TY - JOUR
T1 - Kinetic separation of amperometric responses of composite redox-active monolayers assembled onto Au electrodes
T2 - Implications to the monolayers' structure and composition
AU - Katz, Eugenii
AU - Willner, Itamar
PY - 1997/6/25
Y1 - 1997/6/25
N2 - Chronoamperometry provides a sensitive method to elucidate the composition and properties of complex redox-active monolayers assembled onto Au electrodes. Chronoamperometry is applied to characterize a redox-active monolayer composed of a bisdiaminobenzoquinone dyad. The different distances of the quinone units in respect to the electrode yield different electron-transfer rate constants, k1 = 25.3 s-1 and k2 = 1.05 s-1, and the surface coverage of the two quinone units is estimated to be ΓQ. = 6.5 × 10-11 mol cm-2 ΓQz = 6.5 × 10-1 mol cm 2. The surface densities of the quinone units coincide nicely with those obtained by voltammetric analysis of the monolayer during the steps of its assembly. Similarly, a binary monolayer consisting of bipyridinium and anthraquione redox-active units was characterized by chronoamperometry. The electron-transfer rate constant to the bipyridinium and anthraquinone components corresponds to k1 = 503 s-1, and k1 = 62 s-1, respectively, and the surface coverage of the redox-active groups is ΓV2+ = 1.44 × 10-10 mol cm-2 and ΓQ = 0.46 × 10-10 mol cm-2. Kinetic separation of the amperometric response of a redox-active monolayer formed by the coupling of N,N'-bis(7-carboxyheptyl)-4,4′-bipyridinium, V2+-(CO2H)2, to a cystamine-modified monolayer on an Au electrode, reveals the formation of two redox-active group within the monolayer assembly: one redox-active form consists of a single-point attachment of V2+ -(CO2H)2 to the electrode, whereas the second form includes the bifunctional, two-point linkage of V2+-(CO2H)2 to the monolayer. The surface coverage of the two redox-active forms corresponds to Γ1 = 1.11 × 10-10 and Γ2 = 1.13 × 10-10 mol cm-2, respectively. The electron-transfer rate constants to the single-point-asaociated bipyridinium sites and to the two-point linkage bipyridinium units are k1 = 508 s-1 and k2 = 896 s-1, respectively. Chronoamperormetric analysis of microperoxidase-11 assembled as a monolayer on an Au electrode reveals that the heme-substituted oligopeptide binds to the surface by two different modes. These include the covalent linkage of carboxylic functions associated with the porphyrin ligand or the peptide backbone to the primary cystamine monolayer assembled onto the Au electrode.
AB - Chronoamperometry provides a sensitive method to elucidate the composition and properties of complex redox-active monolayers assembled onto Au electrodes. Chronoamperometry is applied to characterize a redox-active monolayer composed of a bisdiaminobenzoquinone dyad. The different distances of the quinone units in respect to the electrode yield different electron-transfer rate constants, k1 = 25.3 s-1 and k2 = 1.05 s-1, and the surface coverage of the two quinone units is estimated to be ΓQ. = 6.5 × 10-11 mol cm-2 ΓQz = 6.5 × 10-1 mol cm 2. The surface densities of the quinone units coincide nicely with those obtained by voltammetric analysis of the monolayer during the steps of its assembly. Similarly, a binary monolayer consisting of bipyridinium and anthraquione redox-active units was characterized by chronoamperometry. The electron-transfer rate constant to the bipyridinium and anthraquinone components corresponds to k1 = 503 s-1, and k1 = 62 s-1, respectively, and the surface coverage of the redox-active groups is ΓV2+ = 1.44 × 10-10 mol cm-2 and ΓQ = 0.46 × 10-10 mol cm-2. Kinetic separation of the amperometric response of a redox-active monolayer formed by the coupling of N,N'-bis(7-carboxyheptyl)-4,4′-bipyridinium, V2+-(CO2H)2, to a cystamine-modified monolayer on an Au electrode, reveals the formation of two redox-active group within the monolayer assembly: one redox-active form consists of a single-point attachment of V2+ -(CO2H)2 to the electrode, whereas the second form includes the bifunctional, two-point linkage of V2+-(CO2H)2 to the monolayer. The surface coverage of the two redox-active forms corresponds to Γ1 = 1.11 × 10-10 and Γ2 = 1.13 × 10-10 mol cm-2, respectively. The electron-transfer rate constants to the single-point-asaociated bipyridinium sites and to the two-point linkage bipyridinium units are k1 = 508 s-1 and k2 = 896 s-1, respectively. Chronoamperormetric analysis of microperoxidase-11 assembled as a monolayer on an Au electrode reveals that the heme-substituted oligopeptide binds to the surface by two different modes. These include the covalent linkage of carboxylic functions associated with the porphyrin ligand or the peptide backbone to the primary cystamine monolayer assembled onto the Au electrode.
UR - http://www.scopus.com/inward/record.url?scp=0031165883&partnerID=8YFLogxK
U2 - 10.1021/la961095e
DO - 10.1021/la961095e
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AN - SCOPUS:0031165883
SN - 0743-7463
VL - 13
SP - 3364
EP - 3373
JO - Langmuir
JF - Langmuir
IS - 13
ER -