CHE 4341 Chapter Notes - Chapter 4: Isoelectric Point, Tyrosine, Titration Curve
Document Summary
Titration type #1 without pkr"s (glycine, ala, val, etc. ) +1 charge at low ph everything is protonated: A+1 form (nh3) group w/lowest pka (most acidic) gets titrated first == cooh: ph very low: Overall net charge = +1: special case: half equivalent of strong base ph = pka (ha = a-) Amino group isn"t touched (pka is too high), so its" still : +1. Cooh: half of ha and a- form : . 5(0) + . 5(-1) = -0. 5 overall net charge = +0. 5: when cooh is finished titrating and we add 1 equivalent of strong base: We haven"t titrated the amino group yet! Net charge: -1 (cooh) + +1 (nh3) = 0 [isoelectric zwitterion] >> next titration: the alpha amino group (pka = 9. 5 for all amino acids: overall net charge when at ph = 9. 5 (1. 5 equivalent of strong base)
