The main difference between the two is that L-glutamine is "free form". This means that it is "free" from being bonded to other amino acids, which makes it less stable. Glutamine peptides on the other hand are not "free"; instead it is bonded to other amino acids with peptide bonds. This makes it more stable and better assimilated by the body. Glutamine peptide is much more stable in solution, higher temperatures, and low PH than free form glutamine (free form L-glutamine tends to break down to ammonia and glutamic acid rather quickly in solution). The digestive tract has peptide transport systems that allow peptides to be better absorbed and utilized than free form amino acids.