Cross-polarization/magic-angle spinning 13C nuclear magnetic resonance study of cellulose I–ethylenediamine complex

Ethylenediamine pretreatment changes cellulose allomorph and lignin structure of lignocellulose at ambient pressure

BACKGROUND

Pretreatment of lignocellulosic biomass is essential to increase the cellulase accessibility for bioconversion of lignocelluloses by breaking down the biomass recalcitrance. In this work, a novel pretreatment method using ethylenediamine (EDA) was presented as a simple process to achieve high enzymatic digestibility of corn stover (CS) by heating the biomass-EDA mixture with high solid-to-liquid ratio at ambient pressure. The effect of EDA pretreatment on lignocellulose was further studied.

RESULTS

High enzymatic digestibility of CS was achieved at broad pretreatment temperature range (40-180 °C) during EDA pretreatment. Herein, X-ray diffractogram analysis indicated that cellulose I changed to cellulose III and amorphous cellulose after EDA pretreatment, and cellulose III content increased along with the decrease of drying temperature and the increase of EDA loading. Lignin degradation was also affected by drying temperature and EDA loading. Images from scanning electron microscope and transmission electron microscope indicated that lignin coalesced and deposited on the biomass surface during EDA pretreatment, which led to the delamination of cell wall. HSQC NMR analysis showed that ester bonds of p-coumarate and ferulate units in lignin were partially ammonolyzed and ether bonds linking the phenolic monomers were broken during pretreatment. In addition, EDA-pretreated CS exhibited good fermentability for simultaneous saccharification and co-fermentation process.

CONCLUSIONS

EDA pretreatment improves the enzymatic digestibility of lignocellulosic biomass significantly, and the improvement was caused by the transformation of cellulose allomorph, lignin degradation and relocalization in EDA pretreatment.

Advances in solid-state NMR of cellulose

Nuclear magnetic resonance (NMR) spectroscopy is a well-established analytical and enabling technology in biofuel research. Over the past few decades, lignocellulosic biomass and its conversion to supplement or displace non-renewable feedstocks has attracted increasing interest. The application of solid-state NMR spectroscopy has long been seen as an important tool in the study of cellulose and lignocellulose structure, biosynthesis, and deconstruction, especially considering the limited number of effective solvent systems and the significance of plant cell wall three-dimensional microstructure and component interaction to conversion yield and rate profiles. This article reviews common and recent applications of solid-state NMR spectroscopy methods that provide insight into the structural and dynamic processes of cellulose that control bulk properties and biofuel conversion.

A preliminary spectroscopic investigation on the molecular interaction of metal-diphenylthiocarbazone complex with cellulose biopolymer and its application

Biopolymer adsorbents are versatile in their application for removal of heavy metals. The present work is focused towards the preliminary study of the interaction of diphenylthiocarbazone (DTZ) complex of chromium(VI) in acidic medium with cellulose biopolymer. Chromium-DTZ complex could be quantitatively adsorbed on a cellulose column in the pH range 1.0-2.5 and the effect of various experimental parameters such as stability of the column and the complex, column breakthrough volume, and interfering ions have been studied in detail. The probable mechanism of adsorption of complex on the cellulose biopolymer was corroborated using Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and solid state 13C nuclear magnetic resonance techniques (CP-MAS). The pores formed due to the hydrogen bond between the cellulose layers and then the ensuing occupation of the complex between these layers and on the surface of the biopolymer layer through electrostatic attractive force and Π interaction of aromatic ring with cellulose are expected to play a vital role in the interaction. The cellulose column could be regenerated using environmentally benign polyethylene glycol-400 (PEG-400) in acidic medium. The cellulose biosorbent has been successfully tested to study the removal of chromium as its dithizone complex from synthetic and real waste water samples.

Synthesis of methyl 4′-O-methyl-β-d-cellobioside-13C12 from d-glucose-13C6. Part 2: Solid-state NMR studies

Double Quantum (DQ) NMR, which utilizes the magnetic dipole interaction between the (13)C atoms, was used for the complete assignment of the (13)C NMR resonances to the corresponding carbon ring positions for the monoclinic and triclinic allomorphs of methyl 4'-O-methyl-beta-D-cellobioside-(13)C(12)(1-(13)C(12)), a cellodextrin model compound of cellulose (13)C-perlabeled at the cellobiose core. The through-space interactions were used to identify the direct chemical bonds between adjacent carbon atoms in the rings. More importantly, the (13)C NMR signals of the carbon sites C1' and C4 involved in the glycosidic bond were identified. This allowed for the complete (13)C chemical shift assignment, that when combined with the X-ray crystallography data provides a complete characterization.