Oxygen channeling

Peroxidases from saliva, crevicular fluid, bacteria, and fungi may contribute to this reaction in caries lesions. Although deeper layers of the carious microflora are assumed to be anaerobic, the oxygen required for the reaction may reach the deeper parts of the plaque via oxygen channels (Marquis, 1995). Lactobacilli, however, cause browning of dentin in the absence of tyrosinase (Dreizen et ah, 1957). 

In order to avoid the described problems, antibody-based assays have been developed. As mentioned above, usually a primary antibody recognizes the modification, which in turn is then quantitated. One of these approaches is based on the technology of AlphaScreen (Amplified luminescent Proximity Homogeneous Assay) [51, 52], also known as luminescent oxygen channeling immunoassay (LOCI) [53], a method that can be used to study protein-protein interactions in general. In this case the enzymatic transfer of acetyl groups to a histone peptide is determined. 

Ullman, E.F., Kirakossian, H., Singh, S., Wu, Z.P., Irvin, B.R., Pease, J.S., Switchenko, A.C., Irvine, J.D., DafForn, A., Skold, C.N. et al. (1994) Luminescent oxygen channeling immunoassay measurement of particle binding kinetics by chemiluminescence. Proceedings of the National Academy of Sciences of the United States of America, 91, 5426-5430. 

Murray J, Barber J. Structural characteristics of channels and pathway in photosystem II including the identification of an oxygen channel. J Struct Biol 2007 159 228-37. 

Trends in biochemical screening assays seem to favor the use of multi-function PMT-based readers that allow for various MTP well densities (96, 384, and 1536 well plates), can handle a number of readout formats such as prompt fluorescence, luminescence, fluorescence polarization, time-gated fluorescence, and luminescent oxygen channeling or AlphaScreen. Examples of this type including the Perkin Elmer EnVision, TECAN-Ultra, BMG FluoStar, and LJL Analyst GT can be employed for a variety of the assay technologies described above. 

Ullman, E.F. et al. 1994. Luminescent oxygen channeling immunoassay measurement of particle binding kinetics by chemiluminescence. Proc. Natl. Acad. Sci. USA 91, 5426-5430. 

Anderson, J.M. (2001) Does functional photosystem II complex have an oxygen channel, FBBS Lett. 488, 1-4. 

Oxidant Channel Mass Balance. Using the Faraday relationship as for the fuel, the consumption of oxygen in the oxygen channel of unit cell (k, ) becomes... 

Figure 3.37. Computed velocity fields (m/s) for flows in adjacent interdigitated oxygen channels (with gas diffusion layer on the left side) of a PEM fuel cell (A inlet, C outlet, in x-y plane). In the middle (B), the flow from one gas channel through the gas diffusion layer to the adjacent gas channel is shown in the z-y plane, for the midpoint of the cell extension in the z-direction. The flows in A and C are for the midpoint value of z. (From S. Um and C. Wang (2004). Three-dimensional analysis of transport and electrochemical reactions in polymer electrolyte fuel cells. /. Power Sources 125, 40-51. Used with permission from Elsevier.)...

Fig. 27 Local polarization curves at the indicated distances from the inlet of the oxygen channel (0 is at the inlet, 1 is at the outlet). Shown is the local polarization voltage versus local current density. All values are dimensionless.

UUman EF, Kirakossian H, Singh S, Irvin BR, Irvine JD, Wagner DB. Luminescent oxygen channeling immunoassay (LOCI) for human thyroid stimulating hormone. In Campbell AK, Kricka LJ, Stanley PE eds, Bioiuminescence and chemiluminescence. Fundamentals and applied aspects. Chichester Wiley, 1994 6-19. 

The Amplified Luminescent Proximity Homogeneous Assay (AlphaScreen ) developed by BioSignal, is a bead-based, non-radioactive assay technology. It uses the principle of luminescent oxygen channeling, which was first described in 1994 by Ullman [173], who two years later demonstrated a broad spectrum of applications for such immunoassays [174]. This principle senses the proximity of two beads, a donor and an acceptor bead, which is mediated by the interaction of molecules on the surfaces of the two beads. 

Fig. 6.25. Diagram of the various hypothetical channels for the oxidation of polyphenols in the presence of traces of oxygen channel A, formation of a free radical in C2 channel B, formation of an aryloxy free radical (de Freitas,...

Plastic membranes Longitudinal blood channel Longitudinal oxygen channel... 

The last assumption means that local electroosmotic flux of water in membrane is exactly counterbalanced by back diffusion. Recent studies [14,27] have shown that in a wide range of operating conditions total transfer coefficient of water from the anode to the cathode does not exceed 0.2. Since electroosmotic drag coefficient in Nafion is 1.5 [28], we conclude that the average over the cell surface electroosmotic flux in the membrane is almost fully compensated for by back diffusion. Note that the local value of total water flux in the membrane may significantly deviate from the surface-averaged value, e.g. close to the outlet of the oxygen channel [27]. Nevertheless, assumption 5 seems to be a reasonable approximation. 

Kulikovsky, A.A. (2009) Optimal shape of catalyst loading along the oxygen channel of a PEM fuel cell. Electrochim. Acta, 54, 7001-7005. 

Kulikovsky, A.A. (2002) Performance of a polymer electrolyte fuel cell with long oxygen channel. Electrochem. Commun.,... 

Figure 4.2 The profiles of (a) oxygen concentration and (b) local current density along the oxygen channel for the indicated values of oxygen stoichiometry A.

For A close to 1 the ratio j 0)/J is large (Figure 4.4(a)). Thus, the homogenization of local current by nonuniform catalyst loading protects the cell from large overcurrent at the oxygen channel inlet. 

The equations of the previous section allow us to take a next step by taking into account the potential loss resulting from the oxygen transport in the channel. Suppose that the cell has a straight oxygen channel. Let the coordinate z be directed along the... 

FIGURE 5.7 Schematic of a cathode side of the cell with the linear oxygen channel. 

Characteristic length of the conversion domain under poor oxygen transport (cm). Equation 1.87 Oxygen channel length (cm)... 

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