Multiscale modelling investigation of wood modification with acetic anhydride

A density functional theory study on interactions in water-bridged dimeric complexes of lignin

Lignin is the main plant cell wall component responsible for recalcitrance in the process of lignocellulosic biomass conversion into biofuels. The recalcitrance and insolubility of lignin in different reaction media are due in part to the hydrogen bonds and π interactions that hold syringyl (S) and guaiacyl (G) units together and promote the formation of stable water-bridged dimeric complexes (WBDCs): S⋯G and S⋯S, in native lignin. The current understanding of how each type of interaction influences the stability of these complexes within lignin native cell walls is still limited. Here, we found by DFT calculations that hydrogen bonding is more dominant than π-stacking interaction between aromatic rings of WBDCs. Although there is a stronger interaction of hydrogen bonds between subunits and water and higher π-stacking interaction in the S⋯S complex compared to the S⋯G complex, the former complex is less thermodynamically stable than the latter due to the entropic contribution coming from the methoxy substituents in the S-unit. Our results demonstrate that the methoxylation degree of lignin units does not significantly influence the structural geometries of WBDCs; if anything, an enhanced dispersion interaction between ring aromatics results in quasi-sandwich geometries as found in "coiled" lignin structures in the xylem tissue of wood. In the same way as that with ionic liquids, polar solvents can dissolve S-lignin by favorable interactions with the aliphatic hydroxyl group in the α-position as the key site or the aromatic hydroxyl group as the secondary site.

Fungal enzyme degradation of lignin-PLA composites: Insights from experiments and molecular docking simulations

Fungal enzymes are effective in degrading various polymeric materials. In this study, we assessed the initial degradation of composites consisting of lignin-poly(lactic acid) (PLA) with both unmodified lignin (LIG) and oxypropylated lignin (oLIG) incorporated at 10 % and 40 % weight within the PLA matrix in a fungal environment. Trametes versicolor fungi were used, and the samples were treated only for eight weeks. Although there was no significant difference in weight loss, the degradation process impacted the chemical and thermal properties of the composites, as shown by Fourier transform infrared spectroscopy (FTIR) and Differential scanning calorimetry (DSC) analyses. After the degradation process, the carbonyl index values decreased for all composites and the hydroxyl index values increased for LIG/PLA and a reverse trend was observed for oLIG/PLA composites. The first heating scan from DSC results showed that the melting peak and the cold crystallization peak disappeared after the degradation process. Microscopic analysis revealed that LIG/PLA exhibited higher roughness than oLIG/PLA. Molecular docking simulations were carried out using guaiacylglycerol-β-guaiacyl ether (GGE) and lactic acid (LA) as model compounds for lignin and PLA, respectively, with laccase (Lac) enzyme for Trametes versicolor. The docking results showed that GGE had the strongest binding interaction and affinity with Lac than lactic acid and oxypropylated GGE. The oxypropylated GGE formed a shorter hydrogen bonding with the Lac enzyme than GGE and LA. The trend associated with the degradation of composites from experimental and molecular docking findings was consistent. This combined approach provided insights into the degradation process using fungi and had the potential to be applied to different polymeric composites.

Dispersion-corrected DFT calculations and umbrella sampling simulations to investigate stability of Chrysin-cyclodextrin inclusion complexes

The study of inclusion complexes of Chrysin (ChR) with three forms of cyclodextrins (CDs) α-, β-, and γ-CD was accomplished to examine the stability of ChR inside the central cavities of CDs. The aim of study was to identify the most suitable form of CD to improve the hydro-solubility of poorly soluble ChR bioactive molecule. Microsecond timescale molecular dynamics (MD) simulations were performed on four inclusion complexes (α-CD/ChR, β-CD/ChR, and two conformations of γ-CD/ChR) to examine the dynamics of ChR inside the cavity of CDs. The first conformation of γ-CD/ChR inclusion complex (γ-CD1/ChR) was identified to possess the highest affinity between host and guest molecule on the basis of binding energy calculated by employing Molecular Mechanics Poisson-Boltzmann Surface Area (MM-PBSA) and umbrella sampling simulations. To further strengthen the claims of classical and biased MD studies, Our own N-layered Integrated molecular Orbital and Molecular mechanics (ONIOM) (wB97XD/6-311+g(d,p):pm7) calculations were performed on the selected inclusion complexes. The ONIOM based complexation energy reaffirmed that ChR had highest affinity for the γ-CD1 host molecule. Further, the non-covalent interaction analysis was conducted using Multiwfn software on QM-optimized inclusion complexes with wB97XD/6-311+G(d,p) model chemistry, revealing non-covalent interactions between ChR and CDs. This atomic level information helped us to gain better insights into critical atoms of ChR and CD that participated in intermolecular interactions and identify γ-CD as a suitable host molecule for improving the hydro-solubulity of ChR. The structural insights would help to derive new derivatives of γ-CD with better host capacity.

Lignin to value-added products: Research updates and prospects

Due to the urgent need for renewable and clean energy, the efficient use of lignin is of wide interest. A comprehensive understanding of the mechanisms of lignin depolymerization and the generation of high-value products will contribute to the global control of the formation of efficient lignin utilization. This review explores the lignin value-adding process and discusses the link between lignin functional groups and value-added products. Mechanisms and characteristics of lignin depolymerization methods are presented, and challenges and prospects for future research are highlighted.

Role of Noncovalent Interactions in N,P-Functionalized Luminescent Carbon Dots for Ultrasensitive Detection of Moisture in D2O: Boosting Visible-NIR Light Sensitivity

It is highly desirable to design cost-efficient and eco-friendly fluorometric sensors that can efficiently detect water contamination in D₂O and other expensive organic solvents. Herein, we have synthesized N,P-codoped carbon dots (N,P-CDs) from o-phenylene diamine (o-PDA) and H₃PO₄ through the bottom-up carbonization method. Heteroatom co-doping increases the absorption cross section in the visible-NIR range, followed by the formation of stable emissive states in longer-wavelength regions. We have critically investigated the noncovalent interactions (especially H-bonding interactions) of various surface functional groups with surrounding solvent media through a detailed structure-property correlation. Based on the sensitivity of noncovalent H-bonding interactions to the stability of longer-wavelength emissive domains, we have utilized these N,P-CDs as cost-effective fluorometric sensors of water/moisture contamination in D₂O especially under visible-NIR light; the optical sensitivity reaches up to 0.1 volume (%) level. The detailed sensing mechanism has been further supported by a computational study through a simple visualization approach by mapping and analyzing all possible noncovalent interactions between the CDs and the solvent medium.