On the Mechanism of Genipin Binding to Primary Amines in Lactose-Modified Chitosan at Neutral pH
Chiara Pizzolitto, Michela Cok, Fioretta Asaro, Francesca Scognamiglio, Eleonora Marsich, Francesco Lopez, Ivan Donati, Pasquale Sacco
Abstract
The present manuscript deals with the elucidation of the mechanism of genipin binding by primary amines at neutral pH. UV-VIS and CD measurements both in the presence of oxygen and in oxygen-depleted conditions, combined with computational analyses, led to propose a novel mechanism for the formation of genipin derivatives. The indications collected with chiral and achiral primary amines allowed interpreting the genipin binding to a lactose-modified chitosan (CTL or Chitlac), which is soluble at all pH values. Two types of reaction and their kinetics were found in the presence of oxygen: (i) an interchain reticulation, which involves two genipin molecules and two polysaccharide chains, and (ii) a binding of one genipin molecule to the polymer chain without chain-chain reticulation. The latter evolves in additional interchain cross-links, leading to the formation of the well-known blue iridoid-derivatives.