What is the charge of amino acid in alkaline conditions?

This problem refers to the protein buffer in a living system.


"If the blood pH becomes alkaline, there is a release of a proton from the
$\ce{NH3+}$ ion, which takes the $\ce{NH2}$ form."


I understand that the charge of $\ce{NH2}$ must be negative alone and neutral in an amino group. However, the subject of the protein buffer is very briefly touched upon in the text our lecturer gave us and it doesn't detail the reactions in different $\mathrm{pH}$.


I think that since $\ce{NH3+}$ loses a positive proton to balance the blood pH during alkaline conditions, this must mean it becomes neutral. The problem is: I'm not sure if $\ce{NH2}$ is actually in a group and I suspect that it might be alone, which necessitates that it carry a negative charge.


This is my current understanding of the problem.




Protein buffer refers to the buffering action of amino acid side chains of proteins. The “$\ce{NH3+}$” is more accurately $\ce{R-NH3+}$, becoming $\ce{R-NH2}$ when losing a proton. Other side chains have $\ce{R-COOH}$ or $\ce{R-COO-}$ groups, also helping to buffer.


$\ce{NH2-}$ does not occur in aqueous (biological) systems, it is too strong of a base. However, it does occur in other solvents as part of chemistry in the synthetic lab.


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