A series of ferrocene (Fc)- and cystamine (CSA)-labeled peptides of the sequence [Fc-(Pro-Pro-Gly) n -CSA]2, where n = 1−3, was synthesized and characterized. Peptide 3 forms a trimeric supramolecular structure held together with extensive hydrogen bonding and adopts a collagen-like motif in solution. Cyclic voltammetry (CV) and chronoamperometry (CA) were used to calculate electron-transfer (ET) kinetics. ET rates were 10.9 (2.3) × 103, 6.6 (1.9) × 103, and 4.2 (1.2) × 103 s-1 for peptides where n = 1, 2, and 3, respectively. The peptides, under deuterated conditions (D2O, full exchange of H for D), showed rate constants of 7.3 (1.3) × 103, 5.8 (1.0) × 103, and 3.4 (0.5) × 103 s-1 for n = 1, 2, and 3, respectively. A linear dependence of the ET rate constant and distance is found.

Gold electrodes modiÐed by monolayers of three di †erent long-chain thiol derivatives were studied by electrochemical impedance spectroscopy with a redox probe over a wide temperature range. [Fe(CN) 6 ]4~@3T he impedance characteristics of a bare gold electrode are compared to those of the same electrode modiÐed with n-hexadecanethiol, n-octadecanethiol, and 11-mercaptoundecanoic acid, all between 15 ¡C and 65 ¡C. A strong temperature dependence of the ÐlmsÏ electrical features was observed. All Ðlms show markedly di †erent behaviour below and above a characteristic temperature speciÐc to each Ðlm. It was possible to model bare gold and the thiol-modiÐed electrodes with the Randles circuit over the whole temperature range examined, except for the 11-mercaptoundecanoic acid-modiÐed electrode below its characteristic temperature, which required a di †erent equivalent circuit. Cyclic voltammetry was used to verify the characteristic temperature of each Ðlm. The results are interpreted in terms of a two-dimensional phase transition in these monolayers. The possible nature of this phase transition is discussed.

Langmuir-Blodgett (LB) monolayers of two thiol derivatives-hexadecanethiol (HDM) and octadecanethiol (ODM)-were investigated with regards to behaviour previously reported for self-assembled monolayers (SAMs) of the same compounds (ref. 1, S. H. Gyepi-Garbrah and R. S ˇilerova ´, Phys. Chem. Chem. Phys., 2001, 3, 2117), in order to compare the effects of each film-forming strategy. Langmuir films of HDM and ODM were studied at the air/water interface on a 0.01 M ammonium chloride subphase between 8 and 20 C. The films were more stable at lower temperatures. Monolayers of HDM and ODM were transferred onto gold electrodes at 8, 12 and 16 C by the LB technique. Transfer at 8 C was the most successful, and so the electrical properties of LB films deposited at this temperature were studied by electrochemical methods as a function of temperature from 10 to 65 C in 0.1 M KCl/3 mM [Fe(CN) 6 ] 4À/3À . Cyclic voltammetry and ac impedance spectroscopy revealed temperature dependent behaviour similar to that reported earlier in analogous SAMs of HDM and ODM (ref. 1, S. H. Gyepi-Garbrah and R. S ˇilerova ´, Phys. Chem. Chem. Phys., 2001, 3, 2117). In particular, a transition temperature characteristic for each film was observed as in the SAMs, above and below which the film's electrical properties differed markedly. These temperatures appear to be independent of the method of film formation (LB deposition or self-assembly). However, a comparison of the absolute electrical properties of the LB films and the SAMs suggests that the LB deposition process, in which molecular organization precedes chemisorption, produces films that are more highly organized than those produced by the self-assembly process, in which chemisorption precedes molecular organization.

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