Does arginine gain additional protons on its side chain nitrogens during titration?

[Daemos]

I have a question

When you do a titration curve for Arginine and you start it off in the acid exteme (low pH) does it gain anymore Hydrogens other than the one that always bonds to the COO- group? (so does it gain more than a +2 charge)

To rephrase, do any of the other two Nitrogens (other than the one double bonded to the Carbon in the R-Group) gain additional hydrogens when it acts as a base.

 

[chem_tr]

Yes, the formula should be written in low pH like that:

$$HOOC-CH(NH_3)^+-(CH_2)_3-NH_2^+-C(=NH)-NH_2$$

I don't think that the terminal C(=NH)-NH₂ group takes additional protons, since they seem to be amphoteric.

But I have found this http://www.cem.msu.edu/~reusch/VirtualText/proteins.htm, mentioning that the $C=NH$ group protonates instead to give the same 2+ charge, which is logical as the nitrogen I mentioned is somewhat hindered to react with proton.

I feel confident that the website will help you very much; I've liked it too.

Take care.

 

[Daemos]

thanks a lot for the info :)