Bill B. Elmore

Two-step sequential reaction catalyzed by layer-by-layer assembled urease and arginase multilayers

Abstract Layer-by-layer (LbL) self-assembly was used to build multi-component thin films containing polyions and enzymes: urease (Ur), and arginase (Ar). These multilayers were shown to participate catalytically in a two step sequential decomposition of l -arginine to urea and subsequently to ammonia. Deposition of multilayers was characterized with quartz crystal microbalance (QCM). The following enzyme monolayer stacking architectures were studied: (Ur/PDDA) n , (Ar/PDDA) n , (Ar/PDDA/Ur/PDDA) n , and (Ur/PDDA/Ar/PDDA) n , where n =1–4, PDDA and PSS are, respectively, poly(dimethyldiallyl ammonium chloride) and sodium poly(styrene sulphonate). The layer growth on gold electrode resonator was monitored with QCM and the catalytic activity of the enzyme multilayers was studied with UV–Vis spectroscopy, using a pH-sensitive dye (bromocresol purple). Dependence of film catalytic activity was studied as a function of position and number of the enzyme layers. The assembly with layer sequence {PDDA/PSS/PDDA+(Ur/PDDA/Ar/PDDA) 2 } showed the highest catalytic activity. The order of enzyme multilayers in this architecture corresponds to the two-step sequential reaction: l -arginine→urea→ammonia. The assembly was then fabricated on the tip of a commercial ammonia electrode and detection of l -arginine was demonstrated at physiologically significant concentrations.

Immobilized enzyme studies in a microscale bioreactor

Novel microreactors with immobilized enzymes were fabricated using both silicon and polymer-based microfabrication techniques. The effectiveness of these reactors was examined along with their behavior over time. Urease enzyme was successfully incorporated into microchannels of a polymeric matrix of polydimethylsiloxane and through layer-bylayer self-assembly techniques onto silicon. The fabricated microchannels had cross-sectional dimensions ranging from tens to hundreds of micrometers in width and height. The experimental results for continuous-flow microreactors are reported for the conversion of urea to ammonia by urease enzyme. Urea conversions of > 90% were observed.

Development of novel microscale system as immobilized enzyme bioreactor

This study involves a novel method for immobilized enzyme catalysis. The focus of the work was to design and construct a microscale bioreactor using microfabrication techniques traditionally employed within the semiconductor industry. Enzymes have been immobilized on the microreactor walls by incorporating them directly into the wall material. Fabricated microchannels have cross-sectional dimensions on the order of hundreds of micrometers, constructed using polydimethylsiloxane cast on silicon/SU-8 molds. The resulting ratio of high surface area to volume creates an efficient, continuous-flow reaction system. Transverse features also containing enzymes were molded directly into the channels.

Cellulase activity of trichoderma reesei (RUT-C30) on municipal solid waste

AbtractThis work presents a preliminary investigation ofTrichoderma reesei (RUT-C30) grown on municipal solid waste (MSW). Such a process offers the potential for inexpensive production of cellulase enzymes while reducing the waste stream to landfills. Cellulase enzyme activity for batch-culture growth on MSW compared favorably with growth on refined cellulosic substrates. Cellulase productivity in an initial fed-batch culture reached a maximum of 22 IFPU/L-h with a maximum activity of 1.5 IFPU/mL.

Microbial liquefaction of lignite pretreated with dilute acid at elevated temperature and pressure

Two microbial cultures—ML-13 (aCandida sp.) and LSC (a fungal isolate from the University of Arkansas)—have been employed in the direct liquefaction of Louisiana lignite. Lignite samples were pretreated with nitric acid and microbial culture broths at elevated temperatures and pressures. Subsequent treatment with active cultures and culture derivatives resulted in significant solubilization of the lignite. Up to 50% liquefaction of pretreated coal (20% HNO3 at ambient temperature and pressure) was observed in 4 d with ML-13 cultures, whereas almost 80% liquefaction occurred in a similar time period when exposing pretreated lignite to an autoclaved, cell-free culture broth.

Enzyme catalyzed biochemical production in a polydimethylsiloxane microreactor

Study of an aqueous-phase reaction in an enzyme- catalyzedpolydimethylsiloxane (PDMS) microreactor is underway. In the present work, urease - an enzyme that catalyzes urea to ammonia and carbon dioxide has been immobilized within open microchannels of 450 micrometers (micrometers ) in diameter or less. Microchannels are templated within PDMS. Preliminary results demonstrate the proof of concept for conversion biochemicals via a PDMS-based microreactor system.

Microbial Conversion of Synthesis Gas Components to Useful Fuels and Chemicals

Enriched culture techniques have been used to isolate microbial cultures exhibiting growth on synthesis gas components. Three rod-shaped, gram-positive cultures have been isolated from petroleum-contaminated soil, a cow manure-soil mixture, and sheep rumen fluid. Each culture exhibits growth on carbon monoxide as its primary carbon source, producing alcohols and acids in the fermentation medium. Quantities of up to 7.5, 0.58, and 0.25 g/L of acetate, ethanol, and methanol, respectively, have been produced in batch culture with lesser amounts of acetone, butyric, and propionic acid detected.

Enhancing design of immobilized enzymatic microbioreactors using computational simulation

In continuous-flow enzymatic microbioreactors, enzymes on the channel walls catalyze reaction(s) among feed chemicals, resulting in the production of some desirable material or the destruction of some undesirable material. Computational models of microbioreactors were developed using the CFD-ACE+ multiphysics simulation package. These models were validated via comparison with experimental data for the destruction of urea, catalyzed by urease. Similar models were then used to assess the impact of internal features on destruction efficiency. It was found that triangular features within the channels enhanced the destruction efficiency more than could be attributed to the increase in surface area alone.

Heterogeneous catalysis in a microscale reactor fabricated from a biologically active polymer

Micro-scale biochemical reactors have been developed from a polydimethylsiloxane/enzyme (PDMS-E)biopolymer. Micro-reactor channels 125 micrometers in depth, 500 micrometers wide by 50 centimeters long contain fixed triangular features for enhanced fluid mixing. All channel features are composed of the same PDMS-E material. Conversions of urea by urease enzyme of up to 70% have been obtained at an overall flowrate of 0.4 mL/min. Additional PDMS-E biopolymer systems containing amyloglucosidase (for converting starch to glucose) have demonstrated enzymatic activity.

Experimental system for the study of gas-solid heterogeneous catalysis in microreactors

An experimental system has been designed and constructed to conduct gas- solid heterogeneous catalytic reactions in microreactors. This apparatus is inteded to be used for any exothermic or endothermic reaction, including those with multiple feeds. It can be used to test the effectiveness of a microreactor design for a particular catalyst or to test the behavior of the catalyst itself. The system uses a test block that is plumbed for multiple feeds and vacuum to hold down a standard size microreactor chip. This chip has two exit vias, which includes one for the reactor effluent and one for the exit stream from a possible reactor membrane wall. The reactors are systems of channels with a smallest cross-dimension as small as 5 micrometers. The experimental system is equipped with temperature control and automatic data acquisition. The reactors can be stacked in order to scale up to higher throughput. A simulator has been developed that accounts for the unique physical aspects of reaction and flow in very small channels. Along with design, it assist in determining operating conditions and interpreting experimental results.