Stopping reaction

Phosphatidylcholine Apply phospholipase C solution as a band, dry, apply sample solution to enzyme band, stop reaction with hydrochloric acid vapor. sn-l,2-Digly-cerides are produced. [43]... 

Have efficient refrigeration systems ready to try to stop reactions likely to speed up or for which the preliminary analysis showed them to be exothermic. Flooding systems might be needed in extreme situations and if the compounds are incompatible with water. 

The extent to which peeling occurs is controlled by a much slower reaction, known as the stopping reaction. This also involves the reducing end of the molecule but in either an isomerised or a non-isomerised form (Figure 3.17). 

Figure 3.17 Alkaline chain stabilisation (stopping) reactions of cellulose.

Substrate Reagent to stop reaction Color of product/wavelength for quantification... 

This stopping or stabilization reaction with cellulose was presumed to involve a saccharinic acid rearrangement of the reducing group on the terminal D-glucose residue. This mechanism was confirmed by the formation of D-glucometasaccharinic acid, which still remained attached as the terminal unit (73). The stopping reaction is presented in Scheme 13. 

In many polymerization processes traces of impurities such a water will stop reaction because just one molecule that attaches to the end of the growing chain will kiU it. For addition polymerization this will occur whenever a chain-terrninating species is added with a concentration higher than the initiator [A],. 

Stop reaction by blowing into lOyu.1 formamide-dye mixture. 

Stop reaction by adding 10 ftl phenol (water saturated)... 

Stop reaction Remove the foil and add 100 xL of Stopping Solution POD to each well, keeping to the same timing as in 8. Dispense substrate . 

Fig. 2-34. Stopping reaction. 1 —>2, 1,2-Enediol formation 2 — 3, j3-hydroxy elimination 3 —> 4, tautomerization 4 —> 5, benzilic acid rearrangement leading to a glucometasaccharinic acid end group, (cf. Fig. 2-33.)...

Fig. 7 -31. Peeling and stopping reactions of polysaccharides (Sjostrom, 1977). R = polysaccharide chain and R = CH2OH (cellulose and glucomannans) or H (xylan). Cellulose and glucomannans (R = CH2OH) (1) 3-Deoxyhexonic acid end groups (metasaccharinic acid), (2) 2-C-methylglyceric acid end groups, (3) 3-deoxy-2-C-hydroxymethylpentonic acid (glucoisosaccharinic acid), (4) 2-hydroxypropanoic acid (lactic acid), and (5) 3,4-dideoxypentonic acid (2,5-dihydroxypentanoic acid). Xylan (R = H) (3) 3-Deoxy-2-C-hydroxymethyltetronic acid (xyloisosaccharinic acid), (4) 2-hydroxypropanoic acid (lactic acid), and (5) 2-hydroxybutanoic acid. 1977. TAPPI. Reprinted from Tappi 60(9), p. 152, with permission.

The processes discussed above pertain to the main reactions of cotton with alkaline solutions up to temperatures of 120-130°C. Above 170°C, a random scission of glycosidic bonds in accessible regions occurs, leading to the rapid production of shorter chain molecules with new reducing end units. These immediately participate in the peeling and stopping reactions just described. 

Figure 9.116 Reversed-phase HPLC for monitoring the formation of 8-OHIPA from IPA. Aliquots (20 /xL) of the stopped reaction mixture were injected onto a /xBondapak Cig column and eluted with 40% aqueous methanol at a flow rate of 1 mL/min. IPA (peak A) is eluted after 8-OH IPA (peak B), which is absent at zero time. The chromatograms are from aliquots taken at 0,30,60, and 90 minutes. (From Chism et al 1984.)...

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