Fig 6. Photolysis of Ncm-caged amino acids.

Light absorption leads to the transient aci-nitro intermediate, which decomposes into the free amino acid and the spent cage (7-formyl-6-nitrosocoumarin). The caged molecules are depicted as N-protonated species because the pK_as for the α-amino groups are all estimated to be higher than physiologic pH (details in S3 Text).