Redox-active probe molecules

An alternative approach for utilizing DNA thin films for electrochemical sensors involves using redox-active probe molecules intercalated into the Ji-stack. Fig 5-lb. This approach has been successfully employed in the design of electrochemical assays for hybridization,single-base mismatches, and chemical modifications and lesions within duplex DNA. It has also provided provocative experimental results regarding charge transport through the double helix. ... 

The aptamer described above was attached to the surface of the silica colloidal crystal comprising 290 nm silica spheres (resulting in 22.5 nm radius nanopores) via maleimide-activated support. The transport rate of a redox-active probe molecule (ferrocene dimethanol) through the resulting nanoporous films was measured as a function of cocaine concentration using cyclic voltammetry. A neutral redox probe, Fc(CH20H)2, was used to exclude the possibility that the observed changes in the molecular transport would result from electrostatic effects [26,27]. 

Different stimuli could trigger the transition of the smart polymer making it possible to produce membranes whose permeabihties respond to these stimuh. When a copolymer of NIPAAM with triphenylmethane leucocianide was grafted to the membrane, it acquired photosensitivity—uv irradiation increases permeation through the membrane (78). Fully reversible, pH-switchable permselectivity for both cationic and anionic redox-active probe molecules was achieved by depositing composite films formed from multilayers of amine-terminated dendrimers and poly(maleic anhydride-co-methylvinyl ether) on gold-coated silicon (79). 

Aptamer based biosensors, for example for recombinant human erythropoietin (as model analyte), can be made more sensitive by amplification with a boronic acid tethered gold nanoparticle that is then associated with an alkaline phosphatase to produce a redox active probe molecule. A similar re-usable bio-immuno-sensor has been suggested for carcinoembryonic antigen. A phenylboronic acid is assembled on gold to (reversibly) bind the antibody horseradish peroxidase conjugate. Interaction with the antigen slows down the hydrogen peroxide reduction. An HIV-1 immunoassay based on electroluminescence has been proposed by Zhou etaV In this process the... 

The interfacial capacitance can also provide a significant insight into the permeability of interfacial supramolecular assemblies. While information of this kind complements studies using redox-active probes in solution, it also provides information on a significantly shorter length scale, i.e. that of electrolyte ions and solvent molecules. For example, for dense, defect-free monolayers, the limiting capacitance is very much lower (5-10 pF cm-2) than that found for an unmodified interface (20-60 pF cm 2). 

The main framework is made up of five key modules for chemical library editing, enumeration, conversion, visualization, and analysis. The operations of these functionalities are accomplished by the various applications at the resource layer. For the purpose of illustration, the compound calothrixin B, a secondary metabolite isolated from the Calothrix cyanobacteria (11-13), is used as the scaffold molecule with the variable functional groups Rw] attached (Fig. 18.1). The calothrixins are redox-active natural products which display potent antimalarial and anticancer properties and thus there is interest in probing the physical as well as biological profiles of their derivatives (14). In this exercise, six functional groups have been selected as the building blocks (Table 18.1). 

The active site on the surface of selective propylene anmioxidation catalyst contains three critical functionalities associated with the specific metal components of the catalyst (37—39) an CC-H abstraction component such as Bi3+, Sb3+, or Te4+ an olefin chemisorption and oxygen or nitrogen insertion component such as Mo6+ or Sb5+ and a redox couple such as Fe2+/Fe3+ or Ce3+/ Ce4+ to enhance transfer of lattice oxygen between the bulk and surface of the catalyst. The surface and solid-state mechanisms of propylene ammoxidation catalysis have been determined using Raman spectroscopy (40,41), neutron diffraction (42—44), x-ray absorption spectroscopy (45,46), x-ray diffraction (47—49), pulse kinetic studies (36), and probe molecule investigations (50). 

Investigations of protein-protein ET reactions have provided important insights into biological electron flow [10-14]. Natural systems, however, often are not amenable to the systematic studies that are required for evaluation of the key ET parameters 2 and Nab- A successful alternative approach involves measurements of ET in metalloproteins that have been labeled with redox-active molecules [15-19]. By varying the binding site and chemical composition of the probe molecule, it has been possible to elucidate the factors that control the rates of long-range ET reactions in proteins. 

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