5 research outputs found
Effect of Nonionic Surfactants on Dispersion and Polar Interactions in the Adsorption of Cellulases onto Lignin
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
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
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
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
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