Starch-primulin fluorescence

Summary Intact starch grains with primulin give initially a blue fluorescence that is weakly polarized. As more dye enters the grain, the fluorescence color gradually changes to a yellow-green fluorescence that is strongly polarized. Where the structure of the grain is disorganized, the primulin-starch complex fluoresces yellow. A bright yellow rim about all intact grains is interpreted as a Becke line.Fluorescence colors of primulin-starch are essentially unaffected by hydrogen ion concentration, by the presence of salts, by the solvent in which the primulin is dissolved, and by the dye fraction (of acetoneseparated primulin fractions) used as a solute. These colors have no relation to the type of starch in the primulin-starch complex.Absorption and fluorescence spectra of primulin and its fractions vary with the concentration of the dye, the nature of the solvent, and the nature of the fraction. Three types of primulin-solvent association are envisioned: primulin anion in water; primulin molecule hydrogen-bonded to solvent or substrate molecule in non-aqueous medium; primulin dimeric association-at high concenntrations-in non-aqueous medium.Primulin-starch fluorescence colors are explicable on the basis of dye concentration and pore size in the starch grain. Pore spaces that will accept dye molecules are estimated to have a diameter between 7 and 20°.