Redox (In)activations of Metalloenzymes: A Protein Film Voltammetry Approach

International audienceRedox metalloenzymes are omnipresent in living organisms where they catalyze key cellular reactions with great efficiency. These enzymes can often be reversibly placed into inactive states following changes in redox conditions. This is a hindrance for their use in biotechnological devices, and also a complication for their study via a structure/function approach, because structural data alone usually is not enough to discriminate between active and inactive states. However, these inactive states can also inform on the chemistry of the enzyme's active sites and on their catalytic cycles. A technique that has proved particularly valuable in the last decades for studying these processes is protein film voltammetry (PFV), in which an enzyme is immobilized on an electrode in a configuration where direct electron transfer is possible. In this article, we review the studies of redox (in)activation processes using PFV, present the theory for a number of cases (reversible inactivations, irreversible activations), and give guidelines to obtain and interpret suitable kinetic data

Carbon Dioxide Utilisation -The Formate Route

UIDB/50006/2020 CEEC-Individual 2017 Program Contract.The relentless rise of atmospheric CO2 is causing large and unpredictable impacts on the Earth climate, due to the CO2 significant greenhouse effect, besides being responsible for the ocean acidification, with consequent huge impacts in our daily lives and in all forms of life. To stop spiral of destruction, we must actively reduce the CO2 emissions and develop new and more efficient “CO2 sinks”. We should be focused on the opportunities provided by exploiting this novel and huge carbon feedstock to produce de novo fuels and added-value compounds. The conversion of CO2 into formate offers key advantages for carbon recycling, and formate dehydrogenase (FDH) enzymes are at the centre of intense research, due to the “green” advantages the bioconversion can offer, namely substrate and product selectivity and specificity, in reactions run at ambient temperature and pressure and neutral pH. In this chapter, we describe the remarkable recent progress towards efficient and selective FDH-catalysed CO2 reduction to formate. We focus on the enzymes, discussing their structure and mechanism of action. Selected promising studies and successful proof of concepts of FDH-dependent CO2 reduction to formate and beyond are discussed, to highlight the power of FDHs and the challenges this CO2 bioconversion still faces.publishersversionpublishe

Planck early results: first assessment of the High Frequency Instrument in-flight performance

The Planck High Frequency Instrument (HFI) is designed to measure the temperature and polarization anisotropies of the Cosmic Microwave Background and galactic foregrounds in six wide bands centered at 100, 143, 217, 353, 545 and 857 GHz at an angular resolution of 10' (100 GHz), 7' (143 GHz), and 5' (217 GHz and higher). HFI has been operating flawlessly since launch on 14 May 2009. The bolometers cooled to 100 mK as planned. The settings of the readout electronics, such as the bolometer bias current, that optimize HFI's noise performance on orbit are nearly the same as the ones chosen during ground testing. Observations of Mars, Jupiter, and Saturn verified both the optical system and the time response of the detection chains. The optical beams are close to predictions from physical optics modeling. The time response of the detection chains is close to pre-launch measurements. The detectors suffer from an unexpected high flux of cosmic rays related to low solar activity. Due to the redundancy of Planck's observations strategy, the removal of a few percent of data contaminated by glitches does not affect significantly the sensitivity. The cosmic rays heat up significantly the bolometer plate and the modulation on periods of days to months of the heat load creates a common drift of all bolometer signals which do not affect the scientific capabilities. Only the high energy cosmic rays showers induce inhomogeneous heating which is a probable source of low frequency noise.Comment: Submitted to A&A. 22 pages, 6 tables, 21 figures. One of a set of simultaneous papers for the Planck Missio

Planck pre-launch status : The Planck mission

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Planck early results. II. The thermal performance of Planck

The performance of the Planck instruments in space is enabled by their low operating temperatures, 20 K for LFI and 0.1 K for HFI, achieved through a combination of passive radiative cooling and three active mechanical coolers. The scientific requirement for very broad frequency coverage led to two detector technologies with widely different temperature and cooling needs. Active coolers could satisfy these needs; a helium cryostat, as used by previous cryogenic space missions (IRAS, COBE, ISO, Spitzer, AKARI), could not. Radiative cooling is provided by three V-groove radiators and a large telescope baffle. The active coolers are a hydrogen sorption cooler (<20 K), a 4He Joule-Thomson cooler (4.7 K), and a 3He-4He dilution cooler (1.4 K and 0.1 K). The flight system was at ambient temperature at launch and cooled in space to operating conditions. The HFI bolometer plate reached 93 mK on 3 July 2009, 50 days after launch. The solar panel always faces the Sun, shadowing the rest of Planck, and operates at a mean temperature of 384 K. At the other end of the spacecraft, the telescope baffle operates at 42.3 K and the telescope primary mirror operates at 35.9 K. The temperatures of key parts of the instruments are stabilized by both active and passive methods. Temperature fluctuations are driven by changes in the distance from the Sun, sorption cooler cycling and fluctuations in gas-liquid flow, and fluctuations in cosmic ray flux on the dilution and bolometer plates. These fluctuations do not compromise the science data

Influence of Surface Defectivity on the Performances of Silicon Heterojunction Solar Cells

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Understanding of the Influence of the Surface Defectivity on Silicon Heterojunction Cell Performance

International audienceThe fabrication process of silicon heterojunction (SHJ) solar cells can induce locally depassivated regions (so-called defectivity) because of transportation steps (contact with belts, trays, etc) or simply the environment (presence of particles embedded within surface thin films). This surface passivation spatial heterogeneity is gaining interest as it may hinder the SHJ efficiency improvements allowed by incremental process steps optimizations. An experimentally-supported simulation study is proposed and applied on full size M2 SHJ cells in order to understand how the local a-Si:H/c-Si interface passivation loss impacts the overall cell performance. A simulation framework (developed on ATLAS Silvaco) was first validated through comparisons with experimental results. This step allowed then to use simulations results further to explore and understand the physics behind the defectivity-induced efficiency loss. The cell performance drop due to depassivated regions was attributed to a bias-dependent minority carrier recombination current flow towards the depassivated region, which is shown to affect mainly the Fill Factor