HRTEM image contrast of short range order in Ni4Mo

The high resolution transmission electron microscope (HRTEM) imaging of short range order (SRO) in Ni4Mo was investigated by means of multi-slice image simulations. The HRTEM images of Ni4Mo exhibit locally bright dot patterns corresponding to the [001] projections of the N2M2-type (chalcopyrite-like) structure. The multi-slice simulations revealed that the N2M2 patterns are rationalized as the projection patterns of the SRO structure which consists of subunit cell clusters of D1a, D022 and Pt2Mo structures. The N2M2-type image contrast appears when both the fundamental fcc lattice reflections and the 1 1/2 0 diffuse scattering of SRO contribute enough to imaging. This suggests that a good coincidence in intensity distribution between the Fourier power spectra of HRTEM images and the electron diffraction patterns is one of the conditions for the image contrast of SRO to be interpreted in terms of the projection contrast.     

Premonitory effects near critical transition temperature in ordering systems – a Monte Carlo simulation

Premonitory effects manifest themselves in an ordering transition of the first kind (order) in the form of anomalously high short-range order (SRO) intensity at temperatures marginally above T _c, the critical transition temperature. This intensity located at the superlattice positions of the long-range ordered (LRO) phase is often attributed to the formation of ‘heterophase fluctuations’ resembling clusters of the LRO phase. Monte Carlo simulations in a hypothetical system showing FCC-to-L1₂ ordering transition have been carried out here to shed some light on this phenomenon and to look into the atomic configurations that make up these fluctuations.     

Monte Carlo simulation of antiphase boundaries and growth of antiphase domains in Al5Ti3 phase in Al-rich γ-TiAl intermetallics

Predominantly two kinds of antiphase boundaries (APBs) form in Al₅Ti₃, which is an Al-rich ordered derivative of the γ-TiAl (L1₀) phase. This phase can be viewed as a periodic arrangement of lean rhombs and squares on the Ti-rich (002) planes of the tetragonal L1₀. Energies of the two types of APBs were varied in a Monte Carlo simulation by suitably changing the pair interaction parameters. APBs of both types form boundaries of Al₅Ti₃ antiphase domains (APDs), which coarsen with time. An important observation in this regard is that mostly facetted APBs form at lower ageing temperatures, whereas curved APBs appear to form at relatively higher ageing temperatures. The findings of this work suggest that there exists a critical temperature, akin to the roughening transition temperature for crystals, that marks the transition from facetted to curved APBs.     

Nucleophilic addition of sulfonamides to bromoacetylenes: facile preparation of pyrroles

Nucleophilic addition of sulfonamides to 1-bromo-1-alkynes provided (Z)-N-(1-bromo-1-alken-2-yl)-p-toluenesulfonamides in good yield and in a highly regio- and stereoselective manner. Treatment of product (Z)-N-(1-bromo-1-octen-2-yl)-N-allyl-p-toluenesulfonamide with a palladium catalyst under Heck conditions afforded 1-(p-toluenesulfonyl)-2-hexyl-4-methylpyrrole in good yield. Other pyrroles with various substituents can also be prepared in good yield by this method.     

Free radical scavenging and radioprotective effects of carnosine and anserine

Two histidine-containing natural dipeptides, carnosine and anserine (β-alanyl-1-methyl-l-histidine), have been examined for their antioxidant and radioprotective abilities. Pulse radiolysis studies indicated the antioxidative properties of carnosine and anserine aqueous solutions at different pH. The rate constants for the reaction OH radical with carnosine at neutral pH were determined to be 5.3×10⁹ M⁻¹ s⁻¹ at 300 nm, and 4.1×10⁹ M⁻¹ s⁻¹ at 400 nm, respectively. Carnosine and anserine also protected plasmid pUC18 DNA from X-ray radiation-induced strand breaks as evidenced from the studies by agarose gel electrophoresis. Carnosine showed higher protective efficiency under the experimental conditions. Our data demonstrated that carnosine and anserine may play an important role in the maintenance of the antioxidant system.     

Iron-catalyzed δ-selective conjugate addition of methyl and cyclopropyl Grignard reagents to α,β,γ,δ-unsaturated esters and amides

Iron-catalyzed δ-selective conjugate addition of methyl and cyclopropyl Grignard reagents to α,β,γ,δ-unsaturated esters and amides took place in good yields to give products exclusively with cis-β,γ-olefinic bond.