1,721,095 research outputs found
Exploration of new uracil-based compounds as novel inhibitors of Hepatitis C Virus replication
Full text linkHepatitis C Virus (HCV) is a major public health problem worldwide. While highly efficacious directly-acting antiviral agents have been developed in recent years, their high costs and relative inaccessibility make their use limited. In this thesis, new uracil-based compounds have been evaluated as potential antiviral drugs against HCV. Using several biochemical and virological assays to investigate virus infection and replication, it has been shown that these compounds are able to significantly reduce viral genomic replication with their IC50 values in the nanomolar range. Finally, these compounds have been shown to block the de novo RNA synthesis and that effect is dependent on a chemical structure of the compounds
Using thermoanalytical data: Part 6. Heat transfer contribution in TG/DTA/DSC data processing: non-isothermal kinetics — do they become “applied science” by exiting the “dichotomy”?
No full textAbstract
After a brief overview of the state of the art of kinetic study of solid state reactions, a new promising approach is described. Whilst details of such an approach have been previously reported, the model and its performances are presented here as an overall picture, including the evaluation of the heat transfer perturbations induced in both TG and DTA/DSC. A summary of the results obtained with CaC2O4·H2O is also reported, and a strategy is suggested, which should be used when facing the problem of such a kinetic evaluation or, in general, when processing data according to an assumed model
Using thermoanalytical data. Part 2. The dependence of kinetic data available from thermogravimetry on sample and instrument parameters: a method for calculating ‘true’ kinetic parameters
No full textAbstract Kinetic data available from TG measurements are discussed with respect to thermal coefficients such as sample specific heat, reaction enthalpy, instrument heat-transfer coefficient and heat capacity. The dependence of the available kinetic parameters Z, E and N on these thermal coefficients is examined using a numerical model. A relationship is also derived for calculating the kinetic parameters from experimental TG curves whilst taking into account the perturbation induced by the above-cited thermal coefficients. The dehydration of calcium oxalate is used to evaluate experimentally the predictive power of the kinetic parameters obtained in this way, i.e. their ability to describe the sample behaviour under a wide range of operational conditions (different masses and heating rates), including isothermal reactions
Determination of diclofenac salts in pharmaceutical formulations"
No full textTwo methods for the determination of the diclofenac salts [sodium (DS) or diethylammonium (DA)] in three pharmaceutical formulations (tablets, suppositories and gel) are presented. In the first, diclofenac salt is determined both, by measuring the absorbance of the solutions at a fixed wavelength (lambda = 276 nm) and using a multi-wavelength computational program to process the spectrophotometric data in a selected range (lambda = 230-340 nm). The above method can not be applied to the analysis of gel formulations because of the opalescence of these solutions. In this case, the analysis is performed measuring the peak-to-peak amplitude in the first-derivative UV spectrum (D-1 261.296). In the second method, diclofenac (DH) is precipitated in acid medium and determined by the analysis of the endothermic peak (t(p) = 182 degrees C) in the DSC curve obtained in nitrogen atmosphere. Finally, some aspects of chemical (solubility, acid-base equilibria, redox reaction), spectroscopic (UV, LR) and thermoanalytical (TG, DSC) behaviour of DS and DH and the values of the parameters which enable to calculate the UV spectrum of DS in aqueous solution are reported
Using thermoanalytical data Part 4. Processing of DTA/DSC curves to calculate reaction enthalpy and kinetic parameters. An application to calcium oxalate
No full textWith regard to single step reactions, a new approach to the processing of DTA/DSC curves is presented, taking into account the heat transfer into the instrument. It is an extension of a previous physical model, that allowed the calculation of true kinetic parameters from TG curves. The peak area can be properly calculated as well as the degree of reaction, this also being suitable for kinetic parameters calculation. Through numerical simulations, other methods for DTA/DSC curve processing are discussed with respect to that proposed. By TG and DTA, the true kinetic parameters have been finally determined for the second and third steps of the thermal decomposition of CaC2O4.H2O, to complete previously reported data for the first dehydration step. The agreement of the results with isothermal experiments seems to indicate a way to escape from the dichotomy between isothermal and non-isothermal kinetics. Several other approaches to non isothermal kinetics are reviewed and discussed. The software developed is also briefly described
DSC in the chemical analysis of drugs. Determination of diclofenac in pharmaceutical formulations
No full textDifferential scanning calorimetry was applied to the determination of diclofenac in three 'Voltaren' formulas. The pharmaceutical products (soluble tablets, suppositories and vials) were selected in order to show that calorimetric analysis is an easy technique to perform and can be competitive with other conventional methods.
In the tablets diclofenac (DH) was determined, without any pre-treatment, from the area of the endothermic peak which occurs at about 180%C in the DSC curve obtained in N-2 atmosphere. In the analysis of the suppositories and vials, nitrilotriacetic acid (NTA) was added to transform the diclofenac sodium salt (DS) into the thermally active form (DH). In both cases, it was necessary to eliminate the interference of excipient by cyclohexane extraction (suppositories) or by a multistep program for the DSC run (vials).
The accuracy of the results and the simplicity of the procedure justify the important role of DSC in the analysis of these drugs and certainly of several other commercial products
Tracing the origin of extra virgin olive oils by infrared spectroscopy and chemometrics: A case study
No full textIn this paper, the potential of coupling mid- and near-infrared spectroscopic fingerprinting techniques and chemometric classification methods for the traceability of extra virgin olive oil samples from the PDO Sabina was investigated. To this purpose, two different pattern recognition algorithm representative of the discriminant (PLS-DA) and modeling (SIMCA) approach to classification were employed. Results obtained after processing the spectroscopic data by PLS-DA evidenced a rather high classification accuracy. NIR providing better predictions than MIR (as evaluated both in cross-validation and on an external test set). SIMCA confirmed these results and showed how the category models for the class Sabina can be rather sensitive and highly specific. Lastly, as samples from two harvesting years (2009 and 2010) were investigated, it was possible to evidence that the different production year can have a relevant effect on the spectroscopic fingerprint. Notwithstanding this, it was still possible to build models that are transferable from one year to another with good accuracy. (C) 2011 Elsevier B.V. All rights reserved
Tracing the origin of foodstuff: a chemometric challenge
No full textThe increased information available to the consumers together with the competition following the institution of the Common Market (EU countries) has led safety, nutritional value, eating characteristics, ethical, environmental, economic and social aspects to be more and more important and essential topics for the food industry. In a single word, there is an increasing demand for “quality”, as a primary criterion to access the market.
Accordingly, a particular aspect of quality which has been gathering more and more attention during the recent years is that of the typicity of the product. In fact, it has been widely reported in the literature that the geographic, production and species origin of a foodstuff are important variables regulating the overall quality of the product. This issue has been recognized by the European Union by the introduction of the Designations of Origin (PDO and PGI). The products which are labeled by this Denomination must be produced in a well defined geographic area and manufactured using only one or few specified botanical or animal varieties.
As a consequence, having accurate and precise analytical methods for the traceability of the origin of a foodstuff is an issue that is becoming more and more relevant. In this framework, while the possibility of identifying chemical markers of geographic, production or species origin is currently being explored using different fingerprinting techniques, it is widely recognized that, whatever the technique(s) chosen, the use of mathematical and statistical methods (chemometrics) to process the experimental data is essential to obtain a reliable authentication of the product.
In this communication, the successful use of different chemometric pattern recognition methods for the traceability of food products will be presented
Cobalt(III) aminoacidate bis-phenanthroline chlorides: preparation and characterisation by thermal analysis and other analytical methods
No full textAbstract: The thermal properties of some mixed complexes of Co(III) with omicron-phenanthroline and several amino acids were determined by thermogravimetry (TG) and differential thermal analysis (DTA). The thermal stability derived from decomposition temperatures is discussed in terms of the molecular properties of the amino acids which affect the distribution of the intermolecular bonds in the solid lattice. With reference to the weight losses and IR spectra of the heated compounds, the thermal decomposition pathways of these complexes were also determined. Modifications to the methods of preparation cited in the literature were also proposed to increase the yields and to simplify operating procedures
MIXED COMPLEXES BETWEEN COPPER(II), CHROMIUM(III) AND DIETHYLENETRIAMINEPENTACETIC ACID (DTPA)
No full textThe reaction between copper(II) and chromium(III)-DTPA complex has been investigated in aqueous solution by potentiometric and UV-vis spectrophotometric measurements. Copper (II) forms mononuclear complex species, as well as mixed complexes with hydrogen and hydroxide ions, the stability constants of which have been calculated at 20-degrees-C in 1.0 mol dm-3 (Na,H)ClO4. A solid species has also been prepared and analysed by IR spectroscopy and thermal measurements
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