Gradient, generation across the

Separations are usually performed isothermally. Temperature programming is impossible with wide bore columns owing to the uneven radial temperature gradients generated across the column diameter. Temperature programming is only possible with long, narrow bore columns, and then only slowly. Separated components are detected by a thermal conductivity or flame ionization detector connected to the column via a splitter, so that only a few percent of the total column flow is diverted to the detector. 

A recent review of bipolar electrochemistry focuses on the basic principles of controlling solution, rather than electrode potentials, and includes many demonstrated and possible applications [12]. The potential gradient generated across the bulk solution covering the electrode arrays controls the anode-to-cathode potential difference, which drives electrochemical reactions to generate optically detectable anodic products. Various wireless bipolar electrode array configurations and applications are considered. 

Figure 4. Finite element modeling results showing the stress gradient generated across the cross-section in rocket motor nozzles during the early stages of firing (red signifies tensile stress) [Pluscauskis, 2008]...

FIGURE 21.22 The proton and electrochemical gradients existing across the inner mitochondrial membrane. The electrochemical gradient is generated by the transport of protons across the membrane. 

Fig. 3-4 Electron transport process schematic, showing coupled series of oxidation-reduction reactions that terminate with the reduction of molecular oxygen to water. The three molecules of ATP shown are generated by an enzyme called ATPase which is located in the cell membrane and forms ATP from a proton gradient created across the membrane.

The rate of movement of a charged particle is also related to the voltage gradient applied across the supporting medium, which is quoted in volts per centimetre (i.e. the distance between electrodes). The current generates heat,... 

Isoelectric focusing is a procedure used to determine the isoelectric point (pi) of a protein (Fig. 3-21). A pH gradient is established by allowing a mixture of low molecular weight organic acids and bases (ampholytes p. 81) to distribute themselves in an electric field generated across the gel. When a protein mix-... 

Action potentials are waves of depolarization and repolarization of the plasma membrane. In a resting nerve cell, the electric potential gradient (At//) across the plasma membrane is about —70 mV, inside negative. This potential difference is generated mainly by the unequal rates of diffusion of K+ and Na+ ions down concentration gradients maintained by the Na+-K+ ATPase. 

M EXPERIMENTAL FIGURE 8-19 Electron transfer from reduced cytochrome c (Cyt c " ) to O2 via the cytochrome c oxidase complex is coupled to proton transport. The oxidase complex is incorporated into liposomes with the binding site for cytochrome c positioned on the outer surface, (a) When O2 and reduced cytochrome c are added, electrons are transferred to O2 to form H2O and protons are transported from the inside to the outside of the vesicles. Valinomycin and are added to the medium to dissipate the voltage gradient generated by the translocation of H, which would otherwise reduce the number of protons moved across the membrane, (b) Monitoring of the medium pH reveals a sharp drop in pH following addition of O2. As the reduced cytochrome c becomes fully oxidized, protons leak back into the vesicles, and the pH of the medium returns to its initial value. Measurements show that two protons are transported per O atom reduced. Two electrons are needed to reduce one O atom, but cytochrome c transfers only one electron thus two molecules of Cyt c are oxidized for each O reduced. [Adapted from B. Reynafarje et al., 1986, J. Biol. Chem. 261 8254.1... 

When there is concentration difference of solutes across an ion exchange membrane (driving force difference of chemical potential) the solute diffuses through the membrane. Thus, a diffusion potential corresponding to the concentration gradient is generated across the membrane. The flux of i through the membrane, J is expressed by the Nemst-Planck equation as... 

The blue oxidases are soluble extracellular enzymes (see, e.g., Messerschmidt ) whereas the terminal respiratory oxidases are membrane bound and use the free energy available from this reaction to pump protons across the membrane. The transmembrane proton and voltage gradient generated by the oxidase and other components of the aerobic respiratory chain is converted directly to more useful forms by a number of membrane-bound energy-conserving systems, such as the ATP synthase and secondary active transport systems (see, e.g., Calhoun et... 

The pumping of protons generates an electrochemical gradient (Ap) across the membrane composed of the membrane potential and the proton gradient. ATP synthase contains a proton pore through the inner mitochondrial membrane and a catalytic headpiece that protrudes into the matrix. As protons are driven... 

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