A photostable Ru(2,2-biquinoline)2(3-(2-pyridyl)-5-(4-carboxyphenyl)-1,2,4-triazolate) (Ru(biq)2(trzbenzCOOH)) complex that exhibits near-infrared (NIR) emission centred at 786 nm is reported. The parent complex was conjugated via amide coupling to a cell-penetrating peptide sequence octa-arginine (R8), and two signal peptide sequences; the nuclear localizing sequence (NLS) VQRKRQKLMP and the mitochondria penetrating peptide (MPP) FrFKFrFK(Ac) (r = D isomer of arginine, Ac = terminal lysine amine acetyl blocked). Notably, none of the peptide conjugates were cell-permeable as chloride salts but efficient and rapid membrane permeation was observed post ion exchange with perchlorate counterion. Also, surprisingly, all three peptide conjugates exhibited potent dark cytotoxicity in both CHO and HeLa cell lines. The peptide conjugates induce cell death through a caspase dependent apoptotic pathway. At the minimum concentration of dye (approx. 15 μM) required for cell imaging, only 20% of the cells were viable after a 24 h incubation period. To overcome cytotoxicity, the parent complex was PEGylated; this dramatically decreased cytotoxicity, where 50% of cells were viable even at 150 μM concentration after 24 h. Confocal luminescence microscopy indicated that all four bioconjugates, peptides in perchlorate form and polyethylene glycol (PEG) in chloride form, were rapidly internalized within the cell. However, interestingly the precise localisation by the signal peptides observed in related complexes was not observed here and the peptide conjugates were unsuitable as luminescent probes for cell microscopy due to their high cell toxicity. The poor targeting of signal peptides in this instance is attributed to the high lipophilicity of the metal centre.

中文翻译：

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光稳定的近红外发射钌（II）结合物；活细胞的摄取和生物活性。

具有光稳定性的Ru（2,2-联喹啉）2（3-（2-吡啶基）-5-（4-羧苯基）-1,2,4-三唑酸酯）（Ru（biq）2（trzbenzCOOH））络合物呈现出接近报告了中心位于786 nm的红外（NIR）发射。通过酰胺偶联将母体复合物缀合至细胞穿透肽序列八-精氨酸（R8）和两个信号肽序列；核定位序列（NLS）VQRKRQKLMP和线粒体穿透肽（MPP）FrFKFrFK（Ac）（r =精氨酸的D异构体，Ac =末端赖氨酸胺被乙酰基阻断）。值得注意的是，没有肽缀合物作为氯化物盐是细胞可渗透的，但是在与高氯酸盐抗衡离子进行离子交换后观察到有效且快速的膜渗透。而且，令人惊讶地，所有三种肽缀合物在CHO和HeLa细胞系中均显示出强的暗细胞毒性。肽缀合物通过半胱天冬酶依赖性凋亡途径诱导细胞死亡。在细胞成像所需的最小染料浓度（约15μM）下，在24小时的孵育期后，只有20％的细胞能够存活。为了克服细胞毒性，将母体复合物聚乙二醇化。这大大降低了细胞毒性，即使24小时后即使浓度为150μM，也有50％的细胞存活。共聚焦发光显微镜表明，所有四种生物共轭物，即高氯酸盐形式的肽和氯化物形式的聚乙二醇（PEG），都在细胞内迅速内化。然而，有趣的是，此处未观察到在相关复合物中观察到的信号肽的精确定位，并且由于其高细胞毒性，因此肽缀合物不适合用作细胞显微镜的发光探针。