TRANSIENT MAGNETIC CIRCULAR DICHROISM

将开发一种新技术来延长时间 磁性圆二色(MCD)测量的分辨率 从毫秒的时间范围来看，标准技术可以 决心，到纳秒的时间范围内。MCD将在 强磁场作用下的激光光解样品 场(100 KGauss)，并使用最近演示的 一种以纳秒为单位测量圆二向色性的方法 时间尺度。瞬变MCD技术具有广泛的 潜在的应用，因为MCD可以在任何光线下诱导- 用足够强的磁场吸收样品。这是 与CD相反，CD需要手性样品，并且线性 二向色性，这需要定向样品。卓有成效的 一种高时间分辨率的MCD信号测量技术 将是生物物理学的重要工具，因为它将提供 结构MCD研究和动力学研究之间的联系。自.以来 生物过程取决于生物的结构特性 分子，并且本质上是动态的，这种联系显然是 巨大的潜在效用。这项研究的目标将是 开发和评估瞬时MCD的有用性 技术作为生物物理研究的工具。 该方法将初步应用于受激态。 游离基的卟啉。它们强烈的、经过充分研究的基态 MCD、合适的激发态寿命和光谱的缺乏 基态和激发态吸收之间的重叠提供了 检测瞬时MCD的极佳条件。瞬变 还将获得铜的激发态的MCD光谱 卟啉和Ru2+双卟啉。此外，MCD 将获得由以下物质产生的基态瞬变的光谱 7-羟基黄酮光互变异构化、光解离 四苯基镍卟啉在碱性溶剂中的轴向配体， 以及一氧化碳氧合肌红蛋白的光解。最后， 细胞色素蛋白的瞬时MCD已经被“脉冲-- 被光解得到的溶剂化电子还原 将对亚铁氰化物进行研究。

A new technique will be developed which extends the time resolution of magnetic circular dichroism (MCD) measurements from the millisecond time regime, which standard techniques can resolve, to the nanosecond time regime. MCD will be induced in a laser-photolysed sample by application of a strong magnetic field (100 kgauss) and measured with a recently demonstrated method of measuring circular dichroism (CD) on a nanosecond time scale. The transient MCD technique has a wide range of potential applications since MCD can be induced in any light- absorbing sample by a sufficiently strong magnetic field. This is in contrast to CD, which requires a chiral sample, and linear dichroism, which requires an oriented sample. An effective technique for measuring MCD signals with high time resolution would be an important tool for biophysics since it would provide a link between structural MCD studies and kinetic studies. Since biological processes depend on structural properties of biological molecules and are dynamic in nature, this linkage is clearly of great potential utility. The goal of this research will be to develop and assess the usefulness of the transient MCD technique as a tool for biophysical studies. Initial application of the method will be made to excited states of free-base porphyrins. Their intense, well-studied ground state MCD, suitable excited state lifetimes, and the lack of spectral overlap between ground and excited state absorptions provide excellent conditions for detecting transient MCD. Transient MCD spectra will also be obtained for excited states of copper porphyrins and Ruthenium biporphyrins. In addition, MCD spectra will be obtained for ground state transients generated by phototautomerization of 7-hydroxyflavone, photodissociation of axial ligands from nickel tetraphenylporphyrin in basic solvents, and the photolysis of carbonmonoxymyoglobin. Finally, the transient MCD of cytochrome proteins that have been "pulse- reduced" by solvated electrons obtained by photolysis of ferrocyanide will be studied.