Titrate A Peptide and Determine pI

1. View the white board lesson onTitration of Histidine and pI determination
2. Each group will have a different Peptide,
Orange: YIQA
Gold: GWET
Green: SCLF
Blue: VRPN
Purple: MDKI
pKa for the carboxy terminus = 3.0, the amino terminus = 8.0, use the pK_R from the book.

For Wednesday, September 24th on two sheets of paper (or less):

1. Draw your peptide (all bonds, with every proton on the molecule) and put the pKa values next to each ionizable hydrogen
2. Use short hand notation to show each structure of your peptide as each proton is ionized (see the histidine lesson)
3. Draw a curve for the titration of 0.12M peptide with 0.2M sodium hydroxide.
4. Include all volumes and pH values for

• the beginning, when no base has been added
• each endpoint
• each half way point
• the last endpoint
• the pI

Show the equations that you used to calculate each of the above pH values.