1,721,095 research outputs found
La critica dei soggetti collettiva tra l'Ideologia tedesca e il Diciotto Brumaio
No full textThis essay first takes into account a methodological issue, which concerns the relationship between two very different writings such as The German Ideology and The 18 Brumaire of Louis Bonaparte. Starting from the highlighting of their continuity in the construction of the materialist approach to history by Marx and Engels, the essay develops the Marxian critique of bourgeois political concepts (constitution, people, democracy, etc.), which allows the author to show the dichotomous character of capitalist society, as well as the fiction of any attempt to unify it. On the contrary, Marx shows how the class struggle continuously divides any attempt to give life to a unitary collective subject, and how any project of institutionalisation of the conflict is always challenged by the original contradiction, which manifests itself first of all on the imaginative level and on the level of passions, first of all fear
Percorsi dell'emancipazione: oltre il dualismo tra soggetto individuale e soggetto collettivo
No full textL'emancipazione costituisce una posta in gioco cruciale nell'intero itinerario di Marx (e di Engels), risultando sorretta dal tentativo politico di superamento della dicotomia moderna fra soggetto individuale e soggetto collettivo. Tale elemento si distende fra teoria e politica. Si rivela necessario tenere in costante considerazione lo stretto nesso, ma nello stesso tempo il mai perfetto compattamento fra le dimensioni indicate
Candida freyschussii: an oleaginous yeast producing lipids from glycerol
No full textA surplus of glycerol is obtained from biodiesel manufacturing and represents a waste product whose applications are lacking. Thus, the use of glycerol as substrate for fermentation processes yielding valuable products is very attractive. In this study, the utilization of glycerol as a growth substrate for the cultivation of oleaginous yeasts was explored with the aim to produce microbial oils. Forty strains of environmental non-conventional yeasts belonging to 19 different species were screened for the ability to grow on glycerol and produce intracellular lipids in a medium containing an excess of this carbon source (C:N = 48:1). Three strains, belonging to the species Candida freyschussii, Pichia farinosa, and Saccharomyces spencerorum, depleted 40 g/L glycerol within 120 h and produced intracellular lipids. C. freyschussii yielded the highest amounts, lipids accounting for the 33 % of biomass on dry basis. 1H-NMR analysis revealed that the lipid extract did not contain detectable free fatty acids and was composed mostly of triacylglycerols. Lipid composition, determined by GC-MS analysis, was similar to plant oils, and may be optimal feedstock for biodiesel production, being dominated by monounsaturated C16 and C18. As in other oleaginous yeasts, lipid production by C. freyschussii sp. increased with the increase of the C:N ratio of the medium, but growth was inhibited at glycerol concentrations higher than 40 g/L. As a result, lipid production was the highest with 40 g/L glycerol, yielding 4.7 g/L lipids, with a mean volumetric productivity of 0.15 g/L/h. In order to prevent growth inhibition over 40 g/L glycerol and extend the lipogenic phase, different fed-batch strategies were tried. The best performing processes took advantage from the feeding with concentrated media exhibiting the same C:N ratio of the basal medium, leading to very productive high cell density cultures. With the continuous feeding of 20X-concentrated medium, 29 g/L lipids (i.e. the 32 % of biomass) were obtained in 100 h of cultivation, with a mean volumetric productivity of 0.30 g/L/h. The values herein reported are among the highest yield and productivity values ever obtained for fermentative processes exploiting oleaginous fungi to produce lipids from glycerol. Therefore, C. freyschussii could be considered as an interesting microorganism to convert glycerol into microbial oils for biofuel industr
Glutaryl-7-ACA acylase: a new tool for the biocatalyzed kinetic resolution of racemic amines and alcohols
No full textThe enzymes D-amino acid oxidase and glutaryl-7-ACAacylase (GA) are currently utilised for the industrial productionof 7-aminocephalosporanic acid (7-ACA, 2), an importantprecursor of semisyntetic cephalosporins. Specifically,GA is devoted to the cleavage of the amide bond betweenglutaric acid and 7-ACA in the intermediate glutaryl-7-ACA(1).The synthetic performances of this enzyme towards 1have been widely investigated, while very little is known onGA substrate specificity.We have found that an industrial GAis very specific for the acyl moiety that has to be released, theglutaryl derivatives being by far the best substrates. On theother hand, this enzyme accepts a wide variety of “leavinggroups”. Not only N-glutarate of b-lactam derivatives, butalso N-glutaryl aminoacids as well as N-glutarylamides (aromaticand aliphatic) could be hydrolysed by GA, which, additionally,showed a significant esterase activity. Morenotably, GA-catalysed hydrolyses were highly enantioselectiv
Kinetic resolutions of racemic amines and alcohols catalyzed by an industrial glutaryl-7-aminocephalosporanic acid acylase with unexpected broad substrate specificity
No full textAn industrial glutaryl-7-aminocephalosporanic acid acylase (GAR) possesses a significant broad substrate specificity that crosses over the usual cephalosporanic skeleton. Enantioselective amidase and even esterase activities have been observed with all the glutarates of racemic substrates investigated, with a stereopreference for the (S)-enantiomer. The different physical-chemical properties of reagents and products allow their easy separation by solvent extraction, avoiding cumbersome chromatography or distillation processes during reaction work-up. (C) 2003 Elsevier Science Ltd. All rights reserved
Enantioselective esterase activity of an industrial glutaryl acylase
No full textThe unexpected esterase activity of an industrial glutaryl acylase was investigated. Glutaryl esters of a series of primary and secondary alcohols as well as of phenols were all efficiently hydrolyzed, the only exception being the sterically hindered glutarate of thymol. The enantioselectivities of the acylase, which were evaluated with three of these substrates, were quite low (E values ranging between 1.9 and 7.2), but were significantly improved by substrate and/or solvent engineering. Enantiomerically enriched hydrolyzed alcohols and unreacted glutarates can be easily separated by selective extraction, thus avoiding chromatographic steps
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