Redox sensors

Recently, Astruc et al. [189] reported novel amido-ferrocene dendrimers (e.g., 91) which were shown to act as supramolecular redox sensors for the recognition of small inorganic ions (Fig. 41). It was further observed that as the den-drimer generation number increased the sensitivity to the guest molecules also increased as observed by cyclic voltammetry experiments. 

Wilson HL, Dipp M, Thomas JM, Lad C, Galione A, Evans AM 2001 ADP-ribosyl cyclase and cyclic ADP-ribose hydrolase act as a redox sensor. A primary role for cyclic ADP-ribose in hypoxic pulmonary vasoconstriction. J Biol Chem 276 11180-11188... 

RegB Histidine protein kinase Redox sensor RegB 37 53 Global regulation... 

Vinokurov lA. A new kind of redox sensor based on conducting polymer-films. Sens Actual B... 

Lemmon, T.L., J.C. Westall, and J.D. Ingle, Jr. 1996. Development of redox sensors for environmental applications based on immobilized redox indicators. Anal. Chem. 68, 947-953. 

Recognition of fluoride in aqueous media is particularly difficult due to the strongly hydrated nature of the anion. Shinkai and co-workers have demonstrated that ferrocene-boronic acid 27 acts as a selective redox sensor for fluoride which operates in H20 [23]. The favourable interaction between boron and fluoride (a hard acid and hard base, respectively) generates a stability constant of 700 M"1 for the fluoride-ferrocenium complex. Stability constants for both the bromide and chloride complexes are <2 M"1. 

Trx and Grx being the key redox sensors, their functions are modulated by ROS. While at a lower dose, ROS can induce their expression, thereby eliciting an adaptive response massive generation of ROS inactivates these proteins by posttranslational modifications (Kondo et al. 2006). In heart failure patients, a significant correlation between the serum concentration of Trx-1 and the severity of the disease has also been documented (Jekell et al. 2004). The increased Trx-1 activity is likely to be due to the adaptive response during the failure to compensate for the increased ROS activities. 

Lillig, C.H., Bemdt, C., Vergnolle, O., Lonn, M.E., Hudemann, C., Bill, E., and Holmgren, A. 2005. Characterization of human glutaredoxin 2 as iron-sulfur protein a possible role as redox sensor. Proc. Natl. Acad. Sci. USA 10 8168-8173. 

Keywords Anion ATP Dendrimer Halide Nanoparticle Organometallic Redox Sensor... 

Redox potential is measured potentiometrically with electrodes made of noble metals (Pt, Au) (Fig. 12). The mechanical construction is similar to that of pH electrodes. Accordingly, the reference electrode must meet the same requirements. The use and control of redox potential has been reviewed by Kjaergaard [218]. Considerations of redox couples, e.g. in yeast metabolism [47], are often restricted to theoretical investigations because the measurement is too unspecific and experimental evidence for cause-effect chains cannot be given. Reports on the successful application of redox sensors, e.g. [26,191], are confined to a detailed description of observed phenomena rather than their interpretation. 

The application of a redox sensor in a control loop has been reported by Memmert and Wandrey [274] who controlled xylanase production of Bacillus amyloliquefaciens by defined oxygen limitation redox electrodes refer essentially to dissolved oxygen concentration below 10 mmol 1 102. This property was also promoted to determine the quality of anaerobic processes [403]. 

Redox series of metal-polypyridines still await their practical exploration. The existence of multistep, reversible, sequential reduction processes, each step occurring at a defined potential and being localized at a specific molecular site, is very promising for possible applications in molecular electronics. This would require to organize the active complexes in films, polymers or supermolecules. Up to now, only the electrochromic behavior of some [Ru(N,N)a] + complexes has been explored with potential applications in electrochromic glasses, displays and redox sensors [206, 262, 264]. 

Pownceby M. 1. and O Neill H. St. C. (1994) Thermodynamic data from redox reactions at high temperatures IV. Calibration of the Re-Re02 oxygen buffer from EMF and NiO -I- Ni — Pd redox sensor measurements. Contrib. Mineral. Petrol. 118, 130-137. 

Valerio C, Fillaut J-L, Ruiz J, Guittard J, Blais J-C, Astruc D (1997) The dendritic effect in molecular recognition ferrocene dendrimers and their use as supramolecular redox sensors for the recognition of small inorganic anions. J Am Chem Soc 119 2588-2589... 

Zhang QH, Wang SY, Nottke AC, Rocheleau JV. Piston DW. Goodman RH (2006) Redox sensor CtBP mediates hypoxia-induced tumor cell migration. Proc Natl Acad Sci USA 103 9029-9033... 

As illustrated in Fig. 1, methionine synthase is positioned at the intersection between transsulfuration and methylation pathways. As a consequence, its level of activity exerts control over cellular redox status, since it determines the proportion of HCY that will be diverted toward cysteine and GSH synthesis. Methionine synthase activity is exceptionally sensitive to inhibition during oxidative stress, primarily because its cobalamin cofactor is easily oxidized (Liptak and Brunold, 2006). This allows methionine synthase to serve as a redox sensor, lowering its activity whenever the level of oxidation increases, until increased GSH synthesis brings the system back into balance. Electrophilic compounds, such as oxygen-containing xenobiotic metabolites, also react with cobalamin, inactivating the enzyme and increasing diversion of HCY toward GSH synthesis (Watson et al., 2004). Thus, methionine synthase is a sensor of both redox and xenobiotic status. 

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