Insight into the Structural Features of Caragana Korshinskii and Two Derivatives Through the Complementary Advantages of Multiple Techniques

Abstract

Caragana korshinskii (Ck) is a typical tillering deciduous shrub that can be used for soil and water conservation, and its branches have certain medicinal value. Structural features of Ck, subcritical hydrolysis-derived residue (RCH) and bio-oil (SPEA) were evaluated by the complementary advantages of various characterization tools. Solid-state 13C NMR analysis shows that Caliphatic moieties dominate Ck, while O atoms are mainly distributed in >C-O-. Core units of most aromatic clusters are polysubstituted benzene rings. XPS and TG/DTG analyses indicate that subcritical hydrolysis and accompanying thermochemical reactions promote the cleavage of -COO-, >Cal-X (dominated by >Cal-O-), and >N-X bridged bonds in Ck, and involve the release of pyridinic N and pyrrolic N. According to FTIR fitting analysis, SPEA contains abundant aliphatic and >C=O/>C-O- moieties, while RCH is characterized by lignin. GC/MS and 1H NMR analyses further show that >CalOH, >Car-O-, and >C=O are 3 core classes in SPEA, and alkanols, cyclanols, arenols, alkoxy-substituted phenols, and ketones dominate. In addition, aromatics are mostly ortho-para substituted and mainly attributed to the release of inherent guaiacyl/syringyl units and the cleavage of >C-O-C< bonds. Aliphatic ketones, tetrahydrofurans, and tetrahydropyrans are mainly derived from the hydrolysis of cellulose and hemicellulose. On this basis, the structure information with higher accuracy, including four basic units, bridged bonds, and aromatic fragments, was obtained by GC/MS and 2D NMR matching. Bridged bonds involve β-O-4, α,β-diaryl ethers, β-5, β-β, and carbohydrates, while aromatic fragments refer to guaiacyl/syringyl, ferulate, p-hydroxybenzoate, and p-coumarate units as well as cinnamyl alcohol end-group.

Keywords: Caragana korshinskii, Subcritical hydrolysis, Bio-oil, Residue, Chemical structures