Synthesis and photochemical properties of nitro-naphthyl chromophore and the corresponding immunoglobulin bioconjugate

Synthesis, photochemistry, and biomolecular caging properties of a new chromophore namely 3-nitro-2-naphthalenemethanol are described. This chromophore is photoexcitable with photons in 350-400 nm range and in several solvents including aqueous medium. On irradiation, it gives the expected nitroso-aldehyde photoproduct with high quantum yield (0.6-0.8). Further, it can be conveniently coupled to the amino residues of immunoglobulin (IgG) using diphosgene. Irradiation of the resulting IgG-nitronaphthyl chromophore bioconjugate at 380 nm causes photorelease of IgG as evidenced by Protein-A affinity binding studies. The bioconjugate showed low level of binding to Protein-A. However, the binding increases after irradiation and, thus, modifies the Fc site of the IgG. Electrophoresis studies of the irradiated bioconjugate show that IgG does not undergo fragmentation or molecular weight change under the irradiation conditions. Thus, 3-nitro-2-naphthalenemethanol can be used as a photocaging agent under physiological conditions at wavelengths, which does not cause significant damage to the biomolecule. The work provides new directions for the development of organic chromophores for biomolecular caging applications.