pH-Dependent Excited-State Dynamics of [Ru(bpy)₃]²⁺-Modified Amino Acids:  Effects of an Amide Linkage and Remote Functional Groups

Abstract

The pH-dependent photophysical properties of a series of polypyridyl ruthenium-substituted amino acids were investigated by steady-state and time-resolved luminescence spectroscopy. [H(3)N-DAPA(Rub(2)m)-OH](PF(6))(3) (1), [H(3)N-DABA(Rub(2)m)-OH](PF(6))(3) (2), [H(3)N-Orn(Rub(2)m)-OH](PF(6))(3) (3), and [H(3)N-Lys(Rub(2)m)-OH](PF(6))(3) (4) were obtained by formation of an amide link between the omega-NH(2) group of the respective commercially available amino acid and [Rub(2)(m-OH)](2+) (b = bipyridine, m-OH = 4'-methyl-2,2'-bipyridine-4-carboxylic acid). Due to the absence of significant electronic interactions between the ruthenium chromophore and the amino acid moieties, the energetics and extinction coefficients of the absorption spectra of 1-4 do not change as a function of pH. The luminescence intensities of these complexes, however, show a marked dependence on pH. At low pH (<2), quenching via excited-state protonation of the amide link leads to short lifetimes. In the pH 2-8 range, the lifetimes depend on the amino acid side chain length of the complex. At high pH (>9), lifetimes are approaching that of [Ru(bpy)(3)](2+), suggesting that the amino acid moiety has a negligible effect on nonadiabatic pathways in the excited-state decay of the ruthenium moiety. Our results are discussed with respect to the rapidly growing interest in ruthenium-substituted amino acids as spectroscopic and mechanistic tools in biological systems.

Anion receptor coordination tripods capped by [9]ane-S3

“…Complex 6 required more careful solvent balance, eventually involving a mixture of acetone, diethyl ether and ethyl acetate to remove the majority of the excess ligand by recrystallisation, although some ligand was still found to be present by 1 2+ proved difficult, as a result of steric crowding about the metal centre. By contrast, compounds 1-6 based on [9]ane-S 3 are significantly more stable than their 6 -arene counterparts with respect to 50 solvolysis. Monitoring the 1 H-NMR spectra of the complexes showed that after a period of one week in solution, only a small proportion (<10%) of the tripodal complex had degraded to form dipodal complex and free ligand.…”

“…In previous work we have produced a range of ruthenium(II) dipodal receptors in which an 6 -arene ligand caps three fac coordination site of the octahedral metal centre. Anion binding occurs via two amino-or ureidopyridine ligands while the remaining coordination site is occupied by a chloride ligand.…”

“…The thioether displaces three of the coordinated DMSO molecules and remains coordinated to the ruthenium centre with a high degree of stability, although coordinated pyridines in the resulting [9]ane-S 3 complexes can be displaced in the presence of acetonitrile. Metathesis of the counter anions from chloride to hexafluorophosphate was achieved through addition of AgPF 6 and subsequent removal of the precipitated AgCl to give an activated solvate complex which was used in situ. Addition of a range of 3-substituted pyridine ligands gave complexes 1 -6 15 (Scheme 1), containing either a secondary amine or a urea as the anion binding functionality.…”

“…In addition a diamagnetic centre is desirable from the point of view of NMR spectroscopic characterisation. These requirements tend to favour low-spin d 6 centres such as molybdenum(0), 40 rhenium(I), ruthenium(II), rhodium(III) and iridium(III).…”

High-sensitivity staining of proteins for one- and two-dimensional gel electrophoresis using post migration covalent staining with a ruthenium fluorophore

“…The first buffer evaluated was the one recommended by Fluka, the 0. [17] on the pH dependence of the maximum emission intensities of different ruthenium complexes, solutions with more acidic pH were evaluated for the stain dilution. An unbufferred 20% ethanol solution, which led to a measured pH 4.5, allows the visualization of proteins, but very slightly.…”