Xinye Liu and Laith Samarah, GW Department of Chemistry Graduate Students

 

The Wagner Lab and the Vertes Lab

 

Iron catalyst facilitated synthesis of ammonia from N2 and water at high efficiency by electrolysis

Xinye Liu | Graduate Student – Licht Lab

An electrosynthetic process to produce ammonia that avoids the greenhouse gas carbon dioxide is presented here. The electrocatalytic process combines water and nitrogen to directly generate ammonia at high coulombic efficiency. Catalyst enhancements were studied and improved from our early advances, by varying particle size, catalyst calcination preparation conditions, variation of catalyst carbon conductive matrix support, types and amounts of additives for better carbon coating of the catalyst, etc. Two sets of iron oxide catalysts were probed, nano- sized iron oxides and micron sized nano-oxides formed by calcination of micron sized iron metal particles. A 2µm nano-graphite carbon as the catalyst coating yields higher rates of ammonia than larger sized carbons or iron oxides without the coating. The catalysts from iron metal were made by ano-graphite coated iron oxide. Ammonia syntheses were investigated in two configurations (1) with free catalyst suspended in the electrolyte, and (2) with the catalyst confined to the cathode.

 

A Single-Cell Look at Biological Nitrogen Fixation: Direct Determination of Metabolite Formulas from Isotopic Fine Structures in Heterogeneous Cell Populations

Laith Samarah | Graduate Student – Vertes

LabAnalysis of large cell populations obscures the distinction between different cell types and prevents the detection of cellular heterogeneity in an ensemble of isogenic cells. For example, in legume root nodules, the organs associated with biological nitrogen fixation, plant cells infected by diazotrophic bacteria are intimately mixed with uninfected cells. Exploring the metabolic profiles for these heterogeneous systems requires single-cell analysis methods. We combined fiber-based laser ablation electrospray ionization (f-LAESI) with a 21 Tesla Fourier transform ion cyclotron resonance mass spectrometer (21T FT-ICR-MS) for the direct analysis of single infected cells and uninfected cells in soybean root nodules. Over 100 compounds were tentatively assigned based on ultra-high mass accuracy, and elemental formulas for 47 of these were verified by isotopic fine structures (IFS). Comparing the calculated IFS patterns for possible ions with the experimental data enabled the identification of close-to-isobaric compounds with different elemental compositions. Single-cell analysis revealed differences in the abundances of compounds between infected and uninfected cells. Infected cells showed higher abundances for nitrogen-containing compounds and lipids compared to uninfected cells. Heterogeneity among 124 infected cells was observed by determining the metabolic noise. Gamma, normal, and bimodal distributions of certain metabolite abundances were recorded, and the metabolic noise levels varied for different metabolites. For example, several primary metabolites, and secondary metabolites endogenous to plants, exhibited relatively low metabolic noise. Conversely, lipids associated with plant and bacteroid membranes showed greater noise levels, indicating a larger variance.