Elemental and molecular mass spectrometric strategies for probing interactions between DNA and new Ru(ii) complexes containing phosphane ligands and either a tris(pyrazol-1-yl)borate or a pyridine bis(oxazoline) ligand

Abstract

In the present work we evaluate the potential as chemotherapeutic agents of two groups of new Ru(II) complexes containing water soluble phosphane ligands and either a tris(pyrazol-1-yl)borate (Tp) or a pyridine bis(oxazoline) (pybox) ligand and their interactions with DNA. Since the interaction of these drugs can be diverse (from binding to DNA nucleobases to intercalation within the DNA strands), different approaches need to be taken for addressing such possibilities. In this regard, mass spectrometry, MS (elemental and molecular), has been exploited in this study to unequivocally elucidate the structures of the interaction products (molecular MS) and their quantity (elemental MS). First, a systematic evaluation of the interaction of the four Ru–Tp complexes with the individual DNA nucleotides revealed the formation of the Ru–Tp complex containing the phosphane 1-CH₃-PTA and chloride as ligands (Asr3), which is the most reactive species providing positive interactions with 2′-deoxyguanosine-5′-monophosphate (dGMP) in a 1 : 1 stoichiometry confirmed by electrospray MS (ESI-MS). The further coupling of liquid chromatography to inductively coupled plasma mass spectrometric (ICP-MS) detection permitted Ru-specific detection to obtain quantitative data on the interaction showing reaction yields >75%. This interaction was also confirmed, when dGMP was present in an oligonucleotide structure, by both MS techniques and also in the case of DNA. On the other hand, if the Ru-complex interaction with DNA occurs through the intercalation between the DNA strands without specific binding, alternative analytical techniques need to be applied. Here, we illustrate the use of column-gel electrophoresis (GE) on-line coupled to ICP-MS which is a suitable technique to address conformational changes in plasmid DNA induced by interaction with the two assayed Ru–pybox complexes.