nb198
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Converting amino acid salts to freebase amino acids?
I would like to convert lysine HCl into freebase lysine. What is the best method to do this?
I was hoping it would be similar to freebasing cocaine with sodium bicarbonate, but the amino acids seem to be a little harder.
Even with the HCl removed, the freebase lysine is still very soluble in water. Also, the carboxylic acid will become COO-Na+.
Any suggestions would be helpful.
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DraconicAcid
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Sodium bicarbonate should do the trick, but you'll still have a zwitterion (NH3+-CHR-CO2-), which will
still be water soluble.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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nb198
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Quote: Originally posted by DraconicAcid  | | Sodium bicarbonate should do the trick, but you'll still have a zwitterion (NH3+-CHR-CO2-), which will
still be water soluble. |
According to this link: The solubility of lysine in water goes from 16.7m (molality) at pH 8 to 1.7m at pH 11. Do you think I could saturate water
with lysine HCl and then add concentrated NaOH solution and crash out some of the lysine?
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DraconicAcid
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http://pac.iupac.org/publications/pac/pdf/1997/pdf/6905x0935...
It should work.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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nb198
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haha, that was the link i found. I somehow didn't copy paste it in my post...
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AvBaeyer
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Typically, amino acid salts are "freebased" using ion exchange columns such as Dowex50 and eluting the amino acid with dilute pyridine solution. The
eluate containing the amino acid-pyridine salt is then free dried under high vacuum which removes the water and pyridine leaving behind the free amino
acid. It is otherwise very difficult to obtain free amino acids from solution. Sometimes they will separate or crystallize at the isoelectric point
for the particular amino acid but this is not easy to do.
In the case of lysine hydrochloride, using sodium bicarbonate to neutralize the hydochloride will not work as the terminal amino group of lysine is a
stronger base than bicarbonate. You would need to carefully titrate the HCl with hydroxide but because of the great solubilty of the zwitterion,
isolation of the lysine free base will be very difficult if even possible. In fact, lysine is always isolated as its hydrochloride not as its
"freebase." If you can find it, see Greenstein and Winitz, "Chemistry of the Amino Acids," vol 3 which contains a chapter on lysine.
AvB
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nb198
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| Quote: Originally posted by AvBaeyer | Typically, amino acid salts are "freebased" using ion exchange columns such as Dowex50 and eluting the amino acid with dilute pyridine solution. The
eluate containing the amino acid-pyridine salt is then free dried under high vacuum which removes the water and pyridine leaving behind the free amino
acid. It is otherwise very difficult to obtain free amino acids from solution. Sometimes they will separate or crystallize at the isoelectric point
for the particular amino acid but this is not easy to do.
In the case of lysine hydrochloride, using sodium bicarbonate to neutralize the hydochloride will not work as the terminal amino group of lysine is a
stronger base than bicarbonate. You would need to carefully titrate the HCl with hydroxide but because of the great solubilty of the zwitterion,
isolation of the lysine free base will be very difficult if even possible. In fact, lysine is always isolated as its hydrochloride not as its
"freebase." If you can find it, see Greenstein and Winitz, "Chemistry of the Amino Acids," vol 3 which contains a chapter on lysine.
AvB |
Thanks. Yeah, I assumed bicarb would be too weak. I am starting to think that isolating the "freebase" form is not worth the time or effort.
I will definitely check out that book when I get the chance!
[Edited on 16-4-2014 by nb198]
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