"Amines are bases at physiological pH"...?

[Mission Medical]

I'm reading a site regarding biochemistry stating that amino groups have a pKa of 9 and are bases at physiological pH (~7). However, in organic chemistry, we were taught that when the pH is below the pKa, the pH is acidic relative to the compound, so the compound exists in the acidic form, which is true in this case because the amino group is protonated. That protonation is a result of the fact that the amino group is basic in nature, but why is the site saying that an amino group is a base at physiological pH? Isn't it existing in its acidic form at physiological pH?

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[QrtrLifeCrisis]

At ~pH 7, if you tossed an amino group into the mix, it would act like a base and form its conjugate acid. Not sure where the confusion is...are you concerned about the semantics?

 

[Mission Medical]

Yes, the semantics are really what's confusing me. I get what you're saying. If you throw in an amino group at pH = ~7, it acts as a base and forms the conjugate acid, which is what I was saying as well. I guess what the site means when it says that an amine is a base at physiological pH is that the amine will pick up a base at this pH. The part that confused me was that in my organic chemistry class we would have said that the amine exists in its acidic form at this pH. I think the two statements are just different ways of getting across the same idea though since the amine would exist in its acidic (protonated) form because it acted like a base and picked up a proton at physiological pH.

 

[rfvbnmju]

I think the two statements are just different ways of getting across the same idea though since the amine would exist in its acidic (protonated) form because it acted like a base and picked up a proton at physiological pH.

Yes! That's the right idea!

 

[QrtrLifeCrisis]

Yes, the semantics are really what's confusing me. I get what you're saying. If you throw in an amino group at pH = ~7, it acts as a base and forms the conjugate acid, which is what I was saying as well. I guess what the site means when it says that an amine is a base at physiological pH is that the amine will pick up a base at this pH. The part that confused me was that in my organic chemistry class we would have said that the amine exists in its acidic form at this pH. I think the two statements are just different ways of getting across the same idea though since the amine would exist in its acidic (protonated) form because it acted like a base and picked up a proton at physiological pH.

You know your stuff. Don't worry about the semantics. Go with what you've learned in class and not what's listed on some silly website.

 

[Like]

I only clicked on this thread because I read amines as animes.
Nah but you got things well sorted out here already.