Loss Of CO Research Articles

Unraveling the decarboxylation dynamics of the fluorescein dianion with fragment action spectroscopy

The decarboxylation dynamics of the doubly deprotonated fluorescein dianion, Fl2-, are investigated by recording fragment action spectra for the anion, Fl-, and its decarboxylated analog, Fl-CO2-, using a new reflectron secondary mass spectrometer. The formation of the anion, Fl-, is directly investigated by photoelectron imaging. The Fl- and Fl-CO2- action spectra indicate that, for λ < 400nm, one-photon dissociative photodetachment, i.e., simultaneous decarboxylation and electron loss, competes with photodetachment, whereas for λ > 400nm, decarboxylation only proceeds following electron loss via a sequential two-photon process. The primary decarboxylation pathway is the ready loss of CO2 from the relatively short-lived intermediate excited state, Fl-[D1], which is formed by electron loss from the dianion via resonant tunneling through the repulsive Coloumb barrier associated with a high-lying excited dianion state, Fl2-[S2].

Improving the Stability, Selectivity, and Cell Voltage of a Bipolar Membrane Zero‐Gap Electrolyzer for Low‐Loss CO2 Reduction

AbstractElectrolyzers for CO2 reduction containing bipolar membranes (BPM) are promising due to low loss of CO2 as carbonates and low product crossover, but improvements in product selectivity, stability, and cell voltage are required. In particular, direct contact with the acidic cation exchange layer leads to high levels of H2 evolution with many common cathode catalysts. Here, Co phthalocyanine (CoPc) is reported as a suitable catalyst for a zero‐gap BPM device, reaching 53% Faradaic efficiency to CO at 100 mA cm−2 using only pure water and CO2 as the input feeds. It is also shown that the cell voltage can be lowered by constructing a customized BPM using TiO2 water dissociation catalyst, however this is at the cost of decreased selectivity. Switching the pure‐water anolyte to KOH improved both the cell voltage and CO selectivity (62% at 200 mA cm−2), but cation crossover could cause complications. The results demonstrate viable strategies for improving a BPM CO2 electrolyzer toward practical‐scale CO2‐to‐chemicals conversion.

Gas-phase formation of Grignard-type organolanthanide (III) ions RLnCl3 - : The influences of lanthanide center and hydrocarbyl group.

Compared with organomagnesium compounds (Grignard reagents), the Grignard-type organolanthanides (III) exhibit several utilizable differences in reactivity. However, the fundamental understanding of Grignard-type organolanthanides (III) is still in its infancy. Decarboxylation of metal carboxylate ions is an effective method to obtain organometallic ions that are well suited for gas-phase investigation using electrospray ionization (ESI) mass spectrometry in combination with density functional theory (DFT) calculations. The (RCO2 )LnCl3 - (R = CH3 , Ln = La-Lu except Pm; Ln = La, R = CH3 CH2 , CH2 CH, HCC, C6 H5 , and C6 H11 ) precursor ions were produced in the gas phase via ESI of LnCl3 and RCO2 H or RCO2 Na mixtures in methanol. Collision-induced dissociation (CID) was employed to examine whether the Grignard-type organolanthanide (III) ions RLnCl3 - can be obtained via decarboxylation of lanthanide chloride carboxylate ions (RCO2 )LnCl3 - . DFT calculations can be used to determine the influences of lanthanide center and hydrocarbyl group on the formation of RLnCl3 - . When R = CH3 , CID of (CH3 CO2 )LnCl3 - (Ln = La-Lu except Pm) yielded decarboxylation products (CH3 )LnCl3 - and reduction products LnCl3 ·- with a variation in the relative intensity ratio of (CH3 )LnCl3 - /LnCl3 ·- . The trend is as follows: (CH3 )EuCl3 - /EuCl3 ·- < (CH3 )YbCl3 - /YbCl3 ·- ≈ (CH3 )SmCl3 - /SmCl3 ·- < other (CH3 )LnCl3 - /LnCl3 ·- , which complies with the trend of Ln (III)/Ln (II) reduction potentials in general. When Ln = La and hydrocarbyl groups were varied as CH3 CH2 , CH2 CH, HCC, C6 H5 , and C6 H11 , the fragmentation behaviors of these (RCO2 )LaCl3 - precursor ions were diverse. Except for (C6 H11 CO2 )LaCl3 - , the four remaining (RCO2 )LaCl3 - (R = CH3 CH2 , CH2 CH, HCC, and C6 H5 ) ions all underwent decarboxylation to yield RLaCl3 - . (CH2 CH)LaCl3 - and especially (CH3 CH2 )LaCl3 - are prone to undergo β-hydride transfer to form LaHCl3 - , whereas (HCC)LaCl3 - and (C6 H5 )LaCl3 - are not. A minor reduction product, LaCl3 ·- , was formed via C6 H5 radical loss of (C6 H5 )LaCl3 - . The relative intensities of RLaCl3 - compared to (RCO2 )LaCl3 - decrease as follows: HCC > CH2 CH > C6 H5 > CH3 > CH3 CH2 >> C6 H11 (not visible). A series of Grignard-type organolanthanide (III) ions RLnCl3 - (R = CH3 , Ln = La-Lu except Pm; Ln = La, R = CH3 CH2 , CH2 CH, HCC, and C6 H5 ) were produced from (RCO2 )LnCl3 - via CO2 loss, whereas (C6 H11 )LaCl3 - did not. The experimental and theoretical results suggest that the reduction potentials of Ln (III)/Ln (II) couples as well as the bulkiness and hybridization of hydrocarbyl groups play important roles in promoting or limiting the formation of RLnCl3 - via decarboxylation of (RCO2 )LnCl3 - .

Thermometric and chemical studies of fluid inclusions in sphalerite from Rhodope lead-zinc deposits: Shumachevski Dol – Gyudyurska (Madan District) and Kenan Dere (Laki District), Bulgaria

The objects of this study are fluid inclusions in sphalerite crystals or selected parts of them from two Central Rhodopean deposits: Shumachevski Dol – Gyudyurska (Madan District) and Kenan Dere (Laki District). A set of data for temperature of homogenization and total salinity are presented. The locations of coupled data in coordinates Th vs total salinity reveal that the Kenan Dere sphalerite has been deposited from solutions of higher temperature (280–374 °C) and lower salinity (2–5 wt.% NaCl-eqv.). Conversely, the Shumachevski Dol and Gyudyurska sphalerites show lower Th = 200–230 °C and somewhat higher salinity (S = 6–12 wt.% NaCl-eqv.). Furthermore, it is likely that both late Kenan Dere and Gyudyurska sphalerites were deposited at 30–50 °C lower temperatures than the earlier ones. Additionally, Decrepitation Inductively-Coupled-Plasma Atomic-Emission-Spectrometry was applied to determine the cations in the inclusion solute. The vacuum decrepitation was also used for liberating the volatiles (H2O, CO2) and analysing them by mass spectrometry. On that account, more detailed preliminary studies of the process of decrepitation were performed. However, the Zn-concentration in sphalerite-hosted fluid inclusions cannot be evaluated and the results from syngenetic quartz offer the only possibility for obtaining information about ore-element content. On the basis of a compilation of both present and previously published data, it can be concluded that the hydrothermal fluid under the Central Rhodope Dome was constituted in situ as a closed system at a depth of ~1 km, under nearly lithostatic pressure (~200 bars), T ≥ 350 °C, and NaCl-dominated salt content ~10%. Under these conditions, a solution with a pH of ~4.0–4.5 contains ore elements (Fe, Zn, Pb) as soluble chlorido-complexes; for Zn, the total concentration may reach 1 wt.%. Sulphide-S compound under these conditions is H2S. The sphalerite deposition follows a reverse path of the chemical reactions. The elevation of the hydrothermal fluid along the extensional dislocations results in boiling (i.e., separation of CO2) and cooling. The temperature decrease destabilizes the chlorido-complexes and leads to an increase in the Zn2+ activity. On the other hand, CO2 loss enhances pH, and thus dissociates H2S, yielding HS- and S2- ions, needed for sphalerite deposition.

Dissolution Profiles of Poorly Soluble Drug Salts in Bicarbonate Buffer.

The purpose of the present study was to investigate the effect of buffer species on the dissolution profiles of poorly soluble drug salts, focusing on bicarbonate buffer (BCB). Pioglitazone HCl (PIO HCl) and dantrolene sodium (DNT Na) were used as model drugs. Non-sink dissolution tests were performed using phosphate buffer (PB) and BCB (pH 6.5, buffer capacity: 4.4mM/pH, ionic strength: 0.14M, with/ without bile micelles). The pH value of BCB was maintained using a floating lid that avoided the loss of CO2. The particles collected at the early stage of dissolution (< 5min) were analyzed by powder X-ray diffraction, polarized light microscopy, and scanning electron microscopy. A bulk-phase pH shift precipitation test was also performed. The dissolution of PIO HCl was slower in BCB than in PB, whereas that of DNT Na was faster in BCB than in PB. The same trend was observed in the presence of bile micelles. Free-form precipitation on the surface of salt particles was observed early in their dissolution in both BCB and PB. However, the surface textures in BCB and PB were different. The bulk-phase precipitation of PIO was little affected by buffer species, whereas that of DNT was affected, but oppositely to the dissolution profile. The dissolution profiles of PIO HCl and DNT Na in BCB were markedly different from those in PB. Free-form precipitation on the particle surface, rather than in the bulk phase, was affected by buffer species in the dissolution test.

Iron Removal as Goethite from Synthetic Laterite Leach Solutions.

The aim of this study was to precipitate goethite from high-iron(II)-bearing atmospheric and heap leach solutions of lateritic nickel ore generated either by reductive leaching of the ore or by reducing Fe(III) of the leach solution to Fe(II) using a suitable reducing agent and to understand the Ni and Co losses during the iron precipitation. Removal of Fe was carried out using an oxidative hydrolysis technique targeting goethite precipitation from a synthetic laterite leach solution containing Fe as ferrous (Fe(II)), Al, Mg, Ni, Co, Cr, Mn, Cu, and Zn using limestone as the neutralizing agent and air as an oxidant. The behavior of goethite precipitation and the losses of Ni and Co were examined under various conditions of pH, temperature, and Fe concentration. The precipitation of Fe increased with increasing pH, temperature, and feed Fe(II) concentration. Precipitation at pH ∼4.0-4.1 (measured at ambient temperature) and 90 °C resulted in ∼96-97% Fe removal from a feed solution containing more than 50 g/L Fe(II), giving ∼1 g/L Fe in the final liquor. Goethite formation was confirmed as a result of the Fe precipitation, and it appeared to take place via ferrihydrite/schwertmannite intermediate phases. The crystallinity of the goethite increased with time, temperature, and feed Fe(II) concentration. The goethite precipitate was found to be associated with an alunite phase. Losses of Ni and Co during Fe precipitation increased with pH, temperature, and feed Fe(II) concentration. The losses were significant above pH 4 and found to be ∼7-22% Ni and 4-19% Co in the pH range 4.1-5. The test results indicate that efficient Fe removal via goethite precipitation can be achieved from reduced atmospheric and heap leach solutions of laterite ore; however, careful pH control is required to minimize the loss of Ni and Co during this precipitation.

Diazene Chemistry: Metal-Free Models of N2 Reduction Intermediates.

Interest in main group chemistry related to the Haber-Bosch process has drawn less attention than that of transition metal species. Herein, we show that the steric demands in (tBuO2CN)2 block initial interaction of B(C6F5)3 with nitrogen and prompt loss of methylpropene and CO2 to diazene (N2H2) borane adduct 1 and the analogous hydrazine (N2H4) adduct 2. These species react with basic phosphines to give anions of 3 and 5 containing N2H and N2H3 fragments, respectively. While these species are not derived directly from N2, they represent metal-free species containing N2Hn (n = 1-4) fragments, which model plausible intermediates in the reduction of N2.

Propiolic Acid on Cu(100) and Oxygen-Precovered Cu(100): Multiple Adsorption States and Diversified Reaction Routes

Multiple adsorption geometries and diversified reaction pathways of the bifunctional propiolic acid (HC≡C–COOH) on Cu(100) and oxygen-covered Cu(100) (O/Cu(100)) have been investigated, using the surface analytical techniques of X-ray photoelectron spectroscopy, reflection–absorption infrared spectroscopy, and temperature-programmed reaction/desorption, with the assistance of density functional theory calculations. Upon adsorption on O/Cu(100) at 105 K, the deprotonation occurs promptly to form perpendicular HC≡C–COO (propiolate) with the COO attaching to the surface. Decomposition of this intermediate results in the loss of CO and CO2 at ∼230 K and formation of the plausible surface intermediates of CCCOOH, tilted HCCCOO, and CCH. The first two are derived from rearrangement or geometric transformation of the perpendicular HC≡C–COO. CCH is the precursor for the C2H2 desorption at ∼335 K. C2 (acetylide) and >C═C═O (ketenylidene) exist on the surface at higher temperatures and are responsible for the desorption of CO and CO2 at 580 K. On Cu(100), adsorption of propiolic acid at 105 K generates tilted HCCCOOH and HCCCOO, via the HCC group bonding to the surface. Perpendicular HC≡C–COO is an additional species found at a higher coverage. Hydrogenation of the HCCCOO occurs, possibly involving the surface species of CHCHCOO and CH2CCOO. H2, H2O, CO, and CO2 evolve from decomposition of these carboxylates at ∼315 K, also forming perpendicular CH2═CHCOO and >C═C═O. Adsorbed CH3CH2COO can be produced at a higher coverage. In addition, C2H2 and C2H4 desorb at ∼360 K. Decomposition of the perpendicular CH2═CHCOO, >C═C═O, and CH3CH2COO is responsible for the products of H2, CO, CO2, and C6H6 found at ∼550 K.

Reliable quantification of citrate isomers and isobars with direct-infusion tandem mass spectrometry

Direct-infusion tandem mass spectrometry (DI-MS/MS) is an excellent tool for large cohort high-throughput quantitative metabolomics, MS imaging and single cell studies but incapable of discriminating isomers/isobars with similar MS spectral features. With experimental and density-functional theory (DFT) approaches, here, we comprehensively investigated the fragmentation pathways and characteristics of differential ion-mobility spectrometry (DMS) for three citrate isomers (citrate, isocitrate, glucaro-1,4-lactone) and an isobar (quinate) co-existing in biological sample such as urine. Results showed that all these compounds gave better MS spectra in negative-ion mode than positive-ion one and had numerous fragment ions under collision-induced dissociation (CID) with sequential losses of H2O and CO2. All observed fragment ions were assignable by combining experimental with DFT calculation results. A DI-DMS-MS/MS method was then developed to simultaneously quantify these four isomers/isobars with m/z 191–87 (CoV, −5.5 V), 191–73 (CoV, −3.5 V), 191–85 (CoV, −29.5 V) and m/z 191–93 (CoV, −41.5 V) for citrate, isocitrate, glucaro-1,4-lactone and quinate, respectively. The low limit-of-quantification was below 5.5 nM whilst accuracy was above 94% for all above compounds. The urinary concentrations of them in human and C57BL/6 mouse samples were further quantified showing clear inter-individual and inter-species level differences with significantly higher levels of isocitrate, glucaro-1,4-lactone and quinate in human urine samples than mouse ones. This provides an approach to understand the detailed fragmentation pathways for organic isomers/isobars and a high-throughput MS strategy to quantify them in complex mixtures for metabolomics, lipidomics, foodomics and exposomics especially when chromatographic separations are not useable.

Collisional heating of icy planetesimals – I. Catastrophic collisions

ABSTRACTPlanetesimals in the primordial disc may have experienced a collisional cascade. If so, the comet nuclei later placed in the Kuiper belt, scattered disc, and Oort Cloud would primarily be fragments and collisional rubble piles from that cascade. However, the heating associated with the collisions cannot have been strong enough to remove the hypervolatiles that are trapped within more durable ices, because comet nuclei are rich in hypervolatiles. This places constraints on the diameter of the largest bodies allowed to participate in collisional cascades, and limits the primordial disc lifetime or population size. In this paper, the thermophysical code nimbus is used to study the thermal evolution of planetesimals before, during, and after catastrophic collisions. The loss of CO during segregation of CO2:CO mixtures and during crystallization of amorphous H2O is calculated, as well as mobilization and internal relocation of CO2. If an amorphous H2O host existed, and was protected by a CO2:CO heat sink, only diameter $D\lt 20\, \mathrm{km}$ (inner disc) and $D\lt 64\, \mathrm{km}$ (outer disc) bodies could have been involved in a collisional cascade. If CO2 was the only CO host, the critical diameters drop to D &amp;lt; 20–$32\, \mathrm{km}$. Avoiding disruption of larger bodies requires a primordial disc lifetime of &amp;lt;9 Myr at 15 au and &amp;lt;50–70 Myr at 30 au. Alternatively, if a 450 Myr disc lifetime is required to associate the primordial disc disruption with the Late Heavy Bombardment, the disc population size must have been 6–60 times below current estimates.

Tuning flow-through cu-based hollow fiber gas-diffusion electrode for high-efficiency carbon monoxide (CO) electroreduction to C2+products

Electrochemical carbon monoxide reduction (CORR) to C2+ products has advantages over electrochemical CO2 conversion (CO2RR) as issues such as carbonation, and CO2 loss during CO2RR are omitted in CORR due to the stability of CO in alkaline solutions. Facing common challenges as CO2RR, CORR suffers more from mass transport resistance and intrinsically lower aqueous CO solubility. Therefore gas-diffusion electrodes (GDEs) are desired to boost the formation of triple phases and active sites to obtain higher reaction rates. Herein, for the first time Cu-based hollow fiber GDEs (HFGDEs) are tuned for CORR to C2+ products. By growing a layer of Cu nanocubes as the catalyst layer on HFGDEs, non-selective pristine copper HFGDE became highly selective for C2+ products (FE>90%), with ethylene as the main product (FE>65%), owing to the dominant Cu (100) facet in Cu nanocubes with high C2+ selectivity. In addition, ultra-high ethylene partial current density of > 470 mA cm−2 at − 0.8 V vs. RHE in 5.0 M KOH was obtained, owing to the abundant porosity and surface area available for triple-phase formation on microtubular GDEs and their enhanced mass transport. The electrodes exhibited one of the highest partial current densities achieved for ethylene production, indicating the promises of flow-through hollow fiber configuration for other desired products or gas-phase electrochemical reactions with low aqueous solubility.

Modelling post-plasma quenching nozzles for improving the performance of CO2 microwave plasmas

Given the ecological problems associated to the CO2 emissions of fossil fuels, plasma technology has gained interest for conversion of CO2 into value-added products. Microwave plasmas operating at atmospheric pressure have proven to be especially interesting, due to the high gas temperatures inside the reactor (i.e. up to 6000 K) allowing for efficient thermal dissociation of CO2 into CO and O2. However, the performance of these high temperature plasmas is limited by recombination of CO back into CO2 once the gas cools down in the afterglow. In this work, we computationally investigated several quenching nozzles, developed and experimentally tested by Hecimovic et al., [1] for their ability to quickly cool the gas after the plasma, thereby quenching the CO recombination reactions. Using a 3D computational fluid dynamics model and a quasi-1D chemical kinetics model, we reveal that a reactor without nozzle lacks gas mixing between hot gas in the center and cold gas near the reactor walls. Especially at low flow rates, where there is an inherent lack of convective cooling due to the low gas flow velocity, the temperature in the afterglow remains high (between 2000 and 3000 K) for a relatively long time (in the 0.1 s range). As shown by our quasi-1D chemical kinetics model, this results in a important loss of CO due to recombination reactions. Attaching a nozzle in the effluent of the reactor induces fast gas quenching right after the plasma. Indeed, it introduces (i) more convective cooling by forcing cool gas near the walls to mix with hot gas in the center of the reactor, as well as (ii) more conductive cooling through the water-cooled walls of the nozzle. Our model shows that gas quenching and the suppression of recombination reactions have more impact at low flow rates, where recombination is the most limiting factor in the conversion process.

Periodic Graphics: Mucus, tears, and saliva

Chemical educator and Compound Interest blogger Andy Brunning looks at the biochemistry of our snot, spit, and tears To download a pdf of this article, visit http://cenm.ag/snotspittears. References used to create this graphic: Bardow, Allan, Dennis Moe, Bente Nyvad, and Birgitte Nauntofte. “The Buffer Capacity and Buffer Systems of Human Whole Saliva Measured without Loss of CO2.” Arch. Oral Biol. (Jan. 2000). DOI: 10.1016/S0003-9969(99)00119-3 . Fenna, R., J. Zeng, and C. Davey. “Structure of the Green Heme in Myeloperoxidase.” Arch. Biochem. Biophys. (Jan. 1995). DOI: 10.1006/abbi.1995.1086. Kirby, Anthony J. “The Lysozyme Mechanism Sorted—after 50 Years.” Nat. Struct. Mol. Biol. (Sept. 2001). DOI: 10.1038/nsb0901-737. A collaboration between C&EN and Andy Brunning, author of the popular graphics blog Compound Interest To see more of Brunning’s work, go to compoundchem.com. To see all of C&EN’s Periodic Graphics, visit http://cenm.ag/periodicgraphics .

Inhomogeneities in the Catholyte Channel Limit the Upscaling of CO2 Flow Electrolysers.

The use of gas diffusion electrodes that supply gaseous CO2 directly to the catalyst layer has greatly improved the performance of electrochemical CO2 conversion. However, reports of high current densities and Faradaic efficiencies primarily come from small lab scale electrolysers. Such electrolysers typically have a geometric area of 5 cm2, while an industrial electrolyser would require an area closer to 1 m2. The difference in scales means that many limitations that manifest only for larger electrolysers are not captured in lab scale setups. We develop a 2D computational model of both a lab scale and upscaled CO2 electrolyser to determine performance limitations at larger scales and how they compare to the performance limitations observed at the lab scale. We find that for the same current density larger electrolysers exhibit much greater reaction and local environment inhomogeneity. Increasing catalyst layer pH and widening concentration boundary layers of the KHCO3 buffer in the electrolyte channel lead to higher activation overpotential and increased parasitic loss of reactant CO2 to the electrolyte solution. We show that a variable catalyst loading along the direction of the flow channel may improve the economics of a large scale CO2 electrolyser.

How the Birch effect differs in mechanisms and magnitudes due to soil texture

Global climate change is predicted to intensify temperature and precipitation extremes, exposing soils to frequent and/or intense alternate wetting and drying regimes. Rewetting a dry soil causes a burst of CO2 known as the “Birch effect”. This spike in respiration can be attributed to: (i) release of cellular solutes (metabolites) accumulated during drought due to rapid increase in water potential upon re-wetting; (ii) sudden death of certain microbes serving as carbon (C) sources for surviving microbes, leading to microbial community shifts; and (iii) release of physically protected C due to aggregate breakdown upon repeated drying-wetting. The relative importance of these mechanisms may change in different soil textures, but very few studies examine all three processes. In this study, we evaluated the effects of repeated drying and wetting cycles (transient state moisture conditions) on the Birch effect and elucidated the mechanisms that contributed to this effect in different textured soils. Soils of three distinct textures (sandy, loamy, and clayey) were incubated for 140 days under five alternate cycles of drying (10% WHC) and wetting (100% WHC) conditions. Control soils were held at 55% WHC for the same duration. Microbial biomass C (MBC), extractable organic C (EOC), metabolites, microbial community structure, and changes in aggregate associated C were determined at each time point. Sandy soil had the lowest respiration rate followed by loamy and clayey soils, and cumulative CO2 loss was higher under transient moisture state compared to steady state. In sandy and clayey soils, changes in bacterial abundance controlled the Birch effect, while in loamy soil, the release of aggregate protected C majorly controlled the Birch effect.

Increasing cellular fitness and product yields in Pseudomonas putida through an engineered phosphoketolase shunt

BackgroundPseudomonas putida has received increasing interest as a cell factory due to its remarkable features such as fast growth, a versatile and robust metabolism, an extensive genetic toolbox and its high tolerance to oxidative stress and toxic compounds. This interest is driven by the need to improve microbial performance to a level that enables biologically possible processes to become economically feasible, thereby fostering the transition from an oil-based economy to a more sustainable bio-based one. To this end, one of the current strategies is to maximize the product-substrate yield of an aerobic biocatalyst such as P. putida during growth on glycolytic carbon sources, such as glycerol and xylose. We demonstrate that this can be achieved by implementing the phosphoketolase shunt, through which pyruvate decarboxylation is prevented, and thus carbon loss is minimized.ResultsIn this study, we introduced the phosphoketolase shunt in the metabolism of P. putida KT2440. To maximize the effect of this pathway, we first tested and selected a phosphoketolase (Xfpk) enzyme with high activity in P. putida. Results of the enzymatic assays revealed that the most efficient Xfpk was the one isolated from Bifidobacterium breve. Using this enzyme, we improved the P. putida growth rate on glycerol and xylose by 44 and 167%, respectively, as well as the biomass yield quantified by OD600 by 50 and 30%, respectively. Finally, we demonstrated the impact on product formation and achieved a 38.5% increase in mevalonate and a 25.9% increase in flaviolin yield from glycerol. A similar effect was observed on the mevalonate-xylose and flaviolin-xylose yields, which increased by 48.7 and 49.4%, respectively.ConclusionsPseudomonas putida with the implemented Xfpk shunt grew faster, reached a higher final OD600nm and provided better product-substrate yields than the wild type. By reducing the pyruvate decarboxylation flux, we significantly improved the performance of this important workhorse for industrial applications. This work encompasses the first steps towards full implementation of the non-oxidative glycolysis (NOG) or the glycolysis alternative high carbon yield cycle (GATCHYC), in which a substrate is converted into products without CO2 loss These enhanced properties of P. putida will be crucial for its subsequent use in a range of industrial processes.

Liberation of carbon monoxide from formic acid mediated by molybdenum oxyanions.

Multistage mass spectrometry experiments, isotope labelling and DFT calculations were used to explore whether selective decarbonylation of formic acid could be mediated by molybdate anions [(MoO3)x(OH)]- (x = 1 and 2) via a formal catalytic cycle involving two steps. In step 1, both molybdate anions undergo gas-phase ion-molecule reactions (IMR) with formic acid to produce the coordinated formates [(MoO3)x(O2CH)]- and H2O. In step 2, both coordinated formates [(MoO3)x(O2CH)]- undergo decarbonylation under collision-induced dissociation (CID) conditions to reform the molybdate anions [(MoO3)x(OH)]- (x = 1 and 2), thus closing a formal catalytic cycle. In the case of [MoO3(O2CH)]- an additional decarboxylation channel also occurs to yield [MoO3(H)]-, which is unreactive towards formic acid. The reaction between [Mo18O3(18OH)]- and formic acid gives rise to [Mo18O3(O2CH)]- highlighting that ligand substitution occurs without 18O/16O exchange between the coordinated 18OH ligand and HC16O2H. The reaction between [(MoO3)x(OD)]- (x = 1 and 2) and DCO2H initially produces [(MoO3)x(OH)]- (x = 1 and 2), indicating that D/H exchange occurs. DFT calculations were carried out to investigate the reaction mechanisms and energetics associated with both steps of the formal catalytic cycle and to better understand the competition between decarbonylation and decarboxylation, which is crucial in developing a selective catalyst. The CO and CO2 loss channels from the monomolybdate anion [MoO3(O2CH)]- have similar barrier heights which is in agreement with experimental results where both fragmentation channels are observed. In contrast, the dimolybdate anion is more selective, since the decarbonylation pathway of [(MoO3)2(O2CH)]- is both kinetically and thermodynamically favoured, which agrees with experimental observations where the CO loss channel is solely observed.

Studying manganese carbonyl photochemistry in a permanently porous metal-organic framework.

Mn(diimine)(CO)3X (X = halide) complexes are critical components of chromophores, photo- and electrocatalysts, and photoactive CO-releasing molecules (photoCORMs). While these entities have been incorporated into metal-organic frameworks (MOFs), a detailed understanding of the photochemical and chemical processes that occur in a permanently porous support is lacking. Here we site-isolate and study the photochemistry of a Mn(diimine)(CO)3Br moiety anchored within a permanently porous MOF support, allowing for not only the photo-liberation of CO from the metal but also its escape from the MOF crystals. In addition, the high crystallinity and structural flexibility of the MOF allows crystallographic snapshots of the photolysis products to be obtained. We report these photo-crystallographic studies in the presence of coordinating solvents, THF and acetonitrile, showing the changing coordination environment of the Mn species as CO loss proceeds. Using time resolved experiments, we report complementary spectroscopic studies of the photolysis chemistry and characterize the final photolysis product as a possible Mn(ii) entity. These studies inform the chemistry that occurs in MOF-based photoCORMs and where these moieties are employed as catalysts.

High-throughput UV-photofragmentation studies of thymine and guanine.

High-throughput photofragmentation studies of thymine and guanine were performed at 257 and 343 nm and for a wide range of ionisation laser intensities. Combining a continuous laser-based thermal desorption source with femtosecond multiphoton ionisation using a 50 kHz repetition rate laser allowed us to produce detailed 2D maps of fragmentation as a function of incident laser intensity. The fragmentation was distinctly soft, the parent ions being at least an order of magnitude more abundant than fragment ions. For thymine there was a single dominant fragmentation channel, which involves consecutive HNCO and CO losses. In contrast, for guanine there were several competing ones, the most probable channel corresponding to CH2N2 loss through opening of the pyrimidine ring. The dependence of parent ion abundance on the ionisation laser intensity showed that at 257 nm the ionisation of thymine is a 1 + 1 resonance enhanced process through its open-shell singlet state.

Degradation of selected perfluoroalkyl substances (PFASs) using AlF3 in water.

The conversion of representative perfluorinated carboxylic acids and perfluorinated sulfonic acids in aqueous solutions into the corresponding perfluoroalkenes is investigated by using electronic structure methods. It is demonstrated that the use of aluminum trifluoride enables such conversions even at room temperature (with the reaction completion time not exceeding 1 minute). The mechanism of the reactions studied involves the withdrawal of F- from either the carboxylic or the sulfonic anion by AlF3 which leads to the formation of a stable AlF4- anion and a perfluoroalkene compound (which can be further decomposed to a series of nonfluorinated products) accompanied by CO2 or SO3 loss.