Synthesis and evaluation of benzothiazolyl and benzimidazolyl asparagines as amino acid based selective fluorimetric chemosensors for Cu2+

A series of emissive N-tert-butyloxycarbonyl benzyl ester asparagines bearing benzothiazole and benzimidazole units at the side chain, functionalised with electron donor or acceptor groups, were evaluated as novel amino acid based fluorimetric chemosensors for transition metal cations, such as Cu2+, Zn2+, Co2+ and Ni2+. Selective removal of the protecting groups at the N- and C-terminals was carried out in order to assess the influence of the presence of blocking groups on the overall coordination ability. The results indicate that there is a strong interaction through the donor N, O and S atoms at the side chain of the various asparagines, with high selectivity towards Cu2+ in a 1:1 complex stoichiometry. Association constants and detection limits for Cu2+ were calculated. The photophysical and metal ion sensing properties of these asparagines suggest that they can be suitable for incorporation into peptidic chemosensor frameworks.