Structure and Reversible Pyran Formation in Molybdenum Pyranopterin Dithiolene Models of the Molybdenum Cofactor

The syntheses and X-ray structures of two molybdenum pyranopterin dithiolene complexes in biologically relevant Mo(+4) and Mo(+5) states are reported. Crystallography reveals these complexes possess a pyran ring formed through a spontaneous cyclization reaction of a dithiolene side-chain hydroxyl group at a C=N bond of the pterin. NMR data on the Mo(+4) complex suggests a reversible pyran ring cyclization occurs in solution. These results provide experimental evidence that the pyranopterin dithiolene ligand in molybdenum and tungsten enzymes could participate in catalysis through dynamic processes modulated by the protein

Interactions Of Ruthenium(II) Polypyridyl Complexes With Human Telomeric DNA

Eight [Ru(bpy)₂L]²⁺ and three [Ru(phen)₂L]²⁺ complexes (where bpy = 2,2′-bipyridine and phen = 1,10-phenanthroline are ancillary ligands, and L = a polypyridyl experimental ligand) were investigated for their G-quadruplex binding abilities. Fluorescence resonance energy transfer melting assays were used to screen these complexes for their ability to selectively stabilize human telomeric DNA variant, Tel22. The best G-quadruplex stabilizers were further characterized for their binding properties (binding constant and stoichiometry) using UV–vis, fluorescence spectroscopy, and mass spectrometry. The ligands\u27 ability to alter the structure of Tel22 was determined via circular dichroism and PAGE studies. We identified me₂allox as the experimental ligand capable of conferring excellent stabilizing ability and good selectivity to polypyridyl Ru(II) complexes. Replacing bpy by phen did not significantly impact interactions with Tel22, suggesting that binding involves mostly the experimental ligand. However, using a particular ancillary ligand can help fine-tune G-quadruplex-binding properties of Ru(II) complexes. Finally, the fluorescence “light switch” behavior of all Ru(II) complexes in the presence of Tel22 G-quadruplex was explored. All Ru(II) complexes displayed “light switch” properties, especially [Ru(bpy)₂(diamino)]²⁺, [Ru(bpy)₂(dppz)]²⁺, and [Ru(bpy)₂(aap)]2²⁺ Current work sheds light on how Ru(II) polypyridyl complexes interact with human telomeric DNA with possible application in cancer therapy or G-quadruplex sensing