molecules Article The Importance of Reaction Conditions on the Chemical Structure of N,O-Acylated Chitosan Derivatives Agnieszka Piegat 1,* , Agata Goszczy ´nska 1, Tomasz Idzik 2 and Agata Niemczyk 1 1 West Pomeranian University of Technology Szczecin, Faculty of Chemical Technology and Engineering, Polymer Institute, Division of Functional Materials and Biomaterials, 45 Piastow Ave, 70-311 Szczecin, Poland 2 West Pomeranian University of Technology Szczecin, Faculty of Chemical Technology and Engineering, Department of Organic and Physical Chemistry, 42 Piastow Ave, 71-065 Szczecin, Poland * Correspondence:
[email protected]; Tel.: +48-91-449-44-55 Academic Editor: Massimiliano Fenice Received: 16 July 2019; Accepted: 21 August 2019; Published: 22 August 2019 Abstract: The structure of acylated chitosan derivatives strongly determines the properties of obtained products, influencing their hydrodynamic properties and thereby their solubility or self-assembly susceptibility. In the present work, the significance of slight changes in acylation conditions on the structure and properties of the products is discussed. A series of chitosan-acylated derivatives was synthesized by varying reaction conditions in a two-step process. As reaction media, two diluted acid solutions—i.e., acetic acid and hydrochloric acid)—and two coupling systems—i.e., 1-ethyl-3-(3-dimethyl-aminopropyl)-1-carbodiimide hydrochloride (EDC) and N–hydroxysulfosuccinimide (EDC/NHS)—were used. The chemical structure of the derivatives was studied in detail by means of two spectroscopic methods, namely infrared and nuclear magnetic resonance spectroscopy, in order to analyze the preference of the systems towards N- or O-acylation reactions, depending on the synthesis conditions used. The results obtained from advanced 1H-13C HMQC spectra emphasized the challenge of achieving a selective acylation reaction path.