Phillip K. Koech

A reversible zwitterionic SO2-binding organic liquid

N,N-Dibutylundecanolamine is a liquid that chemically binds SO2 to form a viscous zwitterionic liquid that contains 35% by wt. SO2 at standard temperature and pressure. SO2 is chemically bound to the alcohol component as an alkylsulfite, which is then stabilized by the amine. The zwitterionic liquid can be reverted to its non-ionic form and recycled by thermally stripping the SO2 under vacuum at temperatures near 70 °C. N,N-Dibutylundecanolamine is a potential flue gas desulfurizing solvent because it is chemically selective to bind SO2 but not basic enough to chemically bind CO2.

Synthesis and application of pyridine-based ambipolar hosts: control of charge balance in organic light-emitting devices by chemical structure modification.

We studied the influence of a pyridine moiety versus a phenyl moiety when introduced in the molecular design of an ambipolar host. These pyridine-based host materials for organic light-emitting diodes (OLEDs) were synthesized in three to five steps from commercially available starting materials. The isomeric hosts have similar HOMO/LUMO energies; however, data from OLEDs fabricated using the above host materials demonstrate that small structural modification of the host results in significant changes in its carrier-transporting characteristics.

Anhydrous tertiary alkanolamines as hybrid chemical and physical CO2 capture reagents with pressure-swing regeneration

Anhydrous DMEA, DEEA and DIPEA are found to absorb carbon dioxide under pressure via chemical binding and physical absorption. The chemical CO2-bound derivatives of these materials are zwitterionic alkylcarbonate salts which are characterized by high-pressure 13C NMR. DMEA, DEEA and DIPEA absorb 20 wt.%, 17 wt.% and 16 wt.% carbon dioxide, respectively, at 300 psig (20.6 ATM). An increasing chemical carbon dioxide uptake capacity trend of DMEA > DEEA > DIPEA is observed while the physical CO2 absorption trend is DIPEA > DEEA > DMEA. DMEA captures up to 45 mole % (20 wt.%) of CO2 at 500 psig via both chemical binding and physical absorption. The amount of chemically bound and physically absorbed CO2 is directly linked to the CO2 pressure over the liquid. The zwitterion DMEA-CO2 regenerates CO2 and DMEA upon depressurization, allowing for an economical pressure swing regeneration rather than thermal regeneration. DMEA absorbs/releases CO2 repeatedly with no decline in capacity.

Low viscosity alkanolguanidine and alkanolamidine liquids for CO2 capture

Global carbon dioxide (CO2) emission is expected to increase tremendously with the shift to coal-powered plants for energy generation. Capture and sequestration of CO2 are needed to mitigate environmental effects. Solvents currently used for this are the energy-intensive aqueous amines. Here we present 10 advanced solvents called alkanolguanidines and alkanolamidines that are potentially energy-efficient CO2-capture solvents. These solvents were synthesized in 1–3 steps from commercially available materials. One alkanolamidine derived from a 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) base core has a low vapor pressure and a high viscosity, resulting in low CO2 uptake capacity at standard temperature and pressure (STP). Three imidazoline base derived alkanolamidines were non-viscous but do not bind CO2 at STP, however, under mild pressure they effectively capture 7–10 wt%, making them suitable for high-pressure CO2 capture. Six novel alkanolguanidine molecules have low vapor pressure and low viscosity (<10 cP) which enable high CO2 uptake at STP. These compounds bind CO2 chemically via the alcohol moiety forming zwitterionic guanidinium and amidinium alkylcarbonate ionic liquids. These materials can be regenerated thermally by heating the alkylcarbonate to 75 °C. CO2 binding capacities of up to 12 wt% were achieved using several of these compounds at STP. Through this study we found that alkanolguanidines have low viscosity, are non-volatile, have high CO2 uptake at STP and are tolerant to water; thus we selected one compound for physical property testing.

Suite of activity-based probes for cellulose-degrading enzymes.

Microbial glycoside hydrolases play a dominant role in the biochemical conversion of cellulosic biomass to high-value biofuels. Anaerobic cellulolytic bacteria are capable of producing multicomplex catalytic subunits containing cell-adherent cellulases, hemicellulases, xylanases, and other glycoside hydrolases to facilitate the degradation of highly recalcitrant cellulose and other related plant cell wall polysaccharides. Clostridium thermocellum is a cellulosome-producing bacterium that couples rapid reproduction rates to highly efficient degradation of crystalline cellulose. Herein, we have developed and applied a suite of difluoromethylphenyl aglycone, N-halogenated glycosylamine, and 2-deoxy-2-fluoroglycoside activity-based protein profiling (ABPP) probes to the direct labeling of the C. thermocellum cellulosomal secretome. These activity-based probes (ABPs) were synthesized with alkynes to harness the utility and multimodal possibilities of click chemistry and to increase enzyme active site inclusion for liquid chromatography-mass spectrometry (LC-MS) analysis. We directly analyzed ABP-labeled and unlabeled global MS data, revealing ABP selectivity for glycoside hydrolase (GH) enzymes, in addition to a large collection of integral cellulosome-containing proteins. By identifying reactivity and selectivity profiles for each ABP, we demonstrate our ability to widely profile the functional cellulose-degrading machinery of the bacterium. Derivatization of the ABPs, including reactive groups, acetylation of the glycoside binding groups, and mono- and disaccharide binding groups, resulted in considerable variability in protein labeling. Our probe suite is applicable to aerobic and anaerobic microbial cellulose-degrading systems and facilitates a greater understanding of the organismal role associated with biofuel development.

Chemically selective gas sweetening without thermal-swing regeneration

Natural gas purifications using chemically selective hydrogen sulfide (H2S) sorbents could be more efficient if chemical selectivity for H2S could be maintained without thermal regeneration of the sorbent. We used tertiary alkanolamines to reversibly capture H2S in the absence of water to produce hydrosulfide-based ionic liquids in high yield. These alkanolammonium hydrosulfide ionic liquids release H2S by exposure to inert gas or by mild heating. H2S can be rapidly and nearly quantitatively released at ambient temperature from the alkanolammonium hydrosulfide ionic liquids by the addition of nonpolar antisolvents, some of which naturally phase separate from the spent alkanolamine. The antisolvent-induced regeneration of the alkanolamine potentially allows an efficient H2S gas scrubbing process that is chemically selective and can be operated continuously at or near ambient temperature.

Water-Lean Solvents for Post-Combustion CO2 Capture: Fundamentals, Uncertainties, Opportunities, and Outlook

This review is designed to foster the discussion regarding the viability of postcombustion CO2 capture by water-lean solvents, by separating fact from fiction for both skeptics and advocates. We highlight the unique physical and thermodynamic properties of notable water-lean solvents, with a discussion of how such properties could translate to efficiency gains compared to aqueous amines. The scope of this review ranges from the purely fundamental molecular-level processes that govern solvent behavior to bench-scale testing, through process engineering and projections of process performance and cost. Key discussions of higher than expected CO2 mass transfer, water tolerance, and compatibility with current infrastructure are presented along with current limitations and suggested areas where further solvent development is needed. We conclude with an outlook of the status of the field and assess the viability of water-lean solvents for postcombustion CO2 capture.

Live Cell Discovery of Microbial Vitamin Transport and Enzyme-Cofactor Interactions.

The rapid completion of microbial genomes is inducing a conundrum in functional gene discovery. Novel methods are needed to shorten the gap between characterizing a microbial genome and experimentally validating bioinformatically predicted functions. Of particular importance are transport mechanisms, which shuttle nutrients such as B vitamins and metabolites across cell membranes and are required for the survival of microbes ranging from members of environmental microbial communities to pathogens. Methods to accurately assign function and specificity for a wide range of experimentally unidentified and/or predicted membrane-embedded transport proteins, along with characterization of intracellular enzyme-cofactor associations, are needed to enable a significantly improved understanding of microbial biochemistry and physiology, microbial interactions, and microbial responses to perturbations. Chemical probes derived from B vitamins B1, B2, and B7 have allowed us to experimentally address the aforementioned needs by identifying B vitamin transporters and intracellular enzyme-cofactor associations through live cell labeling of the filamentous anoxygenic photoheterotroph, Chloroflexus aurantiacus J-10-fl, known to employ mechanisms for both B vitamin biosynthesis and environmental salvage. Our probes provide a unique opportunity to directly link cellular activity and protein function back to ecosystem and/or host dynamics by identifying B vitamin transport and cofactor-dependent interactions required for survival.

Dynamic Acid/Base Equilibrium in Single Component Switchable Ionic Liquids and Consequences on Viscosity.

The deployment of transformational nonaqueous CO2-capture solvent systems is encumbered by high viscosities even at intermediate uptakes. Using single-molecule CO2 binding organic liquids as a prototypical example, we present key molecular features that control bulk viscosity. Fast CO2-uptake kinetics arise from close proximity of the alcohol and amine sites involved in CO2 binding in a concerted fashion, resulting in a Zwitterion containing both an alkyl-carbonate and a protonated amine. The population of internal hydrogen bonds between the two functional groups determines the solution viscosity. Unlike the ion pair interactions in ionic liquids, these observations are novel and specific to a hydrogen-bonding network that can be controlled by chemically tuning single molecule CO2 capture solvents. We present a molecular design strategy to reduce viscosity by shifting the proton transfer equilibrium toward a neutral acid/amine species, as opposed to the ubiquitously accepted zwitterionic state. The molecular design concepts proposed here are readily extensible to other CO2 capture technologies.

Pore-Engineered Metal–Organic Frameworks with Excellent Adsorption of Water and Fluorocarbon Refrigerant for Cooling Applications

Metal-organic frameworks (MOFs) have shown promising behavior for adsorption cooling applications. Using organic ligands with 1, 2, and 3 phenylene rings, we construct moisture-stable Ni-MOF-74 members with adjustable pore apertures, which exhibit excellent sorption capabilities toward water and fluorocarbon R134a. To our knowledge, this is the first report of adsorption isotherms of fluorocarbon R134a in MOFs. The adsorption patterns for these materials differ significantly and are attributed to variances in their hydrophobic/hydrophilic pore character associated with differences in pore size.