Analytical Chemistry Tools:

LC-Tandem MS/MS: The Dismukes lab is equipped with commercial QQQ and Q-TOF mass spectrometers coupled to LC chromatographic separation systems for nano-flow LC and 2D nano-cube LC. These are among the most sensitive mass spectrometers available (lod = Femtogram). They feature robust operation and amenability towards the detection of small, polar metabolites. The use of isotopic-labeled inputs also allows for the direct time-resolved monitoring of pathway fluxes. Chemical extraction parameters have been optimized for Synechococcus sp. PCC7002. Cellular metabolites are extracted by ice cold extraction buffer. The extracts are subsequently separated using Reversed-phase Ion-pairing (RIP) chromatography, the effluent of which is analyzed using a Agilent 6400 Series Triple Quadrupole (QQQ) mass spectrometer. Targeted metabolites are detected via predetermined mass breakdown channels, and concentrations are estimated based on compound-specific calibration curves.

We develop selective and robust catalysts that electrochemically convert carbon dioxide (CO2) into sustainable chemical feedstocks and could ultimately be coupled to the recycling of environmental CO2. The catalysts employed are transition metal phosphides and their doped derivatives that form distinct crystalline structure types, enabling selection of chemical reactivity towards desired products including high molecular weight solid polymers. Selecting the catalyst’s elemental composition and crystal structure allows for tuning of the chemical, physical, and electrical properties to achieve the best match with desired product and application.

Transition metal phosphides are efficient hydrogen evolution catalysts due to their ability to abstract protons from water and transfer electrons to them, forming adsorbed hydrides. Since CO2 reduction also requires multiple transfers of adsorbed hydrogen and electrons, these catalysts are also effective for the reduction of CO2. Additionally, these catalysts bind CO2 relatively strongly, allowing for the formation of C3, C4 and Cn products at ambient conditions and aqueous solution. It is also our belief that when utilizing iron and nickel phosphides, the reaction proceeds through hydride transfer, and therefore carbon monoxide is not an intermediate. This opens up a new reaction pathway with minimal overpotential requirements. 

Natural photosynthesis dominates the biosphere as the most widespread and successful metabolism on Earth. Among photosynthetic organisms the oxygenic phototrophs are the most prolific, comprising all known species of cyanobacteria, algae, and higher plants. The early ancestors of these organisms transformed the surface of Earth beginning circa 3 billion years ago from a drab alumino-silicate composite to a lush green carpet visible from Outer Space. These organisms power the planet using the Photosystem II (PSII) enzyme to split water, yielding O2, hydrogen reductants, and proton gradients (energy). Remarkably, only one PSII enzyme has evolved on Earth.

Our goal is to reveal the range of kinetic and energetic performance by photosynthetic water oxidation enzymes in vivo, selected from diverse microbial phototrophs, cyanobacteria and microalgae. The outcome is a fundamental understanding of the principles of light energy conversion to chemical energy and the mechanisms used to oxidize water in nature. Supported by DOE-BES.

• Cyanobacterial fermentative H² production
• Algal photo-H² production
• Food vs. Biomass energy feedstocks:
• Cofermentation for enhanced biomass conversion efficiency
• Lipid biosynthesis and conversion to fuels
• High throughput screening for lipid productive algal strains

  

Photoautotrophic carbon fluxomics

Our goal is to use flux balance analysis (FBA, left figure) and isotopically nonstationary metabolic flux analysis (INST-MFA, right figure) to quantitatively understand carbon flux distributions and pathway utilizations of the cyanobacterium Synechococcus sp. PCC 7002 during photosynthesis. The outcome also helps discover new roles of existing metabolic pathways.