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Mariano Venanzi venanzi@uniroma2.it

Biosystems, Energy and Cultural Heritage: Materials Enhancement for Technological Applications Rome, July 3 2013. Peptide-based Self-Assembled Monolayers as a New Tool for Bioinspired Nanotechnology. Mariano Venanzi venanzi@uniroma2.it. Peptide Self-Assembled Monolayers. Smart!.

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Mariano Venanzi venanzi@uniroma2.it

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  1. Biosystems, Energy and Cultural Heritage: Materials Enhancement for Technological Applications Rome, July 3 2013 Peptide-based Self-Assembled Monolayers as a New Tool for Bioinspired Nanotechnology Mariano Venanzi venanzi@uniroma2.it

  2. Peptide Self-Assembled Monolayers Smart! Easy! Au Densely packed! Stable! Ordered!

  3. Peptide Self-Assembled Monolayers Applications: • Sensing • Tissue Engineering • Electronics • Coating • Surface engineering

  4. Outline • Two case studies: • Electron Transfer through peptide SAMs • Photosensitive Polypeptide mimicking Elastin

  5. Case study 1: ET through peptide SAMs A bicomponent peptide SAM formed by antiparallely oriented peptides A8Pyr/SSA4WA SSA4WA A8Pyr Langmuir (2012) 28, 2817-2826

  6. STM imaging 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 V Intensity: 60 pA I/V curve 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. Current (nA) Bias Potential (V)

  7. Photocurrent Generation in anodic conditions 325 315 335 305 345 295 355 A8Pyr/SSA4WA A8Pyr/SSA4WA Pyr SSA6 W Au

  8. What about the molecular mechanism of ET? e- e- Pathway II: interchain + through-bridge hν antenna effect δ+ Trp δ- dipole effect δ- δ+ Pathway I: through-bridge + through-space junction effect (Au+-S-)

  9. Antenna effect Trp enhances the efficiency of inter-chain ET! A8Pyr/SSA4WA A8Pyr/SSA6

  10. Case study 1: ET through peptide SAMs A peptide horizontally layered on the gold surface Fc- CO(Adt-Ala-Aib)2OMe Adt Fc = Ferrocene

  11. 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

  12. 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.

  13. Dependence on the applied bias potential k(η) = k° exp [(1-α) nFη/RT] k° = (13 ± 2) s-1 k° = (1±0.5) s-1

  14. α = (0.35±0.07)

  15. XPS 161.5eV e 162.1eV  bonded S 163.7 eV  free S 165.3 eV  oxidized S

  16. Fc-CO-Aib-Ala-Aib-Adt-Ala-Aib-O-CH3 k0 = (11±3)s-1

  17. Case study 2: A photosensitive SAM based on a polypeptide mimicking Elastin C-[(VPGVG)2(VPGE0.5G)(VPGVG)2]n (AzoGlu15) λ=370 nm Dark or λ=455 nm Trans Cis E0.5 = 50% of Glutamic residues functionalized with azobenzene molecules

  18. The trans isomer is more stable by ~50 kJ·mol-1, while the barrier for photoisomerization is ~200 kJ·mol-1. Thermal (dark) cis→trans relaxation of AzoGlu15 in a phosphate buffer solution at pH=4 (T=10°C). 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 electrode Blue: gold electrode modified by the linked AzoGlu15 SAM.

  19. C-(VPGVG)2(VPGE0.5G)(VPGVG)2]n (AzoGlu15) It shows a pH-dependent sol→gel Inverse Temperature Transition, driven by the extent of hydrophobic interactions. T < Ttr: ordered clathrate-like water structures surrounded the apolar groups. T>Ttr: release of water molecules, collapse of polymer chains, phase separation. pH=2.5 pH=4.0 AzoGlu15 with azobenzene in the cis form is less hydrophobic than the trans isomer! pH=7.0

  20. A photoswitchable system for photocurrent generation AzoGlu15 Photocurrent in the Trans form Photocurrent (nA) Undecanthiol Time (s) Trans PG Trans Abs The 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. Cis PG Photocurrent (nA) Cis Abs λ (nm)

  21. Synthesis of conformationally-constrained peptides Claudio Toniolo, Fernando Formaggio Chemistry Dept. – University of Padova (Italy) Synthesis of photoresponsive peptides mimicking Elastin José C. Rodriguez-Cabello, Ana M. Textera Dept. Physics of Condensed Matter Dept. – University of Valladolid (Spain) Lab. of Physical Chemistry of Biomolecules Antonio Palleschi Gianfranco Bocchinfuso Emanuela Gatto (Photocurrent) Claudia Mazzuca Lorenzo Stella Mario Caruso (Photoresponsive polymer/ Adt peptides) Chemistry Dept. – University of Roma Tor Vergata

  22. Peptide Materials. From Nanostructures to Applications. C. Aleman, A. Bianco, M. Venanzi Eds. Wiley&Sons (2013) Please, buy the book! I get royalties from Wiley.

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