(400c) Thermodynamics of Lignin Dimers and ?-Cyclodextrin Complexes

Authors: 
Moradipour, M., University of Kentucky
Knutson, B. L., University of Kentucky
Rankin, S. E., University of Kentucky
Lynn, B. C., University of Kentucky
Kamali, P., University of Kentucky
Tong, X., Louisiana State University
Moldovan, D., Louisiana State University
Lignin is an organic structural polymer in and between the cell walls of plants. Due to lignin’s complex structure, a heterogeneous mixture of lignin derivatives are obtained when lignin is depolymerized. Developing methods to selectively separate, purify, and valorize lignin small derivatives is challenging. Cyclodextrins (CDs), particularly β-CD, are commonly used as chirally selective adsorbents for many applications including agriculture, pharmaceuticals, and analytical chemistry. CDs are shaped like truncated cones with a hydrophilic surface and a hydrophobic core, which provide host-guest size and structure selectivity.

Understanding the interactions of lignin-derived small molecules with CDs in solution will support our efforts to create selective immobilized CD-MSNPs, whose binding with small molecules can also be quantified with isothermal titration calorimetry (ITC). The present work aims to study binding of β-CD to three types of lignin dimers including two derivatives of βO4’ dimers of coniferyl alcohol (GG lignin dimer) as well as pinoresinol (G-ββ-G) using ITC. The equilibrium binding constant (K) and the thermodynamic binding energies (ΔH, ΔS, and ΔG) for dimer-β-CD complexes are determined from fitting binding models to the ITC data. The results of this work show that guiacylglycerol guaiacol ester with a hydroxypropenyl (HOC3H4-) tail (G-βO4’-G) binds to the β-CD through a different mechanism than pinoresinol and commercially available guaiacylglycerol-β-guaiacyl ether (G-βO4’-truncG) lignin dimer. The results for the G-βO4'-G are in good agreement with molecular simulations conducted for the same system. We also demonstrate that CD-lignin interactions can be used to develop selective separation strategies for lignin-derived small molecules, and investigated the surface modification techniques to attach β-CD directly to the silica MSNPs, with a goal of using the silica particles for selective capture of lignin-derived small molecules.