L11 - Biophysical Chemistry Chemistry 24a Winter Term...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Biophysical Chemistry Chemistry 24a Winter Term 2009-10 Instructor: Sunney I. Chan Lecture 11 February 3, 2010 Polarized Light. Optical Rotation and Optical Rotatory Dispersion. Circular Dichroism. Interaction of Molecules with Circularly Polarized Light Polarization of light Polarized light : If all the waves have the same E linearly polarized as above, the light is plane polarized (plane defined by the electric field direction and the direction of propagation of the light wave). direction of propagation of light E as viewed along z direction wave linearly polarized along x- direction Polarization of light Unpolarized light : direction of propagation of light E as viewed along z direction wave linearly polarized along x- direction E of different waves as viewed along direction of propagation: electric fields oscillating in all directions in xy plane.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Plane-polarized light Plane-polarized light can be produced by passing unpolarized light through a highly anisotropic material (e.g., Polaroid), which absorbs all light with E pointing in one-direction (i.e., horizontal), thereby leaving only rays whose electric field point vertically. Another method is to pass the unpolarized light through a Nicol prism, which removes light polarized in one direction by reflection. Plane-polarized may be considered as a super- position of left- and right-circularly polarized light in equal proportions. x y z E Clockwise 1 : E R = i E o *cos ω t + j E o *sin ω t Counter-clockwise: E L = i E o *cos ω t - j E o *sin ω t E R + E L = i 2E o *cos ω t 1 as viewed from the direction of on-coming light wave. Optical Rotation and Optical Rotatory Dispersion Molecules with chiral centers are optically active! Optical Rotation When plane-polarized light passes through an optically active substance, the plane of polarization is rotated. Polarimeter sample Detector α = angle of rotation of the plane of rotation polarizer Monochromator (selects v, λ of light) cell path ; concentration c analyzer
Background image of page 2
Detector measures the intensity of the transmitted light. A “null” method is usually used; i.e., the analyzer is set such that light that is passed by the first polarizer (say vertically polarized) is absorbed by the analyzer. If the sample rotates the plane of the polarization of the light incident on it, say, by angle α , then the analyzer must be rotated by angle α to attain null at the detector; i.e., polarizer and analyzer are rotated by 90º + α vs each other. Specific rotation Specific rotation (in degrees) is defined as follows: [ α ] λ t = 100 α / c where is the path length of cell in decimeters (1 decimeter = 10 cm); λ is the wavelength of the light; c is the concentration of the solute in grams per 100 ml solution; and t is the temperature in ºC. Examples of optical rotation
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/27/2010 for the course BI 110 taught by Professor Richards,j during the Winter '08 term at Caltech.

Page1 / 15

L11 - Biophysical Chemistry Chemistry 24a Winter Term...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online