Measurement of Local DNA Reorganization on the Picosecond and Nanosecond Time Scales

Picosecond and nanosecond dynamics in the interior of DNA are observed for the first time as a dynamic Stokes shift in the fluorescence of a specially designed base-pair analogue. A recently synthesized coumarin C-riboside has been incorporated into an oligonucleotide in place of a normal purine·pyrimidine base pair. The dynamic Stokes shift of this probe occurs with components near 300 ps and 13 ns. These times are too long for solvent relaxation or simple vibrational motion of the DNA framework. They imply that the interior of DNA is a unique dynamic environment unlike either a fluid or a molecular crystal.