Mark A. Plummer

Brief communication: Modeling the folding and hydrogen production of Clostridium acetobutylicum and Clostridium saccharobutylium mutants using electrostatic potential surfaces and molecular dynamics

Electrostatic potential surfaces (EPS) were used with molecular dynamics to model the folding mechanisms and kinetics of hydrogenase mutants from wild types Clostridium acetobutylicum and Clostridium saccharobutylium. The purpose of the EPS approach was to incorporate long range electrostatic forces between widely separated regions of the mutants which contain 575 amino acids. Also, it was demonstrated that the ratio of positive to negative EPS of unfolded mutants could be used to predict the production of molecular hydrogen from the folded mutants. Using the prediction model, mutant compositions were determined that should yield hydrogen of up to 40 times that obtainable from the wild type C. acetobutylicum. It is expected that the developed EPS techniques can be used to study the folding of other proteins and to predict the reactivity of the folded protein structures.

Sodium and hydrogen tetrachloroaluminate catalysts for molecular weight reduction of hydrocarbons

Abstract Sodium and hydrogen tetrachloroaluminates (NaAlCl4 and HAlCl4) have been evaluated as catalysts for the molecular weight reduction of hydrocarbons. The NaAlCl4 is the major molecular weight reduction and synthesis component, and HAlCl4 adds a hydrogenation function. The optimum catalyst composition, for the petroleum AC-20 resid and shale oil feeds studied, was found to be 2.5–4.5 wt.% HAlCl4 in NaAlCl4. To convert these feeds completely into gasoline range materials, a hydrogen partial pressure and a hydrogen consumption of 950 psia and 900 scf/bbl, respectively, are estimated to be required. About 40% of the hydrogen consumption would be for contaminant removal. Above a hydrogen partial pressure of about 450 psia, the liquid products produced contained less than 100 ppm each of sulfur and nitrogen contaminants. The C6C13 molecular weight portion of the liquid products contained about 55% aromatics, 8% naphthenes, 33% branched paraffins and 4% normal paraffins (weight basis).

Using directed evolution to improve hydrogen production in chimeric hydrogenases from Clostridia species

Hydrogenases are enzymes that play a key role in controlling excess reducing equivalents in both photosynthetic and anaerobic organisms. This enzyme is viewed as potentially important for the industrial generation of hydrogen gas; however, insufficient hydrogen production has impeded its use in a commercial process. Here, we explore the potential to circumvent this problem by directly evolving the Fe-Fe hydrogenase genes from two species of Clostridia bacteria. In addition, a computational model based on these mutant sequences was developed and used as a predictive aid for the isolation of enzymes with even greater efficiency in hydrogen production. Two of the improved mutants have a logarithmic increase in hydrogen production in our in vitro assay. Furthermore, the model predicts hydrogenase sequences with hydrogen productions as high as 540-fold over the positive control. Taken together, these results demonstrate the potential of directed evolution to improve the native bacterial hydrogenases as a first step for improvement of hydrogenase activity, further in silico prediction, and finally, construction and demonstration of an improved algal hydrogenase in an in vivo assay of C. reinhardtii hydrogen production.

Hydrocarbon absorption in tetrachloroaluminate catalysts effects of catalyst cation, hydrocarbon polarity and charge transfers via molecular modeling

Abstract Absorption levels were obtained for five hydrocarbons of increasing polarity in three tetrachloroaluminate catalysts of increasing cation size. Obtained absorption levels were found to correlate with cation size and hydrocarbon polarity. Molecular modeling was used to calculate charge transfers from absorbed hydrocarbons to the catalysts. Obtained charge transfers were also found to correlate with hydrocarbon absorption levels. Lastly, polarities calculated for absorbed free-radicals suggest a mechanism for previous findings. In the previous effort, resid conversion was found to go through a maximum with increasing hydrogen tetrachloroaluminate contents in a sodium tetrachloroaluminate catalyst.