Chromatography - Net Charge

1. Oct 19, 2007

fuzzy

1. The problem statement, all variables and given/known data
What procedures would you use to obtain gram quantities of each of the following compounds, free of each of the other compounds?
Glycine - monoamino, monocarboxylic amino acid
Glucose - non-ionic monosaccharide
Starch - non-ionic large polysaccharide
Glucose - 5-phosphate - anionic monosaccharide phosphate
mRNA - polyanionic nucleic acid

Compound||||||||||||||||MW
Glycine|||||||||||||||||||75
Glucose||||||||||||||||||180
starch||||||||||||||||||||>>30,000
glucose-5-phosphate||||||258
mRNA|||||||||||||||||||||>>30,000

To answer this question, you must make use of the ionic character of each compound. For example, fructose is non-ionic monomer whereas glycogen is also non-ionic but a polymer. So gel filtration would be useful in this case.

Note that ribose-5-phosphate has three negative charges whereas tRNA has many negative charges and the MW is many folds larger than ribose-5-phosphate.

Alanine is an amino acid with either positive, or neutral, or negative charge depending on the pH of the buffer used.

(when it says ribose I think it means glucose, same for tRNA and mRNA... that's what you get for copy-paste!)

2. Relevant equations
I think we're only allowed to use three columns, DEAE, CM and Gel.
DEAE=anion exchanger (negative will stick)
CM= cation exchanger (positive will stick)
Gel= filters by size of the molecule...

3. The attempt at a solution
Gel filtration will be good for the non-ionic ones:glucose and starch but if it's used first, it will just give 2 solutions filled with junk, so it has to be used last.
mRNA is negative, glucose-5 is negative, but, mRNA is more negative because of polyanionic.
glycine is... some website said it was non-ionic??

k so nothing is positive?

DEAE-> sticks the mRNA, gluc-5... glucose-5 will come out first followed by mRNA. 2 Solutions down, 3 to go...

solution with: glycine, starch, glucose
CM-> does nothing unless glycine is positive; then you're left with starch and glucose
Gel->starch first, then glucose
done!
But... IS GLYCINE POSITIVE?!?!?!? otherwise it wouldn't work...
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Oct 19, 2007

chemisttree

What is the pKb of the glycine (amine part) and the pKa of the carboxylic acid part? Can you find a pH where the ammonium will not be protonated? What will happen to the carboxylic acid at that pH? Is there a pH where the ammonium will be protonated and the carboxylic acid remain in the acid form?