Formation of isolated DNA bases pairs and their water clusters

我们已经开发了一种新的激光解吸方法结合超声射流技术用于生产冷分离的DNA碱基簇及其水合簇。这种方法被发现是特别有效的，在生产水化集群的非挥发性分子，从而在微观上理解的DNA的水合结构的有用。结果表明，碱基对的激发态动力学强烈依赖于相应的碱基的互变异构体。例如，嘌呤碱基鸟嘌呤揭示了其激发态寿命为亚皮秒量级的规范形式的互变异构体，而其他非规范形式的互变异构体具有纳秒寿命。此外，腺嘌呤的激发态动力学在水合后显著改变。这是由最初的激发态的超快弛豫到一个低洼的激发态和随后的解离解释。发现这与2-氨基嘌呤的结果是一致的，其中没有超快动力学发生，因此被认为是强fluorescent.We也成功地生产水合簇的DNA核苷鸟苷与高效率，通过采用这种解吸技术。这是首次报道在孤立条件下观察到冷水合核苷簇。鸟苷类化合物的电子光谱在水化过程中发生了明显的红移，表明激发态动力学受到溶剂化的影响，这种激光解吸技术有望成为热脆性生物分子蒸发的有效方法

We have developed a novel laser desorption method in combination with the supersonic-jet technique for producing cold isolated clusters of the DNA bases and their hydrated clusters. This method is found to be especially effective in producing hydrated clusters of the nonvolatile molecules and thus useful in the microscopic understanding of hydration structures of DNA. The results show that excited-state dynamics of the base pairs are strongly dependent on the tautomers of the respective bases. For example, the purine base guanine reveals a tautomers of the canonical form whose excited-state lifetime is on the order of subpicosecond while other tautomers of non-canonical forms have nanosecond lifetimes. Furthermore, excited-state dynamics of adenine are altered significantly upon hydration. This is explained by the ultrafast relaxation of the initially excited state to a low-lying excited state and subsequent dissociation. This is found to be consistent with the result for 2-aminopurine in which no ultrafast dynamics occurs and thus is known to be strongly fluorescent.We have also succeeded in producing hydrated clusters of the DNA nucleoside guanosines with high efficiency by employing this desorption technique. This is the first report of the observation of cold hydrated clusters of the nucleosides under isolated conditions. The electronic spectra of guanosines are found to be significantly red-shifted upon hydration, suggesting that the excited state-dynamics are affected by the solvation.This laser desorption technique is expected to be effective for vaporizing thermally fragile biomolecules