(Protein) Electrochemistry. Outline

Transcription

1 (Protein) Electrochemistry Monday June 4, 2012 Sean J. Elliott, Boston University Outline Theory of Electrochemistry and Voltammetry Practical Details Electrocatalysis and analysis Alternatives: Potentiometry Data Analysis / SOAS / References

2 Theory of Electrochemistry & Voltammetry What is happening to i, E and t...

3 What is happening to i, E and t... What is happening in voltammetry? Bard and Faulkner, Electrochemical Methods

4 In diffusional voltammetry, concentrations of ox/red change in time and space Mass Transport: Fick s Laws for Diffusion c i c flux i = D i i x t = D i 2 c i x 2 I nf = D i c i x x=0 I nf A = D O c o (x, t) x x=0 Current always linked to Diffusion coefficient! Dealing with diffusion, with analytes in solution: ELECTRODE ROTATION Inevitably, we ll need to worry about diffusion, particularly with enzymes... but now, getting back to voltammograms

5 Potential Step Techniques O + n e- k1 k-1 R E2 I = nf D1/2 c 0 1/2 t 1/2 E1 t Coupled Reactions Preceding Chemical Reactions A B ± n e- B C Following Chemical Reactions A ± n e- B B C Catalytic Reactions A ± n e- B + Z B A + Y ECE Reactions A ± n1 e- B C ± n2 e- C B D

6 Preceding Chemical Reactions w/ Diffusion A O ± n e- k1 k-1 O R c A t = 2 c A x 2 + k 1(c 0 Kc A ) c O t = D 2 c O x 2 k 1 (c 0 Kc A ) if b= (Kk1t 1/2 ) It 1/2 = p b exp(b 2 )erfc(b) where p = nf D 1/2 c A Potential Sweep Techniques - Ultra Microelectrodes (UMEs) i(t) = nf AD1/2 o C o 1/2 t 1/2 (1 + ) = exp nf RT (E Eo ) i(t) = i d(t) 1 + = D 1/2 O D R E = E o lnd1/2 R nf D 1/2 O + RT + RT nf lni d( ) i( ) i( ) E = E 1/2 + RT nf lni d( ) i( ) i( )

7 i (E-E1/2) E = E 1/2 + RT nf lni d( ) i( ) i( ) Potential Sweep Techniques: Cyclic Voltammetry Bard and Faulkner, Electrochemical Methods

8 Enter, the voltammogram! American Conventions

9 European Conventions Reversibility

10 Considering coupled phenomena: preceding rxn A B ± n e- B C Considering coupled phenomena: following rxn A ± n e- B C B

11 What happens when following rxn is reversible or not? Multiple redox couples? Em = -180 mv -90 mv 0 mv +180 mv

12 Can you tell which is which?

13 A general solution to the issues of diffusion Immobilized E m backward scan ip α ν forward scan area α Coverage δ = 3.53RT n app F A quick case study: fcc3 Flavocytochrome c3 (fcc3) is a fumarate reductase from Shewanella species; some have been found to be ironresponsive, and multiple gene copies are found in many Shewanellas 1QJD.pdb

14 J. Am. Chem. Soc., 124 (20), , Biochemistry, 38 (11), , 1999

15 Leger and Bertrand, Chem Rev, 2008 Outline Theory of Electrochemistry and Voltammetry Practical Details Electrocatalysis and analysis Alternatives: Potentiometry Data Analysis / SOAS / References

16 Bard and Faulkner, Electrochemical Methods Bard and Faulkner, Electrochemical Methods

17 Electrode Design Shape: disk, rod, spheres, plates, hanging drop All typical macro-electrode Electrode Materials Gold: polycrystalline (wire), vapor deposited, flameannealed (111 surface) ITO/ATO: increasingly popular; optically transparent semiconductor carbon: HOPG, pyrolytic graphite, graphite particles, carbon felt, Ketjel black

18 Protein adsorption every protein is different On Graphite: co-adsorbates...? Mg 2+, [Cr(NH3)6] 2+ electrode aminoglycosides: polymixin, neomycin, tobramycin other polymers: poly-lysine cationic surfactants: DDAB (dimethyl didodecyl bromide) quasi-covalent attachment Protein adsorption On Gold: alkane thiol chain length X X X X X X X S S S S S S S electrode Avila, et al. J. Phys. Chem. B, 2000, 104 (12), pp X =...? hydrophobic, alcohol, amine

19 Protein adsorption every protein is different how to create a protein film = how to grow crystals variable protein trick ph AvFdI only acidic ph values work v. well concentration yeast CCP only dilute protein works concentration PDO only concentrated works set voltage SDH required a voltage of -0.2 V or less vs deposition with rotation deposition requires time NarGHI azurin slow rotation for minutes required at open circuit best behaved if incubated for hours at 4C, or minutes at 30 C requires co-adsorbates H2ase requires neomycin or polymixin inhibited by co-adsorbates cyt c554 on graphite, no co-adsorbates can be used Protein adsorption every protein is different of course, the method may also alter Em... N. europaea H. thermophilum co-adsorbates have been found to alter potential... Zu, et al. Biochemistry, 2003, 42, pp Ye, et al. Inorg. Chem., 2005, 44 (24), pp

20 Outline Theory of Electrochemistry and Voltammetry Practical Details Electrocatalysis and analysis: Examples Alternatives: Potentiometry Data Analysis / SOAS / References Interfacial ET rates The Laviron Method

21 Leger and Bertrand, Chem Rev, 2008 Determining ket: cytochrome c555 (soluble and membranous) from Aquifex aeolicus soluble form membrane form X X X X X vs X X X X S S S S S S S S S S electrode electrode FEBS Letters, Volume 539, Issues 1-3, 27 March 2003, p

22 H + Coupling in ET case study: Av FdI [3Fe4S] 0/2- [4Fe4S] 2+/1+ [3Fe4S] 1+/0 1FDD.pdb Duff, et al., J. Am. Chem. Soc., 1996, 118 (36), pp J. Am. Chem. Soc., 120 (28), , 1998

23 J. Am. Chem. Soc., 120 (28), , 1998 Electrochemical Catalysis: examples

24 Journal of Electroanalytical Chemistry Volume 562, Issue 1, 15 January 2004, Pages Electrochemical Catalysis

25 difference in o o EO/I - EI/R o E-Eo/r (V) Different Phenomena in Catalytic direct voltammetry Mass-Transport Control interfacial ET control Slow substrate-binding, slow product-release Redox-linked activation/deactivation Reversible Catalytic Chemistry Inter-protein or Intra-protein limitations Detection of redox-linked intermediates

26 Mass Transport Control Allochromatium vinosum NiFe H2ase Biochemistry, 38 (28), , Biochemistry, 40 (37), , E (mv vs SHE)

27 An alternative to CV: chronoamperometry NapAB: nitrate reductase Bertrand, et al. J. Phys. Chem. B., in press Reversible Redox Reactions Biochemistry, 40 (37), , 2001.

28 Complications from Substrate Binding Biochemistry, 43 (3), , Different Phenomena in Catalytic direct voltammetry Mass-Transport Control interfacial ET control Slow substrate-binding, slow product-release Redox-linked activation/deactivation Reversible Catalytic Chemistry Inter-protein or Intra-protein limitations Detection of redox-linked intermediates

29 Activation/Inactivation Cyclic voltammograms for a film of H2ase measured at different temperatures as indicated. Other conditions: 1 bar H2, scan rate 0.3 mv s-1, rotation rate 2500 rpm, ph 8.8. The vertical bar on the curves indicates the position of Eswitch. Arrows indicate the direction of the potential cycle. J. Am. Chem. Soc., 125 (28), , 2003 Intra-Protein Complications Chicken liver sulfite oxidase J. Am. Chem. Soc., 124 (39), , 2002

30 Outline Theory of Electrochemistry and Voltammetry Practical Details Electrocatalysis and analysis Alternatives: Potentiometry Data Analysis / SOAS / References Potentiometry Dutton, P.L. Methods in Enzymology, v. 54

31 Potentiometry Dutton, P.L. Methods in Enzymology, v. 54

32 R. Thauer, Bacteriol. Rev. 1977(41) Mediators Ferrocene Methanol, Ferroceneacetic acid Em7 = +440, +375 mv; n = 1 2-Hydroxyl-1,4-naphthoquinone Em7 = -145 mv, n = 2 Janus Green Em7 = -220, n = 2 Dichlorindophenol Em7 = +215, n = 2 Anthraquinone-2,6-disulfonate Em7 = -145 mv, n = 2 Anthraquinone-2-sulfonate Em7 = -185, n = 2 N-methyl phenazonium methosulfate (PMS) Em7 = 80 mv, n = 2 Safranine Em7 = -290, n = 2 N-methyl phenazonium ethosulfate (PES) Em7 = 55 mv, n = 2 N-methyl 1-hydroxyphenazonium methosulfate Em7 = -34 mv, n = 2 N,N -Dimethyl-1,4-bipyridinium dichloride Em7 = -430 mv, n = 1 N,N -Dibenzyl-1,4-bipyridinium dichloride Em7 = -311 mv, n = 1

33 Outline Theory of Electrochemistry and Voltammetry Practical Details Electrocatalysis and analysis Alternatives: Potentiometry Data Analysis / SOAS / References Data Analysis DigiSim - from BAS SOAS - from C. Léger

34 References Text books [1] Electrochemical Methods: fundamental and applications, Bard and Faulkner, (Wiley, 2004). [2] Compton, R. G. & Banks, C. E. Understanding voltammetry (Imperial College Press, 2011). [3] Newman, J. & Thomas-Alyea, K. E. Electrochemical systems (Wiley Interscience, 2004). [4] Levich, V. G. Physical hydrodynamics (Prentice-Hall, Inc., 1962). [5] Savéant, J. M. Elements of molecular and biomolecular electrochemistry (Wiley, 2006). Reviews [1] Direct electrochemistry of redox enzymes as a tool for mechanistic studies, Léger and Bertrand, Chemical Reviews, 2008 [2] Enzymes as working or inspirational electrocatalysts for fuel cells and electrolysis, Cracknell and Armstrong, Chemical Reviews, 2008