Ultraviolet difference spectroscopy protein structure

Fig. I. Absorption spectrum of bacteriorhodopsin from the ultraviolet to the infrared. By using incident light in different regions of the spectrum, vibrational spectroscopy can be used to probe different aspects of protein structure. The IR portion of the spectrum was obtained in a D2O buffer.

Since Hg(II) has a closed-shell electronic structure, it is often considered spectroscopically silent in optical and EPR spectroscopy. Recent advances in a variety of spectroscopic techniques have made this description of Hg(II) complexes obsolete. Relativistic effects tend to lower energy of the Hg 6s orbital (156), and consequently the LMCT spectra of Hg(II) tetrahalides and three- or four-coordinate alkyl thiolate complexes are distinctly different than those obtained for two-coordinate complexes. As described below, ultraviolet spectroscopy has provided details about the Hg(II) coordination in the MerR protein (202, 210). 

Circular Dicfaroism.—In its application to proteins, circular dichroism (c.d.) is generally used to obtain information about conformation (secondary structure) and conformational changes. Peptides continue to be studied, both in their own right and as models for proteins. The c.d. spectra of benzyloxycarbonyl Val-(Ala),-OEt in different solvents have been examined. In dioxan, negative and positive bands were seen at 228— 9 and 212— 3 nm respectively and it was deduced that the peptide was in a bend conformation. The use of c.d. in the vacuum ultraviolet range (near 150 nm), and of infrared spectroscopy, allowed the /S-structure to be established for oligomers (2—7 residues) of L-leucine, S-cyclohexyl-L-alanine, and L-phenylalanine. ... 

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