The synthesis and photophysical characterization of two osmium(II) polypyridyl complexes, [Os(TAP) 2 dppz] 2+ ( 1 ) and [Os(TAP) 2 dppp2] 2+ ( 2 ) containing dppz (dipyrido[3,2- a :2′,3′- c ]phenazine) and dppp2 (pyrido[2′,3′:5,6]pyrazino[2,3- f ][1,10]phenanthroline) intercalating ligands and TAP (1,4,5,8-tetraazaphenanthrene) ancillary ligands, are reported. The complexes exhibit complex electrochemistry with five distinct reductive redox couples, the first of which is assigned to a TAP-based process. The complexes emit in the near-IR ( 1 at 761 nm and 2 at 740 nm) with lifetimes of >35 ns with a low quantum yield of luminescence in aqueous solution (∼0.25%). The Δ and Λ enantiomers of 1 and 2 are found to bind to natural DNA and with AT and GC oligodeoxynucleotides with high affinities. In the presence of natural DNA, the visible absorption spectra are found to display significant hypochromic shifts, which is strongly evident for the ligand-centered π–π* dppp2 transition at 355 nm, which undergoes 46% hypochromism. The emission of both complexes increases upon DNA binding, which is observed to be sensitive to the Δ or Λ enantiomer and the DNA composition. A striking result is the sensitivity of Λ- 2 to the presence of AT DNA, where a 6-fold enhancement of luminescence is observed and reflects the nature of the binding for the enantiomer and the protection from solution. Thermal denaturation studies show that both complexes are found to stabilize natural DNA. Finally, cellular studies show that the complexes are internalized by cultured mammalian cells and localize in the nucleus.

Defining the subcellular localisation of the proteome for an organism of interest is a critical next step following genome sequencing. Knowledge of protein subcellular localisation provides insight into the functionality of the normal cell, as well during disease states. However, the presence of gene isoforms, alternative splicing and posttranslational modifications significantly increase the number of protein variants encoded by a single gene, making this a complex task. In the last 20 years, parallel approaches using fractionation and mass spectrometry, synthesis of large libraries of open reading frames fused to genes encoding fluorescent proteins, as well as production of thousands of antibodies have all contributed to the systematic analysis of protein localisation. Alongside these methods, improved bioinformatic predictors, machine learning and deep learning algorithms have also evolved as essential tools. A combinatorial approach of these methods now brings us close to systematically defining the subcellular proteome for many organisms. Key Concepts Subcellular localisation is a critical determinant in understanding protein function. Data from genome sequencing projects provide the fundamental information from which approaches to understand protein localisation can be initiated. Parallel approaches using fluorescence microscopy are being applied in a high‐throughput manner to systematically reveal the subcellular localisation of large numbers of proteins in different cells. The primary techniques to determine protein localisation are mass spectrometry‐based proteomics, production of antibodies and expression of fluorescently tagged proteins. There is increasing use of computational biology tools to aid the automated classification of subcellular localisation. Large image datasets can be interrogated by machine learning software algorithms to automatically classify proteins to specific localisations. Deep learning methods, which can work independently of training datasets, have become the newest tool to automatically assign protein localisation from image sets. Automated approaches combining both experimental and computational methods are likely to become the primary means by which subcellular localisation is determined from new cell systems.

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