Acide butanoïque

Résumé

L'acide butanoïque, aussi appelé acide butyrique du grec βουτυρος (beurre), est un acide carboxylique saturé de formule CH3CH2CH2-COOH On le trouve par exemple dans le beurre rance, le parmesan, et le contenu gastrique, où il dégage une odeur forte et désagréable. L'acide butyrique peut être perçu à partir d'environ selon les sources. Dans des conditions normales de température et de pression, l'acide butanoïque est un liquide légèrement huileux qui se solidifie à et dont le point d'ébullition est de . Il est facilement soluble dans l'eau, l'éthanol, et l'éther et se dissocie de son solvant par l'addition de chlorure de calcium. Le dichromate de potassium et l'acide sulfurique l'oxydent en dioxyde de carbone et en acide acétique, alors que le permanganate de potassium alcalin l'oxyde seulement en dioxyde de carbone. De plus, il a pour isomère de constitution l'acide 2-méthylpropanoïque, qui lui doit son deuxième nom d'acide isobutyrique. C'est aussi un acide gras à courte chaîne

Source officielle

https://fr.wikipedia.org/wiki/Acide_butano%C3%AFque

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MR is a well-established technique routinely used in preclinical and clinical studies. This thesis focussed on the improvement of sensitivity of different methods in MR. Hyperpolarized 129Xe gas is used for studying pulmonary disease or cerebral perfusion. When hyperpolarization is conducted inside a polarizer, the achieved solid state polarization is currently limited to a few percent. One aim of this thesis was to counteract this bottleneck by investigating the effect of microwave frequency modulation for different spin systems. An increase in nuclear 129Xe spin polarization up to 14.5% was achieved compared to the polarization obtained without frequency modulation. Electron spin-lattice relaxation times T1S, as short as 5 ms, correlated directly with the gain in 129Xe nuclear polarization due to microwave frequency modulation, irrespective of the solvent or its deuteration. Simulations of the electron spin system confirmed that microwave frequency modulation could be an efficient method to considerably enhance nuclear spin polarization in short T1S matrices or in the presence of large linewidth radicals by promoting spectral diffusion. DNP matrices can also be hyperpolarized through non-persistent radicals generated by UV-irradiation. They have the advantage of quenching upon dissolution, yielding a hyperpolarized solution with no need for radical filtration. Radical precursors researched up to date either yielded low 13C polarization, contained toxic matrix components or interfered with metabolic processes. Therefore, the two novel endogenously-occurring precursors, alpha-ketovalerate (akV) and alpha-ketobutyrate (akB) were investigated. Liquid state polarization of the metabolic substrate glucose increased to 16.3% using akB compared with 13.3% obtained with pyruvate. [1-13C]butyric acid was polarized to 12.1% for akV and 12.9% for akB and used for in vivo hyperpolarized cardiac MRS. Hyperpolarized [1-13C]butyrate metabolism in the heart revealed label incorporation into a wide range of metabolites. This study demonstrated the potential of using UV-induced radicals generated in the endogenously-occurring metabolites akV and akB as polarizing agents, enabling high polarization without requiring radical filtration for radical-free hyperpolarized MRI. While MRI requires RF coils that generate high B1 homogeneity, MRS strongly depends on high sensitivity and potentially high B1 efficiency to allow for short-TE acquisitions. Two custom-made 1H coils resonating at 600 MHz, a single-channel saddle coil and an 8-leg quadrature birdcage coil, were investigated with respect to those criteria for applications at ultra-high field (14.1 T). The saddle coil yielded a 54% higher transmit field efficiency with a 20% higher SNR compared to the birdcage coil after full-FOV corrections. Using the saddle coil in glycoCEST imaging of a homogeneous phantom resulted in an MTR asymmetry coefficient of variation as small as 5.2% over an 11 mm diameter ROI. Overall, the saddle coil provided a good compromise between globally homogeneous excitation and high sensitivity. Finally, it was successfully used to map skeletal muscle glycogen content in vivo. This thesis focused on improving MR sensitivity by means of adequate custom-made RF coils as well as DNP through the implementation of a method capitalizing on electronic spin properties and the development of novel endogenous precursors for in vivo hyperpolarized MRI.

EPFL2021

Chargement

Labor division in engineered cross-kingdom consortia: Consolidated bioprocessing of lignocellulosic biomass to carboxylic acids

Robert Lawrence Shahab

Lignocellulose is a renewable source of fixed carbon and a promising substrate for the production of chemicals and fuels in second generation biorefineries. In this thesis, we engineered artificial microbial consortia for consolidated bioprocessing (CBP) of lignocellulose to carboxylic acids and ethanol. Inspired by natural ecosystems following the principle of labor division, we distributed the required metabolic capabilities among different specialized microorganisms. As a vast majority of product-forming microorganisms is non-cellulolytic the fungus Trichoderma reesei was employed to produce cellulolytic enzymes. For the production of lactic acid from steam-pretreated beech wood, the aerobic fungus T. reesei was co-cultivated with the non-cellulolytic facultative anaerobic bacterium Lactobacillus pentosus. The known instability problem of such a cooperator-cheater community was overcome by enforced niche differentiation. To this end, a novel stirred tank bioreactor was engineered that was equipped with a continuously aerated, oxygen permeable membrane that locally provided oxygen for the aerobic fungus in an otherwise anaerobic bioreactor. The success of this strategy was shown by the formation of a fungal biofilm on the membrane's surface and a lactic acid concentration of 19.8 gL-1 (85.2 % of theoretical maximum). For the production of various carboxylic acids, obligate and strict anaerobic bacteria were added to the community of T. reesei and L. pentosus. The lactic acid bacterium metabolically funneled the heterogeneous lignocellulosic carbohydrates to lactate as central intermediate in synthetic food chains and with that, compensated for missing metabolic capabilities of the anaerobic secondary fermenters. The feasibility and modularity of the lactate platform was shown by the direct production of acetic, propionic, butyric, valeric and hexanoic acid from beech wood. Integration of the obligate anaerobes Clostridium tyrobutyricum or Veillonella criceti resulted in 196.5 kg butyric acid or 113.6 kg propionic and 133.3 kg acetic acid, respectively, per ton beech wood. For the production of mixtures of volatile fatty acids (VFAs) with up to six carbon atoms from beech wood the non-cellulolytic strict anaerobe Megasphaera elsdenii was integrated into the lactate platform and 220 kg total VFAs per ton beech wood were produced. By adding C. tyrobutyricum or V criceti to a three-member microbial community it was shown that the ratio of odd- and even-numbered VFAs can be tuned through intra-consortium competition. For the production of ethanol from lignocellulose, T. reesei and Saccharomyces cerevisiae were co-cultivated. They formed a two-layered biofilm on the aerated membrane. The in situ degradation of ethanol was dedicated to aerobic metabolism and strategies to tune the oxygen supply were provided. An advanced bioreactor was engineered and applied that provided multiple niches for the co-cultivation of microorganisms with highly diverse requirements for abiotic parameters (e.g. oxygen, light) to widen the product range. The demonstrated co-cultivation of T. reesei and the microalgae Chlamydomonas reinhardtii in a two-layered biofilm is an important milestone towards the direct production of lipids from lignocellulose. The results of this thesis illustrate the potential of community-based CBP of renewable lignocellulosic biomass to fuels and chemicals in second generation biorefineries in tomorrow's bioeconomy.

EPFL2019

Chargement

Transient gene expression (TGE) is based on episomal DNA expression. This technique is used for the production of recombinant proteins that can be used as therapeutics. TGE is for example extremely useful for shortening the time between candidate proteins screening and their production. Understanding and optimizing TGE is a major concern in the field of recombinant proteins. Thus, we selected here two different approaches to further improve TGE. First, we studied effect of signal peptide (SP) modification on TNFR-Fc protein in transiently transfected HEK293E and CHO-DG44 cells. Secondly, we studied effect of Valproic acid on the production of TNFR-Fc protein in HEK293E cells and on its influence on plasmid methylation. Modification of TNFR-Fc was done with eighteen others SPs. Artificial SPs exhibiting different scores using a prediction method and SPs coming from naturally secreted proteins were tested. None of them could induce a better secretion than the native SP. Nevertheless, they all showed comparable secretion abilities, except one that could not induce protein secretion. We showed here that SP modification could not increase protein secretion in HEK293E or in CHO-DG44. But also that without a valid SP, protein secretion is inhibited. Addition of VPA in HEK293E cells transfected with pXLG-A3 plasmid increased IgG productivity by 11 fold. Nevertheless, we showed here that VPA did not increase TNFR-Fc productivity to the same extent (1.2 fold) even by optimization of its concentration. Furthermore, we investigated the effect of plasmid methylation (TNFRFc and IgG) on TGE using VPA. We found that IgG expression was less influenced by this modification than TNFR-Fc. In fact, TNFR-Fc plasmid methylation drastically decreased specific productivity (0.2 fold). And VPA could almost entirely compensate this effect (0.8 fold). We therefore hypothesized that VPA has an impact on pDNA methylation in the context of TGE.

2011

Chargement

EPFL2021

Labor division in engineered cross-kingdom consortia: Consolidated bioprocessing of lignocellulosic biomass to carboxylic acids

Robert Lawrence Shahab

EPFL2019