DEAE cellulose

[chiddler]

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TBR poses this in a question as if it should be common knowledge. DEAE cellulose carries a positive charge at neutral pH.

Is this something I should know?

 

[cfive22]

TBR poses this in a question as if it should be common knowledge. DEAE cellulose carries a positive charge at neutral pH.

Is this something I should know?

Was there any information about pKa or pH given in the passage? You definitely don't need to know it as common knowledge.

 

[chiddler]

Was there any information about pKa or pH given in the passage? You definitely don't need to know it as common knowledge.

yes. at pH 6.2. but regardless, at this pH we have to know if the binding molecules is positive or negative. For example, glutamic acid would be net negative while tyrosine will be positive at this pH.

 

[MedPR]

yes. at pH 6.2. but regardless, at this pH we have to know if the binding molecules is positive or negative. For example, glutamic acid would be net negative while tyrosine will be positive at this pH.

How do you know that tyrosine will be positive?

 

[chiddler]

How do you know that tyrosine will be positive?

the passage gives the pKa values to me. For tyrosine, it is 2, 9, and 10. So at pH 6, both nitrogen groups are protonated. Net + charge.

 

[MedPR]

the passage gives the pKa values to me. For tyrosine, it is 2, 9, and 10. So at pH 6, both nitrogen groups are protonated. Net + charge.

Oh ok thanks. I was worried I was missing something. So it's net positive because the carbonyl is deprotonated and both of the amines are protonated so its a net +1, correct?

pka > pH = protonated
pka < pH = deprotonated

 

[chiddler]

Oh ok thanks. I was worried I was missing something. So it's net positive because the carbonyl is deprotonated and both of the amines are protonated so its a net +1, correct?

pka > pH = protonated
pka < pH = deprotonated

yup yup. correct.

 

[mcloaf]

I think if you actually needed the charge of an ion-exchange medium like DEAE cellulose, they would give it to you. It bothered me that TBR expected you to memorize that, but I guess it can't hurt.