Hydrogen translocations

Remote Functionalization C-H Activation. Substituted 7V (alkoxy)thiazolethiones have been applied in selective C-EI activation reactions. For example, 5-bromohydrins that serve as starting materials for succeeding polar transformations have been prepared from 7V-(l-pentyloxy)-5-(jO-methoxyphenyl)-4-methyl-thiazole-2(3//) thione and BrCCl3 (eq 8). This reaction is preferentially conducted under thermal conditions since the effectiveness of the underlying 1,5-hydrogen translocation benefits from elevated temperatures. ... 

Intramolecular HAS induced by reducing reagents has been intensively applied to obtain a large number of compounds, where either alkyl, vinyl, aryl, or heteroaryl radicals successfully add onto arenes [31b, 40]. Different synthetic strategies, such as ring expansion [41], ipso substitution [42], 1,5-hydrogen translocation, and tandem cyclization [43], among others, have been applied to afford important cyclic compounds such as phenanthridines [44], polycyclic arenes [45], 6//-benzo[c] chromen-6-ones [13a], and strained helicenes [46]. 

The use of radical translocation to generate cyclic radicals which can then add intramolecularly in a stereoselective manner to give addition products has been reported. The diastereoselective addition at C(4) of 1,3-oxazolidinones was examined using this approach. Thus, 1,5-hydrogen translocation from the aryl radical generated from (51) gives the C(4) radical, which can undergo radical addition to acrylate to furnish a 3 1 mixture of diastereomers (52). ... 

Another competing reaction is the intermolecular replacement of bromine by hydrogen in the radical translocating group. Additional approaches capitalizing on stereospecific hydrogen translocation to the anomeric radical have been described by Crich [186, 187]. Despite excellent stereoselectivity, the radical approach is rendered impractical by the circuitous methods needed for generation of the key anomeric radical [51]. 

SCHEME 25.36. A 1,5-hydrogen translocation to begin a radical process. 

The C-centered radical is thought initially to rearrange to a S-centered radical via a 1,3-hydrogen shift, followed by a radical translocation from sulfur to the silicon surface on the neighboring row. The abstraction of a H-atom from... 

Mitchell s chemiosmotic theory postulates that the energy from oxidation of components in the respiratory chain is coupled to the translocation of hydrogen ions (protons, H+) from the inside to the outside of the inner mitochondrial membrane. The electrochemical potential difference resulting from the asymmetric dis-... 

Figure 18.6 Energetics of the ORR at the heme/Cu site of CcO the enzyme couples oxidation of ferroc3ftochrome c (standard potential about —250 mV all potentials are listed with respect to a normal hydrogen electrode) to reduction of O2 (standard potential at pH 7 800 mV). Of the 550 mV difference, only 100 mV is dissipated to drive the reaction 220 mV is expanded to translocate four protons from the basic matrix compartment to the acidic IMS (inter-membrane space). In addition 200 mV is converted into transmembrane electrostatic potential as ferroc3ftochrome is oxidized in the IMS, but the charge-compensating protons are taken from the matrix. The potentials are approximate.

In series with a desolvation energy barrier required to disrupt aqueous solute hydrogen bonds [14], the lipid bilayer offers a practically impermeable barrier to hydrophilic solutes. It follows that significant transepithelial transport of water-soluble molecules must be conducted paracellularly or mediated by solute translocation via specific integral membrane proteins (Fig. 6). Transcellular permeability of lipophilic solutes depends on their solubility in GI membrane lipids relative to their aqueous solubility. This lumped parameter, membrane permeability,... 

Calcium oxalate monohydrate responsible for the formation of most kidney stones significantly increased mitochondrial superoxide production in renal epithelial cells [42], Recombinant human interleukin IL-(3 induced oxygen radical generation in alveolar epithelial cells, which was suppressed by mitochondrial inhibitors 4 -hydroxy-3 -methoxyacetophe-none and diphenylene iodonium [43]. Espositio et al. [44] found that mitochondrial oxygen radical formation depended on the expression of adenine nucleotide translocator Anti. Correspondingly, mitochondria from skeletal muscle, heart, and brain from the Antl-deficient mice sharply increased the production of hydrogen peroxide. 

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