Why amino acids as Zwitterons in solid state and ph neutral?

In summary, the reason why amino acids exist as zwitterions in solid state and at pH 7 is due to the balance of concentration of OH- and H2O, as well as the equilibrium constant. This is because at a pH of 7, which is above the pKa of the carboxyl group and below the pKa of the amino group, the amino acid will exist in a zwitterionic state containing both a COO- and an NH3+ group. This also explains why writing Lewis structures for amino acids at low and high pH is an extension of this concept.
  • #1
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Hi forum goersI'm reviewing some coursework for my General Chemistry class and cannot seem to find a reasonable explanation of why amino acids exist as zwitterons in solid state and ph7 solutions. I'm fairly certain the explanation has to do with its solubility in water, but I am not sure.

Here is my thought process.
Amino acids tend to exist as zwitterons because when in the solid state, there is no reaction for the positive charge(i think positive charge) to be pulled from the amino acid to the water.

And in neutral ph's amino acids exist because of the balance of concentration of OH- and H2O, or similar idea of balance of concentration. It has something to do with equilibrium constant. I don't really know.

The next (and last topic) on my objectives sheet says to know how to write Lewis structures for amino acids as they exist in low pH and high pH.
I believe this is a further extension of why amino acids exist as zwitterons in neutral pH. I will tackle this one after getting clarification.

Thanks for looking, have a good one!
Any clarification is great, thank you!
 
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  • #2
The carboxyl group on an amino acid generally has a pKa of around 2, while the amino group has a pKa around 9. Remember, when pH=pKa, the ionizable group exists half in its protonated form, and half in its deprotonated form. The deprotonated form of the carboxyl group is COO-; the deprotonated form of the amino group is NH2. At a pH above the pKa, the group exists primarily in its deprotonated from.
That being said, at pH 7, which is above the pKa of the carboxyl group, but below the pKa of the amino group, the amino acid will exist in a zwitterionic state containing both a COO- and an NH3+ group.
 

1. Why are amino acids considered Zwitterons in solid state?

Amino acids are considered Zwitterons in solid state because they contain both a positively charged amino group and a negatively charged carboxyl group. This combination of charges allows them to exist as dipolar ions, also known as Zwitterions, in a neutral pH environment.

2. What role does pH neutrality play in amino acids being Zwitterons?

pH neutrality is essential for amino acids to exist as Zwitterons. In a neutral pH environment, the number of positively charged hydrogen ions is equal to the number of negatively charged hydroxide ions. This balance of charges allows the amino and carboxyl groups to remain charged and form a Zwitterion.

3. How do amino acids behave in a solid state?

In a solid state, amino acids exist as a crystalline structure. The positively charged amino groups and negatively charged carboxyl groups form strong ionic bonds with each other, creating a stable and compact structure. This is why amino acids are often found in the solid form in nature.

4. What is the significance of amino acids being Zwitterons in solid state?

Amino acids being Zwitterons in solid state is significant because it allows them to form strong ionic bonds with each other, resulting in stable and compact structures. This is important for the function of many biological molecules, such as proteins, which are made up of long chains of amino acids held together by these bonds.

5. Are there any exceptions to amino acids being Zwitterons in solid state and pH neutrality?

Yes, there are some exceptions. Some amino acids, such as glycine, do not have a chiral carbon and therefore cannot exist as Zwitterions. Additionally, extreme pH levels can disrupt the balance of charges and prevent amino acids from existing as Zwitterions. However, in most cases, amino acids do behave as Zwitterons in a solid state and at a neutral pH.

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