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Lecture 5 Bioelectronics

Lecture 5 Bioelectronics

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Lecture 5 Bioelectronics

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  1. Lecture 5 Bioelectronics Nature’s transistors, rectifiers, capacitors ………..

  2. Current through your mitochondria [O2] ADP ADP ADP Time Slope  current

  3. The respiratory chain

  4. The mitochondrial battery Sugar E (mV) -400 0 +600 Drop in E across gaps is conserved as proton gradient for ATP synthesis O2+ 4H+ 2H2O

  5. Cytochrome c Oxidase An electron transfer-driven proton pump electrons H+ 5 metals ions 3 -redox centres CuA (Bi-nuclear Cu) Haem a Haem a3 - Cub Mitochondrialmembrane O2 + 4e- + 4H+ 2 H2O

  6. HQNO Protein based conducting pathways Formate Dehydrogenase

  7. Multielectron catalysts - molecular wires? Nitrite reductase NO2- + 10H+ + 8e- NH4+ + 2H2O Hydroxylamine oxidase NH2OH  HNO2 + 4H+ + 4e-

  8. Inspiration from Nature - molecular wires conducting in water 12nm

  9. Marcus Theory For non-adiabatic electron transfer between donor and acceptor separated by distance R. D-|A+ D|A kETis a function of: Distance between D and A Driving force

  10. Nature knows Marcus Theory Distance b ~ 1.4 Å-1 • Driving force • ~ 0.7 eV Page et al Nature (1998)

  11. A physicist’s current is a biochemists rate 1013s-1 = 1.6 µA 109s-1 = 0.16 nA 103s-1 = 0.16 fA Distance If b ~ 1.4 Å-1 then rate drops 10 fold every increase of 1.6Å between donor and acceptor

  12. _ _ + + Protein based conducting pathways - mobile carriers Interprotein electron transfer - the cytochrome c/cytochrome b5 paradigm • Stopped-flow kineticsOne of fastest known interprotein ET reactionsDiffusion limited at low I Still 108 M-1 s-1 at physiological I • Affinity measurements(by Spectrometry and potentiometry)Weak complex - KD 100µM at physiological I • Potential measurements at bulk equilibrium and by direct electrochemistry at surfacesCyt b5 redox potential goes up 40-80mV when bound to a positively charged surface

  13. Multihaem cytochromes - nature’s electrical contacts • React with solid metal oxides • Mobilisation of FeII from solid iron oxides • Reduction of soluble UVI to insoluble UIV oxides • Shewanella - 39 multihaem cytochome genes

  14. heterogeneous ET contact resistance 2D packing and interprotein ET + - Drain Source Surface attachment/localisation Bias application? Gating? A protein based transistor for nanotechnology?

  15. + - A biochemically gated transistor? Analyte

  16. Haem - a cofactor of choice 1.5nm • A conductor - cytochromes • A catalyst - P450’s • A carrier of dioxygen - globins • A sensor - for O2, CO, NO, oxidation state - globins, CooA, PAS etc

  17. COO- H3N+ COO- S S N N N N S S S S How do we connect electronically to proteins? Protein electrochemistry Needs functionalised surfaces - e.g. SAMs on gold, ‘Special’ Graphite Thiopyridine Small peptides

  18. AR NR AO NO Cytochrome c electrochemistry Electrochemically driven conformational change. i short timescale <100ms long timescale >1000s V Red Ox N-state His-Fe-Met +270mV A-state His-Fe-Lys -220mV

  19. 500bp – 170nm Electrochemistry and nanotechnology • AFM on DNA aligned proteins • Electrochemical AFM • Electrochemical STM • Test conductance of assembliese.g. two tip STM or patterned electrodes and conducting AFM tips