Synthesis and Biological Activities of Luminescent 5,6-Membered Bis(Metallacyclic) Platinum(II) Complexes

Four couples of 5,6-membered bis(metallacyclic) Pt(II) complexes with acetylide and isocyanide auxiliary ligands have been prepared and characterized. The structures of (-)-2 and (-)-3 are confirmed by single-crystal X-ray diffraction, showing a distorted square-planar coordination environment around the Pt(II) nucleus. Both solutions and solid samples of all complexes are emissive at RT. Acetylide-coordinated Pt(II) complexes have a lower energy emission than those isocyanide-coordinated ones. The emission spectra of N^N'*C-coordinated Pt(II) derivatives show a lower energy emission maximum relative to N^C*N'-coordinated complexes with the same auxiliary ligand. Moreover, the difference between cyclometalated N^N'*C and N^C*N' ligands exerts a more remarkable effect on the emission than the auxiliary ligands acetylide and isocyanide. Cytotoxicity and cell imaging of luminescent 5,6-membered bis(metallacyclic) Pt(II) complexes have been evaluated.

A redox-activated Pt(IV) pro-probe: From G-quadruplex imaging to cancer therapy

Efficient uptake to both cytoplasm and nucleus in live cells remains a key obstacle for G-quadruplex targeting fluorophores. We developed a Pt(IV) complex by oxidizing a bisphenanthrolinyl Pt(II) complex, which is our first generation G-quadruplex specific fluorogenic probe.¹⁵ The axial lipophilic ligand assists Pt(IV) pro-probe to enter live cells and reach the nucleus rapidly. In situ reduction of Pt(IV) pro-probe restores parental Pt(II) complex, and sequentially lights up both RNA and DNA G-quadruplexes in live cancerous cells simultaneously. Pt(IV) pro-probe shows potent cytotoxicity after long time incubation as a dual-functional theranostic agent.

A theoretical study on the on-off phosphorescence of novel Pt(ii)/Pt(iv)-bisphenylpyridinylmethane complexes

An in-depth theoretical study on the Pt(ii)/Pt(iv)-bisphenylpyridinylmethane complexes was carried out, which focused on the geometric/electronic structures, excitation procedures, on-off phosphorescence mechanisms, and structure-optical performance relationships. The key roles of the linkages (LK) connected in the middle of phenylpyridines were carefully investigated using multiple wavefunction analysis methods, such as non-covalent interaction (NCI) visualizations and natural bond orbital (NBO) studies. The phosphorescence-off phenomenon was considered by hole-electron analysis and visualizations, spin-orbit coupling (SOC) studies, and NBO analysis. Through these investigations, the relationship of the substituents in LK and the optical performances were revealed, as well as the fundamental principles of the phosphorescence-quenching mechanism in Pt(iv) complexes, which pave the way for further performance/structural renovation works. In addition, an intuitive visualization method was developed using a heatmap to quantitatively express the SOC matrix elementary (SOCME), which is helpful for big data simplification for phosphorescence analysis.

Portrait of a Family of Highly Stabilizing and Selective Guanine Quadruplex Platinum(II)-Based Binders

The long-standing history of platinum coordination complexes in nucleic acid recognition attests to the unique suitability of such species for therapeutic applications. Here, we report the synthetic exploration and development of a family of di-imine ligands, and their platinum(II) complexes, elaborated on a 3-(2-pyridyl)-[1,2,4]triazolo[4,3-a]pyridine platform which, in its unsubstituted form, has recently been shown to display exceptional capabilities for guanine quadruplex (G4) targeting. The identification of facile, high-yielding synthetic methods for the derivatization of this platform for the incorporation of additional sites of interactions with guanine quadruplex loops and grooves, along with the optimization of platinum(II) complexation methods, are discussed. Gratifyingly, preliminary biophysical screening of this novel family of binders validates all but one family members as robust G4 binders and highlights enhanced selectivity for quadruplex versus duplex DNA compared to the parent compound. These results bear promise for practical developments based on this platform.

Ginsenoside Compound K Assisted G-Quadruplex Folding and Regulated G-Quadruplex-Containing Transcription

Ginsenoside compound K (CK) is one of the major metabolites of the bioactive ingredients in Panax ginseng, which presents excellent bioactivity and regulates the expression of important proteins. In this work, the effects of CK on G-quadruplexes (G4s) were quantitatively analyzed in the presence and absence of their complementary sequences. CK was demonstrated to facilitate the formation of G4s, and increase the quantity of G4s in the competition with duplex. Thermodynamic experiments suggested that the electrostatic interactions were important for G4 stabilization by CK. CK was further found to regulate the transcription of G4-containing templates, reduce full-length transcripts, and decrease the transcription efficiency. Our results provide new evidence for the pharmacological study of ginsenosides at the gene level.

Study on the Functionalization and Signaling Efficiency of the Hybridization Chain Reaction Using Traditional and Single Molecular Characterizations

As an important enzyme-free amplifier, the hybridization chain reaction (HCR) uses an ssDNA to trigger cycled displacement interactions between substrate hairpins and finally form elongated dsDNA concatamer mixtures. In many cases, to provide a signal probe or advanced function, additional oligonucleotides (named hairpin tails) have to be extended upon classic HCR hairpin substrates, but by doing so the HCR assembly efficiency and signal-to-noise ratio (SNR) may get seriously reduced. In this Article, a rational and general model that may guide the study on HCR functionalization and signaling efficiency is provided. We rationally design a four-hairpin model HCR system (4H-HCR) in which one or more hairpin substrates are appended with additional tails as a signaling probe. After HCR assembly, two adjacent tails are supposedly integrating into a full G-quadruplex structure to provide the evidence or signal for the assembly. A systematic study has been applied to reveal the relationship between the "tail-design" with assembly efficiency and SNR. A clear design rule-set guiding the optimized assembly and signal has been provided for traditional electrophoresis and G-quadruplex-enhanced fluorescence signal. Importantly, solid-state nanopore single molecular detection has been innovatively introduced and recommended as an "antirisk" and "mutual benefit" readout to traditional G-quadruplex signaling. Nanopore detection can provide a clear signal distinguished before and after the HCR reaction, especially when the traditional G-quadruplex-enhanced signal only provides low SNR. The G-quadruplex, in turn, may enhance the nanopore signal amplitude via increasing the diameter of the HCR products.

Metal complexes as optical probes for DNA sensing and imaging

Transition and lanthanide metal complexes have rich photophysical properties that can be used for cellular imaging, biosensing and phototherapy. One of the applications of such luminescent compounds is the detection and visualisation of nucleic acids. In this brief review, we survey the recent literature on the use of luminescent metal complexes (including Re^I, Ru^II, Os^II, Ir^III, Pt^II, Eu^III and Tb^III) as DNA optical probes, including examples of compounds that bind selectively to non-duplex DNA topologies such as quadruplex, i-motif and DNA mismatches. We discuss the applications of metal-based luminescent complexes in cellular imaging, including time-resolved microscopy and super-resolution techniques. Their applications in biosensing and phototherapy are briefly mentioned in the relevant sections.