Biomedical subjects

Hongfei Jia

Publications and source records attributed to Hongfei Jia.

6 recordsLinked to original sources

PubMed2007

Crosslinked enzyme aggregates in hierarchically-ordered mesoporous silica: a simple and effective method for enzyme stabilization.

alpha-chymotrypsin (CT) and lipase (LP) were immobilized in hierarchically-ordered mesocellular mesoporous silica (HMMS) in a simple but effective way for the enzyme stabilization, which was achieved by the enzyme adsorption followed by glutaraldehyde (GA) crosslinking. This resulted in the formation of nanometer scale crosslinked enzyme aggregates (CLEAs) entrapped in the mesocellular pores of HMMS (37 nm), which did not leach out of HMMS through narrow mesoporous channels (13 nm). CLEA of alpha-chymotrypsin (CLEA-CT) in HMMS showed a high enzyme loading capacity and significantly increased enzyme stability. No activity decrease of CLEA-CT was observed for 2 weeks under even rigorously shaking condition, while adsorbed CT in HMMS and free CT showed a rapid inactivation due to the enzyme leaching and presumably autolysis, respectively. With the CLEA-CT in HMMS, however, there was no tryptic digestion observed suggesting that the CLEA-CT is not susceptible to autolysis. Moreover, CLEA of lipase (CLEA-LP) in HMMS retained 30% specific activity of free lipase with greatly enhanced stability. This work demonstrates that HMMS can be efficiently employed as host materials for enzyme immobilization leading to highly enhanced stability of the immobilized enzymes with high enzyme loading and activity.

Chymotrypsin↗

PubMed2006

Challenges in biocatalysis for enzyme-based biofuel cells.

Enzyme-based biofuel cells are attracting attention rapidly partially due to the promising advances reported recently. However, there are issues to be addressed before biofuel cells become competitive in practical applications. Two critical issues are short lifetime and poor power density, both of which are related to enzyme stability, electron transfer rate, and enzyme loading. Recent progress in nanobiocatalysis opens the possibility to improve in these aspects. Many nano-structured materials, such as mesoporous media, nanoparticles, nanofibers, and nanotubes, have been demonstrated as efficient hosts of enzyme immobilization. It is evident that, when nanostructure of conductive materials are used, the large surface area of these nanomaterials can increase the enzyme loading and facilitate reaction kinetics, and thus improving the power density of biofuel cells. In addition, research efforts have also been made to improve the activity and stability of immobilized enzymes by using nanostructures. It appears to be reasonable to us to expect that progress in nanostuctured biocatalysts will play a critical role in overcoming the major obstacles in the development of powerful biofuel cells.

Bioelectric Energy Sources↗

PubMed2005

Simple synthesis of hierarchically ordered mesocellular mesoporous silica materials hosting crosslinked enzyme aggregates.

Hierarchically ordered mesocellular mesoporous silica materials (HMMS) were synthesized using a single structure-directing agent. The mesocellular pores are synthesized without adding any pore expander; the pore walls are composed of SBA-15 type mesopores. Small-angle X-ray scattering revealed the presence of uniform pore structures with two different sizes. Using HMMS as a nanoscopic template, hierarchically ordered mesocellular mesoporous carbon (HMMC) and polymer (HMMP) materials were synthesized. HMMS was used as a host for enzyme immobilization. To improve the retention of enzymes in HMMS, we adsorbed enzymes, and then employed crosslinking using glutaraldehyde (GA). The resulting crosslinked enzyme aggregates (CLEAs) show an impressive stability with extremely high enzyme loadings. For example, 0.5 g alpha-chymotrypsin (CT) could be loaded in 1 g of silica with no activity decrease observed with rigorous shaking over one month. In contrast, adsorbed CT without GA treatment resulted in a lower loading, which further decreased due to continuous leaching of adsorbed CT under shaking. The activity of crosslinked CT aggregates in HMMS was approximately 10 times higher than that of the adsorbed CT, which represents a 74-fold increase in activity per unit weight of HMMS due to higher CT loading.

Adsorption↗

PubMed2004

Enabling multienzyme biocatalysis using nanoporous materials.

Multistep reactions catalyzed by a covalently immobilized enzyme-cofactor-enzyme system were achieved. Lactate dehydrogenase (LDH), glucose dehydrogenase (GDH), and cofactor NADH were incorporated into two porous silica glass supports. One of the glass supports had pores of 30 nm in diameter, while the other was of 100-nm pore size. Effective shuttling of the covalently bound NADH between LDH and GDH was achieved, such that regeneration cycles of NADH/NAD(+) were observed. The glass of 30-nm pore size afforded enzyme activities that were about twice those observed for the glass of 100-nm pore size, indicating the former provided better enzyme-cofactor integration. The effect of the size of spacers was also examined. The use of longer spacers increased the reaction rates by approximately 18 times as compared to those achieved with glutaraldehyde linkage. It appeared that the concave configuration of the nanopores played an important role in enabling the multistep reactions. The same multienzyme system immobilized on nonporous polystyrene particles of 500-nm diameter was only approximately 2% active as the glass-supported system. It is believed that the nanoporous structure of the glass supports enhances the molecular interactions among the immobilized enzymes and cofactor, thus improving the catalytic efficiency of the system.

Catalysis↗

PubMed2003

Catalytic behaviors of enzymes attached to nanoparticles: the effect of particle mobility.

Nanoparticles provide an ideal remedy to the usually contradictory issues encountered in the optimization of immobilized enzymes: minimum diffusional limitation, maximum surface area per unit mass, and high effective enzyme loading. In addition to the promising performance features, the unique solution behaviors of the nanoparticles also point to a transitional region between the heterogeneous (with immobilized enzymes) and homogeneous (with soluble free enzymes) catalysis. The particle mobility, which is related to particle size and solution viscosity through Stokes-Einstein equation, may impact the reaction kinetics according to the collision theory. The mobility-activity relationship was examined through experimental studies and theoretical modeling in the present work. Polystyrene particles with diameters ranging from 110-1000 nm were prepared. A model enzyme, alpha-chymotrypsin, was covalently attached to the nanoparticles up to 6.6 wt%. The collision theory model was found feasible in correlating the catalytic activities of particles to particle size and solution viscosity. Changes in the size of particles and the viscosity of reaction media, which all affect the mobility of the enzyme catalyst, evidently altered the intrinsic activity of the particle-attached enzyme. Compared to K(M), k(cat) appeared to be less sensitive to particle size and viscosity.

Calcium Carbonate↗

PubMedDate not supplied

Enzyme-carrying polymeric nanofibers prepared via electrospinning for use as unique biocatalysts.

Improvement of catalytic efficiency of immobilized enzymes via materials engineering was demonstrated through the preparation of bioactive nanofibers. Bioactive polystyrene (PS) nanofibers with a typical diameter of 120 nm were prepared and examined for catalytic efficiency for biotransformations. The nanofibers were produced by electrospinning functionalized PS, followed by the chemical attachment of a model enzyme, alpha-chymotrypsin. The observed enzyme loading as determined by active site titration was up to 1.4% (wt/wt), corresponding to over 27.4% monolayer coverage of the external surface of nanofibers. The apparent hydrolytic activity of the nanofibrous enzyme in aqueous solutions was over 65% of that of the native enzyme, indicating a high catalytic efficiency as compared to other forms of immobilized enzymes. Furthermore, nanofibrous alpha-chymotrypsin exhibited a much-improved nonaqueous activity that was over 3 orders of magnitude higher than that of its native counterpart suspended in organic solvents including hexane and isooctane. It appeared that the covalent binding also improved the enzyme's stability against structural denaturation, such that the half-life of the nanofibrous enzyme in methanol was 18-fold longer than that of the native enzyme.

Animals↗