MRS Fall 2009: Monday afternoon, part 2
Back in the Room 303* for Symposium AA til the end... I'm still surprised there aren't more people here. I think the potential of this work is enormous, and I expected more than the two dozen in the audience.
AA2.5 "Recyclable biocatalysts: enzyme immobilisation on magnetic nanoparticles cellulose hydrolysis" Patrick A. Johnson (Univ. Wyoming)
As the speaker notes, he's in an interesting position, working on bioethanol in the Chemical and Petroleum Engineering part of the university.,,
Just as in conventional catalysis, enzymes are the most expensive part of the process; he's looking at making recyclable catalysts. Here, he's working on crosslinking and immobilising them to improve the long-term stability. They use magnetite nanoparticles that are first silylated with amines or glycidoxy groups, then PEGylated, and then coupled to lysines on the enzyme surface. For the nanoparticles, there is a tradeoff between particle size and magnetic susceptibility. The smallest particles also suffered from low reusability -- they were difficult to recover. Larger particles with glucose oxidase retained 80% activity after 10 cycles. As one would expect for enzymes with less mobility, the immobilised enzymes showed greater thermal stability.
"AA2.6 Novel Carbon MEMS platform for genetically engineer enzyme based implantable biofuel cell" Gobind Bisht (UC Irvine)
This one is close to my heart. He's working with glucose oxidase (GOx) and bilirubin oxidase (BOx). They're using carbon MEMS to create high aspect ratio structures. Here they're working with pattern, pyrolysed SU-8. (Their group has a spin out for CMEMS for Li-C batteries.) They put the SU-8 into an oxygen plasma to create oxo functional groups, then attaching GOx. They've attached hydroquinone to the surface to act as a mediator to the GOx. (I found it strange that there didn't seem to be any non-catalytic response from the tethered HQ, but I might have missed it.) They worked to improved conduction by coating with poly(pyrrole), but the PPy redox dominated the voltammetry.
AA2.7 "Molecular simulation evidence for processive motion of Trichoderma reesei Cel7A during cellulose depolymerization" Xiongce Zhao and others (ORNL, Vanderbilt, NREL)
The problem with cellulose hydrolysis is that its multi-scale organisation creates highly crystalline, insoluble structures. However, there are many hydrogen bonding sites. CBH-I has two domains, one binding domain to recognise the surface and one catalytic domain to hydrolyse it. Between them is a mannose-coated linker peptide that maintains relative orientation of the domains and protects them from proteolysis. So, how does it work? Is it working like a spring or caterpillar? He's working out what the role of this linking domain is through computer simulations of the thermodynamic properties (in particular the free energy) of the stretching and compression of the linker. What wasn't clear to me was how the model accounted for the steric bulk the the two domains would impose on the allowable structures. However, he found two clear free energy minima with a barrier of 20-30 kcal/mol between them (I read it like that off the graph; the conclusions slide shows 10 kcal/mol).
*A bit poorly set up, in my opinion... I wish the main entrance were on the opposite side.
AA2.5 "Recyclable biocatalysts: enzyme immobilisation on magnetic nanoparticles cellulose hydrolysis" Patrick A. Johnson (Univ. Wyoming)
As the speaker notes, he's in an interesting position, working on bioethanol in the Chemical and Petroleum Engineering part of the university.,,
Just as in conventional catalysis, enzymes are the most expensive part of the process; he's looking at making recyclable catalysts. Here, he's working on crosslinking and immobilising them to improve the long-term stability. They use magnetite nanoparticles that are first silylated with amines or glycidoxy groups, then PEGylated, and then coupled to lysines on the enzyme surface. For the nanoparticles, there is a tradeoff between particle size and magnetic susceptibility. The smallest particles also suffered from low reusability -- they were difficult to recover. Larger particles with glucose oxidase retained 80% activity after 10 cycles. As one would expect for enzymes with less mobility, the immobilised enzymes showed greater thermal stability.
"AA2.6 Novel Carbon MEMS platform for genetically engineer enzyme based implantable biofuel cell" Gobind Bisht (UC Irvine)
This one is close to my heart. He's working with glucose oxidase (GOx) and bilirubin oxidase (BOx). They're using carbon MEMS to create high aspect ratio structures. Here they're working with pattern, pyrolysed SU-8. (Their group has a spin out for CMEMS for Li-C batteries.) They put the SU-8 into an oxygen plasma to create oxo functional groups, then attaching GOx. They've attached hydroquinone to the surface to act as a mediator to the GOx. (I found it strange that there didn't seem to be any non-catalytic response from the tethered HQ, but I might have missed it.) They worked to improved conduction by coating with poly(pyrrole), but the PPy redox dominated the voltammetry.
AA2.7 "Molecular simulation evidence for processive motion of Trichoderma reesei Cel7A during cellulose depolymerization" Xiongce Zhao and others (ORNL, Vanderbilt, NREL)
The problem with cellulose hydrolysis is that its multi-scale organisation creates highly crystalline, insoluble structures. However, there are many hydrogen bonding sites. CBH-I has two domains, one binding domain to recognise the surface and one catalytic domain to hydrolyse it. Between them is a mannose-coated linker peptide that maintains relative orientation of the domains and protects them from proteolysis. So, how does it work? Is it working like a spring or caterpillar? He's working out what the role of this linking domain is through computer simulations of the thermodynamic properties (in particular the free energy) of the stretching and compression of the linker. What wasn't clear to me was how the model accounted for the steric bulk the the two domains would impose on the allowable structures. However, he found two clear free energy minima with a barrier of 20-30 kcal/mol between them (I read it like that off the graph; the conclusions slide shows 10 kcal/mol).
*A bit poorly set up, in my opinion... I wish the main entrance were on the opposite side.
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