ON THE CONFORMATION OF BILIRUBIN DIMETHYL ESTER FROM CIRCULAR-DICHROISM SPECTROSCOPY

Unlike the parent diacid, the dimethyl ester of (alpha-R,alpha'-R)-dimethylmesobilirubin-XIII-alpha exhibits only a weak bisignate circular dichroism (CD) spectrum in a wide variety of solvents. This implies a loss of conformation stabilization afforded (in the diacid) by intramolecular hydrogen bonding, and with it the loss of an allosteric effect that forces the parent acid into the P-helicity conformational enantiomer.