Chemical Uncouplers

Clearly, from the discussion above, many different classes of chemistry could theoretically satisfy the physicochemical requirements for uncoupling. This is also the case in practice, with a wide range of different chemical types showing fungicidal (and wider agrochemical) effects. Table 13.4.1 lists a selection of the most important of these, along with some key references. 

Although all of the chemical classes in Table 13.4.1 have activity against plant pathogenic fungi, commercially three are of particular interest dinitrophenols, arylhydrazones and diarylamines. 

The dinitrophenols were the first group of uncouplers to be commercialized, and representatives of this group have found use as herbicides, insecticides/ acaricides and fungicides. However, several have been superseded due to their toxicity and lack of selectivity. 

The most significant of the dinitrophenols still used as a fungicide is dinocap, marketed by Dow under the trade name Karathane. This compound is sold as a 

Pro-pesticide of active phenol (dinoseb) largely superseded 

---

FIGURE 19-19 Two chemical uncouplers of oxidative phosphorylation. Both DNP and FCCP have a dissociable proton and are very hydrophobic. They carry protons across the inner mitochondrial membrane, dissipating the proton gradient. Both also uncouple photophosphorylation (see Fig. 19-57). 

DNP is a chemical uncoupler of electron transport and oxidative phosphorylation. 

Uncoupling of respiration from phosphorylation can also be achieved chemically. Chemical uncouplers such as DNP or FCCP act by dissipating the proton gradient. Addition of an uncoupler to mitochondria stimulates oxygen utilization even in the absence of added ADP. No phosphorylation occurs under these... 

Chemical uncouplers, also known as proton ionophores, are lipid-soluble compounds that rapidly transport protons from the cytosolic to the matrix side of the inner mitochondrial membrane (Fig. 21.11). Because the proton concentration is higher in the intermembrane space than in the matrix, uncouplers pick up protons from the intermembrane space. Their lipid solubility enables them to diffuse through the inner mitochondrial membrane while carrying protons and release these... 

Chemical uncouplers can also influence cell fate other than through depletion of ATP [153, 154] and their action to depolarize membranes outside of the mitochondrion also needs to be considered with respect to their overall effects on the target cell or organism for instance, they have been shown to dissipate plasma membrane potential and to destabilize lyzosomes [155, 156]. 

The timescale is just one sub-classification of chemical exchange. It can be further divided into coupled versus uncoupled systems, mutual or non-mutual exchange, inter- or intra-molecular processes and solids versus liquids. However, all of these can be treated in a consistent and clear fashion. 

Solution—Diffusion Model. In the solution—diffusion model, it is assumed that (/) the RO membrane has a homogeneous, nonporous surface layer (2) both the solute and solvent dissolve in this layer and then each diffuses across it (J) solute and solvent diffusion is uncoupled and each is the result of the particular material s chemical potential gradient across the membrane and (4) the gradients are the result of concentration and pressure differences across the membrane (26,30). The driving force for water transport is primarily a result of the net transmembrane pressure difference and can be represented by equation 5 ... 

Examination of equation 5 shows that if there are no chemical reactions, (R = 0), or if R is linear in and uncoupled, then a set of linear, uncoupled differential equations are formed for determining poUutant concentrations. This is the basis of transport models which may be transport only or transport with linear chemistry. Transport models are suitable for studying the effects of sources of CO and primary particulates on air quaUty, but not for studying reactive pollutants such as O, NO2, HNO, and secondary organic species. 

Certain chemical substances have been known for many years to uncouple oxidation firm phosphorylation and to inhibit active transport, and for this reason they are named imcoupling agerrts. They are beheved to act by rendering the membrane permeable to protons hence short-circuiting the potential gradient or protonmotive force. 

Clark-Lewis I, Schumacher C, Baggiofini M, Moser B. Structure-activity relationships of interleukin-8 determined using chemically synthesized analogs. Critical role of NH2-terminal residues and evidence for uncoupling of neutrophil chemo-taxis, exocytosis, and receptor binding activities. J Biol Chem 1991 266 23128-34. 

Fractional time stepping is widely used in reacting-flow simulations (Boris and Oran 2000) in order to isolate terms in the transport equations so that they can be treated with the most efficient numerical methods. For non-premixed reactions, the fractional-time-stepping approach will yield acceptable accuracy if A t r . Note that since the exact solution to the mixing step is known (see (6.248)), the stiff ODE solver is only needed for (6.249), which, because it can be solved independently for each notional particle, is uncoupled. This fact can be exploited to treat the chemical source term efficiently using chemical lookup tables. 

For isolated molecules a variety of approaches have proved useful in the interpretation of vibrational spectra. Firstly, a species may approximate to a symmetry higher than its actual. In such cases a correlation with-descent in symmetry from — the higher symmetry usually simplifies the interpretation of its spectra. Secondly, local group vibrations, essentially uncoupled from the vibration of other equivalent or near-equivalent groups, may occur. Thirdly, chemically distinct groups may couple... 

---