Microhydration Effects on the Ultrafast Photodynamics of Cytosine: Evidences for a Possible Hydration-Site Dependence.
Ultrafast excited-state deactivation dynamics of small cytosine (Cy) and 1-methylcytosine (1mCy) microhydrates, Cy⋅(H2O)1-3 and 1mCy⋅(H2O)1,2, produced in a supersonic expansion have been studied by mass-selected femtosecond pump-probe photoionization spectroscopy at about 267 nm excitation. The seeded supersonic expansion of Ar/H2O gas mixtures allowed an extensive structural relaxation of Cy and 1mCy microhydrates to low-energy isomers. With the aid of electronic structure calculations, we assigned the observed ultrafast dynamics to the dominant microhydrate isomers of the amino-keto tautomer of Cy and 1mCy. Excited-state lifetimes of Cy⋅(H2O)1-3 measured here are 0.2-0.5 ps. Comparisons of the Cy⋅H2O and 1mCy⋅H2O transients suggest that monohydration at the amino Watson-Crick site induces a substantially stronger effect than at the sugar-edge site in accelerating excited-state deactivation of Cy.
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.).
Jr-Wei
JW
Ho
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.).
Hung-Chien
HC
Yen
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.).
Hui-Qi
HQ
Shi
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.).
Li-Hao
LH
Cheng
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.).
Chih-Nan
CN
Weng
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.).
Wei-Kuang
WK
Chou
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.).
Chih-Chung
CC
Chiu
Department of Chemistry, National Tsing Hua University, Hsinchu, Taiwan 30043 (R.O.C.). pycheng@mx.nthu.edu.tw.
Po-Yuan
PY
Cheng
D003596:Cytosine / Q000031:analogs & derivatives / Q000737:chemistry*; D055668:Photochemical Processes; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D014867:Water; D003596:Cytosine
cytosine; excited-state dynamics; femtochemistry; microhydration; nucleobases