How to change from peptide-trifluoroacetate to peptide-acetate?

[yuanhenglidlut]

Hi guys:
I have synthesised some peptides using the Fmoc/tBu protocol. As we know, after preparative HPLC separation using CH3CN(0.1%TFA) and H2O(0.0875%) as the eluent and final lyophilization, the peptide exists in the form of trifluoroacetate. My question is how to change the peptide-trifluoroacetate into the form of peptide-acetate? Thanks for your comments!

[ask03]

Am not sure about 'acetate' form but if you can get yout peptide in 'Chloride' form. Mostly, your positively charged residues exist in trifluoroacetate form. i.e.R and K. So based on the number of your positively charged residues in your sequence, you calculate the appropriate concentration of HCL that is required. Once you know this value, incubate your peptide in that HCL conc. and then lyophilise it. If you dissolve your peptide in water, the trifluoroacetate ions might just come off too, but am not sure about that.. Refer to the paper by VALERY V. ANDRUSHCHENKO, HANS J. VOGEL and ELMAR J. PRENNER*

[glbiochem]

It's easy to switch under weak ion-exchange resin(very cheap) column.
Above HCl switch method is not good enough like the paper. We tried before, but the analysis result despair me. The rest TFA content is higher than standard request.

[harryntn]

Originally Posted by yuanhenglidlut

Hi guys:
I have synthesised some peptides using the Fmoc/tBu protocol. As we know, after preparative HPLC separation using CH3CN(0.1%TFA) and H2O(0.0875%) as the eluent and final lyophilization, the peptide exists in the form of trifluoroacetate. My question is how to change the peptide-trifluoroacetate into the form of peptide-acetate? Thanks for your comments!

Dissolve back in water and load back onto HPLC column equilibrated with 0.1 % HOAc and 1% Acetonitrile. Once reloaded onto HPLC column, 2-3 column volumes of 0.1% HOAc (buffer A) to flush the tfa salts out of system. Now, run your gradient up in ACN with 0.1% HOAc / ACN and collect the OAc salt form of your peptide.