pKa of glu & arg

I don't quite understand your question.
Did the side chains react before determining their pKa?

I guess you're referring to ionic interaction between carboxylate on glumatic acid residue & protonated guanidine (guanidinium).

Apart from ionic interaction, there should also be hydrogen bond between the carboxylate and guanidinium.

Deprotonation from guanidinium would probably disrupt the H-bond and is unfavorable (endothermic).

Thus: less likely to deprotonate --> less likely to give proton --> less acidic --> larger pKa


2012-08-31 18:03:06 補充：
Ming, what's your point?
Asking the asker to ask somebody else? Is that your "answer"??

2012-09-01 03:39:35 補充：
Ming, I bet you just know nothing about this kind of questions.
If you know, you could have at least gave him some hints, instead of babbling useless "suggestion".
This is not a secondary school question. It's not likely you can find the "teacher" asking trivial Qs.

2012-09-01 03:42:56 補充：
1.
the glutamate has already lost the proton. how come it still has the pKa?
Or it's just some conventions not in field of chemistry?

2.
the question is not clear for me. perhaps your field is different from mine, so we're talking in diff. languages (lol

You may ask for assistance from your chemistry teacher.