Presentation on theme: "Electrochemistry and molecular recognition. Non-Faradiac process: Process such as absorption or desorption, in which charge does not across the interface,"— Presentation transcript:
Electrochemistry and molecular recognition
Non-Faradiac process: Process such as absorption or desorption, in which charge does not across the interface, but external current can flow because of the surface potential change etc. (e.g. C d )
s = i + o Total current density IHP OHP Electrical Double Layer
300A (10 -2 M) Diffuse layer
Cyclic Voltammetry E = E i + vt (forward sweep) E = E s – vt (reverse sweep) I: initial S: Switching
Cell Design should exclude oxygen and moisture. Glove boxes or glove bags are necessary sometimes.
Solvents Should be stable to the redox conditions Electrolytes Bu 4 NBF 4 Bu 4 NPF 6 Bu 4 NClO 4 e.g. Bu 4 NPF 6 in CH 3 CN: +3.4 to –2.9 v
Working electrodes The WE should have a facile electron transfer with electroactive species. The factors behind are not well understood. Pretreatment or polishing of the electrode-surface is necessary. Pt, glassy carbon, gold, silver, amalgams are common materials for the WE.
Reference electrodes Electrode potential does not change when current increases.
Faradiac process: Electron transfer causes oxidation and reduction to occur. This process is governed by Faraday’s law (e.g. R)
E 1/2 = (E pc +E pa )/2 = E o + (RT/nF)ln where = (D(O)/D(R)) 1/2
CV for absorbed monolayer CV curve for reduction of absorbed O and sweep reversal. e p.1/2 = 3.53RT/nF
Schematic configuration of photoactivated molecular switches:
(A) Chronoamperometric responses of the assembly consisting of the ferrocene- functionalized -cyclodextrin threaded onto the azotranslocation benzene-alkyl chain and blocked by the anthracene barrier. (a) Monolayer in trans-azobenzene state. (b) Monolayer in cis- azobenzene state. (B) Cyclic variation of the electron transfer rates of trans the ferrocene- functionalized b-cyclodextrin in the molecular ‘train- shuttle’ upon reversible photoisomerization of the monolayer: ( )monolayer in trans-azobenzene state, ( ) monolayer in cis-azobenzene state.
(A) Cyclic voltammetric response of cytochrome c (0.1mM) at a mixed 6a/b and pyridine monolayer-modified electrode in (a) the 6a and (b) the 6b states. Inset: switching behavior of the system; circles and squares represent the photoisomerizable units in the spiropyran and the merocyanine states, respectively. (B) The same system with COx (1 M) and O2 and in (a) the 6a and (b) the 6b states. Inset: Switching behavior (as for part A).
From Enzyme to Molecular Device. Exploring the Interdependence of Redox and Molecular Recognition
Phenyl receptor 6a, which cannot form appreciable aromatic - aromatic contacts with bound flavin 1, causes an 18 mV shift in the E1/2 of flavin 1 to less negative values, accompanied by an enhancement of the reversible reoxidation wave. These two effects are indicative of the stabilization of Fl(rad) - by hydrogen bonding, as observed in the flavin 1 - receptor 2 complex. The -stacking receptors 6b,c, however, shift the flavin 1 E1/2 to more negative values, making flavin 1 harder to reduce.