5 research outputs found

    Effect of Nonionic Surfactants on Dispersion and Polar Interactions in the Adsorption of Cellulases onto Lignin

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    Residual lignin in pretreated biomass impedes enzymatic hydrolysis. Nonionic surfactants are known to enhance the enzymatic hydrolysis of lignocellulosic biomass but their mechanisms of action are incompletely understood. This study investigates the effect of a nonionic surfactant, Tween 80, on the adsorption of cellulases onto model lignin substrates. Lignin substrates were prepared by spin coating of flat substrates with three different types of lignin: organosolv lignin, kraft lignin, and milled wood lignin. The functional group distributions in the lignins were quantitatively analyzed by <sup>31</sup>P NMR spectroscopy. The surface energies and surface roughnesses of the substrates were determined by contact angle measurements and atomic force microscopy, respectively. Tween 80 and cellulase adsorption onto the lignin substrates was analyzed with a quartz crystal microbalance with dissipation monitoring. Tween 80 adsorbed rapidly and primarily (≥85%) via dispersion interactions onto the lignin substrates and effected solubilization of lignin molecules, most notably with organosolv lignin, having the largest dispersive surface energy component and smallest molar mass. Cellulase adsorption onto the lignin substrates was mostly irreversible and had both a rapid and a gradual adsorption stage. Rapid cellulase adsorption was primarily (≥64%) mediated by dispersion interactions. The subsequent gradual mass increase is postulated to involve swelling of the lignin substrates. Adsorbed Tween 80 rendered lignin surfaces more hydrophilic by increasing their polar surface energy component and reduced both the extent of rapid cellulase adsorption as well as the rate of the subsequent gradual mass increase. The effect of Tween 80 on the rate and extent of the gradual mass increase depended strongly on the chemical properties of the lignin

    Effects of Sulfate Groups on the Adsorption and Activity of Cellulases on Cellulose Substrates

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    Pretreatment of lignocellulosic biomass with sulfuric acid may leave sulfate groups on its surface that may hinder its biochemical conversion. This study investigates the effects of sulfate groups on cellulase adsorption onto cellulose substrates and the enzymatic hydrolysis of these substrates. Substrates with different sulfate group densities were prepared from H<sub>2</sub>SO<sub>4</sub>- and HCl-hydrolyzed and partially and fully desulfated cellulose nanocrystals. Adsorption onto and hydrolysis of the substrates was analyzed by quartz crystal microbalance with dissipation monitoring (QCM-D). The surface roughness of the substrates, measured by atomic force microscopy, increased with decreasing sulfate group density, but their surface accessibilities, measured by QCM-D H<sub>2</sub>O/D<sub>2</sub>O exchange experiments, were similar. The adsorption of cellulose binding domains onto sulfated substrates decreased with increasing sulfate group density, but the adsorption of cellulases increased. The rate of hydrolysis of sulfated substrates decreased with increasing sulfate group density. The results indicated an inhibitory effect of sulfate groups on the enzymatic hydrolysis of cellulose, possibly due to nonproductive binding of the cellulases onto the substrates through electrostatic interactions instead of their cellulose binding domains

    Surface-Initiated Dehydrogenative Polymerization of Monolignols: A Quartz Crystal Microbalance with Dissipation Monitoring and Atomic Force Microscopy Study

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    This work highlights a real-time and label-free method to monitor the dehydrogenative polymerization of monolignols initiated by horseradish peroxidase (HRP) physically immobilized on surfaces using a quartz crystal microbalance with dissipation monitoring (QCM-D). The dehydrogenative polymer (DHP) films are expected to provide good model substrates for studying ligninolytic enzymes. The HRP was adsorbed onto gold or silica surfaces or onto and within porous desulfated nanocrystalline cellulose films from an aqueous solution. Surface-immobilized HRP retained its activity and selectivity for monolignols as coniferyl and <i>p</i>-coumaryl alcohol underwent dehydrogenative polymerization in the presence of hydrogen peroxide, whereas sinapyl alcohol polymerization required the addition of a nucleophile. The morphologies of the DHP layers on the surfaces were investigated via atomic force microscopy (AFM). Data from QCM-D and AFM showed that the surface-immobilized HRP-initiated dehydrogenative polymerization of monolignols was greatly affected by the support surface, monolignol concentration, hydrogen peroxide concentration, and temperature

    Chitinase Activity on Amorphous Chitin Thin Films: A Quartz Crystal Microbalance with Dissipation Monitoring and Atomic Force Microscopy Study

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    Chitinases are widely distributed in nature and have wide-ranging pharmaceutical and biotechnological applications. This work highlights a real-time and label-free method to assay Chitinase activity via a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The chitin substrate was prepared by spincoating a trimethylsilyl chitin solution onto a silica substrate, followed by regeneration to amorphous chitin (RChi). The QCM-D and AFM results clearly showed that the hydrolysis rate of RChi films increased as Chitinase (from <i>Streptomyces griseus</i>) concentrations increased, and the optimal temperature and pH for Chitinase activity were around 37 °C and 6–8, respectively. The Chitinase showed greater activity on chitin substrates, having a high degree of acetylation, than on chitosan substrates, having a low degree of acetylation

    Ultrathin Chitin Films for Nanocomposites and Biosensors

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    Chitin is the second most abundant biopolymer and insight into its natural synthesis, enzymatic degradation, and chemical interactions with other biopolymers is important for bioengineering with this renewable resource. This work is the first report of smooth, homogeneous, ultrathin chitin films, opening the door to surface studies of binding interactions, adsorption kinetics, and enzymatic degradation. The chitin films were formed by spincoating trimethylsilyl chitin onto gold or silica substrates, followed by regeneration to a chitin film. Infrared and X-ray photoelectron spectroscopy, X-ray diffraction, ellipsometry, and atomic force microscopy were used to confirm the formation of smooth, homogeneous, and amorphous chitin thin films. Quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange experiments showed these films swelled with 49% water by mass. The utility of these chitin films as biosensors was evident from QCM-D and surface plasmon resonance studies that revealed the adsorption of a bovine serum albumin monolayer
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