Plastid stability

Like chlorophyll, plastoquinone A has a nonpolar terpenoid or isoprenoid tail, which can stabilize the molecule at the proper location in the lamellar membranes of chloroplasts via hydrophobic reactions with other membrane components. When donating or accepting electrons, plastoquinones have characteristic absorption changes in the UV near 250 to 260, 290, and 320 nm that can be monitored to study their electron transfer reactions. (Plastoquinone refers to a quinone found in a plastid such as a chloroplast these quinones have various numbers of isoprenoid residues, such as nine for plastoquinone A, the most common plastoquinone in higher plants see above.) The plastoquinones involved in photosynthetic electron transport are divided into two categories (1) the two plastoquinones that rapidly receive single electrons from Peso (Qa and Qb) and (2) a mobile group or pool of about 10 plastoquinones that subsequently receives two electrons (plus two H+ s) from QB (all of these quinones occur in the lamellar membranes see Table 5-3). From the plastoquinone pool, electrons move to the cytochrome b f complex. 

Kim J, Eichacker LA, Rudiger W et al. Chlorophyll regulates accumulation of the plastid-encoded chlorophyll proteins P700 and D1 by increasing apoprotein stability. Plant Physiol 1994 104 907-916. 

Figures 8.34-8.36 show plots of lAog Umfi versus 1/< >2 for a few typical PVC formulations [89,90]. In Rg. 8.34, the effect of the amount of plastid r, namely, dioctyl phthalate on the MFl, can be readily calculated from the linear plot. The presence of the plasticizer increases the free volume and reduces the Tg of PVC. The effect of this on the flow behavior of PVC can be readily understood through the use of the suggested model given by Eq. (8.84). The effect of the plasticizer amoimt on MFI in the presence of stabilizers and lubricants has been shown in Figs. 8.35 and 8.36.

The base polymer for this t5q>e of sealant exists in the form of an emulsion of micron- and submicron-sized partides of the polymer suspended in water. The base polymer formed by free radical polymerization may be a homopolymer of an acrylic monomer but is more likely to be a copolymer of a number of different monomers chosen to provide the correct balance of properties. The polymer latex has to be made more permanent and therefore a nonionic surfactant such as a nonyl phenol/ polyethylene oxide is added to help stabilize the emulsion. Other additives to the sealant formulation include plastid-zers, fillers, solvents, and silanes. A plasticizer is added to the formulation in order to improve upon or maintain the flexibility of the sealant. Solvents (usually a small amount) are added to improve the tooling of the sealant after it is applied. In addition, a solvent could be a material such as ethylene or propylene glycol which can improve the resistance of the packaged sealant to temperatures below freezing. The most widely used filler for this type of sealant is calcium carbonate. Silanes are often added to acrylics to improve the wet adhesion of the sealant to glass. Other additives include antimildew agents (for tub and tile applications) and clay for rheological control. 

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