Sink effects

Agitator failure either due to electrical or mechanical failure could result in loss of system control and "hot spots" in the reactor. In suspension systems loss of agitation could negate much of the "heat sink" effect as the immiscible phases separate and stratify. 

The method for creating acceptor sink condition discussed so far is based on the use of a surfactant solution. In such solutions, anionic micelles act to accelerate the transport of lipophilic molecules. We also explored the use of other sink-forming reagents, including serum proteins and uncharged cyclodextrins. Table 7.20 compares the sink effect of 100 mM (5-cyclodextrin added to the pH 7.4 buffer in the acceptor wells to that of the anionic surfactant. Cyclodextrin creates a weaker sink for the cationic bases, compared to the anionic surfactant. The electrostatic binding force between charged lipophilic bases and the anionic surfactant micelles... 

Vaccaro, J.R. et al., The use of unique study design to estimate exposure of adults and children to surface and airborne chemicals, in Tichenor, B.A., Ed., Characterizing Sources of Indoor Air Pollution and Related Sink Effects, ASTM STP1287, American Society of Testing Materials, 1996, pp. 166-183. 

There are only a few examples of cationic clusters, which is in keeping with the postulated electron-sink effect of the system of metal-metal bonds. This hypothesis is supported by examination of some properties of the clusters Co3(CO)9(/i3-CR) as reported previously207 209. ... 

Emission test chambers, cells and analytical procedures are now standardized by ISO, ASTM and other authorities (see Table 5.1). However, it is interesting to note that only the ASTM standards take sink effects (see Section 5.3) into account Different types of testing facilities have different properties regarding amount of test specimen, dynamics, time, result and cost. In a small device the test is generally time efficient, but on the other hand sample inhomogeneities will significantly influence the results. In Figure 5.3 some trends are shown in dependency of the chamber/cell size. 

A sink effect is the fact that the released components partially adsorb within the test chamber, for example, at the chamber walls (Sollinger, Levsen and Wiinsch, 1993). This can result in an incorrect reading of the concentration determined at the chamber outlet, which can lead to the wrong emission rate being computed. 

De Bortoli, M., Knoppel, H., Colombo, A. and Kephalopoulos, S. (1996) Attempting to characterize the sink effect in a small stainless steel test chamber, in Characterizing Sources of Indoor Air Pollution and Related Sink Effects (ed. B.A. Tichenor), American Society for Testing and Materials, Philadelphia, PA USA, pp. 305-18. 

Dunn, ).E. and Tichenor, B.A. (1988) Compensating for sink effects in emission test chambers by mathematical modeling. Atmospheric Environment, 22, 885-94. 

Uhde, E. and Salthammer, T. (2006) Influence of molecular parameters on the sink effect in test chambers. Indoor Air, 16, 158-65. 

Recovery >95% toluene and n-C12 (cells) and >80% toluene and n-C12 (chambers) Used as a check against sink effects within the chamber/cell... 

Amino acid racemases are important for bacteria because they need D-alanine in the biosynthesis of cell walls. These enzymes require pyridoxal as the active cofactor. A racemization reaction starts with the aldimine complex between pyridoxal and an a-amino acid (Scheme 2.4). Deprotonation occurs at the a-carbon of amino acid, due to the electron-sink effect of pyridoxal. Reprotonation of the quinonoid intermediate at the opposite side provides the desired product (pathway a in Scheme 2.4). However, reprotonation may also take place at the C4 of pyridoxal (pathway b in Scheme 2.4). This kills the catalyst because one of its product, pyridoxamine, can no longer racemize an amino acid. 

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