1,053 research outputs found
Synthesizing extensional constraints in Ontology-based Data Access
No full textSeveral recent techniques and tools for Ontology-based Data Access (OBDA) make use of the so-called extensional constraints (a.k.a. ABox dependencies). So far, extensional constraints have been mainly considered in a setting where data are represented in an ABox, instead of external data sources connected to the ontology through declarative mappings. Moreover, the issue of how to generate extensional constraints in practice has not been addressed yet. In this paper we first provide a formal account of the notion of extensional constraints in a full-fledged OBDA setting, where an ontology is connected to the data sources of the information system by means of mappings, and then present an approach to the automatic generation of extensional constraints in such a setting. The technique we propose is based on the use of a first-order theorem prover that checks validity of relevant formulas built over the mapping views. The experiments we have carried out in real-world OBDA projects show the effectiveness of our approach in discovering large collections of extensional constraints entailed by the OBDA specification
Preferential Orientation of Fulleropyrrolidine Bisadducts in E7 Liquid Crystal: a Time Resolved EPR Study
No full textSpin correlated radical ion pairs generated by photoinduced electron transfer in composites of sexithiophene/fullerene derivatives: a transient EPR study
No full textPhotoinduced electron transfer was observed in a series of methylsulfanyl sexithiophene/fulleropyrrolidine composites deposited as films. Paramagnetic states were observed by transient EPR spectroscopy in the microseconds time domain. The spectra displayed polarized lines with characteristic antiphase emission/absorption pattern of spin polarization and were assigned to spin correlated radical ion pairs (SCRP) formed by intermolecular electron transfer from sexithiophene donor to C-60 fullerene acceptor molecules. Also transient signals detected at selected magnetic fields showed phase effects that are typical of SCRPs, Spectrum simulation was obtained by allowing for a distribution of respective orientations of the dipolar axes and g-tensors of partners in a pair. Fitting parameters used for one composite were D/g beta = -135 muT and J/g beta = 2.5 muT for dipolar and spin exchange coupling constants, corresponding to an interradical mean distance of 27.4 Angstrom. Similar values were obtained for the other examined systems. Pair structure and dynamics suggest to ascribe the charge-separated state to a radical pair generated after a hopping of the electron-hole charges from a primary pair originated in neighbor molecular sites
Biostimulant Action of Protein Hydrolysates: Unraveling Their Effects on Plant Physiology and Microbiome
No full textPlant-derived protein hydrolysates (PHs) have gained prominence as plant biostimulants because of their potential to increase the germination, productivity and quality of a wide range of horticultural and agronomic crops. Application of PHs can also alleviate the negative effects of abiotic plant stress due to salinity, drought and heavy metals. Recent studies aimed at uncovering the mechanisms regulating these beneficial effects indicate that PHs could be directly affecting plants by stimulating carbon and nitrogen metabolism, and interfering with hormonal activity. Indirect effects could also play a role as PHs could enhance nutrient availability in plant growth substrates, and increase nutrient uptake and nutrient-use efficiency in plants. Moreover, the beneficial effects of PHs also could be due to the stimulation of plant microbiomes. Plants are colonized by an abundant and diverse assortment of microbial taxa that can help plants acquire nutrients and water and withstand biotic and abiotic stress. The substrates provided by PHs, such as amino acids, could provide an ideal food source for these plant-associated microbes. Indeed, recent studies have provided evidence that plant microbiomes are modified by the application of PHs, supporting the hypothesis that PHs might be acting, at least in part, via changes in the composition and activity of these microbial communities. Application of PHs has great potential to meet the twin challenges of a feeding a growing population while minimizing agriculture’s impact on human health and the environment. However, to fully realize the potential of PHs, further studies are required to shed light on the mechanisms conferring the beneficial effects of these products, as well as identify product formulations and application methods that optimize benefits under a range of agro-ecological conditions
Differential scanning calorimetry (DSC) as a tool for studying thermal properties of a crude cellulase cocktail
No full textDifferential scanning calorimetry (DSC) was used as an efficient and rapid tool in studying the conformational transitions between the folded and unfolded structures of cellulolytic enzymes. The thermal properties of two crude hydrolytic enzyme cocktails containing extracellular cellulases from Trichoderma longibrachiatum DIBAF-10 were analyzed and compared with three commercial cellulase preparations. Differences in the thermal behavior of fungal cellulases in the liquid phase, freeze-dried state, liquid formulations in sodium citrate buffer (pH 4.8), and contact with cellulose, carboxymethyl cellulose, and cellobiose were evaluated. DSC profiles of cellulases from the DIBAF-10 strain provided important thermodynamic information about the thermal stability of the included proteins. Crude enzyme cocktails underwent a reproducible and irreversible exothermic aggregation phenomenon at 52.45 +/- 0.90 degrees C like commercial beta-glucosidase. Freeze-dried and resuspended in a sodium citrate buffer, cellulases from T. longibrachiatum showed an endothermic peak dependent on buffer and enzyme concentration. In the enzyme-substrates systems, a shift of the same peak was recorded for all substrates tested. The thermal analysis of freeze-dried cellulase samples in the range of 20-150 degrees C gave information on the denaturation process. In conclusion, we demonstrated that DSC is a cost-effective tool for obtaining "conformational fingerprinting " of crude fungal cellulase preparations.[Graphics
Fullerene derivatives embedded in poly(methylmethacrylate): a laser flash photolysis and time-resolved EPR study
No full textWe have found that the addition of N-methylfulleropyrrolidine to poly(methylmethacrylate) (PMMA), during the thermal polymerization route, produces a new fullerene adduct that has been characterized by time-resolved optical and EPR methods. In fact, a new component appears in the differential absorption spectrum with a lifetime of 350 mu s and a maximum at 850 nm besides the typical component due to fullerene adducts centered around 700 nm, The new component has been attributed to a fullerene adduct crosslinked to the PMMA chains, supporting the active role of such a polymer matrix in modifying the optical properties of fullerene. Time-resolved electron paramagnetic resonance (TREPR) spectrum of this new species exhibits zfs parameters and spin polarization that are similar to those observed for a trans3-trans3-trans3 adduct in a toluene matrix
Inconsistency-tolerant Query Answering in Ontology-based Data Access
No full textOntology-based data access (OBDA) is receiving great attention as a new paradigm for managing information systems through semantic technologies. According to this paradigm, a Description Logic ontology provides an abstract and formal representation of the domain of interest to the information system, and is used as a sophisticated schema for accessing the data and formulating queries over them. In this paper, we address the problem of dealing with inconsistencies in OBDA. Our general goal is both to study DL semantical frameworks that are inconsistency-tolerant, and to devise techniques for answering unions of conjunctive queries under such inconsistency-tolerant semantics. Our work is inspired by the approaches to consistent query answering in databases, which are based on the idea of living with inconsistencies in the database, but trying to obtain only consistent information during query answering, by relying on the notion of database repair. We first adapt the notion of database repair to our context, and show that, according to such a notion, inconsistency-tolerant query answering is intractable, even for very simple DLs. Therefore, we propose a different repair-based semantics, with the goal of reaching a good compromise between the expressive power of the semantics and the computational complexity of inconsistency-tolerant query answering. Indeed, we show that query answering under the new semantics is first-order rewritable in OBDA, even if the ontology is expressed in one of the most expressive members of the DL-Lite family
Vanillin production using metabolically engineered <it>Escherichia coli </it>under non-growing conditions
No full textAbstract Background Vanillin is one of the most important aromatic flavour compounds used in the food and cosmetic industries. Natural vanillin is extracted from vanilla beans and is relatively expensive. Moreover, the consumer demand for natural vanillin highly exceeds the amount of vanillin extracted by plant sources. This has led to the investigation of other routes to obtain this flavour such as the biotechnological production from ferulic acid. Studies concerning the use of engineered recombinant Escherichia coli cells as biocatalysts for vanillin production are described in the literature, but yield optimization and biotransformation conditions have not been investigated in details. Results Effect of plasmid copy number in metabolic engineering of E. coli for the synthesis of vanillin has been evaluated by the use of genes encoding feruloyl-CoA synthetase and feruloyl hydratase/aldolase from Pseudomonas fluorescens BF13. The higher vanillin production yield was obtained using resting cells of E. coli strain JM109 harbouring a low-copy number vector and a promoter exhibiting a low activity to drive the expression of the catabolic genes. Optimization of the bioconversion of ferulic acid to vanillin was accomplished by a response surface methodology. The experimental conditions that allowed us to obtain high values for response functions were 3.3 mM ferulic acid and 4.5 g/L of biomass, with a yield of 70.6% and specific productivity of 5.9 μmoles/g × min after 3 hours of incubation. The final concentration of vanillin in the medium was increased up to 3.5 mM after a 6-hour incubation by sequential spiking of 1.1 mM ferulic acid. The resting cells could be reused up to four times maintaining the production yield levels over 50%, thus increasing three times the vanillin obtained per gram of biomass. Conclusion Ferulic acid can be efficiently converted to vanillin, without accumulation of undesirable vanillin reduction/oxidation products, using E. coli JM109 cells expressing genes from the ferulic acid-degrader Pseudomonas fluorescens BF13. Optimization of culture conditions and bioconversion parameters, together with the reuse of the biomass, leaded to a final production of 2.52 g of vanillin per liter of culture, which is the highest found in the literature for recombinant strains and the highest achieved so far applying such strains under resting cells conditions.</p
Characterization of cellulases produced by trichoderma longibrachiatum DIBAF-10 using differential scanning calorimetry
No full textConversion of cellulose to soluble sugars by enzymatic hydrolysis is a key step for production of biofuels from lignocellulosic biomass. Efficient hydrolysis of cellulose requires the action of three different classes of enzymes: endoglucanase (1,4-β-d-glucan glucohydrolase [EC 3.2.1.4]), exoglucanase (1,4-β-d-glucan cellobiohydrolase [EC 3.2.1.91]), and β-glucosidase (β-d-glucoside glucohydrolase, [EC3.2.1.21]) [1]. Trichoderma longibrachiatum DIBAF-10 produced a cellulase cocktail tailored for the saccharification of milk thistle (Silybum marianum) with the potential to compete with commercial enzymes.
In this study, crude cellulase preparations from T. longibrachiatum DIBAF-10 were thermally studied by differential scanning calorimetry (DSC), to assess the conformational transitions between the folded and unfolded structure of the proteins and the relationship between them and the energetics of their stability. Generally, the aggregation can take place concurrently with the irreversible thermal denaturation and the conformational unfolding or accompanies an exothermal effect that results in formation of precipitation [2]. The study of thermal properties is essential to better characterize and understand the interactions between cellulase and its substrates and their dependence on temperature. In fact, enzyme thermo-stability is essential during saccharification reaction because steam is always used to make the substrates more suitable for the enzymatic hydrolysis [3].
The present work shows that DSC profiles of crude enzyme samples from T. longibrachiatum DIBAF-10 provide important thermodynamic information, about the thermostability of the included proteins. The thermograms of crude enzyme coktails, and of the commercial ones, show similar exothermic peaks at 52,45±0,90°C and 49,5±0,95°C, respectively, and comparable H values. This is probably due to the same conformational change leading to aggregation of proteins.
DSC, moreover, is cost-effective tool to obtain “conformational fingerprinting” of the crude enzyme cellulase preparations
A noncovalently linked, dynamic fullerene porphyrin dyad. Efficient formation of long-lived charge separated states through complex dissociation
No full textPhotoexcitation of a Zn-tetraphenyl porphyrin-fullerene complex leads to electron-transfer with very long lifetimes of the charge-separated pairs
- …
