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500 Chapter 26 AMINO ACIDS, PEPTIDES, PROTEINS, AND NUCLEIC ACIDS: NITROGEN-CONTAINING POLYMERS IN NATURE (b) The pH 7 structure for Sec above is negative. You need to reduce the pH to below 5.2 (the for the SeH group) to begin to see appreciable concentrations of the charge-neutral which would resemble the Cys structure above, right. So the pl = (5.2 + 2.0)/2 = 3.6. (c) More acidic, but also more powerfully nucleophilic. 2S N 60. (a) H H OH 4R (b) (i) (ii) 1. H⁻, H₂O, ; 2. HO⁻, H₂O, 1 Mechanisms: (i) + - O O -:ö: OCH₂CH₃ C 0 C O O O 0 NCH₂ 0