University of Coimbra

About: University of Coimbra is a education organization based out in Coimbra, Portugal. It is known for research contribution in the topics: Population & Context (language use). The organization has 14318 authors who have published 43067 publications receiving 994733 citations. The organization is also known as: UC & Universidade dos Estudos Gerais.

Electrochemical Oxidation of Quercetin

Abstract: The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square-wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3,4-dihydroxyl electron-donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible.

Synergistic effects of water temperature and dissolved nutrients on litter decomposition and associated fungi

Abstract: In woodland streams, the decomposition of allochthonous organic matter constitutes a fundamental ecosystem process, where aquatic hyphomycetes play a pivotal role. It is therefore greatly affected by water temperature and nutrient concentrations. The individual effects of these factors on the decomposition of litter have been studied previously. However, in the climate warming scenario predicted for this century, water temperature and nutrient concentrations are expected to increase simultaneously, and their combined effects on litter decomposition and associated biological activity remains unevaluated. In this study, we addressed the individual and combined effects of water temperature (three levels) and nutrient concentrations (two levels) on the decomposition of alder leaves and associated aquatic hyphomycetes in microcosms. Decomposition rates across treatments varied between 0.0041dayˉ¹ at 5°C and low nutrient level and 0.0100 dayˉ¹ at 15°C and high nutrient level. The stimulation of biological variables at high nutrients and temperatures indicates that nutrient enrichment of streams might have a higher stimulatory effect on fungal performance and decomposition rates under a warming scenario than at present. The stimulation of fungal biomass and sporulation with increasing temperature at both nutrient levels shows that increases in water temperature might enhance fungal growth and reproduction in both oligotrophic and eutrophic streams. The stimulation of fungal respiration and litter decomposition with increasing temperature at high nutrients indicates that stimulation of carbon mineralization will probably occur at eutrophied streams, while oligotrophic conditions seem to be 'protected' from warming. All biological variables were stimulated when both factors increased, as a result of synergistic interactions between factors. Increased water temperature and nutrient level also affected the structure of aquatic hyphomycete assemblages. It is plausible that if water quality of presently eutrophied streams is improved, the potential stimulatory effects of future increases in water temperature on aquatic biota and processes might be mitigated.

Natural Treg cells spontaneously differentiate into pathogenic helper cells in lymphopenic conditions

Abstract: Induction of Forkhead-box p3 (Foxp3) expression in developing T cells upon peptide-MHC encountering has been proposed to define a lineage of committed Treg cells. However, sustained expression of Foxp3 is required for Treg function and what maintains Foxp3 expression in peripheral Treg remains obscure. To address this issue, we monitored natural Treg phenotype and function upon adoptive transfer into lymphocyte-deficient mice. We first show that about 50% of Foxp3-GFP+ Treg isolated from Foxp3gfp KI animals loose Foxp3 expression in severe lymphopenic conditions. We next evidence that the cytokine IL-2, either produced by co-transferred conventional T cells or administrated i.v. prevents Foxp3 downregulation. Moreover, we document that Treg that lost Foxp3 expression upon adoptive transfer produce IL-2 are not suppressive and promote tissue infiltration and damage upon secondary transfer into alymphoid mice. Our findings that Treg convert into pathogenic Th cells in absence of IL-2 provide new clues to the success of Treg-based immune therapies.