This invention relates to Schiff's bases derived from amino acids and hydroxyaryl alkyl ketones, or a plant extract containing the same, having general chemical structure in FIG. 1 for topical application. This invention also relates to certain metal complex of said Schiff's bases, which have a crown-like appearance in their three-dimensional chemical structure, as in FIG. 2. The Schiff's bases and their metal complexes of the present invention are useful for the modulation of metal-activated enzymes and metalloenzymes, such as Phenylalanine Hydroxylase, Tyrosine Transaminase, Phenylalanine Transaminase, Tyrosinase, various MMP (Matrix metalloproteases), Superoxide dismutase, 5-Alpha Reductase, and citrate lyase. These are further suitable for multifunctional topical methods for skin whitening, skin wrinkles reduction, skin antiaging, collagen synthesis, acne control, hair loss prevention, hair graying control, and facial oil control.