Question

(Submit completed assignment via Canvas as a pdf for credit. Show all work.) Dipolar on Draw the structure of L-isoleucine in the zwitterion form, What pH values would you expect this to be the predominant form of this amino acid? 1) 2) If a solution containing isoleucine has a pH of 4 and the concentration of the zwitterion form is 0.02 M, what is the concentration of the fully protonated form? Calculate the isoelectric point of isoleucine (e.g. the pH where the expected charge is 0). 3) 4) Draw a titration curve for a solution containing isoleucine. Start at a pH of 12 and use HCI as the titrant.

Answer 1

CHE O NHg Zwitterion form of L-isoleucine The two pka values of isoleucine are Þka, (- cooH) = 2.36 & pka. (-NH₂) = 9:68 ( thiad sintstone So, ÞI ( Isoelectric point) = 2.36 + 9.68 2PN : 6:02 in The upper structure (Zwitterion form) will be predominent at pH ~ 6.02. 21. Let's concentration of the fully protonated form is x M . Now, from Henderson - Hasselbalch equation [salt] we know, bH - pka + log - acid] Now, putting the values, 4.0 = 2.36 + log (0.02) or 0.02 - 101.64–43.6516 0.02 = 0.00046 x = 4316516 ~ 0.0005 form is 0.0005 M so, conc. of the fully protonated

for isoleucine, pka, (-&-COOH) = 2.36 & pka, (-NH₂) = 9.68 So, Isoelectric point (pI) = þ kas ist pRaz 2.36 +9.68 = 6:02 So, isoelectric point (pI) of isoleucine is 6.02 4. Titration curve for a solution isoleucine with her is as containing follows: 120 pka = 9.68 ÞH 7+ pl = 6:02 Þka, = 2136 volume of Hu added (mi) ,