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"What is the relationship between the pKa and pKb for lysine?
A. pKa1 + pKb1 = 14
B. pKa1 + pKb2 = 14
C. pKa2 + pKb2 = 14
D. pKa2 + pKb3 = 14"
Part of the reasoning in the solution says that the first proton released from the most acidic group (the carboxylic acid terminal) corresponds to the third proton gained by the conjugate base. How do you get "third proton gained?" Which of the groups is gaining the proton and what do I assume the starting structure looks like before I add the protons?
edit: Really, could someone tell me where I could find a source explaining pka and pkb value assignment for amino acids? I tried Googling for lecture notes but I'm having trouble finding what I want. Another question that shows what I'm having trouble with:
"At pH=7, what are the applicable values for histidine?
A. pKa1=1.81, pKa2=6.05, pKb3=4.85
B. pKa3=9.15, pKb2=7.95, pKb1=4.85
C. pKb2=7.95, pKa2=6.05, pKa3=9.15
D. pKa3=9.15, pKb2=7.95, pKb3=12.19"
I understand how to determine which groups are protonated or deprotonated at the given pH but I have no idea what goes into deciding that "since the carboxyl terminal is deprotonated, we consider pKb3 rather pKa1."
A. pKa1 + pKb1 = 14
B. pKa1 + pKb2 = 14
C. pKa2 + pKb2 = 14
D. pKa2 + pKb3 = 14"
Part of the reasoning in the solution says that the first proton released from the most acidic group (the carboxylic acid terminal) corresponds to the third proton gained by the conjugate base. How do you get "third proton gained?" Which of the groups is gaining the proton and what do I assume the starting structure looks like before I add the protons?
edit: Really, could someone tell me where I could find a source explaining pka and pkb value assignment for amino acids? I tried Googling for lecture notes but I'm having trouble finding what I want. Another question that shows what I'm having trouble with:
"At pH=7, what are the applicable values for histidine?
A. pKa1=1.81, pKa2=6.05, pKb3=4.85
B. pKa3=9.15, pKb2=7.95, pKb1=4.85
C. pKb2=7.95, pKa2=6.05, pKa3=9.15
D. pKa3=9.15, pKb2=7.95, pKb3=12.19"
I understand how to determine which groups are protonated or deprotonated at the given pH but I have no idea what goes into deciding that "since the carboxyl terminal is deprotonated, we consider pKb3 rather pKa1."
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