Description
Both the Re-186 and 188 isotopes emit beta and gamma rays with energies suitable for cancer treatment and for diagnostic imaging. Therefore, rhenium complexes are expected to be used as radiopharmaceuticals for simultaneous treatment and diagnosis. In addition, the rhenium complexes with visible luminescence make it easier to visually monitor the tissues and cells in which the complexes accumulate. Since luminescence is affected by the surrounding environment, such as temperature, pH, and oxygen concentration, the luminescence measurement can provide information about the surroundings. In this study, a series of ligands, [2-(3-pyrazolyl)pyridine (H-N2py), 2-[1,2,3]-triazol-4-yl-pyridine (H-N3py), and 2 -(tetrazol-5-yl)-pyridine (H-N4py)] were used. The tricarbonyl Re(I) complexes [ReCl(CO)3(H-N2py)] (1-H), [ReCl(CO)3(H-N3py)] (2-H), [ReCl(CO)3(N4py)]- (3) were newly synthesized. The new complexes were characterized by elemental analysis, single crystal X-ray structure analysis, IR, UV-Vis, and 1H NMR spectroscopy. The complexes 1-H and 2-H are protonated, while 3 is deprotonated because H-N4py has a smaller pKa than H-N2py and H-N3py. The complexes 1-H and 2-H were deprotonated by 1,8-diazabicyclo[5.4.0]undec-7-one in DMSO to give [ReCl(CO)3(N2py)]- (1) and [ReCl(CO)3(N3py)]- (2). The complex 3 was not protonated by an addition of p-toluenesulfonic acid in DMSO. For 1-H, the emission maximum wavelength (em) at 557 nm in DMSO was not changed upon deprotonation, while the emission quantum yield (em) decreased from 5.0 × 10-3 to 7.0 × 10-4. The complex 2-H showed a 17 nm blue shift of the emission maximum from 553 nm to 536 nm upon deprotonation and the em decreased from 3.0 × 10-3 to 1.1 × 10-3. The author is grateful to F-REI (JPFR24040302) for the support of travel expenses.
