TWO-PHOTON STUDIES OF AMINO ACIDS AND NUCLEIC ACIDS

长期目标是实现对较低层的精确描述， 色氨酸和核苷酸的激发态 准确的意义上说，有用的结构和动力学信息， 由紫外吸收、圆二色性、可见双光子 吸收和时间分辨发射。 这三年的重点是 色氨酸的两个最低激发态1 La和1 Lb， 相对能量对分子环境极其敏感。 两 近年来， 新奇的实验 拟议的工作包括旨在 跟踪色氨酸和模型类似物的1 La和1 Lb状态， 环境，包括孤立和复杂的分子，各种冷冻 液氦温度下的溶剂和蛋白质，使用介质 分辨率（0.1 cm-1）激发和检测，以选择 具体网站。 双光子激发将占据重要地位，因为它 可以区分1 La和1 Lb态，即使在喷流冷却的光束。 一个强大 理论部分旨在发展半经验量子方法， 单振动态相对能量的预测水平 这些与分子力学和动力学方法预测 分子环境的影响。 这项工作的一个重要部分是 测试常见的分子动力学方法， 应用于生物聚合物。 上述技术将应用于 核苷酸，其中存在类似的理论困难。 的计算 晶体环境的影响将继续下去，因为它们被发现， 是必不可少的解释光学实验的晶体 核酸碱基 染料的双光子性质研究进展 对于双光子激光扫描显微镜的新技术， 进行。

The long range goals are to achieve accurate descriptions of the lower excited states of the amino acid tryptophan and of the nucleotides -- accurate in the sense that useful structural and dynamical information can be deduced from UV absorption, circular dichroism, visible two-photon absorption, and time resolved emission. This three year period focuses upon the two lowest excited states of tryptophan, 1La and 1Lb, whose relative energy is extremely sensitive to the molecular environment. Both states have been implicated as contributing to the fluorescence in recent novel experiments. The proposed work includes experiments designed to track the 1La and 1Lb states of tryptophan and model analogues in environments including the isolated and complexed molecules, various frozen solvents at liquid helium temperature, and proteins, using medium resolution (0.1 cm-1) excitation and detection to select molecules in specific sites. Two-photon excitation will figure prominently because it can distinguish 1La and 1Lb states, even in the jet-cooled beams. A strong theoretical component aims to develop semiempirical quantum methods to the level of predicting single vibronic state relative energies and to marry these with molecular mechanics and dynamics methods for predicting the effect of the molecular surroundings. An important part of this work is to test the common molecular dynamics methods which are being increasingly applied to biopolymers. The above techniques will be applied to the nucleotides, where similar theoretical difficulties exist. Computations of the effect of crystal environments will be continued because they are found to be essential in the interpretation of optical experiments on crystals of nucleic acid bases. A survey of two-photon properties of dyes being used for the new technique of two-photon laser scanning microscopy will be conducted.