lecture24_2011

lecture24_2011 - SingleMoleculeSpectroscopy Ch 21b Lecture...

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Single Molecule Spectroscopy Ch 21b Lecture #24 March 2nd , 2011 Geoffrey A. Blake
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Where we left off:  Non-radiative channels can severely limit fluorescence. 
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One way around this problem: Use absorption.  Technique we have not talked about: Circular dichroism or optical rotation spectroscopy. Here, we  are interested in the interaction of a sample with polarized light (for such experiments, typically  circularly polarized), and the measurement is taken between crossed polarizers. Light only passes  through the polarizers if the plane of polarization is rotated. Theoretically, it is found that this can  only occur, for isotropic samples, if the transition is both electric and magnetic dipole allowed: If you consult the earlier lecture notes and  then character tables, you’ll find this only  occurs for the  Cn  and  Dn  groups – that is,  for molecules that are  chiral . http://en.wikipedia.org/wiki/Circular_dichrois m
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CD Spectroscopy of Proteins Amino acids are chiral, and the  UV CD response (mostly from  aromatic A.A.) is also sensitive to  the  secondary structure  of the  protein. This can be used to  quickly assess protein stability and  folding without requiring a full  structure determination. UV CD response for a small  protein in three different buffer  solutions. The curves can be used  to assess the thermodynamic  properties of the polymer. (http://www.ap-lab.com/circular_dichroism.htm)
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DNA stretching, Bustamante group (Berkeley), Science (1996) vol. 271, pp. 795-799 For a dielectric bead near a  strong focus, a restoring force is  generated by the photon gradient  (in x, y, and z); an optical trap.  This was done before the MOT  for atoms. The force constants are in the pico-Newton range, ideal 
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This note was uploaded on 01/03/2012 for the course CH 21b taught by Professor List during the Fall '10 term at Caltech.

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lecture24_2011 - SingleMoleculeSpectroscopy Ch 21b Lecture...

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