Luminescent Tricarbonylrhenium(I) Dipyridoquinoxaline Indole Complexes as Sensitive Probes for Indole-Binding Proteins
datasetposted on 07.05.2020, 10:00 by Kenneth Kam-Wing Lo, Ka-Shing Sze, Keith Hing-Kit Tsang, Nianyong Zhu
Luminescent tricarbonylrhenium(I) dipyridoquinoxaline indole complexes [Re(N−N)(CO)3(L)](CF3SO3) (N−N = dipyrido[3,2-f:2‘,3‘-h]quinoxaline (dpq), L = N-(3-pyridoyl)tryptamine (py-3-CONHC2H4-indole) (1a), N-(N-(3-pyridoyl)-6-aminohexanoyl)tryptamine (py-3-CONHC5H10CONHC2H4-indole) (1b); N−N = 2-(n-butylamido)dipyrido[3,2-f:2‘,3‘-h]quinoxaline (dpqa), L = py-3-CONHC2H4-indole (2a), py-3-CONHC5H10CONHC2H4-indole (2b)) and their indole-free counterparts [Re(N−N)(CO)3(py-3-CONH-Et)](CF3SO3) (py-3-CONH-Et = N-ethyl-(3-pyridyl)formamide; N−N = dpq (1c), dpqa (2c)) have been synthesized and characterized. The crystal structure of a related complex, [Re(dpqa)(CO)3(pyridine)](PF6), has also been studied. All the complexes exhibited triplet metal-to-ligand charge-transfer (3MLCT) (dπ(Re) → π*(N−N)) emission in fluid solutions at 298 K and in alcohol glass at 77 K. The emission quantum yields of the complexes were reduced upon changing from CH2Cl2 to aqueous buffer. The reduction was much more significant for the dpqa complexes than the dpq complexes due to the hydrogen-bonding interaction of the amide substituent of the dpqa ligand with water molecules. The interactions of these tricarbonylrhenium(I) complexes with indole-binding proteins including bovine serum albumin and tryptophanase have been studied by emission titrations and inhibition assays, respectively.
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Retriplet metal-to-ligand charge-transfer298 Kdpqa ligandpy -3-CONHindole-free counterpartsdpq complexesalcohol glasswater moleculesemission titrationspy -3-CONHC 5 H 10 CONHC 2 H 4fluid solutionsamide substituentinhibition assays77 Khydrogen-bonding interactionpy -3-CONH 3CH 2 Cl 2dpqa complexesindole-binding proteinsSensitive Probescrystal structurepy -3-CONHC 2 H 43 MLCTemission quantum yieldsserum albumin