Synthesis of spiropyran for gold and silver nanoparticles functionalization

The exogenous control of intracellular properties has a fundamental role in medical treatments, such as cancer photodynamic therapy, where photosensitizers are dosed or accumulated into cells and afterwards “turned on” via selective photoexcitation. Furthermore, the association of photosensitizers with gold nanoparticles (AuNPs) enhances the photodynamic effect. The pH regulation has a fundamental role in several intracellular processes and its variation via exogenous compounds is a potential tool for intervening in the intracellular mechanism. In a recent research we showed both that an exogenous control of pH is possible via purposely synthesized proton caged compounds [ , ] and that the intracellular acidification in enhanced by the association of AuNPs. Another class of pH regulating compounds of potential interest for in vitro experiments are spiropyrans and spirooxazines, because of their reversible ring-opening to the corresponding merocyanines with associated proton caption or release, depending on the direction of the following reaction . Here we report the synthesis of the photoacid 1,9-(Mercaptononyl)-3’,3’-dimethyl-6’-nitrospiro[2H-1-benzopyran-2,2’-(2H) indole], a variant of spiropyrans, functionalized with a thiol group for further functionalization of gold and silver nanoparticles.