Abstract: The present invention relates to the synthesis, composition and use of novel moieties formed by reacting a transimination nucleophilic catalyst, molecular or polymeric, with carbonyl-containing therapeutic or cosmetic moieties. The resultant Schiff base product is highly reactive towards transimination with a biological amine. The catalyst and carbonyl-containing moiety can be molecular or polymeric, and the resultant chemical and physical properties of the Schiff base products can be engineered by appropriate selection of said catalyst. The present invention also relates to the synthesis, composition and use of novel moieties that are used as actives in sunless tanning preparations. The present invention also relates to the use of transimination nucleophilic catalysts to increase the rate at which a carbonyl-containing moiety reacts with a biological amine.