Chirobiotic Vancomycin Reverse Phase separating NSAIDs
Posted: Sun Feb 23, 2014 12:56 am
Hello,
Just been carrying out some separations on Chirobiotic V in the reverse phase using the recommend methanol, acetic acid (glacial) and triethylamine (100/0.1/0.1 % w/v) mobile phase from manufacturer literature.
Seem to have found a trend within the 2-arylpropanoic acid derivatives of NSAIDs that shows an increased retention time/selectivity and resolution which is unrelated to Log P but correlates well with an increasing molecular weight as well as an increasing polar surface area from further investigation.
Obviously from theory it would be expected that compounds that have more hydrophobic interaction would elute slower which can be explained by an increasing molecular weight. As the molecular weight increases the number of aryl/alkyl chains becomes increasingly bigger and therefore there is more opportunity for the compounds to interact within the weak inclusion complexes of the vancomycin as well as being in the perfect position to interact via pi-stacking with the phenyl groups also present.
Obviously acidity is closely related to polarity, although the presence of multiple aryl/alkyl groups should significantly alter the net polarity without changing the acidity of the propanoic carboxylic acid majorly.
However, when it comes to relating the increased polar surface area values I am a little confused, as it seems theoretically the opposite of this should happen. I have hypothesized that is due to pi-pi bonding being relatively non-polar and therefore hydrophobic in nature and therefore an increasing polarity would promote these interactions to a greater degree as well. Although at the same time I would expect these compounds to elute faster because they would more readily interact with the polar mobile phase.
I was wondering if anybody would be able to shed some light onto why this may be! Any feedback would be greatly appreciated.
Thank you!
Just been carrying out some separations on Chirobiotic V in the reverse phase using the recommend methanol, acetic acid (glacial) and triethylamine (100/0.1/0.1 % w/v) mobile phase from manufacturer literature.
Seem to have found a trend within the 2-arylpropanoic acid derivatives of NSAIDs that shows an increased retention time/selectivity and resolution which is unrelated to Log P but correlates well with an increasing molecular weight as well as an increasing polar surface area from further investigation.
Obviously from theory it would be expected that compounds that have more hydrophobic interaction would elute slower which can be explained by an increasing molecular weight. As the molecular weight increases the number of aryl/alkyl chains becomes increasingly bigger and therefore there is more opportunity for the compounds to interact within the weak inclusion complexes of the vancomycin as well as being in the perfect position to interact via pi-stacking with the phenyl groups also present.
Obviously acidity is closely related to polarity, although the presence of multiple aryl/alkyl groups should significantly alter the net polarity without changing the acidity of the propanoic carboxylic acid majorly.
However, when it comes to relating the increased polar surface area values I am a little confused, as it seems theoretically the opposite of this should happen. I have hypothesized that is due to pi-pi bonding being relatively non-polar and therefore hydrophobic in nature and therefore an increasing polarity would promote these interactions to a greater degree as well. Although at the same time I would expect these compounds to elute faster because they would more readily interact with the polar mobile phase.
I was wondering if anybody would be able to shed some light onto why this may be! Any feedback would be greatly appreciated.
Thank you!