TWO-PHOTON STUDIES OF AMINO ACIDS AND NUCLEIC ACIDS

长期目标是实现对较低层的准确描述 氨基酸色氨酸和核苷酸的激发态-- 准确的是有用的结构和动力学信息可以 由紫外吸收、圆二向色性、可见双光子 吸收和时间分辨发射。这三年的重点是 在色氨酸的两个最低激发态1la和1lb上，其 相对能量对分子环境极为敏感。两者都有 最近几个州被认为是造成这种荧光的原因。 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1la和1lb状态 环境包括分离的和复杂的分子，各种冻结的 液氦温度下的溶剂和蛋白质，使用介质 分辨率(0.1 cm~(-1))激发和检测选择分子 特定的站点。双光子激发将非常重要，因为它 可以区分1la和1lb的状态，即使在喷射冷却的光束中也是如此。一个坚强的人 理论部分旨在将半经验量子方法发展到 预测单振子态相对能量与结婚的水平 这些用分子力学和动力学的方法来预测 分子环境的影响。这项工作的一个重要部分是 测试常用的分子动力学方法，这些方法越来越多 应用于生物聚合物。上述技术将应用于 核苷酸，在那里也存在类似的理论困难。的计算 晶体环境的影响将继续下去，因为它们被发现了 在解释晶体的光学实验中是必不可少的 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将是 指挥。

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.