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 ? cm 2? 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