Insulation of the electrical contact between a redox protein and an electrode surface upon association of an antibody to an antigen monolayer assembled on the electrode is used to develop immunosensor devices. In one configuration, a mixed monolayer consisting of the N epsilon-(2,4-dinitrophenyl)lysine antigen and ferrocene units acting as electron transfer mediators is applied to sense the dinitrophenyl antibody (DNP-Ab) in the presence of glucose oxidase (GOx) and glucose. In the absence of DNP-Ab, the mixed monolayer electrode stimulates the mediated electrocatalyzed oxidation of glucose that results in an amplified amperometric response. Association of the DNP-Ab to the modified electrode blocks the electrocatalytic transformation. The extent of the electrode insulation by the DNP-Ab is controlled by the Ab concentration in the sample. In the second configuration, a N epsilon-(2,4-dinitrophenyl)lysine antigen monolayer assembled on a Au electrode is applied to sense the DNP-Ab in the presence of a redox-modified GOx, exhibiting electrical communication with the electrode surface. Two kinds of redox-modified "electrically wired" GOx are applied: GOx modified by N-(ferrocenylmethyl)caproic acid, Fc-GOx, and a novel electrobiocatalyst generated by reconstitution of apo-GOx with a ferrocene-modified FAD semisynthetic cofactor. Electrocatalytic oxidation of glucose by the electrically wired biocatalysts proceeds in the presence of the antigen monolayer electrode, giving rise to an amplified amperometric signal. The electrocatalytic transformation is blocked upon association of the DNP-Ab to the monolayer electrode. The extent of electrode insulation toward the bioelectrocatalytic oxidation of glucose is controlled by the DNP-Ab concentrations in the samples. The application of biocatalysts for amperometric sensing of antigen-antibody interactions at the electrode surface makes the electrode insensitive to microscopic pinhole defects in the monolayer assembly. The antigen monolayer electrode is applied to sense the DNP-Ab in the concentration range 1-50 micrograms mL-1.
Electron transfer processes in monolayer assemblies formed by covalent linkage of JV-methyl-JV'carboxyalkyl-4,4'-bipyridinium (1) to cystamine, chemisorbed onto gold electrodes, are examined. The resulting monolayer exhibits nonordered structure being reflected by a similar rate constant to the bipyridinium redox sites, that is independent of the bridging alkyl chain length, ket = 550 a-1. The nonordered structure is also confirmed by the low electron transfer coefficients aa and ac, corresponding to 0.25 ± 0.05 and 0.3 ± 0.05, respectively. By treatment of the nonordered monolayer assembly with 1-hexadecanethiol, CieSH, a more densely packed organized monolyer is formed, where the alkyl-substituted bipyridinium sites are stretched in the monolayer configuration. In these assemblies the electron transfer rate constants to the bipyridinium sites depend on the alkyl chain length bridging the redox site to the electrode. The electron transfer rate constants follow Marcus theory and the electron tunneling coefficient corresponds to ß = 0.006 A-1.
The monohydroxycalix[6]arene derivative 4a was prepared via photochemical bromination of hexamethoxycalix[6]arene 3a in aq THF. Monohydroxycalix[6]arene 4a and its chloro derivative 5 are useful synthetic intermediates for the preparation of structurally diverse calix[6]arenes functionalized at a single methylene bridge.
Reaction of dioxocalix[4]arene 7 with MeLi followed by 2-fold elimination of water yielded calixarene 8 possessing exocyclic double bonds at two adjacent bridges. Calixarene 8 exists in tetrachloroethane-d2 solution at rt, as a 2.3:1 mixture of the 1,3-alternate and partial cone conformers. Keto[n]calixarenes (n = 5, 6) were prepared via hydrolysis of the bromocalixarenes 11 and 12, followed by CrO3 oxidation of the respective hydroxymethylene derivatives. Addition of MeLi to the ketocalix[n]arenes (n = 4, 5 and 6) followed by elimination of water yielded the corresponding calix[n]radialenes. Calix[5]- and calix[6]radialenes adopt in the crystal irregular alternate (i.e., noncone) conformations.
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.