Taxol (paclitaxel) is a potent anticancer drug first isolated from the Taxus brevifolia Pacific yew tree. Currently, cost-efficient production of Taxol and its analogs remains limited. Here, we report a multivariate-modular approach to metabolic-pathway engineering that succeeded in increasing titers of taxadiene-the first committed Taxol intermediate-approximately 1 gram per liter (~15,000-fold) in an engineered Escherichia coli strain. Our approach partitioned the taxadiene metabolic pathway into two modules: a native upstream methylerythritol-phosphate (MEP) pathway forming isopentenyl pyrophosphate and a heterologous downstream terpenoid-forming pathway. Systematic multivariate search identified conditions that optimally balance the two pathway modules so as to maximize the taxadiene production with minimal accumulation of indole, which is an inhibitory compound found here. We also engineered the next step in Taxol biosynthesis, a P450-mediated 5α-oxidation of taxadiene to taxadien-5α-ol. More broadly, the modular pathway engineering approach helped to unlock the potential of the MEP pathway for the engineered production of terpenoid natural products.Taxol (paclitaxel) and its structural analogs are among the most potent and commercially successful anticancer drugs (1). Taxol was first isolated from the bark of the Pacific yew tree (2), and early-stage production methods required sacrificing two to four fully grown trees to secure sufficient dosage for one patient (3). Taxol's structural complexity limited its chemical synthesis to elaborate routes that required 35 to 51 steps, with a highest yield of 0.4% (4-6). A semisynthetic route was later devised in which the biosynthetic intermediate baccatin III, isolated from plant sources, was chemically converted to Taxol (7). Although this approach and subsequent plant cell culture-based production efforts have decreased the need for harvesting the yew tree, production still depends on plant-based processes (8), with

Regenerable high capacity CO 2 sorbents are desirable for the establishment of widespread carbon capture and storage (CCS) systems to reduce global CO 2 emissions. We report on the marked effects of molten alkali metal nitrates on CO 2 uptake by MgO particles and their impact on the development of highly regenerable CO 2 adsorbents with high capacity (>10.2 mmol g −1 ) at moderate temperatures (∼300 °C) under ambient pressure. The molten alkali metal nitrates are shown to prevent the formation of a rigid, CO 2 -impermeable, unidentate carbonate layer on the surfaces of MgO particles and promote the rapid generation of carbonate ions to allow the high rate of CO 2 uptake.

Electrochemically mediated amine regeneration is a new post-combustion capture technology with the potential to exploit the excellent removal efficiencies of thermal amine scrubbers while reducing parasitic energy losses and capital costs. The improvements result from the use of an electrochemical stripping cycle, in lieu of the traditional thermal swing, to facilitate CO 2 desorption and amine regeneration; metal cations generated at an anode react with the amines, displacing the CO 2 , which is then flashed off, and the amines are regenerated by subsequent reduction of the metal cations in a cathode cell. The advantages of such a process include higher CO 2 desorption pressures, smaller absorbers, and lower energy demands. Several example chemistries using different polyamines and copper are presented. Experimental results indicate an open-circuit efficiency of 54% (15 kJ per mole CO 2) is achievable at the tested conditions and models predict that 69% efficiency is possible at higher temperatures and pressures. A bench scale system produced 1.6 mL min À1 CO 2 while operating at 0.4 volts and 42% Faradaic efficiency; this corresponds to a work of less than 100 kJ per mole. Broader context For the next several decades, coal will remain one of the most utilized sources of electricity in the world. While coal is cheap and abundant, it is also the dirtiest form of fossil fuel. Just one coal-red power plant emits 100's of metric tons per hour of carbon dioxide (CO 2); enough to ll the Empire State Building ve times per day. Carbon capture and sequestration is the only way to satisfy the world's growing energy demands while addressing climate change. Many technologies exist to capture the CO 2 from the ue gas leaving a powerplant. Thermal amine scrubbing is the most developed of these technologies, but is inefficient, capitally expensive, and inapplicable to existing power plants. Electrochemically Mediated Amine Regeneration (EMAR) is new a technology, developed at MIT, which addresses many of the shortcomings of thermal scrubbing while remaining similar enough that the process could be rapidly deployed by industry. We show through modeling and experiments that the EMAR system should be capable at of separating CO 2 for less than 15 kJ per mole with low current densities at 70 C. Our bench-scale system, running at room temperature, operates at 100 kJ per mole.

We report the redox activity of quinone materials, in the presence of ionic liquids, with the ability to bind reversibly to CO2. The reduction potential at which 1,4-naphthoquinone transforms to the quinone dianion depends on the strength of the hydrogen-bonding characteristics of the ionic liquid solvent; under CO2, this transformation occurs at much lower potentials than in a CO2-inert environment. In the absence of CO2, two consecutive reduction steps are required to form first the radical anion and then the dianion, but with the quinones considered here, a single two-electron wave reduction with simultaneous binding of CO2 occurs. In particular, the 1,4-napthoquinone and 1-ethyl-3-methylimidazolium tricyanomethanide, [emim]­[tcm], system reported here shows a higher quinone solubility (0.6 and 1.9 mol·L–1 at 22 and 60 °C, respectively) compared to other ionic liquids and most common solvents. The high polarity determined through the Kamlet–Taft parameters for [emim]­[tcm] explains the measured solubility of quinone. The achieved high quinone solubility enables effective CO2 separation from the dilute gas mixture that is contact with the cathode by overcoming back-diffusive transport of CO2 from the anodic side.

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The complexation and decomplexation of CO2 with a series of quinones of different basicity during electrochemical cycling in dimethylformamide solutions were studied systematically by cyclic voltammetry. In the absence of CO2, all quinones exhibited two well-separated reduction waves. For weakly complexing quinones, a positive shift in the second reduction wave was observed in the presence of CO2, corresponding to the dianion quinone-CO2 complex formation. The peak position and peak height of the first reduction wave was unchanged, indicating no formation of complexes between the semiquinones and CO2. The relative heights of both reduction waves remained constant. In the case of strongly complexing quinones, the second reduction wave disappeared while the peak height of the first reduction wave approximately doubled, indicating that the two electrons transferred simultaneously at this potential. The observed voltammograms were rationalized through several equilibrium arguments. Both weakly and strongly complexing quinones underwent either stepwise or concerted mechanisms of oxidation and CO2 dissociation depending on the sweep rate in the cyclic voltammetric experiments. Relative to stepwise oxidation, the concerted process requires a more positive electrode potential to remove the electron from the carbonate complexes to release CO2 and regenerate the quinone. For weakly complexing quinones, the stepwise process corresponds to oxidation of the uncomplexed dianion and accompanying equilibrium shift, while for strongly complexing quinones the stepwise process would correspond to the oxidation of mono(carbonate) dianion to the complexed semiquinone and accompanying equilibrium shift. This study provides a mechanistic interpretation of the interactions that lead to the formation of quinone-CO2 complexes required for the potential development of an energy efficient electrochemical separation process and discusses important considerations for practical implementation of CO2 capture in the presence of oxygen with lower vapor pressure solvents.

Postsynthetic functionalization of magnesium 2,5-dihydroxyterephthalate (Mg-MOF-74) with tetraethylenepentamine (TEPA) resulted in improved CO adsorption performance under dry and humid conditions. XPS, elemental analysis, and neutron powder diffraction studies indicated that TEPA was incorporated throughout the MOF particle, although it coordinated preferentially with the unsaturated metal sites located in the immediate proximity to the surface. Neutron and X-ray powder diffraction analyses showed that the MOF structure was preserved after amine incorporation, with slight changes in the lattice parameters. The adsorption capacity of the functionalized amino-Mg-MOF-74 (TEPA-MOF) for CO was as high as 26.9 wt % versus 23.4 wt % for the original MOF due to the extra binding sites provided by the multiunit amines. The degree of functionalization with the amines was found to be important in enhancing CO adsorption, as the optimal surface coverage improved performance and stability under both pure CO and CO/HO coadsorption, and with partially saturated surface coverage, optimal CO capacity could be achieved under both wet and dry conditions by a synergistic binding of CO to the amines as well as metal centers.

Siliceous mesostructured cellular foams (MCF) impregnated with polyethylenimine (PEI) of various molecular weights and structures were evaluated as CO 2 adsorbents. The MCF solid support consisted of a well-defined interconnected three-dimensional mesoporous structure with large cell diameter of 30.3 nm and large window diameter of 11.3 nm, filled with polyethylenimine up to 70 weight percent or about 22.3% nitrogen atom by weight of the adsorbents. While other mesoporous solid supports lost their porosity after PEI impregnation, our MCF solid support maintained its pore volume over the range of 1.12 to 1.64 cm 3 g 21 . The importance of the porosity of PEI-impregnated MCF adsorbents for high capacity CO 2 adsorbents was demonstrated. The highest CO 2 sorption capacity (180.6 mg-CO 2 /g-adsorbent or 393.6 mg-CO 2 /g-PEI at 75 uC) was obtained for silica supports loaded with 50 weight percent branched PEI with average molecular weight of 600 g mol 21 . Under dry atmospheric CO 2 gas, this adsorbent reached the theoretical CO 2 capacity of 0.50 mole-CO 2 per mole-nitrogen within less than about 8 min, making this adsorbent one of the most effective CO 2 adsorbents reported. Repeated multiple sorption cycles demonstrated good stability of this adsorbent for CO 2 capture. The initial sorption kinetics determined the overall CO 2 sorption capacity, which was limited by the formation of a carbamate layer as a result of the CO 2 -PEI complexation that due to inhibition of CO 2 diffusion; the kinetics of ''ionic'' gelation of the impregnated PEI by CO 2 controlled the overall performance of the CO 2 adsorbents. At 75 uC, the operating temperature favored the molecular mobility of PEI and unrestricted diffusion of CO 2 to allow the theoretical CO 2 capacity of the PEI to be attained. Lower temperatures limited the mobilities of PEI and CO 2 and the kinetics of ''ionic'' gel formation dominated, causing a lowered overall performance of the CO 2 adsorbents. Overall, this study points to the importance of interconnected porous channel networks to optimize the performance of PEI-impregnated mesoporous silica particles.