A sulfhydryl-reactive ruthenium (II) complex and its conjugation to protein G as a universal reagent for fluorescent immunoassays

Physico-chemical characterization studies of collagen labelled with Ru(II) polypyridyl complex

The rich luminescence behaviour exerted by transition metal complexes has found significant role in the development of biomolecular and cellular probes. The conjugation of fluorophore to a protein has its own advantage over the label-free system due to its high sensitivity. While numerous proteins have been labelled with either organic or inorganic fluorophores, the conjugation of luminescent transition metal complexes with collagen has not yet been attempted. Here, in this study, the conjugation of a Ru(II) polypyridyl complex with collagen was carried out and its physico-chemical characterization was studied. The conjugation of Ru(II) to collagen was characterized by UV-Visible, fluorescence and ATR-FT-IR spectroscopy. The conjugation of Ru(II) did not alter the triple helical structure of the collagen as evidenced from CD spectral data. The luminescence behaviour of the Ru-tagged collagen was found to be similar to that of the commercially available fluorescein isothiocyanate (FITC) tagged collagen with increase in luminescence upon addition of collagenase. Gel-based collagenase assay showed that the digestion of collagen can be vizualized using UV light due to intrinsic fluorophore tag without carrying out the staining-destaining processes. Energy dispersive X-Ray analysis (EDAX) confirms the presence of Ru in Ru-collagen fibrils. To the best of our knowledge, this is the first report on the conjugation of a Ru(II) complex with the fibrous protein collagen that exhibits similar property as of FITC-collagen and can be used as an alternative.

Metal Peptide Conjugates in Cell and Tissue Imaging and Biosensing

Metal complex luminophores have seen dramatic expansion in application as imaging probes over the past decade. This has been enabled by growing understanding of methods to promote their cell permeation and intracellular targeting. Amongst the successful approaches that have been applied in this regard is peptide-facilitated delivery. Cell-permeating or signal peptides can be readily conjugated to metal complex luminophores and have shown excellent response in carrying such cargo through the cell membrane. In this article, we describe the rationale behind applying metal complexes as probes and sensors in cell imaging and outline the advantages to be gained by applying peptides as the carrier for complex luminophores. We describe some of the progress that has been made in applying peptides in metal complex peptide-driven conjugates as a strategy for cell permeation and targeting of transition metal luminophores. Finally, we provide key examples of their application and outline areas for future progress.

Synthesis and DNA interaction studies of Ru(II) cell penetrating peptide (CPP) bioconjugates

The synthesis of the first bioconjugates of a set of ruthenium(II) dipyridophenazine complexes with two different cell penetrating peptides (CPPs) is described. The CPPs, an arginine rich TAT-9 (RKKRRQRRR) sequence and the Xentry peptide (LCLRPVG), were synthesized using standard SPPS protocols, and the bioconjugates were obtained by the microwave-assisted coupling of the HOBt/TBTU preactivated metal complexes with the respective peptides on Wang resin. The racemic metal complexes were obtained by modified literature procedures. The bioconjugates were cleaved from the resin, purified by semi-preparative HPLC and characterized by analytical HPLC, high resolution mass spectrometry (HR-MS), and NMR spectroscopy. Despite the bioconjugation of the peptides to the dppz ligand, DNA intercalation was observed by CD spectroscopy, viscometry and the characteristic switch-on fluorescence of this class of compounds. Furthermore, the cellular uptake of the Xentry bioconjugates was confirmed by live cell imaging. Like the parent metal complexes, the bioconjugates show low in vitro cytotoxicity (IC₅₀ > 80 μM), which is similar to the respective metal complexes alone.