Interactions of endoglucanases with amorphous cellulose films resolved by neutron reflectometry and quartz crystal microbalance with dissipation monitoring.

A study of the interaction of four endoglucanases with amorphous cellulose films by neutron reflectometry (NR) and quartz crystal microbalance with dissipation monitoring (QCM-D) is reported. The endoglucanases include a mesophilic fungal endoglucanase (Cel45A from H. insolens), a processive endoglucanase from a marine bacterium (Cel5H from S. degradans ), and two from thermophilic bacteria (Cel9A from A. acidocaldarius and Cel5A from T. maritima ). The use of amorphous cellulose is motivated by the promise of ionic liquid pretreatment as a second generation technology that disrupts the native crystalline structure of cellulose. The endoglucanases displayed highly diverse behavior. Cel45A and Cel5H, which possess carbohydrate-binding modules (CBMs), penetrated and digested within the bulk of the films to a far greater extent than Cel9A and Cel5A, which lack CBMs. While both Cel45A and Cel5H were active within the bulk of the films, striking differences were observed. With Cel45A, substantial film expansion and interfacial broadening were observed, whereas for Cel5H the film thickness decreased with little interfacial broadening. These results are consistent with Cel45A digesting within the interior of cellulose chains as a classic endoglucanase, and Cel5H digesting predominantly at chain ends consistent with its designation as a processive endoglucanase.

Quartz crystal microbalance with dissipation monitoring and surface plasmon resonance studies of carboxymethyl cellulose adsorption onto regenerated cellulose surfaces.

Adsorption of anionic polyelectrolytes, sodium salts of carboxymethyl celluloses (CMCs) with different degrees of substitution (DS = 0.9 and 1.2), from aqueous electrolyte solutions onto regenerated cellulose surfaces was studied using quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) experiments. The influence of both calcium chloride (CaCl(2)) and sodium chloride (NaCl) on CMC adsorption was examined. The QCM-D results demonstrated that CaCl(2) (divalent cation) caused significantly greater CMC adsorption onto regenerated cellulose surfaces than NaCl (monovalent cation) at the same ionic strength. The CMC layers adsorbed onto regenerated cellulose surfaces from CaCl(2) solutions exhibited greater stability upon exposure to flowing water than layers adsorbed from NaCl solutions. Both QCM-D and SPR results showed that CMC adsorption onto regenerated cellulose surfaces from CaCl(2) solutions increased with increasing CaCl(2) concentration up to the solubility limit (10 mM). Voigt-based viscoelastic modeling of the QCM-D data indicated that the CMC layers adsorbed onto regenerated cellulose surfaces had shear viscosities of η(f) ≈ 10(-3) N·s·m(-2) and elastic shear moduli of µ(f) ≈ 10(5) N·m(-2). Furthermore, the combination of SPR spectroscopy and QCM-D showed that the CMC layers contained 90-95% water. Adsorption isotherms for CMCs in CaCl(2) solutions were also obtained from QCM-D and were fit by Freundlich isotherms. This study demonstrated that CMC adsorption from CaCl(2) solutions is useful for the modification of cellulose surfaces.

Neutron reflectometry and QCM-D study of the interaction of cellulases with films of amorphous cellulose.

Improving the efficiency of enzymatic hydrolysis of cellulose is one of the key technological hurdles to reduce the cost of producing ethanol and other transportation fuels from lignocellulosic material. A better understanding of how soluble enzymes interact with insoluble cellulose will aid in the design of more efficient enzyme systems. We report a study involving neutron reflectometry (NR) and quartz crystal microbalance with dissipation monitoring (QCM-D) of the interaction of a fungal enzyme extract ( T. viride ) and an endoglucanse from A. niger with amorphous cellulose films. The use of amorphous cellulose is motivated by that the fact that several biomass pretreatments currently under investigation disrupt the native crystalline structure of cellulose and increase the amorphous content. NR reveals the profile of water through the film at nanometer resolution and is highly sensitive to interfacial roughness, whereas QCM-D provides changes in mass and film stiffness. NR can be performed using either H(2)O- or D(2)O-based aqueous reservoirs. NR measurement of swelling of a cellulose film in D(2)O and in H(2)O revealed that D/H exchange on the cellulose chains must be taken into account when a D(2)O-based reservoir is used. The results also show that cellulose films swell slightly more in D(2)O than in H(2)O. Regarding enzymatic digestion, at 20 °C in H(2)O buffer the T. viride cocktail rapidly digested the entire film, initially roughening the surface, followed by penetration and activity throughout the bulk of the film. In contrast, over the same time period, the endoglucanase was active mainly at the surface of the film and did not increase the surface roughness.

Topologically Enhanced Dual-Network Hydrogels with Rapid Recovery for Low-Hysteresis, Self-Adhesive Epidemic Electronics.

Dual-network conductive hydrogels have drawn wide attention in epidemic electronics such as epidemic sensors and electrodes because of their inherent low Young's modulus, high skin-compliance, and tunable mechanical strength. However, it is still full of challenges to gain a dual-network hydrogel with high stretchability, low hysteresis, and skin-adhesive performance simultaneously. Herein, to address this issue, a novel dual-network hydrogel (denoted as PAa hydrogel) with polyacrylamide as the first network and topologically entangled polydopamine as the secondary network was prepared through a facile gel-phase in situ self-polymerization and soaking treatment. Benefiting from the topological enhancement as well as the synergetic effects of hydrogen bonds and metal coordination bonds, low modulus (∼10 kPa), excellent stretchability (1090.8%), high compression (90%), negligible hysteresis (η = 0.019, energy loss coefficient), rapid recovery in seconds, and self-adhesion are obtained in the PAa hydrogels. To demonstrate their practical use, a states-independent and skin-adhesive epidemic sensor was successfully attached on human skin for motion detection. What is more, by using the hydrogel as an epidemic electrode, electromyogram signals were accurately detected and wirelessly transmitted to a smart phone. This work offers a new insight to understand the strengthening mechanism of dual network hydrogels and a design strategy for both epidemic sensors and electrodes.

Surface plasmon resonance studies of pullulan and pullulan cinnamate adsorption onto cellulose.

Surface plasmon resonance studies showed pullulan cinnamates (PCs) with varying degrees of substitution (DS) adsorbed onto regenerated cellulose surfaces from aqueous solutions below their critical aggregation concentrations. Results on cellulose were compared to PC adsorption onto hydrophilic and hydrophobic self-assembled thiol monolayers (SAMs) on gold to probe how different interactions affected PC adsorption. PC adsorbed onto methyl-terminated SAMs (SAM-CH(3)) > cellulose > hydroxyl-terminated SAMs (SAM-OH) for high DS and increased with DS for each surface. Data for PC adsorption onto cellulose and SAM-OH surfaces were effectively fit by Langmuir isotherms; however, Freundlich isotherms were required to fit PC adsorption isotherms for SAM-CH(3) surfaces. Atomic force microscopy images from the solid/liquid interfaces revealed PC coatings were uniform with surface roughnesses <2 nm for all surfaces. This study revealed hydrogen bonding alone could not explain PC adsorption onto cellulose and hydrophobic modification of water-soluble polysaccharides was a facile strategy for their conversion into surface modifying agents.