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Singlet excited-state lifetimes of cytosine derivatives measured by femtosecond transient absorption.
Photochemistry and photobiology. Pub Date : 2003 Feb
Malone, Rosalie J, Miller, Angela M, Kohler, Bern

Lifetimes of the lowest excited singlet (S1) electronic states of various derivatives of the pyrimidine nucleobase cytosine (Cyt) were measured by the femtosecond transient absorption technique. The bases were excited in room-temperature aqueous solution at 265 nm using approximately 200 fs pump pulses from a titanium-sapphire laser system. The decay of excited-state absorption (ESA) at visible probe wavelengths was used to determine the S1 lifetimes of a variety of modified Cyt compounds at different pH values by global fitting. Identical lifetimes were observed for Cyt and cytidine (Cyd) within experimental uncertainty, but ESA by the ribonucleoside was considerably stronger, suggesting that the ribose group increases the oscillator strength of the S1 --> SN transition. The S1 lifetime of the important minor base 5-methylcytosine (m5Cyt) is 7.2 +/- 0.4 ps at pH 6.8. The same lifetime was measured for the ribonucleoside 5-methylcytidine, but sugar substitution again increased the strength of the ESA signal. Protonation of Cyd and m5Cyt at low pH led to a modest decrease in their S1 lifetimes. On the other hand, deprotonation of Cyt and m5Cyt significantly increased the lifetime of their respective S1 states. These trends support the intermediacy of the n,pi* state localized on the carbonyl oxygen in the nonradiative decay mechanism of Cyt. Longer S1 lifetimes were observed for 5-fluorocytosine and N4-acetylcytosine. Collectively, these results illustrate the great potential of femtosecond laser spectroscopy for investigating excited-state dynamics in DNA and DNA components.

中文翻译:

通过飞秒瞬态吸收测量的胞嘧啶衍生物的单重态激发态寿命。

通过飞秒瞬态吸收技术测量了嘧啶核苷胞嘧啶(Cyt)的各种衍生物的最低激发单重态(S1)电子态的寿命。使用来自钛-蓝宝石激光系统的约200 fs泵浦脉冲,在265 nm的室温水溶液中激发碱。通过全局拟合,使用可见光探针波长处的激发态吸收(ESA)衰减来确定各种修饰的Cyt化合物在不同pH值下的S1寿命。在实验不确定性范围内观察到Cyt和cytidine(Cyd)的寿命相同,但是核糖核苷的ESA则要强得多,这表明核糖基团增加了S1-> SN跃迁的振子强度。重要的次要碱基5-甲基胞嘧啶(m5Cyt)的S1寿命为7。在pH 6.8下为2 +/- 0.4 ps。测量了核糖核苷5-甲基胞嘧啶的相同寿命,但是糖取代再次增加了ESA信号的强度。Cyd和m5Cyt在低pH下的质子化导致其S1寿命适度降低。另一方面,Cyt和m5Cyt的去质子化显着增加了它们各自S1状态的寿命。这些趋势支持在Cyt的非辐射衰变机理中位于羰基氧上的n,pi *状态的中间性。观察到5-氟胞嘧啶和N4-乙酰胞嘧啶的S1寿命更长。总的来说,这些结果说明了飞秒激光光谱技术在研究DNA和DNA组分的激发态动力学方面的巨大潜力。但是糖替代又增加了ESA信号的强度。Cyd和m5Cyt在低pH下的质子化导致其S1寿命适度降低。另一方面,Cyt和m5Cyt的去质子化显着增加了它们各自S1状态的寿命。这些趋势支持在Cyt的非辐射衰变机理中位于羰基氧上的n,pi *状态的中间性。观察到5-氟胞嘧啶和N4-乙酰胞嘧啶的S1寿命更长。总的来说,这些结果说明了飞秒激光光谱技术在研究DNA和DNA组分的激发态动力学方面的巨大潜力。但是糖替代又增加了ESA信号的强度。Cyd和m5Cyt在低pH下的质子化导致其S1寿命适度降低。另一方面,Cyt和m5Cyt的去质子化显着增加了它们各自S1状态的寿命。这些趋势支持在Cyt的非辐射衰变机理中位于羰基氧上的n,pi *状态的中间性。观察到5-氟胞嘧啶和N4-乙酰胞嘧啶的S1寿命更长。总的来说,这些结果说明了飞秒激光光谱技术在研究DNA和DNA组分的激发态动力学方面的巨大潜力。Cyt和m5Cyt的去质子化显着延长了它们各自S1状态的寿命。这些趋势支持在Cyt的非辐射衰变机理中位于羰基氧上的n,pi *状态的中间性。观察到5-氟胞嘧啶和N4-乙酰胞嘧啶的S1寿命更长。总的来说,这些结果说明了飞秒激光光谱技术在研究DNA和DNA组分的激发态动力学方面的巨大潜力。Cyt和m5Cyt的去质子化显着延长了它们各自S1状态的寿命。这些趋势支持在Cyt的非辐射衰变机理中位于羰基氧上的n,pi *状态的中间性。观察到5-氟胞嘧啶和N4-乙酰胞嘧啶的S1寿命更长。总的来说,这些结果说明了飞秒激光光谱技术在研究DNA和DNA组分的激发态动力学方面的巨大潜力。
更新日期:2017-01-31
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