BL/CH 401 Lecture #3

Acids, Bases, and Buffers Home Page

1. Principle of Ionization of Weak Acids:

2. Titration of a Weak Acid illustrating its Ionization and Buffering Property:

3. Ionization of Simple Amino Acids:

4. Ionization Rules 1:

5. Ionization of Complex Amino Acids:

6. Ionization of His:

7. Calculating pI (Isoelectric Point or pH) of His:

8. Ionization Rules 2:

SUMMARY:

When titrating an amino acid that is fully protonated (ie starting at pH = 1),

the alpha carboxylic acids lose their proton first (all free amino acids have this group),

then side chain carboxylic acids lose their proton next ( for example, Asp and Glu),

then aromatic-like amino side chains lose their proton next (His is the only example),

then alpha amino groups lose their proton next (all free amino acids have this group),

then side chain amino groups lose their proton last (for example, Lys and Arg).

NOTE WELL: The rules apply to small peptides and you need to pratice using these rules with peptides...Go to pK Problems

©Wilbur H. Campbell, 1995, 1996; wcampbel@mtu.edu

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