Convenient green preparation of dipeptides using unprotected α-amino acids

Dipeptides and amides were obtained in high yields from N-carbobenzyloxy α-amino acids and 3-phenylpropanoic acid with unprotected α-amino acids via the corresponding mixed carbonic carboxylic anhydrides using ethyl chloroformate and triethylamine by an ecological and convenient method in which the protection of C-terminals is not needed.     

Multiple Fused Anthracenes as Helical Polycyclic Aromatic Hydrocarbon Motif for Chiroptical Performance Enhancement

Polycyclic aromatic hydrocarbons consisting of three fused anthracene units were designed as new π‐conjugated compounds having helical structures. These expanded helicenes were synthesized by Pt‐catalyzed cycloisomerization of the corresponding ethynyl‐substituted precursors. The nonplanar and helical structure was confirmed by X‐ray analysis and DFT calculations, and the barrier to helical inversion was estimated to be 34 kJ mol^?1. The enantiomers of the diphenyl derivative were successfully resolved by chiral HPLC. Enantiopure samples showed good chiroptical performance in the CD (|Δ?| 1380 L mol^?1 cm^?1) and CPL (|g_lum| 0.013) spectra, and these values were considerably large for simple organic molecules. The unique chiroptical properties are discussed on the basis of the molecular structure and the electronic state with the aid of time‐dependent DFT calculations.     

On finite truncation of infinite shot noise series representation of tempered stable laws

Tempered stable processes are widely used in various fields of application as alternatives with finite second moment and long-range Gaussian behaviors to stable processes. Infinite shot noise series representation is the only exact simulation method for the tempered stable process and has recently attracted attention for simulation use with ever improved computational speed. In this paper, we derive series representations for the tempered stable laws of increasing practical interest through the thinning, rejection, and inverse Lévy measure methods. We make a rigorous comparison among those representations, including the existing one due to Imai and Kawai [29] and Rosiński (2007) [3], in terms of the tail mass of Lévy measures which can be simulated under a common finite truncation scheme. The tail mass are derived in closed form for some representations thanks to various structural properties of the tempered stable laws. We prove that the representation via the inverse Lévy measure method achieves a much faster convergence in truncation to the infinite sum than all the other representations. Numerical results are presented to support our theoretical analysis.     

Hall effect of FeTe and Fe(Se1–xTex) thin films

The Hall effect is investigated in thin-film samples of iron–chalcogenide superconductors in detail. The Hall coefficient (R_H) of FeTe and Fe(Se_1–xTe_x) exhibits a similar positive value around 300 K, indicating that the high-temperature normal state is dominated by hole-channel transport. FeTe exhibits a sign reversal from positive to negative across the transition to the low-temperature antiferromagnetic state, indicating the occurrence of drastic reconstruction in the band structure. The mobility analysis using the carrier density theoretically calculated reveals that the mobility of holes is strongly suppressed to zero, and hence the electric transport looks to be dominated by electrons. The Se substitution to Te suppresses the antiferromagnetic long-range order and induces superconductivity instead. The similar mobility analysis for Fe(Se_0.4Te_0.6) and Fe(Se_0.5Te_0.5) thin films shows that the mobility of electrons increases with decreasing temperature even in the paramagnetic state, and keeps sufficiently high values down to the superconducting transition temperature. From the comparison between FeTe and Fe(Se_1–xTe_x), it is suggested that the coexistence of ‘itinerant’ carriers both in electron and hole channels is indispensable for the occurrence of superconductivity.     

Effect of iron acetylacetonate on physico-chemical properties of waterglass based aerogels by ambient pressure drying

The effect of iron acetylacetonate on the physico-chemical properties of waterglass based silica aerogels by ambient pressure drying has been investigated. Doping the gels with iron acetylacetonat (FeAA) facilitates in the diminution of the density of the aerogels. The well established silica network provides effective confinement of FeAA nanoparticles which resists the collapse of silica network during ambient pressure drying. Therefore, in the present paper, the effects of FeAA on the physico-chemical properties of the aerogels have been studied by varying the FeAA:Na₂SiO₃ molar ratio from 3 × 10⁻⁴ to 6 × 10⁻⁴. The aerogels were prepared via ambient pressure drying and characterized by the bulk density, thermal conductivity and water contact angle. The aerogel’s surface morphology, elemental analysis and pore structure were characterized by means of EDAX and FTIR, TEM and N₂ adsorption- desorption analyzer. The high temperature hydrophobicity of these aerogels was checked by heating them in temperature controlled furnace. Silica aerogels with low density ~0.050 g/cc have been obtained using the molar ratio of Na₂SiO₃:H₂O:FeAA:Citric acid:TMCS at 1:146.67:3 × 10⁻⁴:0.54:9.46, respectively. EDAX and FTIR studies show that the iron species are entrapped in the mesoporous framework and not took part in the bonding with silica.     

Proton transport properties of poly(aspartic acid) with different average molecular weights

We synthesized seven partially protonated poly(aspartic acids)/sodium polyaspartates (P-Asp) with different average molecular weights to study their proton transport properties. The number-average degree of polymerization (DP) for each P-Asp was 30 (P-Asp30), 115 (P-Asp115), 140 (P-Asp140), 160 (P-Asp160), 185 (P-Asp185), 205 (P-Asp205), and 250 (P-Asp250). The proton conductivity depended on the number-average DP. The maximum and minimum proton conductivities under a relative humidity of 70% and 298 K were 1.7 · 10^?3 S cm^?1 (P-Asp140) and 4.6 · 10^?4 S cm^?1 (P-Asp250), respectively. Differential thermogravimetric analysis (TG-DTA) was carried out for each P-Asp. The results were classified into two categories. One exhibited two endothermic peaks between t = (270 and 300) °C, the other exhibited only one peak. The P-Asp group with two endothermic peaks exhibited high proton conductivity. The high proton conductivity is related to the stability of the polymer. The number-average molecular weight also contributed to the stability of the polymer.     

Control of the Solid‐State Chiral Optical Properties of a Supramolecular Organic Fluorophore Containing 4‐(2‐Arylethynyl)‐Benzoic Acid

The solid‐state chiral optical properties of a 4‐(2‐arylethynyl)‐benzoic acid/amine supramolecular organic fluorophore can be controlled by changing the arylethynyl group of the achiral 4‐(2‐arylethynyl)‐benzoic acid component molecule rather than the chirality of the amine component molecule.     

Dichloro­oxo(quinoline‐8‐thiolato‐κ2N,S)(triphenyl­phosphine oxide‐κO)rhenium(V) acetone solvate

The complex mol­ecule in the title compound, [Re(C₉H₆NS)Cl₂O(C₁₈H₁₅OP)]·C₃H₆O, has distorted octa­hedral geometry. The Re=O bond occupies the position trans to the triphenyl­phosphine oxide O atom. The Re—Cl bond trans to the thiol­ate S atom is longer than that trans to the quinoline N atom, implying a stronger trans influence of the S atom. Intra‐ and inter­molecular π–π inter­actions are also observed between the π rings in the complex.