Unprocessed Viral DNA Could Be the Primary Target of the HIV-1 Integrase Inhibitor Raltegravir

Integration of HIV DNA into host chromosome requires a 3′-processing (3′-P) and a strand transfer (ST) reactions catalyzed by virus integrase (IN). Raltegravir (RAL), commonly used in AIDS therapy, belongs to the family of IN ST inhibitors (INSTIs) acting on IN-viral DNA complexes (intasomes). However, studies show that RAL fails to bind IN alone, but nothing has been reported on the behaviour of RAL toward free viral DNA. Here, we assessed whether free viral DNA could be a primary target for RAL, assuming that the DNA molecule is a receptor for a huge number of pharmacological agents. Optical spectroscopy, molecular dynamics and free energy calculations, showed that RAL is a tight binder of both processed and unprocessed LTR (long terminal repeat) ends. Complex formation involved mainly van der Waals forces and was enthalpy driven. Dissociation constants (Kds) revealed that RAL affinity for unbound LTRs was stronger than for bound LTRs. Moreover, Kd value for binding of RAL to LTRs and IC50 value (half concentration for inhibition) were in same range, suggesting that RAL binding to DNA and ST inhibition are correlated events. Accommodation of RAL into terminal base-pairs of unprocessed LTR is facilitated by an extensive end fraying that lowers the RAL binding energy barrier. The RAL binding entails a weak damping of fraying and correlatively of 3′-P inhibition. Noteworthy, present calculated RAL structures bound to free viral DNA resemble those found in RAL-intasome crystals, especially concerning the contacts between the fluorobenzyl group and the conserved 5′C4pA33′ step. We propose that RAL inhibits IN, in binding first unprocessed DNA. Similarly to anticancer drug poisons acting on topoisomerases, its interaction with DNA does not alter the cut, but blocks the subsequent joining reaction. We also speculate that INSTIs having viral DNA rather IN as main target could induce less resistance

Oxidation of porous stainless steel supports for metal-supported solid oxide fuel cells

Oxidation behavior of porous P434L ferritic stainless steel, used for the fabrication of metal-supported solid oxide fuel cells (MS-SOFC), is studied under anodic and cathodic atmospheres. Temperature- and atmosphere-dependence is determined for as-sintered and pre-oxidized stainless steel. Pre-oxidation reduced the long-term oxidation rate. For pre-oxidized samples, the oxidation rate in air exceeds that in humid hydrogen for temperatures above 700 °C. The influence of PrOx, LSCF-SDC, and Ni-SDC coatings is also examined. The coatings do not dramatically impact oxide scale growth. Oxidation in C-free and C-containing anodic atmospheres is similar. Addition of CO2, CH4, and CO to humidified hydrogen to simulate ethanol reformate does not significantly impact oxidation behavior. Cr transpiration in humid air is greatly reduced by the PrOx coating, and a PrCrO3 reaction product is observed throughout the porous structure. A dense and protective chromia-based scale forms on steel samples during oxidation in all conditions. A thin silica enriched oxide layer also forms at the metal-scale interface. In general, the oxidation behavior at 700 °C is found to be acceptable

Oxidation of porous stainless steel supports for metal-supported solid oxide fuel cells

Oxidation behavior of porous P434L ferritic stainless steel, used for the fabrication of metal-supported solid oxide fuel cells (MS-SOFC), is studied under anodic and cathodic atmospheres. Temperature- and atmosphere-dependence is determined for as-sintered and pre-oxidized stainless steel. Pre-oxidation reduced the long-term oxidation rate. For pre-oxidized samples, the oxidation rate in air exceeds that in humid hydrogen for temperatures above 700 °C. The influence of PrOx, LSCF-SDC, and Ni-SDC coatings is also examined. The coatings do not dramatically impact oxide scale growth. Oxidation in C-free and C-containing anodic atmospheres is similar. Addition of CO2, CH4, and CO to humidified hydrogen to simulate ethanol reformate does not significantly impact oxidation behavior. Cr transpiration in humid air is greatly reduced by the PrOx coating, and a PrCrO3 reaction product is observed throughout the porous structure. A dense and protective chromia-based scale forms on steel samples during oxidation in all conditions. A thin silica enriched oxide layer also forms at the metal-scale interface. In general, the oxidation behavior at 700 °C is found to be acceptable

Influence of Shell Thickness on Durability of Ru@Pt Core-Shell Catalysts for Reformate PEM Fuel Cells

For the use of polymer electrolyte membrane fuel cells (PEMFCs) in heavy duty applications, on-site generation of hydrogen rich gas by reforming hydrocarbons or methanol are a suitable alternative to pure H2 due to higher availability and higher energy density of hydrocarbon fuels [1]. The so-called reformate contains in addition of H2 also CO, which is a catalyst poison. PtRu alloys are the most promising catalysts for PEM fuel cells operated with reformate due to their high CO-tolerance [2]. It is known that the less noble Ru is unstable in acidic PEMFC conditions and is lowering the durability of the membrane electrode assembly (MEA) by dissolution and crossing over through the membrane to the cathode [3]. Ru dissolution and crossover result in a decreased CO-tolerance on the anode and a lower activity of the cathode towards oxygen reduction due to Ru blocking the Pt surface of the cathode catalyst [4]. To prolong the lifetime and CO-tolerance of reformate PEMFCs, the stability of the anode catalysts must be improved. One approach is nano-structuring the catalysts by encapsulating the less noble Ru-core with a Pt-shell. In doing so, the corrosion resistant Pt-shell supposes to protect the Ru-core from dissolution and thus mitigates the Ru crossover phenomenon.In this work, the influence of the Pt-shell thickness on the stability and performance of the Ru@Pt catalysts is investigated. Two catalysts with varying Pt-shell thicknesses were synthesized on Vulcan XC72R carbon via a two-step polyol. The catalyst with the thinner Pt-shell is called Ru@1Pt and with the thicker shell Ru@2Pt. The as-synthesized catalysts were physically characterized by XRD, ICP-OES, TEM and EDS. A representative EDS map of Ru@1Pt is shown in fig. 1a. The physical characterization of the obtained catalysts unveils a Ru@Pt core-shell structure with crystalline hcp Ru and fcc Pt. To further investigate the catalysts electrochemically, MEAs were manufactured using Ru@Pt catalysts as anodes and commercial membranes and cathode catalysts. An accelerated stress test (AST) was developed to target Ru dissolution by potential cycling and was applied to investigate and compare the stability of the catalysts. The MEAs were electrochemically characterized by cyclic voltammetry, CO-stripping and U-I curves before, during and after the AST. Post-mortem cross-section STEM analysis of the stressed cells were performed to evaluate the elemental composition and morphology of the anode and cathode after the stress test.During the AST, CO-stripping on the Ru@1Pt anode showed a peak shift to higher potentials, indicating a decrease in CO-tolerance due to Ru loss. By contrast, on the Ru@2Pt anode, the peak shifted to lower potentials implying a stronger promoting influence of Ru. On the cathode side, CV measurements before and after the AST revealed a double layer increase and a decrease in the HUPD. This change implies the poisoning of Pt with Ru and were more pronounced for Ru@1Pt compared to Ru@2Pt. As seen by the CO-stripping and CV results, the Ru dissolution and crossover was more severe for Ru@1Pt than for Ru@2Pt. Hence, a higher fuel cell performance loss was observed for the cell with Ru@1Pt in H2, as can be seen in fig. 1b. In addition, further U-I curves were measured under varying reformate conditions to identify the influence of CO on the cell performance. Cross-section EDS maps of the stressed MEAs were used to evaluate the Ru dissolution and its distribution in the different layers of the MEA. A higher Ru:Pt ratio was found on the cathode for the cell with Ru@1Pt compared to a cell with Ru@2Pt, which further verifies a higher degree of Ru crossover for the catalyst with the thinner Pt-shell. The above findings could evidence that the shell thickness plays a significant role in the corrosion resistance of core-shell reformate anode fuel cell catalysts.References[1] B. Du, R. Pollard, J.F. Elter, M. Ramani, in: F.N. Büchi, M. Inaba, T.J. Schmidt (Eds.), Polymer Electrolyte Fuel Cell Durability, Springer New York, New York, NY, 2009, pp. 341–366.[2] O.A. Petrii, J Solid State Electrochem 12 (2008) 609–642. https://doi.org/10.1007/s10008-007-0500-4.[3] E. Antolini, J Solid State Electrochem 15 (2011) 455–472. https://doi.org/10.1007/s10008-010-1124-7.[4] L. Gancs, B.N. Hult, N. Hakim, S. Mukerjee, Electrochem. Solid-State Lett. 10 (2007) B150. https://doi.org/10.1149/1.2754382.Figure

Picomole scale stereochemical analysis of sphingosines and dihydrosphingosines

We have developed a simple picomole (low nanogram) scale HPLC scheme which can separate all eight isomers of sphingosine and dihydrosphingosine thus leading to the identification of their relative and absolute configurations. The amino group of the sample is derivatized to its fluorescent N-naphthimide which is analyzed by normal and chiral phase HPLC, coupled with fluorescence peak detection. If necessary, the results of this HPLC method can be further corroborated by measurements of circular dichroic (CD) spectra of the N-naphthimido-derivatives and/or N,O-chromophoric derivatives. Copyright (C) 1996 Elsevier Science Lt