Progress in Optical Circular Dichroism



An apparatus first described in 1961 for the measurement of circular dichroism down to 220 mμ has been improved and its range extended down to 185 mμ. Some examples are given in the field of dienes, conjugated ketones, and aromatic chromophores. A more extensive study of protein structures was developed with the following results: (a) helical polypeptides show a complex dichroism in the far ultraviolet with three components (192 mμ, 204 mμ, 225 mμ), characteristic of the helical array of peptide groups; (b) human serum albumin shows a very similar curve of dichroism and is 60% helical; (c) urea denaturation, as judged by dichroism, is a reversible phenomenon; (d) a solvent such as chloroethanol increases the helical content of human serum albumin and clupein and has only a very small action on poly-L-glutamic acid; (e) the rupture of S[BOND]S bonds in human serum albumin favors the attack of denaturing agents such as urea; (f) detergents help to maintain the rigid structure of human serum albumin after the rupture of S[BOND]S bonds.