@article{hu_heitmann_zhong_lucia_argyropoulos_2015, title={Quantitative Study of the Interfacial Adsorption of Cellullase to Cellulose}, volume={119}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.5b02011}, abstractNote={The phenomenon of interfacial adsorption of cellulase to cellulose plays a significant role in its enzymatic conversion to a variety of biomaterials and biofuels. The crystallinity and surface areas are the key substrate characteristics that must be considered in its final conversion to soluble sugars. This research therefore characterized the crystallinity and surface areas of microcrystalline celluloses and hardwood pulps as a function of the interfacial activity of cellulase, and thereafter the effects of these two parameters on adsorption were modeled. The crystallinities were characterized by X-ray diffraction, while surface areas by laser scattering and Congo red adsorption. It was found that cellulase adsorption to cellulose follows a Langmuir model while statistical modeling showed that surface area, crystallinity, and their interactions were determined to be significant for cellulase adsorption over a temperature range of 4–50 °C.}, number={25}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Hu, Gang and Heitmann, John A. and Zhong, Biao and Lucia, Lucian A. and Argyropoulos, Dimitris S.}, year={2015}, month={Jun}, pages={14160–14166} }
 @article{hu_heitmann_rojas_pawlak_argyropoulos_2010, title={Monitoring Cellulase Protein Adsorption and Recovery Using SDS-PAGE}, volume={49}, ISSN={0888-5885 1520-5045}, url={http://dx.doi.org/10.1021/ie100731b}, DOI={10.1021/ie100731b}, abstractNote={Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was employed to study the sorption behaviors of cellulases on microcrystalline celluloses and hardwood pulp. The adsorption and recovery of cellulases from Aspergillus niger and Trichoderma reesei were investigated at 25 °C. Cellulase recovery was conducted by rinsing adsorbed enzymes with sodium acetate buffer, Milli-Q water, and sodium hydroxide solution. The initial, equilibrium, and recovered enzymes were analyzed using SDS-PAGE gels. Gels were scanned and analyzed using ImagePro software. The molecular weights of cellulase proteins were determined using a protein marker having seven known proteins. The cellulase system from Trichoderma reesei had a higher adsorption on all substrates studied than the cellulase system from Aspergillius niger, and higher pH favored desorption from the substrates studied. Experimental results also demonstrated that adsorption and desorption amounts determined by SDS-PAGE were proportional to protein concentrations in their crude mixtures.}, number={18}, journal={Industrial & Engineering Chemistry Research}, publisher={American Chemical Society (ACS)}, author={Hu, Gang and Heitmann, John A., Jr. and Rojas, Orlando J. and Pawlak, Joel J. and Argyropoulos, Dimitris S.}, year={2010}, month={Sep}, pages={8333–8338} }
 @article{hu_heitmann_rojas_2009, title={In Situ Monitoring of Cellulase Activity by Microgravimetry with a Quartz Crystal Microbalance}, volume={113}, ISSN={["1520-6106"]}, DOI={10.1021/jp907155v}, abstractNote={Quartz crystal microgravimetry (QCM) was used to investigate the interactions between cellulase enzymes and model cellulose substrates. The substrates consisted of thin films of cellulose that were spin-coated onto polyvinylamine (PVAm) precoated quartz crystal sensors carrying conductive gold surfaces. In QCM the quartz crystals are piezoelectrically driven and the frequency and dissipation shifts allow monitoring of substrate hydrolysis at various temperatures and enzyme concentrations in situ and in real time. The changes in frequency of cellulose-coated quartz resonators during their incubation in cellulase solutions were related to contributions from the liquid phase properties, the adsorptions of cellulase enzymes, and the hydrolysis of the substrate. Cellulase adsorption was found to be nonspecific and irreversible on gold-, PVAm-, and cellulose-coated quartz crystal sensors. The contribution to frequency shifts due to the bulk fluid properties of the cellulase solutions (at concentrations lower than 0.5 mg/mL) was minimal compared to the frequency shifts produced by cellulase binding. The maximum frequency decreases were fitted to a Langmuir model. The adsorption constant and the maximum adsorption were estimated by the fitting parameters of this model. The hydrolysis process was modeled by using a dose-response model that was then used to estimate the maximum hydrolysis rate, to compare the relative effects of temperature on adsorption and hydrolysis rate, and to obtain the apparent activation energy of cellulose hydrolysis. The hydrolysis rate increased with incubation temperature while apparent adsorption decreased. The apparent activation energy for the hydrolysis of the cellulose films employed was calculated to be 37 kJ/mol.}, number={44}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Hu, Gang and Heitmann, John A., Jr. and Rojas, Orlando J.}, year={2009}, month={Nov}, pages={14761–14768} }
 @article{hu_heitmann_rojas_2009, title={Quantification of Cellulase Activity Using the Quartz Crystal Microbalance Technique}, volume={81}, ISSN={["1520-6882"]}, DOI={10.1021/ac802318t}, abstractNote={The development of more efficient utilization of biomass has received increased attention in recent years. Cellulases play an important role in processing biomass through advanced biotechnological approaches. Both the development and the application of cellulases require an understanding of the activities of these enzymes. A new method to determine the activity of cellulase has been developed using a quartz crystal microbalance (QCM) technique. We compare the results from this technique with those from the IUPAC (International Union of Pure and Applied Chemistry) dinitrosalicylic acid (DNS) standard method and also from biccinchoninic acid and ion chromatography methods. It is shown that the QCM technique provides results closer to those obtained by measuring the actual reducing sugars. The elimination of the use of color development in the standard redox methods makes the QCM platform easier to implement; it also allows more flexibility in terms of the nature of the substrate. Finally, validation of the proposed method was carried out by relating the crystallinity of different substrates to the cellulase activity. Numerical values of cellulase activities measured with the QCM method showed that celluloses with higher crystallinity indices were hydrolyzed slower and to a lower extent than those of lower crystallinity indices for the cellulase mixtures examined.}, number={5}, journal={ANALYTICAL CHEMISTRY}, author={Hu, Gang and Heitmann, John A., Jr. and Rojas, Orlando J.}, year={2009}, month={Mar}, pages={1872–1880} }
 @article{hu_heitmann_rojas_2008, title={Feedstock pretreatment strategies for producing ethanol from wood, bark, and forest residues}, volume={3}, number={1}, journal={BioResources}, author={Hu, G. and Heitmann, J. A. and Rojas, O. J.}, year={2008}, pages={270–294} }