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PKa of alpha amino and epsilon amino


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#1 YuvalKon

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Posted 7 December 2016 - 08:03 PM

Hey everyone, my question is, what makes the different in PKa of alpha amino and epsilon amino in amino acids?

My teacher wrote to us that alpha amino is near the carboxyl group, and the O is electronegative so it want to gain an electron, but I don't get how this thing makes the amino group near the alpha carbon to want to lose a proton?

Thanks :)


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#2 BabcockHall

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Posted 8 December 2016 - 02:43 PM

Your definition of electronegativity is misleading, and not all amino acids have an amino group at the epsilon position.  I would focus on electrostatics.


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#3 YuvalKon

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Posted 9 December 2016 - 12:21 PM

Your definition of electronegativity is misleading, and not all amino acids have an amino group at the epsilon position.  I would focus on electrostatics.

I don't need electrostatics in high level, just some principles in biochemistry.

I didn't say all amino acids, the question is about positive charge amino acids (those that have epsilon amino in the R group), my definitions might be a little wrong but I think I'm clear.

And I'm here to understand things better, and not for someone to tell me how wrong I am, so thanks for nothing.

If anyone else could explain this to me I would be very thankful :)


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#4 BabcockHall

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Posted 9 December 2016 - 03:58 PM

Electronegativity concerns electrons being potentially shared in a covalent or other kind of bond.  Electron affinity is a measure of the change in energy when an atom gains an electron; therefore, it could be thought of as how much an atom wants to gain an electron.  I was thinking of low-level electrostatics.  Pro tip:  being rude to people who are trying to help you is not a winning strategy.


Edited by BabcockHall, 9 December 2016 - 06:34 PM.

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#5 YuvalKon

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Posted 9 December 2016 - 05:45 PM

Electronegativity concerns electrons being potentially shared in a covalent or other kind of bone.  Electron affinity is a measure of the change in energy when an atom gains an electron; therefore, it could be thought of as how much an atom wants to gain an electron.  I was thinking of low-level electrostatics.  Pro tip:  being rude to people who are trying to help you is not a winning strategy.

Well, your first comment was all about how I use the definition wrong, without even trying to explain yourself, so I can't see any helping with leaving a comment that says "You are wrong".

Thanks for the definition tho, but it's still not clear to me how the PKa is effected from the electronegativity.


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#6 hypervalent_iodine

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Posted 10 December 2016 - 12:08 AM

pKa is related to how favoured the product of the acid dissociation is. In other words, how stable the conjugate base is. Think about how electronegativity might effect that.
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#7 BabcockHall

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Posted 12 December 2016 - 05:07 PM

Well, your first comment was all about how I use the definition wrong, without even trying to explain yourself, so I can't see any helping with leaving a comment that says "You are wrong".

Thanks for the definition tho, but it's still not clear to me how the PKa is effected from the electronegativity.

 

Your opening post was poorly formatted and had no pKa values or names of amino acids.  When it was pointed out to you that your understanding of electronegativity was wrong, you should have looked it up yourself.  Helping someone is not the same as doing their work for them.


I don't need electrostatics in high level, just some principles in biochemistry.

I didn't say all amino acids, the question is about positive charge amino acids (those that have epsilon amino in the R group), my definitions might be a little wrong but I think I'm clear.

And I'm here to understand things better, and not for someone to tell me how wrong I am, so thanks for nothing.

If anyone else could explain this to me I would be very thankful :-)

The three amino amino acids with positively charged side-chains have very different structures, and for that reason alone, attempting to explain all of their values with one single concept is unlikely to lead to success.  With respect to the ammonium groups in amino acids both electronegativity and electrostatics are factors (although it might make sense to start with electronegativity).


Edited by BabcockHall, 12 December 2016 - 05:20 PM.

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