L7 - Biophysical Chemistry Chemistry 24a Winter Term...

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Biophysical Chemistry Chemistry 24a Winter Term 2009-10 Instructor: Sunney I. Chan Lecture 7 January 22, 2010 Infrared and Raman Spectroscopy. Infrared and Raman Spectroscopy Infrared spectroscopy: absorption and emission of IR radiation by molecules to change their vibrational and vibrational- rotational energies. Raman spectroscopy – inelastic scattering of Uv-visible radiation coupled with rotational and vibrational transitions of the molecular scatterer. an upper electronic state vibrational states vibrational states rotational & translational states rotational & translational states ground electronic state ~ ~ ~ Vibrational, vibration-rotational absorption spectroscopy an upper electronic state vibrational states vibrational states rotational & translational states rotational & translational states ground electronic state ~ ~ ~ Raman scattering – vibrational Raman Raman scattering – rotational Raman virtual state
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Must include both the nuclei and electrons! For vibrational spectroscopy, Transition dipole moment for bond stretch = ( ∂μ / R) 0 (R – R e ) + …. dipole derivative displacement of bond from equilibrium For a diatomic molecule
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peptides and proteins The peptide bond The condensation of two amino acids to form a peptide bond (screened in green). The oxygen atom of the carbonyl group involved in the peptide bond is a hydrogen bond acceptor (because it has lone electron pair), whereas the hydrogen atom attached to the amide nitrogen is a hydrogen bond donor. These reactions are carried out in the cell in a process called translation. After water is expelled and a peptide is bond, each amino acid is called a residue. Vibrational Spectroscopy of a Peptide
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L7 - Biophysical Chemistry Chemistry 24a Winter Term...

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