ALTERATION OF PROPERTIES OF NATURAL PIGMENTS BY CONJUGATION WITH FIBROIN OR POLYETHYLENE-GLYCOL

Almost all natural pigments exhibit defects when the pigments are extr acted from living bodies; they are much less stable to light than synt hetic dyes, and this accounts for why these pigments have not been wid ely utilized industrially. Another reason is often the poor solubility of natural pigments both in aqueous media and in organic solvents. To overcome these drawbacks, chlorophyll a, beta-carotene and astaxanthi n were adr;orbed on the silk protein, fibroin, to form pigment-fibroin conjugates. These conjugates exhibit high stability to visible and UV light. Similarly, melanin, an insoluble dermal pigment, was coupled w ith polyethylene glycol (PEG). The PEG-melanin conjugate is soluble no t only in aqueous media but also in organic solvents, and exhibits a p hotoprotective effect to UV radiation on the growth of Escherichia col i cells.