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Microhydration Effects on the Ultrafast Photodynamics of Cytosine: Evidences for a Possible Hydration‐Site Dependence
Author(s) -
Ho JrWei,
Yen HungChien,
Shi HuiQi,
Cheng LiHao,
Weng ChihNan,
Chou WeiKuang,
Chiu ChihChung,
Cheng PoYuan
Publication year - 2015
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201507524
Subject(s) - chemistry , excited state , tautomer , relaxation (psychology) , photochemistry , spectroscopy , femtosecond , photoionization , cytosine , crystallography , stereochemistry , atomic physics , ionization , dna , ion , organic chemistry , psychology , social psychology , laser , physics , quantum mechanics , optics , biochemistry
Ultrafast excited‐state deactivation dynamics of small cytosine (Cy) and 1‐methylcytosine (1mCy) microhydrates, Cy⋅(H 2 O) 1‐3 and 1mCy⋅(H 2 O) 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/H 2 O 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⋅(H 2 O) 1‐3 measured here are 0.2–0.5 ps. Comparisons of the Cy⋅H 2 O and 1mCy⋅H 2 O 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.