CHIRAL MICELLAR PORPHYRIN FIBERS WITH 2-AMINOGLYCOSAMIDE HEAD GROUPS

Easily accessible protoporphyrin IX 13,17-bis(glycosamides) form colloidal aqueous solutions which are stable for several months or longer. Electron micrographs show ribbons of an approximate width of 4 nm and lengths of between 20 nm (D-glucosamide) and 5-mu-M (D,L-mannosamide). In one case, gel chromatography was applied in order to acquire the molecular weight, which was determined to be greater-than-or-equal-to 2 x 10(6) D for about 90% of the colloidal particles. The UV-vis spectra of the aqueous suspension show a Soret band which is split by about 100 nm by exciton interactions (460 and 360 nm). Circular dichroism (CD) spectra reveal complex exciton splittings. Both the absorption and CD spectra have been reproduced by simple model calculations. Fluorescence was not present in the aggregate and the aggregates did not quench the fluorescence of the added porphyrins. Two stacked face-to-face dimers with lateral shifts to half a molecule in each direction and no dipole-dipole interactions are proposed to connect to twisted ribbons by strong edge-to-edge interactions. Longevity of the aggregate solutions is traced back to the thinness of the highly curved aggregates and their low dissociation constants (almost-equal-to 10(-7)-10(-6) M).