Cirular Dichroism 朝陽科技大學圆二色性朝陽科技大學.pptVIP

Circular Dichroism Part II. CD spectra of Nucleocide Chromophores of Nucleic Acid p ? p* transitions begin about 300 nm n ? p* buried under p ? p* transitions The intensity of the CD is low because it is a secondary effect of the asymmetric sugar inducing a CD in the chomophoric, but symmetric base. ? Base Stacking CD spectra of Nucleic Acid The benzene-like p-electron systems of the bases make them hydrophobic, so the bases tend to stack in hydrogen bonding solvents to minimize the p-electron surface area exposed to the solvent. The NH, NH2 and CO groups are hydrophilic, so the edges of the bases will interact well with hydrogen bonding solvents For nucleic acids the hydrophobic planes, the hydrophilic edges and charge-charge interactions cause the bases to stack and the polymers to assume a helical structure. The electronic transitions of the chromophoric bases are in close proximity, and can interact to give CD spectra of high intensity. Polymorphic properties of Nucleic Acid Polymorphism of nucleic acid in secondary structure Number of base pairs per turn Inclination of the base with respect to the helix axis The distance of the bases from the helix axis The rise per base-pair Handedness of the helix CD can measure the change in secondary structure as a function of solvent conditions. Circular Dichroism Part III. CD spectra of Protein Amide Chromphore n ? p* centered around 220 nm p ? p* centered around 190 nm n - p* involves non-bonding electrons of O of the carbonyl; p - p* involves the p-electrons of the carbonyl Software for the Analysis of Circular Dichroism Data Tools for analyzing circular dichroism data : LINCOMB and MLR( The method of least squares) CONTIN ? (The ridge regression procedure of Provencher and Gl?ckner) VARSLC (The Variable Selection Method of Johnson and Coworkers ) SELCON (The Self-Consistent Method of Sreerama and Woody ) K2D.(A neural net analysis program of Andrade et al) CCA (The convex constraint algorithm