第七章旋光色散和园二色光谱.pptx

文档介绍：OVERVIEW
 
1. A molecule is optically active if it interacts differently with left and rightcircularly polarized light. This interaction can be detected either as a differential change in velocity of the two beams through the sampleoptical rotatory dispersion (ORD)  or as a differential absorption of each beamcircular dichroism (CD).
2. ORD spectra are characterized by [], which is the specific rotation at a given wavelength, or the molar rotation []. Both have units of degreecm2dmol1. CD spectra are characterized by A (the differential absorption of the two beams) or the molar ellipticity []m, which at a given wavelength is related to A. CD or ORD bands are often referred to as Cotton effects. These can be positive or negative.
3. CD is more frequently used than ORD because of superior instrumentation and the shapes of the CD curves.
 
4. Very few chromophores are intrinsically optically active; those that are active include the amides and disulfide cystine in proteins. Most optical activity of chromophores arises from optical activity induced by interactions with asymmetrically placed neighboring groups.
5. One of the main applications of CD spectra is based on their sensitivity to the secondary structure of proteins. Other uses include detection of conformational changes and measurement of ligand binding.
 
6. Optical activity can also be induced by the application of a ic field, which perturbs the energy levels of the system. This is the basis of ic circular dichroism (MCD). Unlike CD, MCD is largely insensitive to molecular conformation, but it is sensitive to the total concentration of MCDactive chromophores and their local environment.
引言
早在十七世纪,Huggens就发现了光的偏振
到了十九世纪,偏振光开始用于分子的旋光现象的研究
Biot 1881 年发现石英能使偏振光的偏振面旋转,在松节油等液体和某些气体中也发现了这种效应。Biot 在发现旋光现象的同时,还观察到了电气石的园二***。
后来将旋光色散与园二***这两种现象称为科顿效应。
十九世纪中期,许多旋光性的定律开始公式化,并对十九世纪末有机立体化学和有机结构理论的发展起到了直接的推动作用。
1934年,Lowry出版了第一本完整的有关旋光色散的书”Optical Rotatory Power”。
1953年Djerasi实验室建立了第一台偏振光检测仪,从此ORD