1,720,986 research outputs found
Una valutazione sperimentale della variabile affidabilità nella definizione della funzione costo del trasporto delle merci
No full textUna valutazione sperimentale della variabile affidabilità nella definizione della funzione costo del trasporto delle merci
No full textUmbelliferone and esculetin: inhibitors or substrates for polyphenol oxidases?
Full text linkRecently, an interesting debate arose about the nature (substrate versus inhibitor) of esculetin, a coumarin derivative, for mushroom polyphenol oxidase (PPO). The present study examined the behavior of PPOs preparations from fungal and plant origin towards esculetin as a substrate. Both enzymes were able to oxidize esculetin though at a slow rate. A higher sensitivity was reached when the assay was performed in the presence of 3-methyl-2-benzothiazolinone hydrazone (MBTH) even with a lower amount of PPO. These observations unambiguously confirmed that esculetin has to be considered a substrate for mushroom polyphenol oxidase. The oxidation of esculetin was also demonstrated for the first time by a fungal laccase. This should be taken into account because some mushroom PPO preparations could exert contaminant laccase activity. In addition, a PPO preparation from Ferula communis was demonstrated to use esculetin as a substrate. Umbelliferone, the monophenolic precursor of esculetin along the phenylpropanoid pathway, behaved as a competitive inhibitor for the monophenolase activity of mushroom PPO with a K(i) value = 0.014 mM. This is worth a mention because only a few couples of mono- and corresponding o-diphenol show such opposite behavior towards PPO. A possible role of PPO in the esculetin fate along biosynthesis pathway of coumarin derivatives is also discusse
Fe(III)-5,10,15,20-tetrakis(pentafluorophenyl)porphine supported on pyridyl-functionalized, crosslinked poly(vinyl alcohol) as a biomimetic versatile-peroxidase-like catalyst
No full textThis paper describes the immobilization of the commercial synthetic tetrakis(pentafluorophenyl) porphine-iron(III) chloride on pyridyl-functionalized crosslinked poly(vinyl alcohol) and the catalytic activity of the adduct towards oxidation of selected organic substrates by hydrogen peroxide. The obtained adduct was characterized by UV/vis and IR spectroscopies. It showed a noticeable lignin-peroxidase-like catalytic activity; moreover a dramatic activity enhancement was observed in the presence of Mn(2+) under certain experimental conditions, so the preparation could well be classified as a manganese-peroxidase-like catalyst leading to a transient Mn(III) species. Conversion yields for some aromatic compounds (bio)chemically related to lignin, kinetics and operational features of the adduct are also reporte
3-Hydroxykynurenine as a substrate/activator for mushroom tyrosinase
No full text3-Hydroxykynurenine is a tryptophan metabolite with an o-aminophenol structure. It is both a tyrosinase activator and a substrate, reducing the lag phase, stimulating the monophenolase activity, and being oxidized to xanthommatin. In the early stage of monophenol hydroxylation, catechol accumulation takes place, whereas 3-hydroxykynurenine is substantially unchanged and no significant amounts of the o-quinone are produced. These results suggest an activating action of 3-hydroxykynurenine toward o-hydroxylation of monophenols. 3-Hydroxykynurenine could therefore well act as a physiological device to control phenolics metabolism to catechols and quinonoids. (C) 2003 Elsevier Science (USA). All rights reserved
Evaluation of antioxidant capacity of antioxidant-declared beverages marketed in Italy
No full textClinical literature suggests a negative correlation between fruit juice consumption and the occurrence of various diseases. Consequently, many commercially available beverages are based on fruit juices or green tea extracts with specific additives that increase their antioxidant power. In order to fully estimate their potential antioxidant capacity, several products marketed in Italy were analyzed for total phenolics and flavonoids, DPPH scavenging activity, TEAC, FRAP and ORAC-PYR. On average, fruit-based samples had more antioxidants than green teas, but specific additives significantly improved total antioxidant power. Differences between these samples and plain fruit juices were also evaluated. Total antioxidant supply remained almost constant during the entire shelf life of the products
Degradation of Alizarin Red S under mild experimental conditions by immobilized 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine-Mn(III) as a biomimetic peroxidase-like catalyst
No full textAlizarin Red S, an industrially important anthraquinone dye coming from alizarin sulfonation, is a widespread polluting dye, whose inexpensive and environmental friendly elimination from effluents is a serious challenge. In this study we report its decoloration and partial mineralization by H(2)O(2) in the presence of the heterogeneous catalyst obtained from 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine-Mn(III) immobilized on a modified silica support bearing imiclazole functionality. The bleaching process was efficient and took place under very mild experimental conditions, where it mainly led to phthalic acid. Some operational features of the catalytic reaction are described and a chemical mechanism for the bleaching is proposed. Most efficient decoloration was seen at pH 7, the process most probably passing through an unstable anthradiquinone. Also some kinetic features of the catalyst have been studied, and a substrate saturation behavior for both hydrogen peroxide and the dye was observed and quantitatively determined. (C) 2008 Elsevier B.V. All rights reserved
An adaptive nonlinear autoregressive ANN model for high time resolution traffic noise predictions. Experimental results for a port city waterfront
Full text linkIn this research study an adaptive recurrent artificial nonlinear neural network identification model has been developed and experimentally tested for dynamically predicting the traffic noise level Leq,1′ with a time refine ment of 1 min. The model has been successfully applied in three selected positions, representative of the waterfront in a Mediterranean port city. Several maritime cities are exposed to a wide range of road traffic fluctuations that negatively impact liveability in the area concerned. Large volumes of road traffic periodically access the port, dynamically affecting the acoustic scenario in neighbouring areas, especially in seaside towns during the tourist season. A signalized intersection, a roundabout, and a wide entrance to a vehicular underpass have been analyzed in the course of two characteristic periods, during which traffic ranged widely from normal to peak yearly intensity. Detailed traffic data for 15 road lanes and noise sequence regressors have been considered as input data sources. This exploratory investigation reveals a good predictive performance of the
model developed, the prediction error of Leq,1′ falling prevalently within the range ±0.5 dB. The experimental profile of Leq,1′ is well reflected by the simulated sequence, and the auto and cross correlation functions confirm how well the identified neural model is able to explain the functional dependence underlying the experimental observations
Removal of pollutant load from animal wastewaters using a mixed bacterial culture and September 25-28, 2014
No full textTyrosinase inhibition: general and applied aspects
No full textThe active site of tyrosinase is described with a view to depicting its interactions with substrates and inhibitors. Occurrence and mechanism(s) of tyrosinase-mediated browning of agrofood products are reviewed, with regard to both enzymic and chemical reactions, and their control, modulation, and inhibition. Technical and applicational implications are discussed
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