Synthesis, Photophysical and Electrochemical Properties, and Biological Labeling Studies of Cyclometalated Iridium(III) Bis(pyridylbenzaldehyde) Complexes: Novel Luminescent Cross‐Linkers for Biomolecules

Abstract

We report the synthesis, characterization, photophysical, and electrochemical properties of a series of luminescent cyclometalated iridium(III) complexes containing two aldehyde functional groups [Ir(pba)(2)(N-N)](PF(6)) (Hpba=4-(2-pyridyl)benzaldehyde; N-N=2,2'-bipyridine, bpy (1), 1,10-phenanthroline, phen (2), 3,4,7,8-tetramethyl-1,10-phenanthroline, 3,4,7,8-Me(4)-phen (3), 4,7-diphenyl-1,10-phenanthroline, 4,7-Ph(2)-phen (4)). The X-ray crystal structure of complex 1 has been investigated. Upon photoexcitation, complexes 1-4 exhibit intense and long-lived emission in fluid solutions at 298 K and in low-temperature glass. The luminescence is assigned to a triplet intra-ligand ((3)IL) excited state associated with the pba(-) ligand, probably with mixing of some triplet metal-to-ligand charge-transfer ((3)MLCT) (dpi(Ir)-->pi*(pba(-))) character. Since each of these complexes possesses two aldehyde groups, which can react with the primary amine groups of biomolecules to form stable secondary amines after reductive amination, we have investigated the possibility of these complexes as novel luminescent cross-linkers for biological substrates. L-Alanine has been labeled with complexes 1-4 to give the luminescent bioconjugates 1-(Ala)(2)-4-(Ala)(2). These conjugates show strong photoluminescence with long emission lifetimes under ambient conditions. On the basis of the emission energy trend, the excited state of these luminescent bioconjugates is likely to bear a high parentage of (3)MLCT (dpi(Ir)-->pi*(N-N)) character. In addition, the glycoprotein avidin (Av) has also been conjugated with complexes 1-4 to give the bioconjugates 1-Av-4-Av. Upon photoexcitation, these bioconjugates also display intense and long-lived (3)MLCT (dpi(Ir)-->pi*(N-N)) emission in aqueous buffer at 298 K. Furthermore, a heterogeneous competitive assay for biotin has been developed using 2-Av and biotinylated microspheres. We have shown that complexes 1-4 represent a new class of multicolor luminescent cross-linkers for biomolecular species.

Antagonizing STAT3 Dimerization with a Rhodium(III) Complex

“…This data suggests that the covalent binding of 12 to STAT3 is unlikely to play a role in the mechanism of action of this complex and is consistent with previous work by Lo and co-workers, who showed that the reaction of an iridium(III) complex, which also contained the 4-(pyridin-2-yl)benzaldehyde Ĉ N ligand, with alanine formed only trace amounts of adducts, thus indicating facile hydrolysis of the imine intermediates. [21] We next performed a STAT3 pull-down assay using A375 cells co-expressing FLAG-STAT3 and STAT3-GFP to investigate whether 12 could inhibit STAT3 dimerization in cells. In the absence of 12, STAT3-GFP co-immunoprecipitated with FLAG-STAT3 (Figure 3 d).…”

Luminescent Transition Metal Complexes as Biological Labels and Probes

“…The complexes [Ir(pba) 2 (NN )] + (22) coordinated with different diimine ligands (NˆN) and the aldehydecontaining cyclometallating ligand pba -can react with the primary amine of biomolecules to form an imine that can be readily reduced to a stable secondary amine [58]. X-ray crystallographic studies of the bipyridine complex reveal a separation of ca.…”

“…The cross-linked avidin conjugates also show longlived and intense luminescence at an energy similar to that of their alanine counterparts. Given the intense photoluminescence of the avidin conjugates, a simple heterogeneous competitive assay for biotin using one of the con- [58] jugates and biotinylated microspheres has been developed. In the assay, immobilised biotin molecules compete with free biotin analyte on binding to the luminescent avidin conjugate.…”

Exploitation of Luminescent Organometallic Rhenium(I) and Iridium(III) Complexes in Biological Studies

“…+ (31) coordinated with different diimine ligands (N^N) and the aldehyde-containing cyclometallating ligand pba can react with the primary amine of biomolecules to form a stable secondary amine after reduction [72]. + (N^C = ppy, mppy, mppz, bzq, pq; R = NH 2 , CHO, NCS, NHCO-CH 2 I) (32) [65,73,74].…”