Stopped fiow method

Following the original rapid-fiow experiments of Hartridge and Roughton, the introduction of the stopped-fiow method, and the use of electronic techniques for rapid recording,rapid-reaction techniques have found wide apphcation in chemistry and bio-... 

Among many different complexes that have been synthesized in attempt to mimic the structure and/or functionality of SODs (16-22), the most active SOD mimetics known to date are seven-coordinate Mn(II) complexes with macrocyclic ligands derived from C-substituted pentaazacyclopentadecane [15]aneNs and its pyridine derivative (Scheme 4) (12d,16a,23-25). Some of them possess SOD activity that exceeds the one of native mitochondrial MnSOD, and are the first SOD mimetics which entered clinical trials (12d,16a,23,26-28). A few Fe(III) complexes with the same type of ligands have also been studied and they are one of the best iron-based SOD catalysts (18). It should be stressed that the decomposition of superoxide catalyzed by these complexes has been quantified by direct stopped-fiow method, in the presence of a substantial superoxide excess over catalyst, as a reliable method for determining true SOD activity (29). 

The next group of [Ru(bpy)2L2] complexes to be considered involves pyridine-based ligands. The structural and spectroscopic properties of cM-[Ru(bpy)2(py)2] have been reported." Hydrolysis of ci5-[Ru(bpy)2(py)Cl] gives cw-[Ru(bpy)2(py)(H20)] with 80% retention of configuration. Retention of configuration also accompanies the oxidation of the latter to cis-[Ru(bpy)2(py)(0)] " ", racemization of which is slow the use of this Ru complex as a chiral oxidant has been examined." The kinetics of the comproportionation reaction between [Ru (bpy)2(py)(0)] " " and [Ru(bpy)2(py)(H20)] + in MeCN have been studied using stopped-fiow methods. The Ru product is unstable, and in MeCN solution undergoes disproportionation... 

Under steady-state conditions, the cleavage of this substrate obeys Michaelis-Menten kinetics with a. ST of 20 pM and a A of 77 s f The initial phase of the reaction was examined by using the stopped-fiow method. This technique permits... 

Most substituents (Cl, Me, OMe) in the 2-position have only a small effect, if any, on the hydration of the quinazoline cation they are similar in this respect to substituents in the 5-, 6-, and 8-positions (see above). Although hydration in the 2-aminoquinazoline cation was at first considered absent, a closer examination of the entire spectra of both species indicated that the cation spectrum may be that of a mixture. Hydration in the cation has now been confirmed by the rapid-reaction technique (the stopped-fiow method) which showed that the unstable hydrated neutral species had a half-life of 4.0 sec at 20° and pH 9. 60. The 2-hydroxyquinazoline cation has not been studied, but... 

Okhonin, V., Berezovski, M., Krylov, S. N. (2004a). Capillary electrophoresis a non-stopped-fiow method for measuring bimolecular rate constant of complex formation between protein and DNA. J Am Chem Soc 126, 7166-7167. 

Berthelot-1 usual FIA method. Berthelot-2 FIA method with a gas diffusion cell. Berthelot-3 FIA stopped-fiow method with a gas-diffusion cell. Indicator- spectrophotometric method (bromothymolblue) with GD cell. Indicator-2 as Indicator-1, but in the stopped-fiow mode. 

The chemical modification of hen egg-white lysozyme by AT-bromosuccinimide has been studied kinetically using the stopped-fiow method and previous results have been confirmed. One most rapidly reacting L-tryptophan residue (probably Trp-62) was clearly distinguished, by its rate of modification, from four other residues. The residue could be protected by ethylene glycol, chitin, 2-acetamido-2-deoxy-D-glucose, or chitotriose, but not by D-glucono-1,4-lactone. 

The rates of formation and dissociation of cyano-bridged dimers of the type [(CN)5Fe iCNCo iiL5] - and [(CN)5CoCNCo(en)2S03] have been investigated by the stopped-fiow method. Dinuclear complexes are formed on treating the trans-[Co(en)2(S03)(OH2)]+ ion with [Fe(CN)6NO] -, [FeCCN) ] - and [Fe(CN)e] - ions. For example,... 

Table 2 Seiected appiications iiiustrating the advantages of the stopped-fiow technique over equiiibrium methods...

Ephedrine/phenylephedrine IO4- Use of stopped-fiow mixing. Absorbance resulting from formazan formation was monitored at 620 nm. Method of proportional equations... 

Other devices for extraction with trapping of droplets using an ultrasonic nanoliter liquid droplet ejector [41] and multiple opening rectangular recesses [42] have also been developed. As another method of trapping fluids. Sun et al. developed a micro structured device for extraction with stopped-fiow manipulation [43]. 

Most of these investigations were performed using chemical relaxation methods, ultrasonic absorption relaxation for the exchange process and T-jump, p-jump, or stopped-fiow for the micelle formation/breakdown. More recently, NMR methods have started to be used for the same purpose. 

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