How does flow rate affect my peptide purification efficiency when using a small pore stationary phase?

In a previous post, I evaluated how flow rate can impact my purification efficiency using flash chromatography.  I noticed though, at high flow rates a significantly later elution time for my peptide.  I hypothesized that the increased pressure was driving the compound further into the pores, increasing the overall interaction with the stationary phase and causing the increased retention.  We know that the particle size and particle pore size impact resolution and purification efficiency, so how does flow rate play a role with a different stationary phase?

In today’s post I’ll evaluate several flow rates using a reversed phase stationary phase material with slightly larger diameter particles that possess significantly smaller pores.  The smaller pores should limit the access of the peptides to the stationary phase and negatively impact the purification.

Continue reading How does flow rate affect my peptide purification efficiency when using a small pore stationary phase?

Has my peptide undergone an aspartimide rearrangement?

Side reactions.  Words that cause a little shiver to run down every chemists’ spine.  As peptide chemists, we worry about both chemical side reactions like diketopiperazine or aspartimide rearrangements, and secondary structure formation as causes for failed peptide syntheses.  But how do you know what to look for?  What is a susceptible sequence and how can you confirm if one of these structural rearrangements has occurred?

In today’s post, I’ll discuss a couple strategies that have been published that illustrate how to identify if an aspartimide rearrangement has in fact occurred during your peptide synthesis. Continue reading Has my peptide undergone an aspartimide rearrangement?