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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Nucleobase Pair Analogues 2-Pyridone(center dot)Uracil,2-Pyridone(center dot)Thymine,and 2-Pyridone-5-Fluorouracil: Hydrogen-Bond Strengths and Intermodular Vibrations
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Nucleobase Pair Analogues 2-Pyridone(center dot)Uracil,2-Pyridone(center dot)Thymine,and 2-Pyridone-5-Fluorouracil: Hydrogen-Bond Strengths and Intermodular Vibrations

机译：核碱基对类似物2-吡啶酮尿嘧啶，2-吡啶酮胸腺嘧啶和2-吡啶酮-5-氟尿嘧啶：氢键强度和互模振动

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Due to the ultrafast nonradiative decay of the uracil(U),thymine(T),and 5-fluorouracil(5-FU)nucleobases,resolved vibronic spectra of nucleobase dimers with U,T,or 5-FU chromophores have not yet been observed in the gas phase.2(center dot)Pyridone(2PY)is a fluorescent hydrogen-bonding analogue of U with a single N-H donor and C=O acceptor group.We report the mass-selected S_1<-So vibronic spectra of 2PY(center dot)U,2PY(center dot)T,and 2PY(center dot)5(center dot)FU,revealing properties of their H-bonds free of stacking interactions and backbone constraints.The in-plane H-bond vibrations,omicron',lambda',sigma',are observed for all three dimers;the out-of-plane vibrations beta,tau~' and the overtone of the stagger mode 2sigma' are measured for 2PY(center dot)T and 2PY(center dot)U.The experimental frequencies are in good agreement with the ab initio calculated frequencies of the most stable H-bonded isomer,which involves the Nl-H and C2=O groups of U,T,or 5-FU as H donor/acceptor.The H-bond dissociation energies follow the sequence T(approx)U < 5-FU.However,the experimental S_1 state H-bond stretching force constants increase in the sequence U < T < 5-FU.The absence of fluorescence from these dimers implies that the S_1 lifetimes of 2PY in these complexes are>20 times shorter than those in the other 2PY(center dot)Xcomplexes measured so far.Energy transfer from 2PY to U(T,5-FU)is suggested as the cause,which implies that the npi~* S_1 states of U,T,and 5-FU,which have never been directly observed,lie below the Si JUT* state of 2PY.
机译：由于尿嘧啶（U），胸腺嘧啶（T）和5-氟尿嘧啶（5-FU）核碱基的超快非辐射衰变，尚未观察到具有U，T或5-FU发色团的核碱基二聚体的分辨电子光谱2（中心点）吡啶酮（2PY）是具有单个NH供体和C = O受体基团的U的荧光氢键类似物。我们报道了质量选择的S_1 <-So的振动光谱中心点）U，2PY（中心点）T和2PY（中心点）5（中心点）FU，其H键的揭示性质不受堆叠相互作用和主链约束。平面内H键振动，微米对于所有三个二聚体均观察到'，lambda'，sigma';测量了2PY（中心点）T和2PY（中心点）的面外振动beta，tau〜'和交错模式2sigma'的泛音U.实验频率与最稳定的氢键异构体的从头算出的频率非常吻合，其中涉及U，T或5-FU的N1-H和C2 = O组作为H供体/受体.H键解离能遵循序列T（约）U <5-FU。但是，实验S_1状态的H键拉伸力常数在序列U

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