Mariano Venanzivenanzi@uniroma2.it

Peptide-based Self-Assembled Monolayers as a Peptide-based Self-Assembled Monolayers as a New Tool for Bioinspired NanotechnologyNew Tool for Bioinspired Nanotechnology

Biosystems, Energy and Cultural Heritage: Materials Enhancement for Technological Applications

Rome, July 3 2013

Peptide Self-Assembled Monolayers

Au

Stable!

Easy!

Denselypacked!Ordered!

Smart!

• Sensing• Tissue Engineering• Electronics• Coating• Surface engineering

Peptide Self-Assembled Monolayers

Applications:Applications:

• Two case studies:

- Electron Transfer through peptide SAMs

- Photosensitive Polypeptide mimicking Elastin

Case study 1: ET through peptide SAMs A bicomponent peptide SAM formed by antiparallely oriented peptides

A8A8PyrPyr/SSA4/SSA4WWAA

Langmuir (2012) 28, 2817-2826Langmuir (2012) 28, 2817-2826

SSA4SSA4WWAA

A8A8PyrPyr

A8Pyr (bright dots in the STM image) protrudes by 2Å from the covalently linked SSA4WA monolayer.Each dots has a diameter of 1 nm, typical of 310-helix cross-section.Applied bias: 3.8 VIntensity: 60 pA

STM imagingSTM imaging

I/V curveI/V curve

Cu

rren

t (n

A)

Bias Potential (V)

The high symmetry of the I−V response suggests that there is not a preferred direction for ET, supporting the view of an antiparallel orientation of the two peptide chains.

Photocurrent Generation in anodic conditionsPhotocurrent Generation in anodic conditions

295

305315 325 335

345

355

A8Pyr/SSA4WAA8Pyr/SSA4WA

SSA6SSA6

AuAu

A8Pyr/SSA4WAA8Pyr/SSA4WA

PyrPyr

WW

e-

e-

δ-

δ-δ+

δ+

hhνν

junction effectjunction effect

Trp

dipole effectdipole effect

antenna effectantenna effect

Pathway I:Pathway I:through-bridgethrough-bridge+ through-space+ through-space

Pathway II:Pathway II:interchaininterchain

+ through-bridge+ through-bridge

(Au+-S-)

Antenna effectAntenna effect

A8Pyr/SSA4WAA8Pyr/SSA4WA

A8Pyr/SSA6A8Pyr/SSA6

Trp enhances the efficiency of inter-chain ET!

FcFc- CO(- CO(AdtAdt-Ala-Aib)-Ala-Aib)22OMeOMe

S S

CONH

Case study 1: ET through peptide SAMs A peptide horizontally layered on the gold surface

Fc = Ferrocene Adt

The linear dependence of the CV peak intensity on the scan velocity demonstrates that the peptide is covalently linked to the gold surface.

Ip = Nn2F2v/4RT

From this equation, the density of the bound Fc molecules can be easily obtained:

N = (2±1) 10-11 mol/cm2

-5 10-6

0

5 10-6

0.3 0.4 0.5 0.6 0.7 0.8 0.9

255075 100125150175200250

i (A

)

Voltage (V)

-4 10-6

-2 10-6

0

2 10-6

4 10-6

0 50 100 150 200 250 300

i (A

)

scan rate (mV/s)

0,5

1

1,5

2

2,5

3

3,5

0 0,1 0,2 0,3 0,4 0,5

ln (

i /

A)

t (s)

Y = M0 + M1*X

4,006M0

-19,437M1

0,99806R

Y = M0 + M1*X

1,3218M0

-1,5674M1

0,99372R

Chronoamperometry measurements show two different time decays of the current intensity, suggesting two locations of the Fc groups, characterized by different distances from the gold surface.

k(η) = k° exp [(1-α) nFη/RT]

k° = (13 ± 2) s-1

Dependence on the applied bias potential

k° = (1±0.5) s-1

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.4 0.6 0.8 1 1.2 1.4

delta E oxDelta E red

log 1/m

Vp

ox (V

)V

p re

d(V

)

α = (0.35±0.07)

XPS

100 200 300 400 500 600 700

O 1s

C 1s

N1s

Au 4d

Inte

nsi

ty (

arb

. units

)

Binding energy (eV)

Au 4f

170 168 166 164 162 160 158

FIT unbound unbound bound bound data

Inte

nsi

ty (

arb

. units

)

Binding Energy ( eV)

S 2p

161.5eV e 162.1eV bonded S

163.7 eV free S

165.3 eV oxidized S

Fc-CO-Aib-Ala-Aib-Adt-Ala-Aib-O-CH3

k0 = (11±3)s-1

-300 -250 -200 -150 -100 -50 0

y = 2.337 - 0.0014163x R= 0.92618

1

1.5

2

2.5

3

3.5

0 50 100 150 200 250 300

y = 2.4056 + 0.001441x R= 0.99191

Case study 2: A photosensitive SAM based on a polypeptide mimicking Elastin

C-[(VPGVG)C-[(VPGVG)22(VPGE(VPGE0.50.5G)(VPGVG)G)(VPGVG)22]]n n (AzoGlu15) (AzoGlu15)

λ=370 nm

Dark or λ=455 nm

E0.5 = 50% of Glutamic residues functionalized with azobenzene molecules

TransCis

Thermal (dark) cis→trans relaxation of AzoGlu15 in a phosphate buffer solution at pH=4 (T=10°C).

The trans isomer is more stable by ~50 kJ·mol-1, while the barrier for photoisomerization is ~200 kJ·mol-1.

CV experiments show that AzoGlu15 forms a densely-packed SAM on a gold surface, inhibiting almost completely the [Fe(CN)6]3+ discharge.Red: bare electrodeBlue: gold electrode modified by the linked AzoGlu15 SAM.

C-(VPGVG)C-(VPGVG)22(VPGE(VPGE0.50.5G)(VPGVG)G)(VPGVG)22]]n n (AzoGlu15) (AzoGlu15)

It shows a pH-dependent sol→gel Inverse Temperature Transition, driven by the extent of hydrophobic interactions.

T < TT < Ttrtr: ordered clathrate-like water structures surrounded the apolar groups. T>TT>Ttrtr: release of water molecules, collapse of polymer chains, phase separation.

pH=2.5

pH=4.0

pH=7.0

Sol→gel

Temperature

transition

pH 2.5 pH 4 pH 7

Trans 24±4 °C 26±4 °C 28±6 °C

Cis 29±4 °C 31±2 °C 33±3 °C

AzoGlu15 with azobenzene in the cis form is less hydrophobic than the trans isomer!

A photoswitchable system for photocurrent generationA photoswitchable system for photocurrent generationP

hoto

curr

ent (

nA)

Pho

tocu

rren

t (nA

)Time (s)

λ (nm)

Trans PG

Cis Abs

Trans AbsThe photocurrent spectrum

can be modulated by selective excitation of the cis or trans form, as determined by the cis-trans equilibrium in dark or ‘light-on’ conditions.

AzoGlu15 Photocurrent in the Trans form

Undecanthiol

Cis PG

Synthesis of conformationally-constrained peptidesSynthesis of conformationally-constrained peptidesClaudio Toniolo, Fernando FormaggioChemistry Dept. – University of Padova (Italy)

Synthesis of photoresponsive peptides mimicking ElastinSynthesis of photoresponsive peptides mimicking ElastinJosé C. Rodriguez-Cabello, Ana M. TexteraDept. Physics of Condensed Matter Dept. – University of Valladolid (Spain)

Lab. of Physical Chemistry of BiomoleculesLab. of Physical Chemistry of BiomoleculesAntonio PalleschiGianfranco BocchinfusoEmanuela Gatto (Photocurrent) Emanuela Gatto (Photocurrent) Claudia MazzucaLorenzo StellaMario Caruso (Photoresponsive polymer/ Adt peptides)Mario Caruso (Photoresponsive polymer/ Adt peptides)Chemistry Dept. Chemistry Dept. – University of Roma Tor Vergata– University of Roma Tor Vergata

Please, buy the book! I get royalties from Wiley.

Peptide Materials.From Nanostructures to Applications.

C. Aleman, A. Bianco, M. Venanzi Eds.

Wiley&Sons (2013)