RESUMO
Tars are one of the most effective, unknown, and oldest therapies for psoriasis. They include coal tar (CT) and biomass-derived products. These treatments, particularly the CT, have proven to be cost-effective with long remission times compared to other systemic or topical treatments. However, they have hardly evolved in recent years, as they are not well-embraced by clinicians or patients because of concerns regarding cosmesis and safety. This review summarizes current knowledge about the chemical characterization, mechanism of action, toxicity, and clinical studies supporting the use of tars for psoriasis over the last decade. Trends within these above aspects are reviewed, and avenues of research are identified. CT is rich in polycyclic aromatic hydrocarbons, whereas biomass-derived tars are rich in phenols. While the activation of the aryl hydrocarbon receptor is involved in the antipsoriatic effect of CT, the mechanism of action of biomass-derived products remains to be elucidated. No conclusive evidence exists about the risk of cancer in psoriasis patients under CT treatment. Large, randomized, double-blind, controlled clinical trials are necessary to promote the inclusion of tars as part of modern therapies for psoriasis.
Assuntos
Alcatrão , Cosméticos , Fármacos Dermatológicos , Psoríase , Humanos , Alcatrões/efeitos adversos , Psoríase/tratamento farmacológico , Alcatrão/efeitos adversos , Alcatrão/química , Fármacos Dermatológicos/uso terapêutico , Ensaios Clínicos Controlados Aleatórios como AssuntoRESUMO
Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOFMS) has shown great skill in analyzing complex mixtures such as fossil fuels, especially for compounds at low concentrations. The analysis of N-polyaromatic compounds (NPAC) in coal and crude oil is a great challenge for analytical chemistry due to its environmental and technological importance, and also its diversity of concentration in the matrix. This study is the first report in the applicability of GC×GC/TOFMS for detection of NPAC in a coal tar sample with no fractionation. Normally these compounds are analyzed after sample treatment, making the process expensive and time consuming. However, the higher separation power of GC×GC/TOFMS, compared to 1D-GC, produces cleaner mass spectra in complex samples, which helps in identification of analytes with no pre-fractionation. In this paper, the main objectives were to demonstrate the applicability of GC×GC/TOFMS in the speciation and separation between basic and neutral NPAC from coal tar sample derived from fast pyrolysis, without prior sample fractionation. The methodology used here consisted of chromatographic injection of the diluted sample using a conventional columns set and data analysis by ChromaTOF/Excel™ software. Some basic compounds (pyridines and quinolines) and neutral ones (carbazoles and indoles) were detected with good chromatographic separation and spectral similarity. Tools like spectral deconvolution, extracted ion chromatogram (EIC) and dispersion graphics allowed greater security on the identification and separation of NPAC in this complex sample of coal tar, with no pre-treatment.
Assuntos
Alcatrão/química , Cromatografia Gasosa-Espectrometria de Massas/métodos , Compostos de Nitrogênio/análiseRESUMO
Coal is a non renewable fossil fuel, used mainly as a source of electrical energy and in the production of coke. It is subjected to thermal treatment, pyrolysis, which produces coke as a main product, in addition to a condensed liquid by-product, called tar. Tar is a complex mixture of organic compounds which contains different chemical classes, presenting aromatic and sulphur heterocyclic compounds. In general, identification of these compounds requires steps of isolation and fractionation, mainly due to co-elution of these compounds with polyaromatic hydrocarbons (PAH). The objective of this work is to characterize the sulphur compounds present in the coal tar obtained via pyrolysis, using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry detector (GC×GC/TOFMS). Coal samples from the State of Paraná, Brazil were subjected to laboratorial scale pyrolysis. Several experimental conditions were tested, such as sample weight (5, 10 and 15g), heating ramp (10, 25 and 100°C/min) and final temperature (500, 700 and 900°C). Samples were analyzed by one dimensional gas chromatography (1D-GC) coupled to a quadrupole mass spectrometry detector (GC/qMS) and two-dimensional gas chromatography with time-of-flight mass spectrometry detector (GC×GC/TOFMS). The higher amount of sulphur compounds was obtained at a final temperature of 700°C and a heating ramp of 100°C/min. The main classes observed in the color plot were thiophenes, benzothiophenes and alkylated dibenzothiophenes. GC×GC/TOFMS allowed the identification of the greater number of compounds and the separation of several sulphur compounds from one another. Moreover, separation of sulphur compounds from polyaromatic hydrocarbons and phenols was achieved, which was not possible by 1D-GC. Comparing GC×GC/TOFMS and 1D-GC (SIM mode) also showed that 1D-GC, one of the most employed quantification tools for sulphur compounds, can be misleading for detection, identification and quantification, as the number of isomers of sulphur compounds found was greater than theoretically possible.