# Tetrasodium tris(bathophenanthroline disulfonate)ruthenium(II)

Tetrasodium tris(bathophenanthroline disulfonate)ruthenium(II) (Na$_4$Ru(bps)$_3$) is a sodium salt of coordination compound. In this form, it is the salt of a sulfonic acid. This compound is an extension of the phenanthroline series of coordination compounds. Ruthenium(II) tris(bathophenanthroline disulfonate), referring to the anionic fragment, is used as a protein dye in biochemistry for differentiating and detecting different proteins in laboratory settings.
In recent years, 2-D electrophoresis has been widely accepted as a standard procedure to separate complex protein mixtures in proteome studies (Proteomics). Protein visualisation by Ruthenium(II) tris(bathophenthroline disulfonate) has become a firmly established and widely used method in proteomic analysis and a crucial step in gene expression profiling.
For protein detection, it is advantageous to use fluorescent labels containing chromophores which have longer excitation wavelength and emission wavelength than the aromatic amino acids. The dyes used for this important step should combine attributes like good signal to background ratio (contrast), broad linear dynamic range, broad application range, photochemical stability and compatibility to protein identification techniques, e.g. mass spectrometry (MS) or Western blotting.

## History

Originally, the ruthenium transition metal complex, ruthenium(II) tris(4,7-diphenyl-1,10-phenanthroline disulfonate) also termed as ruthenium(II) tris(bathophentroline disulfonate) (RuBPS) was synthesized by Bannwarth as a precursor molecule for a dye that was used as a non-radioactive label for oligo nucleotides. Within 5 years, similar transition metal complexes had been recognized as workable protein detection reagents, and shortly afterwards the europium analog of RuBPS was demonstrated as an effective fluorescent protein detection reagent. The first reported use of RuBPS for protein detection appears to be the commercial release of the proprietary Sypro Ruby protein staining solution in 1999. While Sypro Ruby is proprietary & is not stated to have RuBPS as the major component, it is stated to have ruthenium, and Rabilloud et al. synthesized RuPBS and compared it to Sypro Ruby, finding them to be highly similar, albeit not identical, reagents for fluorescent detection of proteins in polyacrylamide gels. Notably, Rabilloud et al. made their comparisons against the first formulation of Sypro Ruby, the second (and presumed current) formulation of Sypro Ruby has the same product numbers (but distinct lot numbers) and an increased performance with diverse fixative solutions.
The fact that RuBPS is not only easy to synthesize but also easy to handle, induced further developments in this field.

## Ongoing developments

Lamanda et al. improved the RuBPS staining protocol by selectively destaining the polyacrylamide matrix while the protein content remained tinctured. This new technique entailed a variety of advantages like strong signals, ameliorated signal to background ratio, better linearity and advanced baseline resolution. More recently, heteroleptic ruthenium(II) complexes highly similar to RuBPS were shown to have some improved properties, specifically a broader pH range where they could be used.