Bioconjugated Rhenium(I) Complexes with Amino Acid Derivatives: Synthesis, Photophysical Properties, and Cell Imaging Studies

The synthesis of a series of bioconjugated fac tricarbonyl rhenium bis-imine complexes with amino acid ester derivatives and their application in fluorescent microscopy cell imaging is reported. A range of meta- and para-bioconjugated pyridyl derivatives were synthesized, and their photophysical properties were analyzed upon coordination to fac-[Re(bipy)(CO)(3)(CF3SO3)]. Their long lifetimes (270-370 ns) and large Stokes shifts (>140 nm) suggested the new bioconjugated rhenium complexes could be strong candidates for cell imaging applications. All species were taken up by MCF-7 cells and seemed to have a distinct localization pattern. However, while cells incubated with para derivatives had an anomalous cellular growth pattern and suffered from photobleaching upon irradiation, promoting cellular death, those incubated with the meta derivatives behaved in a normal manner and did not photobleach, emphasizing the importance of the ligand design when it is necessary to have an optimum outcome: i.e., cell imaging or phototherapy applications.