Someone once told me they believed that azido functional groups (R-N=N=N) were subject to X-ray photolysis and may not remain intact during crystallography. I can certainly find MANY examples of azido groups that appear NOT to be photolyzed in macromolecular structures in the PDB, beginning with azidothymidine (AZT). But can anyone confirm this rumor with an actual structure (or citation) where the azido group HAS been damaged and cleaved away?
