Design of rhenium(I) polypyridine biotin complexes as a new of luminescent probes for avidin

This paper describes the design of a series of luminescent rhenium(I) polypyridine biotin complexes containing different spacer-arms, [Re(N-N)(CO)₃(py-4-CH2-NH-biotin)](PF₆) (py-4-CH ₂-NH-biotin = 4-(biotinamidomethyl)-pyridine; N-N = 1,10-phenanthroline, phen (1a), 3,4,7,8-tetramethyl-1,10-phenanthroline, Me ₄-phen (2a), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Me ₂-Ph₂-phen (3a), dipyrido[3,2-f.2′,3′-h] quinoxaline, dpq (4a)), [Re(N-N)(CO)₃(py-3-CO-NH-en-NH-biotin)] (PF₆) (py-3-CO-NH-en-NH-biotin = 3-(N-((2-biotinamido)ethyl)amido) pyridine; N-N = phen (1b), Me₄-phen (2b), Me₂-Ph ₂-phen (3b), dpq (4b)), and [Re(N-N)(CO)₃(py-4-CH ₂-NH-cap-NH-biotin)](PF₆) (py-4-CH₂-NH-cap-NH- biotin = 4-(N-((6-biotinamido)hexanoyl)aminomethyl)pyridine; N-N = phen (1c), Me₄-phen (2c), Me₂-Ph₂-phen (3c), dpq (4c)). Upon irradiation, all of the rhenium(I)-biotin complexes exhibited intense and long-lived triplet metal-to-ligand charge-transfer (³MLCT) (dπ(Re) →π* (diimine)) emission in fluid solutions at 298 K. The interactions of these biotin-containing complexes with avidin have been studied by 4′-hydroxyazobenzene-2-carboxylic acid (HABA) assays, emission titrations, and competitive association and dissociation assays. On the basis of the results of these experiments, homogeneous assays for biotin and avidin have been designed. © 2005 American Chemical Society.