On the Mechanism of Genipin Binding to Primary Amines in Lactose-Modified Chitosan at Neutral pH.

Chiara Pizzolitto,Pasquale Sacco,Ivan Donati,Eleonora Marsich,Francesca Scognamiglio,Michela Cok,Francesco Lopez,Fioretta Asaro

doi:10.3390/ijms21186831

Chiara Pizzolitto, Pasquale Sacco + Show 6 more

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https://doi.org/10.3390/ijms21186831

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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.

Highlights

Lactose-modified chitosan, commercially known as CTL, is a bioactive polysaccharide derived from natural resources
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
The presence of the flexible flanking groups endows lactose-modified chitosan with peculiar physical-chemical properties [3], which range from a complete solubility at all pH values to the formation of synergistic mixtures with polyanions [4,5]

Summary

Introduction

Lactose-modified chitosan, commercially known as CTL, is a bioactive polysaccharide derived from natural resources. Due to its polycationic nature and the presence of primary amines from the unreacted glucosamine units, lactose-modified chitosan could form physical and chemical hydrogels, exploiting well known approaches developed for its parent compound chitosan [10,11]. Lactose-modified chitosan forms, in the presence of boric acid, transient networks [12,13] showing strain-hardening and self-healing properties [14]. Concerns on cytotoxicity of the cross-linker limit its use for biomedical applications. For this reason, covalent cross-linkers of natural origin have been sought

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