Self-assembled ferrocenyl

Towards a Two-terminal Solid-state Sensor for CO The CO Dependent Electrochemistry of Self-assembled Ferrocenyl Ferraazetine and 11-Ferrocenylundecyl Thiol. 

A CO Sensor Based Upon Self-assembled Ferrocenyl Ferraazetine. Having demonstrated the CO dependent solid-state electrochemistry of ferrocenyl ferraazetine, we synthesized a ferrocenyl ferraazetine molecule with disulfide functionality (Id). Scheme III. The specific aim was to design a CO sensitive molecule that could be confined to the working electrode of a two-terminal device via monolayer self-assembly techniques. Disulfides have been shown to irreversibly adsorb to Au and Pt surfaces (3-10). NMR and mass spectrometry are consistent with the proposed structure for compound Id. The FTIR spectrum of Id in THF exhibits metal carbonyl bands at 2067,2024,1989,1985 cm similar to the spectra for other ferraazetine derivatives la-c (2,5-6). Like derivatives la-c. Id reacts with CO (1 atm) at 298 K in CH2C12 to form a ferrapyrrolinone complex 2d, equation (3). 

Realization of two-terminal microsensors like that represented in Scheme I depends on the discovery of viable reference and indicator molecules that can be confined to electrode surfaces. Described herein are three different microelectrochemical sensing systems. The first is a three-terminal microelectrochemical sensing system for CO based upon an indicator molecule, ferrocenyl ferraazetine, that selectively reacts with CO (2). The second microelectrochemical system is based upon a disulfide functionalized ferrocenyl ferraazetine that can be adsorbed onto Au or Pt via monolayer self-assembly techniques. Efforts to make a two-terminal CO sensor based upon the... 

Scheme IV. Cross-sectional view of a two-terminal voltammetric microsensor based on the self-assembly of a hydroquinone thiol 5 and a ferrocenyl thiol 4 serving as reference and indicator respectively.

A number of important conclusions were drawn from this study, as follows. Electrochemical reversibility in electroactive self-assembled monolayers depends upon concentration and polarity of a covalently attached redox probe. Reversible surface electrochemistry is observed for the well-diluted ferrocenyl ester. However, reversibility decreases with steric congestion of redox probe because higher redox probe concentrations lead to disorder due to cross-sectional mismatch of the redox probe and the alkyl chain. Reversibility also decreases with a nonpolar redox probe the alkylferrocene (System 4) yields broad peaks with long tails positive of E°, consistent with kinetic dispersion of the redox probes and their differential solvation in the SAM. 

Ferrocenylated ODNs were first immobilized in a self-assembled redox-active monolayer on Au electrodes by Letsinger and co-workers.Upon hybridization of a complementary strand, the electrochemical potential of the ferrocene changes. In addition to applications as electrochemical DNA sensors, such self-assembled DNA monolayers with electro-active groups may provide information on the mechanism of electron transfer through DNA, and indirectly also on molecular mobility within short stretches of DNA. " We have recently extended this idea by the use of immobilized metallocene-labeled PNA on Au electrodes. Because PNA is an uncharged molecule, a surface with improved properties forms, and electrochemical detection, also of single mismatches, is facilitated. 

Physical properties of such mixtures can be manipulated by inserting special functional groups in bolas leading to optical-, electronic-, or magnetic-responsive materials as an example, by introducing a redox active group, such as a ferrocenyl head or disulfide bond, the mixed systems can be converted into redox switchable, self-assembled structures. ... 

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