Concentration- and time-dependent eccentric changes in circular dichroism of saccharide-linked ethynylpyridine oligomer with copper(II) ions

We studied the preparation and circular dichroism (CD) behavior of 2,6-pyridylene ethynylene octameric oligomer linked to a β-d-glucoside moiety with a C20-alkylene chain. The addition of Cu(OTf)(2) salt led to a remarkable enhancement of the first CD band of the oligomer, and an unexpected concentration and time dependency were observed. For example, when 1.0 × 10(-3) M of Cu(OTf)(2) was added to a 1,2-dichloroethane solution of the oligomer (5.0 × 10(-4) M, unit concentration), the CD band appeared in the positive at first and gradually inverted into the negative with time.