Observation of multiple phase transitions in some even n-alkanes using a high resolution and super-sensitive DSC

The phase transitions of even n-alkanes, n-C₃₄H₇₀, n-C₃₆H₇₄, n-C₄₀H₈₂ and n-C₄₂H₈₆ with high purity have been measured using a high resolution and super-sensitive DSC. A new transition in the low temperature phase was observed in all the samples in the heating run. The surface freezing phenomenon was observed by thermal measurement for the first time in all the samples both in the heating and in the cooling run. The difference of the thermal behaviors between the heating and cooling run was also observed in all the samples.     

Two‐Photon Absorption Properties of Dehydrobenzo[12]annulenes and Hexakis(phenylethynyl)benzenes: Effect of Edge‐Linkage

Two‐photon absorption (TPA) properties of two trefoil‐shaped compounds with different edge linkages—tris(hexadehydrotribenzo[12]annulene) and tris(tetradehydrotribenzo[12]annulene)—and three asterisk‐shaped compounds having no edge‐linkage—hexakis(phenylethynyl)benzenes—are investigated experimentally by the open‐aperture Z‐scan and TPA‐induced fluorescence methods with wavelength tuneable femtosecond pulses. The compound with ethynylene edge‐linkage exhibits the most intense TPA (the maximal TPA cross section is 1300±170 GM at 572 nm where 1 GM=10^?50 cm⁴ s molecule^?1 photon^?1). The TPA activity of the compounds is primarily explained in terms of the planarity of the molecules in relation with the type of edge‐linkage.     

Practical synthesis of d-[1-C]mannose, l-[1-C] and l-[6-C]fucose

The chemical synthesis of ¹³C-labeled mannose and fucose is important for the preparation of molecular probes used in the conformational study of the oligosaccharide portions of glycoproteins. A new method for the synthesis of the title [1-¹³C]-labeled compounds via the corresponding olefin compounds, which are in turn derived from d-mannitol or l-arabinose by efficient introduction of ¹³C, by the Wittig reaction using Ph₃P¹³CH₃I and n-BuLi, is described. The introduction of ¹³CH₃I to produce the [1-¹³C]- and [6-¹³C]-labeled compounds was accomplished in 62%, 56%, and 71% yields, respectively. All mannose and fucose protons, from H-1 to H-6, were observed by the HMQC-TOCSY technique using 1:1 mixtures of [1-¹³C]- and [6-¹³C]-labeled compounds.     

Near-infrared Light Emission from Nanomolar-level Singlet Molecular Oxygen Generated with an Ultra low Concentration Mixture of Hypochlorite and Hydrogen Peroxide

Abstract— We report the detection of a weak near-infrared light emission originating from 8 nM singlet molecular oxygen (¹O₂) produced in a mixture of 1 m M hypochlorite (OC1^-) and 8 n M hydrogen peroxide (H₂O₂). The measurements were made with a highly sensitive detection system for ultraweak light emission in the 1.0-1.5 μm wavelength region. The emission intensity exhibited linear dependence for H₂O₂ concentrations in the range of 8-670 n M . The mixture containing a lower concentration (33 μ M ) of OCl^- pseudocontinuously emitted near-infrared light for 5 s. The rate constant for ¹O₂ production obtained from the kinetic analysis agrees with that previously reported. Our results demonstrate the possibility of measuring very low concentrations of ¹O₂ in a OCi-/H₂O² mixture as well as ¹O₂ production in intact living systems.     

New synthesis of secondary carboxamide by using 2-methyl-2-oxazoline as a building block

New method for the synthesis of secondary carboxamides of type, R²NHCOR¹, which utilizes 2-methyl-2-oxazoline as a carboxamide building block and various halides, R²X, has been developed.     

Improvement of stability of a Fe/Mg/Al2O3 catalyst for the decomposition of methane in the presence of O2/CO2

The stability of an Fe/Al₂O₃ catalyst in the methane decomposition in the presence of O₂/CO₂ was found to be improved by the addition of Mg into the catalyst (Mg/Fe=1/1 wt ratio), probably due to suppression of carbon deposition even under CH₄/ O₂/CO₂ (80/10/5 vol. ratio) conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Alkane/Alcohol mixed monolayers at the solid/liquid interface

In this work, we present the behavior of solid monolayers of binary mixtures of alkanes and alcohols adsorbed on the surface of graphite from their liquid mixtures. We demonstrate that solid monolayers form for all the combinations investigated here. Differential scanning calorimetry (DSC) is used to identify the surface phase behavior of these mixtures, and elastic neutron incoherent scattering has been used to determine the composition of the mixed monolayers inferred by the calorimetry. The mixing behavior of the alcohol/alkane monolayer mixtures is compared quantitatively with alkane/alkane and alcohol/alcohol mixtures using a regular solution approach to model the incomplete mixing in the solid monolayer with preferential adsorption determining the surface composition. This analysis indicates the preferential adsorption of alcohols over alkanes of comparable alkyl chain length and even preferential adsorption of shorter alcohols over longer alkanes, which contrasts strongly with mixtures of alkane/alkane and alcohol/alcohol of different alkyl chain lengths where the longer homologue is always found to preferentially adsorb over the shorter. The alcohol/alkane mixtures are all found to phase separate to a significant extent in the adsorbed layer mixtures even when molecules are of a similar size. Again, this contrasts strongly with alkane/alkane and alcohol/alcohol mixtures where, although phase separation is found for molecules of significantly different size, good mixing is found for similar size species.     

Edge-Defined Film-Fed (EFG) Growth of Rare-Earth Orthovanadates REVO4 (RE=Y,Gd): Approaches to Attain High-Quality Shaped Growth

In spite of their superior laser and polarizer properties rare-earth orthovanadates (REVO₄) single crystals have not been adopted yet into extensive industrial applications because of crystal growth difficulties. The main problems of CZ technique are compositional change and diameter instability. This work presents the first attempt to apply the edge-defined film-fed growth (EFG) technique by which well-shaped REVO₄crystals have been grown directly. The capillary properties of YVO₄ and GdVO₄ melt have been measured. The applicability of shaped growth for rare-earth orthovanadate family was approved by successful EFG growth of transparent rod-like macro-defect-free single crystals of YVO₄ and GdVO₄. We address two main approaches to enhance the quality of EFG crystals: (i) meniscus and crystal shape stability dependence on die top shape and (ii) the strategy of effective operating control. Concave die top was found to be the best choice for high-quality EFG growth of REVO₄ along [001] direction. The spectral analysis of weight signal from growing crystal was shown to be a useful feedforward clue to prevent crystallinity degradation at a very early stage. A reasonable stability of the EFG process was achieved using [211], [101], [001] and [100] pulling directions.     

Thermal annealing of FePt thin films by millisecond plasma arc pulses

A series of 20 and 100 nm Fe₅₃Pt₄₇ thin films sputter-deposited onto Si substrates have been thermally annealed using a pulsed thermal plasma arc lamp. A series of one, three or five pulses were applied to the thin films with widths of either 50 or 100 ms. The microstructure and magnetic properties of these annealed Fe₅₃Pt₄₇ films are discussed according to the various annealing conditions and A1 to L1₀ phase transformation. Upon pulse annealing, the average in-plane grain size of 15 nm (nearly equivalent for both film thicknesses) was observed to increase to values near 20 nm. In general, increasing the pulse width or number of pulses increased the L1₀ order parameter, tetragonality of the c/a ratio and coercivity of the specimen. The exception to this trend was for five pulses at 100 ms for both film thicknesses, which indicated a reduction of the order parameter and coercivity. This reduction is believed to be a result of the interdiffusion of Fe and Pt into the Si substrate and the formation of iron oxide clusters in the grain boundaries characterized by atom probe tomography.