You probably won't find extensive research and studies on l-glutamine, because - like every other natural healing substance - it's not patentable and no one stands to gain financially from its sale. However, here are some articles you may find helpful.
Healing a Leaky Gut Naturally
Study: L-glutamine shown to decrease intestinal permeability and promote wound healing
Glutamine and the Immune System
The role of glutamine in the immune system and in intestinal function
A common dose range is 6 to 25 grams divided into 3 doses per day, 30 minutes before meals.
Diagnosed with ulcerative colitis spring 1999. Have been in remission for years with only a few minor blips. Scope on 6/22 showed no inflammation at all.
Maintenance dose sulfasalazine. Probiotics, vitamin D, fiber supplement and fish oil caps. George's aloe vera juice and l-glutamine for gut healing. Mostly grain-free and dairy-free low carb diet.