Generation of reactive intermediates

Generation of Reactive Intermediates via Photolysis of Transition-Metal Polyhydride Complexes... 

Scheme 1 Electrochemical generation of reactive intermediates for polar reactions.

Second, contraptions used for external generation of reactive intermediates are often quite bulky, which may impede the mobility of the experiment. Such contraptions may render it difficult to investigate a sample by several different kinds of spectroscopy. In principle it is possible, with the aid of a gate valve mounted on the vacuum shroud, to construct devices that allow one to retract and detach the external source of a reactive intemediate after a matrix has been built, but the implementation of this strategy is technically quite challenging because high vacuum must be maintained at all times within the cryostat. 

The methods for external generation of reactive intermediates are similar to those used in gas-phase experiments, that is, flash vacuum pyrolysis, passing a... 

Although it has been reported that adsorption is critical for the generation of reactive intermediates, there is still uncertainty as to the role adsorption plays and how it ultimately affects the reaction pathways [50,80]. These reports provide convincing evidence that LH and related kinetic models are good for predictive purposes, only indicative of apparent kinetics, and may be consistent with several different mechanisms. 

Mulder GJ, Kroese ED, Meerman JHN. The generation of reactive intermediates from xe nobio tics by sulphate conjugation and their role in drug toxicity. In Gorrod JW, Oelschlager H, Caldwell J, eds. Metabolism of Xenobiotics. London Taylor Francis, 1988. 

Sonication is a tool for improvement of chemical processes such as photocatalytic reaction. The improvements of reaction rates, yields and selectivity, the generation of reactive intermediate species and so on were reviewed.36) Some examples have been also shown in this chapter. The development of a new reaction pass by the combined effect of photocatalysis and sonolysis is expected in the near future. The contribution to Green Chemistry is one of typical examples. 

Biochemical and molecular toxicology consider events at the biochemical and molecular levels, including enzymes that metabolize xenobiotics, generation of reactive intermediates, interaction of xenobiotics or their metabolites with macromolecules, gene expression in metabolism and modes of action, and signaling pathways in toxic action. 

In this mode, an umpolung of reactivity for the nucleophile occurs, leading to many useful transformations. More complex pathways are not unusual these include addition to multiple bonds, vinylic and acetylenic substitution, rearrangements - some involving ring-expansion or ring-contraction - generation of reactive intermediates, etc. Solvent effects, especially solvent participation, may add new dimensions to reactivity. 

The typical one-electron redox reactions resulting from PET processes can be applied to control the generation of reactive intermediates similar to the way radical enz5unes are performing 112). To achieve an accmnulation of permanent reaction products, as is the case with most oxidoreductase enzymes and photos5mthetic systems, it is very important to provide suitable (photo)-catalytic multielectron transfer (MET) pathways. 

The use of DNA-electrochemical biosensors for the understanding of DNA interactions with molecules or ions exploits the use of voltammetric techniques for in situ generation of reactive intermediates and is a complementary tool for the study of biomolecular interaction mechanisms. 

When spectroelectrochemistry is used as a tool in reaction kinetics, it is important to know accurately the rate of generation of reactive intermediates, that is, the accurate potential of the working electrode. This requirement becomes a particular problem when an OTE is the preferred electrode because of the ohmic drop in the electrode itself and the nonuniform current distributions often encountered. For the OTTLEs in particular, the accurate modeling of the diffusion in the cell also leads to rather complicated mathematical equations [346]. The most profitable way of operation is therefore to use a potential-step procedure where the potential is stepped to a value at which the heterogeneous electron transfer reaction proceeds at the diffusion-controlled rate. In transmission spectroscopy the absorbance, AB(t), of the initial electrode product B, in the absence of chemical follow-up reactions, is given by Eq. (99) [347,348], where b is the extinction coefficient of B. 

Masubuchi N, Makino C, Murayama N. Prediction of in vivo potential for metabolic activation of drugs into chemically reactive intermediate Correlation of in vitro and in vivo generation of reactive intermediates and in vitro glutathione conjugate formation in rats and humans. Chem Res Toxicol. 2007 20(3) 455-464. 

Biotransformation and generation of reactive intermediate metabolites are associated with a variety of toxicities and idiosyncratic reactions.37 Toxicologists should always consider how drug disposition and fate contribute to toxicity, as target organ dosimetry, biotransformation, and detoxification reactions can be important determinants of toxicity. In all cases, understanding how biotransformation may differ across species, with emphasis on human metabolism, is an important component in determining whether preclinical effects are predictive of and relevant for human safety evaluation. 

PFIB is a strong electrophile which reacts with nucleophiles. The toxicity of PFIB may be correlated with its susceptibility to nucleophilic attack and the generation of reactive intermediates. 

Reactions carried out in nonprotic solvents using in situ generation of reactive intermediates have also been studied with A/-methylpyrrole as the substrate. Attempts to achieve good conversions using acetyl... 

Photochemical and Radical Reactions Most photoreactions in the field of nanotube chemistry serve to the generation of reactive intermediates that attack the nanotube afterward. The functionalizing step itself is rarely photochemical. Examples of such a preparatory step prior to functionalization include the conversion of azides into nitrenes or the radical generation from acyl peroxides, iodoalkanes, etc. In the photochemical reaction of nanotubes with osmium tetroxide, on the other hand, the essential step occurs only under irradiation. 

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