Mechanistic Study of Methanol Synthesis from CO₂ and H₂ on a Modified Model Mo₆S₈ Cluster

We report the methanol synthesis from CO₂ and H₂ on metal (M = K, Ti, Co, Rh, Ni, and Cu)-modified model Mo₆S₈ catalyst using density functional theory (DFT). The results show that the catalytic behavior of a Mo₆S₈ cluster is changed significantly due to the modifiers, via the electron transfer from M to Mo₆S₈ and therefore the reduction of the Mo cation (ligand effect) and the direct participation of M in the reaction (ensemble effect) to promote some elementary steps. With the most positively charged modifier, the ligand effect in the case of K–Mo₆S₈ is the most obvious among the systems studied; however, it cannot compete with the ensemble effect, which plays a dominate role in determining activity via the electrostatic attraction in particular to stabilize the CH_<i>x</i>O_<i>y</i> species adsorbed at the Mo sites of Mo₆S₈. In comparison, the ligand effect is weaker and the ensemble effect is more important when the other modifiers are used. In addition, the modifiers also vary the optimal reaction pathway for methanol synthesis on Mo₆S₈, ranging from the reverse water–gas shift (RWGS) + CO hydrogenation as that of Mo₆S₈ to the formate pathway. Finally, K is able to accelerate the methanol synthesis on Mo₆S₈ the most, whereas the promotion by Rh is relatively small. Using the modifiers like Ti, Co, Ni, and Cu, the activity of Mo₆S₈ is decreased instead. The relative stability between *HCOO and *HOCO is identified as a descriptor to capture the variation in mechanism and scales well with the estimated activity. Our study not only provides better understanding of the reaction mechanism and actives on the modified Mo₆S₈ but also predicts some possible candidates, which can be used as a promoter to facilitate the CH₃OH synthesis on Mo sulfides

Preparation of nitrate-selective porous magnetic resin and assessment of its performance in removing nitrate from groundwater

<p>Nitrate-selective, porous magnetic anion-exchange resin (NS-PMAER) with enhanced affinity and higher selectivity for nitrate was synthesized, characterized and its performance in nitrate removal was investigated. The results show that NS-PMAER consists of spherical particles with an average size of 200 μm. It has mean pore diameter, total pore volume, and BET specific surface area of 21.38 nm, 0.3605 cm³/g, and 67.455 m²/g, respectively. The specific saturation magnetization of NS-PMAER was about 10.79 emu/g. Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS) results indicate that NS-PMAER has selectivity for nitrate higher than that of MIEX® resin; its coefficients of selectivity toward nitrate for nitrate and sulfate are 20.978 and 6.769, respectively, higher than those of MIEX® resin (1.256 and 4.342, respectively). Its working exchange capacity was 72.41 mg/mL. Column-exchange experiments’ results suggest that it could be easily regenerated using 1.5 mol/L sodium chloride solution for a contact time of 30 min. Its recovery rate stayed at > 95% even after five rounds of recycling. Results of the pilot test indicate that NS-PMAER could effectively remove nitrate in groundwater, and ensure that nitrate concentrations of effluent to meet the guideline limit for drinking water by the World Health Organization.</p

Determination of association rate constant.

<p>(A) Trypsin (8 nM) was added to a mixture of 760 µM BAPNA and SW-AT-1 at 0 (□), 100 (○), 200 (Δ), 300 (▪), 400 (•) and 500(▴) nM. (B) Chymotrypsin (8 nM) was added to a mixture of 250 µM BTEE and SW-AT-1 at 0 (□), 100 (○), 200 (Δ), 300 (▪), 400 (•) and 500(▴) nM. The progress of enzyme inactivation (<i>inset</i>) was followed by measuring absorbance at 410 nm and 256nm on a microplate reader. Pseudo-first-order rate constants of inhibition (<i>k_obs</i>) were plotted as a function of SW-AT-1 concentration ([I]).</p

Characterization of SW-AT-1.

<p>(A) far-UV CD spectra of rSW-AT-1(left panel) and secondary sructure content (right panel); (B) near-UV CD spectra of rSW-AT-1 at different temperatures (left panel) and maximum aborbance 272-nm and trypsin inhibitory activity at different temperatures (right panel); (C) near-UV CD spectra of rSW-AT-1 at different pHs (left panel) and maximum aborbance at 272-nm and trypsin inhibitory activity at different pHs (right panel); (D) Optimal pH of rSW-AT-1 inhibitory activity for trypsin (left panel) and chymotrypsin (right panel). Bar indicates standard deviation from triplicate determination. P≤0.05 was considered statistically significant.</p

Robotics REU in Undergraduate Engineering Research

<p>The Robotics REU program funded by National Science Foundation (NSF) brings together a dynamic and creative group of undergraduates from UW-Stout and regional universities to create an interdisciplinary research site at UW-Stout. </p><p><br></p><p><i>Presented at Stout Summit, Menomonie, WI, 7 October 2016.</i></p><div><br></div

Effects of N- and C-terminal side regions of RCL on the activity of SW-AT-1.

<p>(A) Antitrypsin and antichymotrypsin activity. Data analysis was performed using the t-test function (P≤0.05). (B) near-UV CD spectra of WT and mutants.</p

The predicted three-dimensional structure of SW-AT-1.

<p>SERPIN Domains was depicted as green, reactive site was depicted as yellow, and mutant sites were depicted as blue. The N and C termini were labeled as N and C, respectively. The structrue was generated using Open-Source PyMOL (v1.4), using <i>Manduca sexta</i> Serpin-protease 1K complex (1SEK) as the template.</p

Stoichiometry of inhibition.

<p>Trypsin and chymotrypsin were incubated respectively with different concentrations of SW-AT-1 at 25°C for 20 min in the appropriate reaction buffer. Residual enzyme activity was measured by adding the appropriate substrate and determining the reaction velocity. The stoichiometry of inhibition was determined by using linear regression to extrapolate to that initial inhibitor/enzyme ratio resulting in complete inhibition of the enzyme.</p

Primers of site-directed mutagenesis.

<p>Primers of site-directed mutagenesis.</p

SDS-PAGE of recombinant His-tagged SW-AT-1.

<p>Lane M, molecular size markers; lane 1, pET-28a vacant vector; lane 2, total protein extracts from <i>E. coli</i> after IPTG-induction; lane 3, total protein extracts from <i>E. coli</i> without IPTG-induction; lane 4, eluted fraction after affinity chromatography. Arrowhead indicated purified rSW-AT-1.</p