On the Understanding of TGO Growth and Spallation in Nickel Aluminides

This paper describes various parameters influencing oxidation kinetics, oxide’s morphology and spallation phenomena encountered while studying nickel aluminides in high temperature oxidation. Questions are raised about the possibility of making precise lifetime or failure predictions of coatings and TBCs systems. Changes in growth mechanism due to the presence of elements other than Ni and Al in nickel-aluminide base coatings, the effect of atmosphere, particularly water vapor, and the effect of surface preparation and of crystallographic orientation are the main parameters discussed in this work

In situ monitoring of galactolipid digestion by infrared spectroscopy in both model micelles and spinach chloroplasts

Galactolipids are the main lipids from plant photosynthetic membranes and they can be digested by pancreatic lipase related protein 2 (PLRP2), an enzyme found in the pancreatic secretion in many animal species. Here, we used transmission Fourier-transform infrared spectroscopy (FTIR) to monitor continuously the hydrolysis of galactolipids by PLRP2, in situ and in real time. The method was first developed with a model substrate, a synthetic monogalactosyl diacylglycerol with 8-carbon acyl chains (C8-MGDG), in the form of mixed micelles with a bile salt, sodium taurodeoxycholate (NaTDC). The concentrations of the residual substrate and reaction products (monogalactosylmonoglyceride, MGMG; monogalactosylglycerol, MGG; octanoic acid) were estimated from the carbonyl and carboxylate vibration bands after calibration with reference standards. The results were confirmed by thin layer chromatography analysis (TLC) and specific staining of galactosylated compounds with thymol and sulfuric acid. The method was then applied to the lipolysis of more complex substrates, a natural extract of MGDG with long acyl chains, micellized with NaTDC, and intact chloroplasts isolated from spinach leaves. After a calibration performed with α-linolenic acid, the main fatty acid (FA) found in plant galactolipids, FTIR allowed quantitative measurement of chloroplast lipolysis by PLRP2. A full release of FA from membrane galactolipids was observed, that was not dependent on the presence of bile salts. Nevertheless, the evolution of amide vibration band in FTIR spectra suggested the interaction of membrane proteins with NaTDC and lipolysis products

Atom probe tomographic study of L10 martensite in a Pt-modified NiCoCrAlYTa bond coating

The L10 martensite formed in a Pt-modified NiCoCrAlYTa bond coating has been investigated by atom probe tomography. It was found that obvious segregation of Co and Cr occurred in the micro-twins zone inside the martensite lath. Based upon the compositional analysis, it is known that Pt destabilizes the β phase and Co and Cr act as β stabilizers with respect to the β→L10 martensitic transformation. In addition, some α-Cr particles precipitated inside the martensite lath

Syntheses of D-Glucosaminyl Bolaamphiphiles

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Synthesis of 3-Azidopropyl-Functionalized GalNAc-β-(1→4)-Gal Natural Disaccharide

Oligosaccharides such as the GalNAc-β-(1→4)-Gal disaccharide are involved in host-pathogen interactions and their synthesis is a continuing challenge for organic chemists. Only a few reports have discussed the synthesis of functionalized GalNAc-β-(1→4)-Gal for its further conjugation and applications in glycobiology. The synthetic route described here is taking advantage of (1) a simple and affordable GlcNAc donor which is epimerized to the more expensive GalNAc donor and (2) a 1,6-anhydro-galactose acceptor exalting the reactivity at the 4-position of galactose. The allyloxycarbonyl (Alloc) protecting group used at the 2-position of the GalNAc residue was important (1) for a successful epimerization of the GlcNAc residue into the corresponding GalNAc donor but also (2) for the stereoselective β-glycosylation through anchimeric assistance. The key disaccharide intermediate was further transformed to a trichloroacetimidate donor which could then be glycosylated with any alcohol. The example chosen here is the 3-azidopropyl aglycon for the design of multivalent glycoclusters.<br /

Synthesis of 3-Azidopropyl-Functionalized GalNAc-β-(1→4)-Gal Natural Disaccharide

Oligosaccharides such as the GalNAc-β-(1→4)-Gal disaccharide are involved in host-pathogen interactions and their synthesis is a continuing challenge for organic chemists. Only a few reports have discussed the synthesis of functionalized GalNAc-β-(1→4)-Gal for its further conjugation and applications in glycobiology. The synthetic route described here is taking advantage of (1) a simple and affordable GlcNAc donor which is epimerized to the more expensive GalNAc donor and (2) a 1,6-anhydro-galactose acceptor exalting the reactivity at the 4-position of galactose. The allyloxycarbonyl (Alloc) protecting group used at the 2-position of the GalNAc residue was important (1) for a successful epimerization of the GlcNAc residue into the corresponding GalNAc donor but also (2) for the stereoselective β-glycosylation through anchimeric assistance. The key disaccharide intermediate was further transformed to a trichloroacetimidate donor which could then be glycosylated with any alcohol. The example chosen here is the 3-azidopropyl aglycon for the design of multivalent glycoclusters