Ultrafast energy exchange via water-phosphate interactions in hydrated DNA.
The ionic phosphate groups in the DNA backbone play a key role for DNA hydration. We study ultrafast vibrational dynamics and local interactions of phosphate groups and water by femtosecond two-color pump-probe spectroscopy. The asymmetric (PO(2))(-) stretching vibration nu(AS)(PO(2))(-) of artificial DNA oligomers containing 23 alternating adenine-thymine base pairs displays a lifetime of 340 fs, independent of the hydration level. For DNA at zero relative humidity, excess energy from the decay of the phosphate excitation is transferred within DNA on a 20 ps time scale. For fully hydrated DNA, the water shells around the phosphates serve as a primary heat sink accepting vibrational excess energy from DNA on a femtosecond time scale. OH stretching excitation of water molecules around fully hydrated DNA induces an ultrafast nu(AS)(PO(2))(-) response which includes rearrangements of the hydration shell and a reduction of the average number of phosphate-water hydrogen bonds.
Szyc
Łukasz
Ł
Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.
Yang
Ming
M
Elsaesser
Thomas
T
D020029:Base Pairing; D004247:DNA / Q000737:chemistry*; D004735:Energy Transfer; D006860:Hydrogen Bonding; D010710:Phosphates / Q000737:chemistry*; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D010710:Phosphates; D014867:Water; D004247:DNA