We studied the selectivity of a functional model of cytochrome c oxidase's active site that mimics the coordination environment and relative locations of Fe(a3), Cu(B), and Tyr(244). To control electron flux, we covalently attached this model and analogs lacking copper and phenol onto self-assembled monolayer-coated gold electrodes. When the electron transfer rate was made rate limiting, both copper and phenol were required to enhance selective reduction of oxygen to water. This finding supports the hypothesis that, during steady-state turnover, the primary role of these redox centers is to rapidly provide all the electrons needed to reduce oxygen by four electrons, thus preventing the release of toxic partially reduced oxygen species.
Surface arrays of single-stranded DNA are at the center of some of the most active areas in biological research. These include conventional applications in genome sequencing and disease diagnostics, as well as more novel emerging examples, such as combinatorial drug and reaction discovery. 1 Most methods of oligonucleotide immobilization rely on traditional nucleophilicelectrophilic reactions to achieve coupling of the oligonucleotide to the surface. 2 Unfortunately, this strategy is susceptible to side reactions, for instance, with amino groups on the nucleotides or the small molecule contaminants inherent to oligonucleotide synthesis. 3 Additionally, popular reactive electrophiles, such as N-hydroxysuccinimide esters, are prone to hydrolysis before and during the coupling reaction, which both reduce coupling yields and can make the yields irreproducible. 4 Accurate and reproducible detection of target oligonucleotides depends on the accuracy and reproducibility with which the surface can be functionalized. In this paper, we report a chemoselective approach to the formation of oligonucleotide probe surfaces using copper(I) tris(benzyltriazolylmethyl)amine (TBTA)-catalyzed triazole formation between a controlled density of azide groups on densely packed selfassembled monolayers (SAMs) and acetylene groups on the oligonucleotide probe to be immobilized. We have found this strategy to be highly predictable, very fast, and resistant to side reactions, unaffected even by the presence of excess nucleophilic or electrophilic impurities.Recently, we have demonstrated that Sharpless "click" chemistry can be used to covalently attach acetylene-bearing molecules to azide-terminated SAMs. 5,6 The surface reaction is quantitative and regioselective, exclusively yielding a single product at a single orientation. The chemistry is orthogonal to most typical organic transformations and thus is chemoselective. 7 Recent studies have demonstrated that the chemistry is well suited for the coupling of biomolecules to surfaces. 8 Although application of this chemistry to the attachment of oligonucleotides may appear straightforward, the majority of past work used free Cu(I), typically generated and maintained in aqueous solution by an excess of reducing agent. Unfortunately, in the presence of dioxygen, Cu(I) rapidly damages DNA via the generation of reactive oxygen species. 9 In order for a surface array of oligonucleotides to be useful as a sensor, the structure of the oligonucleotides must be preserved. Recently, the Sharpless group has introduced a triazolylamine copper ligand, tris-(benzyltriazolylmethyl)amine, that can accelerate the cycloaddition reaction. 10 At the same time, this ligand was found to significantly deter the redox chemistry of Cu(I) with oxygen, which is essential for preventing damage to the oligonucleotides. Encouraged by the highly desirable features of the Cu(I)TBTA-catalyzed azide-alkyne cycloaddition, we studied its applicability to the attachment of oligonucleotide probes onto well-defined SAMs.Oligode...
The rate of electron transfer is measured to two ferrocene and one iron tetraphenylporphyrin redox species coupled through terminal acetylenes to azide-terminated thiol monolayers by the Cu(I)-catalyzed azide-alkyne cycloaddition (a Sharpless "click" reaction) to form the 1,2,3-triazole linkage. The high yield, chemoselectivity, convenience, and broad applicability of this triazole formation reaction make such a modular assembly strategy very attractive. Electron-transfer rate constants from greater than 60,000 to 1 s −1 are obtained by varying the length and conjugation of the electron-transfer bridge and by varying the surrounding diluent thiols in the monolayer. Triazole and the triazole carbonyl linkages provide similar electronic coupling for electron transfer as esters. The ability to vary the rate of electron transfer to many different redox species over many orders of magnitude by using modular coupling chemistry provides a convenient way to study and control the delivery of electrons to multielectron redox catalysts and similar interfacial systems that require controlled delivery of electrons.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.