Phosphorylation of β-cyclodextrin enhances binding with Ru(II)polypyridyl complexes, and promotes selectivity based on chirality and ligand hydrophobicity. For [Ru(phen)2dppz]2+, inclusion of dppz results in a dramatic increase in luminescence with multiple lifetimes. The sensitive response of photophysics to the environment reveals nanoscale variation of polarity.

The luminescence of DNA-bound [Ru(phen)2dppz]2+ is shown to be highly sensitive to environmental conditions such as ionic strength, temperature, and the sequence and secondary structure of the nucleic acid, although not to bulky DNA substituents in the major groove. Each enantiomer has two characteristic lifetimes with any polynucleotide and their relative amplitudes vary as a function of binding ratio. For [poly(dA-dT)]2 as a model sequence, the longer lifetime for Δ-[Ru(phen)2dppz]2+ has been assigned to canted intercalation of the complex and the shorter lifetime is ascribed to symmetric intercalation. At a fixed binding ratio, the longer lifetime amplitude increases with increasing ionic strength, without significant change in lifetimes. Increasing temperature has a similar effect, but also affects lifetimes. In general, emission is strongest with AT-rich polynucleotides and with higher-order secondary structures, with intensity increasing as single-stranded < duplex < triplex. However, sequence-context and secondary duplex structure also influence the photophysics since emission with [poly(dA)]·[poly(dT)] is significantly higher than with [poly(dA-dT)]2 or [poly(rA)]·[poly(rU)]. The strong influence of different environmental conditions on the emission of nucleic acid-bound [Ru(phen)2dppz]2+ reflects subtle heterogeneities that are inherent elements of DNA recognition by small molecules, amplified by large changes in photophysics caused by differential exposure of the dppz nitrogens to groove hydration.

Proflavine diazide (PD) with amido-azide substituents on the amine groups and its N-methylated analogue (MePD) bind strongly to DNA by nearest-neighbour intercalation with little sequence selectivity, presenting reactive azide groups in the major groove. PD is neutral in aqueous solution but experiences binding-coupled protonation on interaction with DNA with an apparent pKa shift of 2.5 units. MePD can be click modified in situ on DNA with alkyne-functionalised thienyl-pyrrole as a precursor for conducting polymer synthesis, and remains intercalated after reaction with the substituents aligned in the groove.

A new copolymer (RuB-PSS) of ruthenium(II)bis-(2,2′-bipyridine)(4-vinyl 2,2′-bipyridine) and styrene sulfonate was prepared which tethers the ruthenium chromophore directly to the polymer backbone. The photophysical properties of the copolymer, and its luminescence quenching by viologens, were compared with those of ruthenium(II)tris-bipyridine, [Ru(bpy)3]2+, bound non-covalently to polystyrenesulfonate (PSS) via hydrophobic and electrostatic interactions. Enhancement of ruthenium polypyridyl complex luminescence in both systems is due to decreased rates of non-radiative decay when removed from bulk water as well as reduced oxygen quenching. Molecular dynamics simulations show an open PSS chain conformation with induction of local curvature around the ruthenium centres. Hence, the complexes remain exposed to water, albeit less so than in bulk solution, as evidenced by low enhancement of bound [Ru(phen)2dppz]2+ emission. Quenching by O2 is hindered for both systems due to combined polarity, ionic strength, and viscosimetric effects that influence local concentrations and diffusion of reactants. Electron transfer quenching of the Ru centre by zwitterionic propyl viologen sulfonate (PVS0) and cationic methyl viologen (MV2+) is enhanced for [Ru(bpy)3]2+/PSS, but retarded for RuB-PSS, despite the attraction of the quenchers for PSS. PSS binding hinders separation of the electron transfer products relative to aqueous solution, excepting an increase for RuB-PSS/PVS0. We conclude that anionic hydrophobic polymers such as PSS can differentially influence forward- and reverse- electron transfer reactions depending on the charge and hydrophobicity of the reactants. In the context of small molecule binding, we find that PSS provides a tenable model for DNA.

A new copolymer (RuB-PSS) of ruthenium(II)bis-(2,2′-bipyridine)(4-vinyl 2,2′-bipyridine) and styrene sulfonate was prepared which tethers the ruthenium chromophore directly to the polymer backbone. The photophysical properties of the copolymer, and its luminescence quenching by viologens, were compared with those of ruthenium(II)tris-bipyridine, [Ru(bpy)3]2+, bound non-covalently to polystyrenesulfonate (PSS) via hydrophobic and electrostatic interactions. Enhancement of ruthenium polypyridyl complex luminescence in both systems is due to decreased rates of non-radiative decay when removed from bulk water as well as reduced oxygen quenching. Molecular dynamics simulations show an open PSS chain conformation with induction of local curvature around the ruthenium centres. Hence, the complexes remain exposed to water, albeit less so than in bulk solution, as evidenced by low enhancement of bound [Ru(phen)2dppz]2+ emission. Quenching by O2 is hindered for both systems due to combined polarity, ionic strength, and viscosimetric effects that influence local concentrations and diffusion of reactants. Electron transfer quenching of the Ru centre by zwitterionic propyl viologen sulfonate (PVS0) and cationic methyl viologen (MV2+) is enhanced for [Ru(bpy)3]2+/PSS, but retarded for RuB-PSS, despite the attraction of the quenchers for PSS. PSS binding hinders separation of the electron transfer products relative to aqueous solution, excepting an increase for RuB-PSS/PVS0. We conclude that anionic hydrophobic polymers such as PSS can differentially influence forward- and reverse- electron transfer reactions depending on the charge and hydrophobicity of the reactants. In the context of small molecule binding, we find that PSS provides a tenable model for DNA.

The luminescence of DNA-bound [Ru(phen)2dppz]2+ is shown to be highly sensitive to environmental conditions such as ionic strength, temperature, and the sequence and secondary structure of the nucleic acid, although not to bulky DNA substituents in the major groove. Each enantiomer has two characteristic lifetimes with any polynucleotide and their relative amplitudes vary as a function of binding ratio. For [poly(dA-dT)]2 as a model sequence, the longer lifetime for Δ-[Ru(phen)2dppz]2+ has been assigned to canted intercalation of the complex and the shorter lifetime is ascribed to symmetric intercalation. At a fixed binding ratio, the longer lifetime amplitude increases with increasing ionic strength, without significant change in lifetimes. Increasing temperature has a similar effect, but also affects lifetimes. In general, emission is strongest with AT-rich polynucleotides and with higher-order secondary structures, with intensity increasing as single-stranded < duplex < triplex. However, sequence-context and secondary duplex structure also influence the photophysics since emission with [poly(dA)]·[poly(dT)] is significantly higher than with [poly(dA-dT)]2 or [poly(rA)]·[poly(rU)]. The strong influence of different environmental conditions on the emission of nucleic acid-bound [Ru(phen)2dppz]2+ reflects subtle heterogeneities that are inherent elements of DNA recognition by small molecules, amplified by large changes in photophysics caused by differential exposure of the dppz nitrogens to groove hydration.

Phosphorylation of β-cyclodextrin enhances binding with Ru(II)polypyridyl complexes, and promotes selectivity based on chirality and ligand hydrophobicity. For [Ru(phen)2dppz]2+, inclusion of dppz results in a dramatic increase in luminescence with multiple lifetimes. The sensitive response of photophysics to the environment reveals nanoscale variation of polarity.