John Moffat Kelly

TRIR spectra show distinctive features when CuTMPyP4 forms a five-coordinate ‘exciplex’ species, e.g. in D ₂ O or with thymine in poly(dT), or the triplet excited state in {d(GC) ₅ } ₂ . They show binding to the C2O of thymine in {d(CGCAAATTTGCG)} ₂ .

Ruthenium polypyridyl complexes are becoming increasingly important as probes for cellular investigations due to their luminescent properties and the possibility of exploiting the interaction with biomolecules due to the differing chirality of their enantiomers. In this study, a DNA light-switch metal complex comprising an intercalating polypyridyl ligand with an amide-linked pentyl chain [Ru(phen)₂(dpqa)]²⁺ (1) (dpqa = 2-pentylamidodipyrido[3,2-f:2',3'-h]-quinoxaline) that undergoes cell internalization is reported. The photophysical properties are dramatically impacted by the amide linker such that 1 is nonluminescent in aqueous media but strongly luminescent when bound to natural DNA. Transient visible absorption and time-resolved infrared measurements show that this is caused by the emissive MLCT excited state being rapidly deactivated in water (11 ps) to another nonemissive excited state with a characteristic infrared spectrum. In the presence of DNA, the delta enantiomer is about 9 times more emissive than the lambda. 1 is internalized by live HeLa cells, and luminescence is observed in hydrophobic pockets. In the presence of the polysorbate 80 nonionic surfactant (Tween 80), which is expected to permeabilize the cell and nuclear membranes, a strong enantiomer-dependent signal was seen from the nucleus.

Correction for ‘Time-resolved infra-red studies of photo-excited porphyrins in the presence of nucleic acids and in HeLa tumour cells: insights into binding site and electron transfer dynamics’ by Páraic M. Keane et al. , Phys. Chem. Chem. Phys. , 2022, 24 , 27524–27531, https://doi.org/10.1039/D2CP04604K.

Time-resolved IR spectra of porphyrins bound to biomolecules are reported. DFT calculations aid porphyrin vibration assignment while distinctive IR bands reveal interactions with therapeutic targets such as quadruplex DNA and proteins in HeLa cells.

A family of six Ru(II) polypyridyl complexes (1–6) which contain phenanthroline-based ligands functionalized with alkyl chains of different lengths (one methyl group, 10 and 21 carbon alkyl chains) and either 1,10-phenanthroline (phen) or 1,4,5,8-tetraazaphenanthrene (TAP) as ancillary ligands have been synthesized and characterized. The influence of the alkyl chain length on their photophysical and photochemical properties as well as in their photobiological applications has been elucidated by monitoring the changes in their MLCT-centered absorption and emission bands. The presence of one methyl group or 10 carbon alkyl chains does not seem to significantly affect the photophysical and photochemical properties of the resulting Ru(II) complexes when compared to the well-known [Ru(phen)₃]²⁺ and [Ru(TAP)₂phen]²⁺. However, an effect on their emission properties and in their ability to photosensitize singlet oxygen is observed for the Ru(II) complexes containing 21 carbon alkyl chains. The binding of these complexes to salmon testes DNA (stDNA) was investigated by observing the changes in the photophysical properties. Complexes 1, 2, 4, and 5 all showed changes in their MLCT bands that could be analyzed using conventional fitting methods, such as the Bard equation. In contrast, complexes 3 and 6, possessing long aliphatic chains, gave rise to nonclassic behavior. In addition to these analyses, both thermal denaturation and circular dichroism studies of 1–6 were carried out in the presence of stDNA which confirmed that these complexes bind to DNA. Confocal microscopy and viability studies in HeLa cervical cancer cells reveal an alkyl chain-length dependence on the cellular uptake and cytotoxicity of the resulting Ru(II) complexes due to an enhancement of their lipophilicity with increasing alkyl chain length. Thus, complexes containing 10 and 21 carbon alkyl chains are rapidly taken up into HeLa cells and, in particular, those with 21 carbon alkyl chains show a significant phototoxicity against the same cell line. Therefore, this study provides further insight into the possible modulation of the photophysical, photochemical, and photobiological properties of Ru(II) polypyridyl complexes by varying the length of the alkyl chains attached to the polypyridyl ligands coordinated to the Ru(II) center and the nature of the auxiliary groups, which we show has a significant effect on photophysical and biological properties.

Two new dinuclear Ru(II) polypyridyl complexes containing an alkyl disulphide functionalised bipyridine-based ligand and either 1,10-phenanthroline (phen) or 1,4,5,8-tetraazaphenanthrene (TAP) as ancillary ligands have been synthesised and characterised. Their attachment onto the surface of gold nanoparticles (AuNPs, average diameter of ca. 2.5 nm) resulted in the formation of two new water-soluble Ru(II)-AuNP conjugates that combine the advantageous properties of both moieties. Both free complexes show the attractive photophysical properties of Ru(II) polypyridyl complexes and a rapid cellular uptake in HeLa cervical cancer cells. However, their corresponding gold conjugates displayed lower quantum yields than those determined for the free complexes presumed to be due to an energy transfer quenching of the Ru(II) luminescence by interaction with the gold surface. Despite their diminished luminescence, confocal fluorescence microscopy studies revealed that the Ru(II)-AuNP conjugates are successfully internalised into HeLa cells and better tolerated than their free complex counterparts after 24 h incubation, which makes them potential luminescent nanomaterials for bioimaging applications.

Ruthenium polypyridyl complexes which can sensitise the photo-oxidation of nucleic acids and other biological molecules show potential for photo-therapeutic applications. In this article a combination of transient visible absorption (TrA) and time-resolved infra-red (TRIR) spectroscopy are used to compare the photo-oxidation of guanine by the enantiomers of [Ru(TAP)₂(dppz)]²⁺ in both polymeric {poly(dG-dC), poly(dA-dT) and natural DNA} and small mixed-sequence duplex-forming oligodeoxynucleotides. The products of electron transfer are readily monitored by the appearance of a characteristic TRIR band centred at ca. 1700 cm⁻¹ for the guanine radical cation and a band centered at ca. 515 nm in the TrA for the reduced ruthenium complex. It is found that efficient electron transfer requires that the complex be intercalated at a G-C base-pair containing site. Significantly, changes in the nucleobase vibrations of the TRIR spectra induced by the bound excited state before electron transfer takes place are used to identify preferred intercalation sites in mixed-sequence oligodeoxynucleotides and natural DNA. Interestingly, with natural DNA, while it is found that quenching is inefficient in the picosecond range, a slower electron transfer process occurs, which is not found with the mixed-sequence duplex-forming oligodeoxynucleotides studied.

Ultrafast time‐resolved infrared (TRIR) is used to report on the binding site of the [Ru(phen)₂(dppz)]²⁺ “light‐switch” complex with both bimolecular (Oxytricha nova telomere) and intramolecular (human telomere) guanine‐quadruplex structures in both K⁺ and Na⁺ containing solutions. TRIR permits the simultaneous monitoring both of the “dark” and “bright” states of the complex and of the quadruplex nucleobase bases, the latter via a Stark effect induced by the excited state of the complex. These data are used to establish the contribution of guanine base stacking and loop interactions to the binding site of this biologically relevant DNA structure in solution. A particularly striking observation is the strong thymine signal observed for the Na⁺ form of the human telomere sequence, which is expected to be in the anti‐parallel conformation.

Ultrafast time resolved infrared (TRIR) is used to report on the binding site of the “light-switch” complex [Ru(phen)₂(dppz)]²⁺ to i-motif structures in solution.