The Acidity of a Carbon Nucleophile Dictates Enantioselectivity and Reactivity in Michael Additions to Aromatic and Aliphatic Enals via Iminium Activation

The Michael addition of activated methylenes to β-substituted α,β-unsaturated aldehydes (enals) via iminium catalysis takes place following reactivity and enantioselectivity patterns which depend on the electronic nature of the substituent in the β position (β-aryl or β-alkyl). Application of the same reaction conditions to both families of enals may result in erratic levels of asymmetric induction in the reactions of β-aryl enals or low reactivity with β-alkyl enals. A systematic analysis of this behavior using phenylacetic acid derivatives as case studies has led us to find a general trend: the different problems found for β-aryl and β-alkyl enals depend on the acidity of the nucleophile, and the outcome of the reaction for both types of enals can be improved substantially by careful choice of catalyst, solvent, and additive. Furthermore, this study has allowed us to understand subtle aspects of this transformation and has enabled the formulation of a general and reliable protocol to obtain high yields and enantioselectivities consistently, regardless of the acidity of the nucleophile and the nature of the substituent (aromatic or aliphatic) at the β positionWe thank CTQ-2009-12168, CAM (AVANCAT CS2009/PPQ-1634), UAM-CAM (CCG10-UAM/PPQ-5769), CTQ-2012-35957, CTQ2015-63997-C2-1-P, CTQ2016-78779-R and FOTOCARBON-CAM S2013/MIT-2841 for financial support. S.D. thanks the Comunidad Autónoma de Madrid (CAM), and E.R. and S.M. thank MICINN, for predoctoral fellowships. P.M. thanks MICINN for a Ramón y Cajal contract and the EU for a Marie Curie grant (CIG: HYPERCAT-30422

Reproducibility and robustness of microbial fuel cells technology

This work focuses on the evaluation of the robustness and reproducibility of the behaviour of microbial fuel cells (MFCs). Up to 112 MFCs were operated simultaneously under the same conditions, finding that the probability of high performance, maximum power, maximum current and internal resistance is 95%, 90%, 96% and 94% respectively. Reproducibility of stacks was also evaluated by testing different electrical connections, finding that when evaluating the performance of 7 stacks of 16 MFCs each connected in parallel and different combinations of series/parallel, the maximum power varies only between 1 and 2 mW. Results obtained also helps to demonstrate that the performance of the bioelectrochemical devices evaluated mainly depended on the internal resistance. All these information is of a great significance for future developments of the technology because it is a real first step in the characterization of the robustness of the bioelectrochemical technology

Biofilm and planktonic population distribution. Key aspects in carbonaceous anodes for microbial fuel cells

BACKGROUND A comparison between different carbon-based anodes used in microbial fuel cells (MFCs) has been carried out. Five different carbonaceous anodes were studied: carbon paper, carbon cloth, carbon foam 30 ppi, carbon foam 80 ppi and carbon felt. RESULTS The current density generated was higher for the MFCs with porous anodes compared with the flat ones, generating up to 14.5 A m−2. However, when the superficial surface was higher than 7500 m2 m−2 the performance did not increase further due to microorganisms transport and mass transfer limitations. Regarding the biochemical performance, a linear relationship between the generated current density and the coulombic efficiency was found. This relationship indicates selection of the electrogenic microbial population when the superficial surface increases. From Illumina MiSeq analyses, it was observed that Shewanella population in the biofilm was c. 14%, while its population was negligible in the planktonic culture. This population distribution can be explained by the low growth rate of the Shewanella. CONCLUSIONS These results demonstrate that the main driving force of the carbonaceous materials performance is the ease of biofilm formation and subsequent population selection, but not on specific electronic properties of the carbon materials. © 2018 Society of Chemical Industr

Driving force behind electrochemical performance of microbial fuel cells fed with different substrates

The performance of miniaturized microbial fuel cells operating with five different substrates (acetate, lactate, glucose and octanoate) were studied with the aim to identify the reason for its different performance. In all cases, the COD removal rate was about 650 mg COD L−1 d−1. However, the bio-electrochemical performance of the MFC was very different, showing the MFC fed with acetate the best performance: 20 A m−2 as maximum current density, 2 W m−2 of maximum power density, 0.376 V of OCV and 12.6% of CE. In addition, the acetate showed the best bio-electrochemical performance in the polarization curves and cyclic voltammetries. These polarization curves were modelled and the key to explain the better electrical performance of acetate was its lower ohmic losses. When working with acetate, its ohmic losses were one log-unit below those attained by the other substrates. These lower ohmic losses were not associated to the electrolyte conductivity of the fuel but to the lower ohmic loses of the biofilm generated

A Critical View of Microbial Fuel Cells: What Is the Next Stage?

Microbial fuel cells (MFCs) have garnered interest from the scientific community since the beginning of this century and this has caused a considerable increase in the scientific production of MFCs. However, the ability of MFCs to generate power has not increased considerably within this timeframe. In recent years, the power generated by MFCs has remained at an almost contact level owing to difficulties in the scale-up of the technology and thus the application of MFCs for powering systems with high energy demands will not be fully developed, at least within a short temporal horizon. Scale-up by increasing the size of the electrodes has failed, because of the wrong assumption that a linear function describes the relationship between the amount of power generated by a MFC and its size. However, more efficient energy generation upon working with small MFCs has been described. This has led to a new approach for scaling up on the basis of miniaturization and replication. Then, MFCs can be connected electrically in series to increase the overall potential and in parallel to increase the overall current. However, cell-voltage reversal and ionic short-circuit issues must be solved for this approach to be successful. Nowadays, the applicability of MFC technology in wastewater treatment does not make any sense in light of the power levels reached, despite the fact that MFCs were seen as a paramount opportunity less than a decade ago. However, MFCs can be used for wastewater treatment with coupled energy generation, as well as for other technologies such as biosensors and biologically inspired robots

On the staking of miniaturized air-breathing microbial fuel cells

This work focuses on the scale-up of the MFCs by miniaturization and multiplication strategy. Performances of five stacks containing 1, 2, 5, 8 and 16 MFCs were compared. Each stack was evaluated under individual, parallel and series electrical connection as well as for cascade or individual hydraulic connection. Cascade feeding mode with a tank per stack favours the COD removal when the number of MFCs in the stack increases. However, despite operating without COD limitations, the energy production was disadvantaged. By changing the feeding system of a tank per stack into an individual tank per MFC, the performance of the whole stack enhances considerably. Stacking in series can increase the voltage 6 times while stacking in parallel can increase the current output about 4 times. For example, 8 MFCs can achieve 2.03 V connected in series and 6.98 mA connected in parallel. In addition, the power can be increased up to about 10 times leading to a power range high enough for real life applications

Assessing the impact of design factors on the performance of two miniature microbial fuel cells

Every day, wastewater treatment requires large amounts of electricity. Microbial Fuel Cells (MFCs) can convert wastewater treatment plants from net power consumers into energy neutral/positive systems by generating electricity from wastewaters. We investigate here the design factors that have major impacts on the performance of two miniature MFCs, and, consequently, of the resulting stack of MFCs. A versatile mathematical model is provided, which simulates the complex MFC system by integrating fluid dynamic principles with mass transport phenomena and (bio)electrochemical reactions. The model is used to support an in-depth study of the two MFCs, which differ for electrode spacing, anodic volume and fluid pattern within the anodic chamber, and to associate any difference in performance to design factors. Finally, system scale-up is demonstrated by generating stacks of the two MFCs. Thanks to the versatility of the model developed, this study becomes a guide for the effective development of future miniature MFCs

Effect of sludge age on the consortium of microorganisms microbial consortia developed in MFCs

BACKGROUND: This work is focused on the assessment of the performance of mini-scale air-breathing microbial fuel cells (MFCs),by monitoring the evolution of the bio-electrogenic activity for a period of 40 days and by comparing the microorganismspopulations developed in each of the MFCs after this period.RESULTS: Five MFCs were operated at sludge ages ranging from 1.4 to 10.0 days. Results showed the superb performance of theMFC operating under a sludge age of 2.5 days. Desulfuromonas, Syntrophothermus, Solitalea, Acholeplasma, Propionicimonas,Desulfobacula and Sphaerochaeta are proposed as potentially responsible for the bio-electrogenic activity.CONCLUSIONS: Microbial population analysis through Illumina amplicon sequencing demonstrated that despite all MFCsbeing seeded with the same mixed culture inoculum, the biological cultures developed in the suspension and the biofilm arecompletely different and depend strongly on sludge age.© 2017 Society of Chemical Industry

Long-term effects of the transient COD concentration on the performance of microbial fuel cells

In this work, the long-term effects of transient chemical oxygen demands (COD) concentrations over the performance of a microbial fuel cell were studied. From the obtained results, it was observed that the repetitive change in the COD loading rate during 12 h conditioned the behavior of the system during periods of up to 7 days. The main modifications were the enhancement of the COD consumption rate and the exerted current. These enhancements yielded increasing Coulombic efficiencies (CEs) when working with COD concentrations of 300 mg/L, but constant CEs when working with COD concentrations from 900 to 1800 mg/L. This effect could be explained by the higher affinity for the substrate of Geobacter than that of the nonelectrogenic organisms such as Clostridia.En este trabajo, se estudiaron los efectos a largo plazo de las concentraciones transitorias de demandas químicas de oxígeno (DQO) sobre el rendimiento de una celda de combustible microbiana. A partir de los resultados obtenidos, se observó que el cambio repetitivo en la tasa de carga de DQO durante 12 h condicionó el comportamiento del sistema durante períodos de hasta 7 días. Las principales modificaciones fueron la mejora de la tasa de consumo de DQO y la corriente ejercida. Estas mejoras produjeron un aumento de las eficiencias de Coulombic (CE) cuando se trabaja con concentraciones de DQO de 300 mg / L, pero CE constantes cuando se trabaja con concentraciones de DQO de 900 a 1800 mg / L. Este efecto podría explicarse por la mayor afinidad por el sustrato de Geobacter que por los organismos no electrogénicos como Clostridia.

Germline gain‐of‐function MMP11 variant results in an aggressive form of colorectal cancer

Abstract Matrix metalloproteinase-11 (MMP11) is an enzyme with proteolytic activity against matrix and nonmatrix proteins. Although most MMPs are secreted as inactive proenzymes and are later activated extracellularly, MMP11 is activated intracellularly by furin within the constitutive secretory pathway. It is a key factor in physiological tissue remodeling and its alteration may play an important role in the progression of epithelial malignancies and other diseases. TCGA colon and colorectal adenocarcinoma data showed that upregulation of MMP11 expression correlates with tumorigenesis and malignancy. Here, we provide evidence that a germline variant in the MMP11 gene (NM_005940: c.232C>T; p.(Pro78Ser)), identified by whole exome sequencing, can increase the tumorigenic properties of colorectal cancer (CRC) cells. P78S is located in the prodomain region, which is responsible for blocking MMP11's protease activity. This variant was detected in the proband and all the cancer-affected family members analyzed, while it was not detected in healthy relatives. In silico analyses predict that P78S could have an impact on the activation of the enzyme. Furthermore, our in vitro analyses show that the expression of P78S in HCT116 cells increases tumor cell invasion and proliferation. In summary, our results show that this variant could modify the structure of the MMP11 prodomain, producing a premature or uncontrolled activation of the enzyme that may contribute to an early CRC onset in these patients. The study of this gene in other CRC cases will provide further information about its role in CRC development, which might improve patient treatment in the future