Å

Propyl-silane

linker 6-8Å

Slide11

Au

Lift off float on (LOFO) -

Au

0.2 mm

2

~

10

7

-10

9

proteins/contact

Hanging Hg drop

Top Electrode

Slide12

Conductive probe AFM

Less defects

Force variation

Slide13

Idealized

Cartoons!

What does a nanoscale experiment look like?

A

10 nm

Metallic substrate

2

μ

m

Slide14

protein junction

Azurin

Device

figure from G.

Noy

and Y.

Selzer

,

Angew

. Chem. Int. Ed. (2010)

Electrophoretic nanowire assembly

of poly-peptide &

protein junctions - suspended nanowire method

Slide15

Current-voltage Characteristics of the different proteins

Same configuration

Same

temperature

Si p

++

SiO

2

SAM

propyl-silane

Slide16

What is the ETp mechanism?

Log conductance

Length (nm)

1

2

3

4

5

6

7

Tunneling

hopping

proteins

8

Net decay

Joachim &

Ratner

,

PNAS,

2005

16

Isied

,

JACS

2004

Gray and Winkler,

2003

Slide17

Hopping ………………

Super-exchange ……..

2-step tunneling ???

Thermally activatedTemperature-independentLower βvalues than for ET in solution

What is the ETp mechanism?

Slide18

1. Vary temperature2. Modify protein:

Remove the

intramolecular cofactorReplace cofactorAdd cofactor

Change binding (to electrode)Change orientation of protein

Not feasible with ET methodologies

What is the ETp mechanism?

Slide19

Temperature dependence

I-V -

Azurin

Azurin covalently bound to the surface

Sepunaru

et al., JACS 2011

Slide20

Cu ion removal

300

meV

Sepunaru

et al., JACS 2011

Slide21

Cu-Az

Ni-

Az

Co-

Az

Zn-

Az

Unpublished Results

Cu ion replacement

Slide22

Au

A

All metal (platinum)

Tip Bias (V)

Our setup

J. Davis

(Oxford)

setup

Our results (6-15 nN)

Literature results (6 nN)

Au

Li et al., ACS

Nano

2012

Connect to what was done before: Conductive probe AFM studies on

Az

Slide23

268K

358K

Temperature-dependent

conductive probe AFM

Holo-Az

Apo-

Az

Li et al., ACS

Nano

2012

Slide24

Force-dependent measurements

Holo-Az

Apo-

Az

Increased force

Increased currents

Same ETp mechanism

Increased force

Different ETp mechanism

Li et al., ACS

Nano

2012

Slide25

Temperature dependent

I-V with

Cyt c

100

meV

Fe

Iron-free

CytC

Holo-CytC

Apo-

CytC

Cyt

C

bound

electrostatically

(

physisorbed

) to surface

Amdursky et al., JACS 2013

What is the ETp mediator?

Slide26

Can we Control

ETp

?‘Doping’ Serum Albumin

Azurin

CytC

Apo-Az

HSA

Slide27

‘doping’ serum albumin with

hemin

Slide28

HSA

HSA-hemin

Amdursky et al., PCCP 2013

‘doping’ serum albumin with

hemin

Slide29

HSA

HSA-

hemin

95

meV

220

meV

HSA-

hemin

CytC

k

ET

=18.3 s

-1

k

ET

=4.8 s

-1

Amdursky et al., PCCP 2013

‘doping’ serum albumin with

hemin

Slide30

What is the ETp mediator?

The conjugated porphyrin ring

, rather than the Fe ion

is the main ETp mediator,

while

Fe

2+/3+

redox controls the transfer

in ET.

‘doping’ serum albumin with

hemin

Amdursky et al., PCCP 2013

Slide31

Ligand/protein

K

a

=4*10

5

Amdursky et al., JACS 2012

‘doping’ serum albumin with

retinoate

-

Can we increase

ETp

efficiency?

Slide32

Amdursky et al., JACS 2012

‘doping’ serum albumin with

retinoate

Slide33

The power of protein ‘doping’

Slide34

The importance of the contact to the electrodes and the orientation

Electrostatic (

physisorbed

) vs. Covalent (chemisorbed) binding

CytC

Amdursky et al., Submitted

Slide35

The importance of the protein’s orientation

Amdursky et al., Submitted

The importance of the contact to the electrodes and the orientation

Slide36

Cyt b562

ACS

Nano

2012, 355

Importance of the Protein’s Orientation

Previous

studies

Slide37

Amdursky et al., Submitted

Importance of the Protein’s Orientation

Slide38

Can we use existing models to describe

solid-state type of ETp?

Slide39

NO distance-current correlation!!!

Amdursky et al., Submitted

Importance of the Protein’s Orientation

Slide40

Clues from computational modeling

D

A

TP – tunneling pathway

Vs.

APD – atomic packing density

Probably, there is no specific pathway in the

ETp

process from one side of the protein to the other

Amdursky et al., TBP

Importance of the Protein’s Orientation

Slide41

Clues from computational modeling:

Cyt

C orientation

D

A

TP – tunneling pathway

vs

.

APD – average packing density

Probably, there is no specific pathway for

ETp

across the protein

Slide42

Conclusions

Electron transport through proteins can be measured by solid state configuration, both on the macro and the

nano

scalesThe electron transport mechanism can be investigated by Changing the temperatureModifying the proteinProteins can be viewed as electronic conducting material with the possibility of doping

The contacts to the electrodes and the orientation of the protein are of prime importance

Molecule

Room Temp. R (

Ω*nm2) for ~4 nm lengthConjugated

~10

7

- 10

9

DNA

~10

7

- 10

10

Proteins

~109 - 10

11Saturated~1018 - 1022

(extrapolated!)

Slide43

Dr. Ann

Erickson

Abd

Elrazek

Haj

Yahia

Dr.

Rotem

Har

Lavan

Dr. Omer

Yaffe

Dr.

Ayelet

VilanNir

K. KedemArava Zohar

Thanks to

students, PDs

& other colleagues

Acknowledgments

Minerva Foundation, Munich

43

Israel

Pecht

Mudi

Sheves

Slide44

Porphyrin- and apo-CytC

Slide45

ET vs. ETp

Waldeck

c.s. – PNA length dependence

ACS

Nano

(2013) 5391