Synthesis, characterisation and bioimaging of a fluorescent rhenium-containing PNA bioconjugate

Abstract

A new rhenium tricarbonyl complex of a bis(quinoline)-derived ligand (2-azido-N,N-bis((quinolin-2-yl)methyl)ethanamine, L-N(3)), namely [Re(CO)(3)(L-N(3))]Br was synthesized and characterized indepth, including by X-ray crystallography. [Re(CO)(3)(L-N(3))]Br exhibits a strong UV absorbance in the range 300-400 nm with a maximum at 322 nm, and upon photoexcitation, shows two distinct emission bands at about 430 and 560 nm in various solvents (water, ethylene glycol). [Re(CO)(3)(L-N(3))]Br could be conjugated, on a solid phase, to a peptide nucleic acid (PNA) oligomer using the copper(I)-catalyzed azide-alkyne cycloaddition reaction (Cu-AAC, "click" chemistry) and an alkyne-containing PNA building block to give Re-PNA. It was demonstrated that upon hybridisation with a complementary DNA strand (DNA), the position of the maxima and emission intensity for the hybrid Re-PNA·DNA remained mainly unchanged compared to those of the single strand Re-PNA. The rhenium-containing PNA oligomer Re-PNA could be then mediated in living cells where they have been shown to be non-toxic contrary to the general notion that organometallic compounds are usually unstable under physiological conditions and/or cytotoxic. Furthermore, Re-PNA could be detected in living cells using fluorescent microscopy.

Enhanced Cytotoxicity through Conjugation of a “Clickable” Luminescent Re(I) Complex to a Cell-Penetrating Lipopeptide

“…Indeed, while the concentration of Re-myr-Tat in the cell medium was five times lower than that of the complex, the cells incubated with Re-myr-Tat appeared much brighter, indicating significantly higher uptake (it is important to keep in mind that the intensity of the emission signal of a compound in the cells sometimes fails to correlate with uptake, as luminescence can be quenched in the cellular environment). 28,64 In terms of subcellular localization, the complex and the bioconjugate were visualized in the cytoplasm (although weak signals were sometimes detected in the nucleoli of cells incubated with the complex), a localization typically observed for this type of Re complex.…”

Evaluation of Perylene Bisimide‐Based RuII and IrIII Complexes as Photosensitizers for Photodynamic Therapy

“…[53] However, our group and others have previously reported that, in some cases, luminescence microscopy can provide inconclusive results on the cellular localization of metal complexes, because of their low emission quantum yields or luminescence quenching. [20,22,68,69] Therefore, we decided to investigate the cellular uptake and organelles localization of the two complexes via ICP-MS. [70] The cellular uptake of 1 and 2 was evaluated on HeLa cells to compare these results with the luminescence microscopy images. HeLa cells were incubated with 1 (4 and 20 μM) and 2 (4 μM) for 4 h in the dark, and the metal content in the entire cell and in the different cellular fractions was then detected by using ICP-MS analysis; the results are reported in Figure S15.…”

Metal–Carbon Bonds in Biopolymer Conjugates: Bioorganometallic Nucleic Acid Chemistry

“…35 Recently, this approach was extended to allow functionalization with different and multiple organometallic moieties 7, potentially giving the resulting oligomer a variety of electrochemical and spectroscopic properties. 31,36 The main application of ferrocene-functionalized oligonucleotides is electrochemical sensing, with a common approach being immobilization on gold electrodes using terminal thiol groups. 15,17,18,37 Such systems typically monitor the changes in current (arising from oxidation of the tag) between singlestranded and duplex DNA, with the unbound probe strand sometimes formed into a hairpin (Figure 3).…”

“…Ferrocene, 28,29 cobaltocenium 6, 29 rhenium and technetium tricarbonyls, 30,31 and ruthenocene 32 have all been tagged to PNA using amide bond forming reactions. Click chemistry has also been used, both to introduce ferrocene to the center of the strand 33 and to synthesize a family of ferrocene-conjugated PNA probes, 34 with the thermal stability of duplexes formed with DNA then investigated.…”