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2. Different effects of carbohydrate binding modules on the viscoelasticity of nanocellulose gels

Author

Rooijakkers, Bart J.M., Arola, Suvi, Velagapudi, Rama, Linder, Markus B., Department of Bioproducts and Biosystems, VTT Technical Research Centre of Finland, Aalto-yliopisto, and Aalto University

Subjects
lcsh:Biochemistry, CBM, Gel, Cellulose nanofibril, lcsh:Biology (General), Family 1 carbohydrate binding module, lcsh:QD415-436, Rheology, lcsh:QH301-705.5
Abstract

Many cellulose degrading and modifying enzymes have distinct parts called carbohydrate binding modules (CBMs). The CBMs have been shown to increase the concentration of enzymes on the insoluble substrate and thereby enhance catalytic activity. It has been suggested that CBMs also have a role in disrupting or dispersing the insoluble cellulose substrate, but dispute remains and explicit evidence of such a mechanism is lacking. We produced the isolated CBMs from two major cellulases (Cel6A and Cel7A) from Trichoderma reesei as recombinant proteins in Escherichia coli. We then studied the viscoelastic properties of native unmodified cellulose nanofibrils (CNF) in combination with the highly purified CBMs to detect possible functional effects of the CBMs on the CNF. The two CBMs showed clearly different effects on the viscoelastic properties of CNF. The difference in effects is noteworthy, yet it was not possible to conclude for example disruptive effects. We discuss here the alternative explanations for viscoelastic effects on CNF caused by CBMs, including the effect of ionic cosolutes.

Published
2020
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3. Optical properties of silicon nanocrystals in silica: Results from spectral filtering effect, m-line technique, and x-ray photoelectron spectroscopy.

Author

Khriachtchev, Leonid, Nikitin, Timur, Oton, Claudio J., Velagapudi, Rama, Sainio, Jani, Lahtinen, Jouko, and Novikov, Sergei

Subjects
OPTICAL properties, SILICON, NANOCRYSTALS, SILICA, X-ray photoelectron spectroscopy, WAVEGUIDES, SILICON oxide
Abstract

The optical properties of silica layers containing silicon nanocrystals are analyzed in terms of spectral filtering in absorbing planar waveguides (cutoff spectra), m-line measurements, and x-ray photoelectron spectroscopy (XPS). The effects of optical dispersion, approximation of weak guiding, and depth dependence of refractive index in a planar waveguide are studied. We compare the measured optical properties of silicon-rich silicon oxide samples with the values estimated by the Bruggeman theory using the XPS structural components. A good agreement between the measured and calculated refractive indices is found. The results for absorption suggest high transparency of the nanoscale-suboxide component in contrast to the corresponding bulk material. The Raman intensity of silicon nanocrystals is proportional to the XPS amount of bulk silicon. The extinction coefficient extracted for the Si component is between the values for crystalline and amorphous silicon. Annealing at higher temperatures decreases the Si component extinction coefficient, which is interpreted as a decrease in the amorphous Si fraction. The XPS method surprisingly suggests a large proportion of silicon suboxide even after annealing at 1200 °C. [ABSTRACT FROM AUTHOR]

Published
2008
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