Updated view of tars for psoriasis: what have we learned over the last decade?

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.

Dehydration Process of Hofmann-Type Layered Solids.

In the present work the dehydration process of layered solids with formula unit M(H2O)2[Ni(CN)4]·nH2O, M = Ni, Co, Mn; n = 1, 2, 4 is studied using modulated thermogravimetry. The results show that water molecules need to overcome an energetic barrier (activation energy between 63 and 500 kJ/mol) in order to diffuse through the interlayer region. The related kinetic parameters show a dependence on the water partial pressure. On the other hand, X-ray diffraction results provide evidence that the dehydration process is accompanied by framework collapse, limiting the structural reversibility, except for heating below 80 °C where the ordered structure remains. Removal of water molecules from the interlayer region disrupts the long-range structural order of the solid.

Industrial application of catalytic systems for n-heptane isomerization.

The ideal gasoline must have a high pump octane number, in the 86 to 94 range, and a low environmental impact. Alkanes, as a family, have much lower photochemical reactivities than aromatics or olefins, but only the highly branched alkanes have adequate octane numbers. The purpose of this work is to examine the possibilities of extending the technological alternative of paraffin isomerization to heavier feedstocks (i.e., n-heptane) using non-conventional catalytic systems which have been previously proposed in the literature: a Pt/sulfated zirconia catalyst and a molybdenum sub-oxide catalyst. Under the experimental conditions at which these catalysts have been evaluated, the molybdenum sub-oxide catalyst maintains a good activity and selectivity to isomerization after 24 h, while the Pt/sulfated zirconia catalyst shows a higher dimethylpentanes/methylhexanes ratio, probably due to a lower operating temperature, but also a high formation of cracking products, and presents signs of deactivation after 8 h. Though much remains to be done, the performance of these catalysts indicates that there are good perspectives for their industrial application in the isomerization of n-heptane and heavier alkanes.

A combined theoretical-experimental study on the acidity of WO(x)-ZrO(2) systems.

This work provides a chemical approach to the relationship between structure and electronic behavior of the active surface of the WO(x)-ZrO(2) system as a function of W loads. This study shows that the electronic hardness (eta), the Lewis and Brønsted acidity are functions of the local coordination and of the polymerization degree of the WO(x) domain. From theoretical calculations the observed behavior in the WO(x)-ZrO(2) system is explained: the Brønsted acidity increases while the Lewis acidity decreases as the W centers go from tetrahedral to octahedral coordination and as the condensation degree of the WO(x) domain increases. Our results also indicate that not all the Brønsted sites in the WO(x) domains are equally acid, and that as the W load increases the most acid sites decrease in number due to the condensation process. This finding also means a decrease on the average acidity per H site. Additionally, our results suggest that for surface densities in the 4-7 W nm(-2) range, mainly dimeric-tungstate species are present. A maximum in Brønsted acidity was observed for a W surface density about 7 W nm(-2).

New insights on molybdenum suboxide: nature of carbons in isomerization reactions.

MoO3 transformations under isomerization process conditions were studied. The products obtained after different times under stream (H2/n-heptane mixture, 18.5 bar, at 370 degrees C) were characterized by X-ray diffraction, Raman spectroscopy, thermal analysis, and high-resolution transmission electron microscopy (HRTEM). Theoretical quantum calculations were carried out with the aim of understanding the paradox of the real active phase in isomerization reactions. Theoretical calculations predict the existence of a metallic-like MoO phase with a structure that matches the X-ray diffraction experimental results. From experimental and simulated HRTEM images it was possible to identify the presence of small MoO cubic crystallites inside MoOx matrix phases. These results also support the previously proposed idea that isomerization reactions take place as a result of the existence of a bifunctional catalyst. The Raman and thermo-programmed oxidation (TPO) analyses show the existence of at least two types of carbonaceous deposits which tend to increase its ordering with the increase of time under stream. The carbon K edge in electron energy loss spectroscopy (EELS) of a sample after 24 h under stream shows that these carbonaceous deposits consist of a mixture of sp2- and sp3-hybridized carbons.