Biochem help (acidic buffers and acidic/basic functional groups in amoxicillin)

[gspsaku]

So we received a homework assignment and there are a few questions I am not sure about. Here they are:

1. So we are given the Melphalan and we are supposed to draw the structure in an aqueous buffer at a pH of 2.0. What does that look like? We certainly did not cover this in class and it's not in our Biochem book. Any suggestions or help would be much appreciated. Is it as simple as protonating the two amine groups and the carboxylic acid since the medium is acidic?

2. We are given amoxicillin which has a phenol, an amine, two amides, a sulfide, and a carboxylic acid group. Which of these functional groups are acidic and which are basic? (I recall our professor mentioning that acidic and basic functional groups are only noted as such if they are ionizable and I don't believe we can ionize an amide, correct?)
 

Edited August 24, 2017 by gspsaku

[BabcockHall]

Do you know the pK_a of the conjugate acid of a typical sulfide?