title: Sodium-ion binding to DNA: detection by ultrafast time-resolved stokes-shift spectroscopy.
abstract: The nature of the counterion is shown to have a pronounced effect on the apparent dynamic polarity in the interior of DNA. Time-resolved Stokes-shift measurements in the 80 ps to 40 ns time range were made on a polarity-sensitive fluorophore (coumarin 102) that replaces a base pair in an oligonucleotide. With sodium counterions, the emission spectrum narrows with time, whereas with tetrabutylammonium counterions, it does not. Our interpretation is that a subpopulation of helices have sodium cations bound in a fashion that slows the normal dynamics.
mesh_terms: D003374:Coumarins / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D009841:Oligonucleotides / Q000737:chemistry; D012964:Sodium / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D003374:Coumarins; D009841:Oligonucleotides; D004247:DNA; D012964:Sodium