Geschwindigkeiten und Produkte der Hochtemperaturkorrosion von Chrom-Eisenlegierungen durch Phosphordampf

Rates and Products in High-Temperature Corrosion of Chromium-Iron Alloys by Phosphorus Vapor A study was undertaken concerning the kinetics and products in the phosphidation of chromium-iron alloys with various compositions at 900 and 1 000°C in phosphorus vapor at 1 atm by a sealed-tube method. X-ray diffraction patterns and an electron microprobe analysis of the products showed that at the outer layers iron phosphides alone were formed for iron-base alloys and both chromium and iron phosphides formed for chromium-base alloys, and that at the phosphide/alloy interface lower phosphides Cr₂P and Fe₂P were formed, corresponding to the compositions of the alloy. The phosphidations proceeded according to a parabolic rate law for all the compositions of the alloy and rate limited by a diffusion of cation in the phosphide lattice. The rate constant decreased generally with an increase in the content of chromium in the alloy.     

Total synthesis of marchantin A,a novel cytotoxic bis(bibenzyl) isolated from liverworts

Total synthesis of marchantin A, a novel cytotoxic bis(bibenzyl) isolated from some liverworts, has been accomplished in 12 steps.     

Synthesis of 2-methylthioindolizine-3-carbonitriles using nitro ketene dithioacetal

The reaction of 1-cyanomethylpyridinium chloride or bromide, 1a-i , with 1,1-bis(methylthio)-2-nitroethylene ( 2 ) in the presence of triethylamine as a base in ethanol gave the corresponding 2-methylthioindolizine-3-carbonitrile 3 and 2-methyl-thio-1-nitroindolizine-3-carbonitrile 4 in good yields, respectively. Compounds 3a,f were key intermediates for the synthesis of cycl[3.2.2]azine derivatives.     

Pyrolysis of amines: Infrared spectrum of vinylamine

The gas-phase infrared absorption bands of vinylamine were observed in the pyrolysis products of amines. These were characterized by doublets reflecting the ground state inversion splitting. Its half-life in the absorption cell was more than 20 min. The general valence force constants were calculated by an ab initio MO method. Some molecular characteristics were compared with those of isoelectronic formamide and investigated by the MO theory.     

A Novel One‐Pot Method for the Synthesis of Pyrimidine Derivatives Using Ketene N,S‐Acetal with Aryl Aldehydes

A very simple and facile one‐pot method for the synthesis of pyrimidine derivatives is presented. In this method, 2‐aryl‐pyrimidine derivatives were prepared by the reaction of ketene N,S‐acetal 1 with commercially available aryl aldehydes by heating under solvent and catalyst‐free conditions. The synthesized pyrimidine derivatives showed blue‐green fluorescence in solid state.     

Bright Solid‐State Emission of Disilane‐Bridged Donor–Acceptor–Donor and Acceptor–Donor–Acceptor Chromophores

The development of disilane‐bridged donor–acceptor–donor (D‐Si‐Si‐A‐Si‐Si‐D) and acceptor–donor–acceptor (A‐Si‐Si‐D‐Si‐Si‐A) compounds is described. Both types of compound showed strong emission (λ_em=ca. 500 and ca. 400 nm, respectively) in the solid state with high quantum yields (Φ: up to 0.85). Compound 4 exhibited aggregation‐induced emission enhancement in solution. X‐ray diffraction revealed that the crystal structures of 2 , 4 , and 12 had no intermolecular π–π interactions to suppress the nonradiative transition in the solid state.     

Contrasting Magnetic Behaviors in Rhodium‐ and Ruthenium‐Doped Cubic Perovskite SrFeO3: Nearly Ferromagnetic Metal versus Spin‐Glass Insulator

The effects of Rh and Ru doping for SrFeO₃, a helimagnetic metal with a cubic perovskite structure, are studied by magnetic and resistivity measurements. Although SrRhO₃ is a paramagnetic metal and SrRuO₃ is a ferromagnetic one, the Rh doping induces a nearly ferromagnetic metallic state, whereas the Ru doping induces a spin‐glass insulating state. Mössbauer measurements evidence a marked difference between SrFe_0.8Rh_0.2O₃ and SrFe_0.8Ru_0.2O₃ in the formal valences of Fe, which are estimated to be 4+ and 3.75+, respectively. The contrasting magnetic behaviors of Rh‐ and Ru‐doped SrFeO₃ are discussed in terms of the subtle balance between the double‐exchange ferromagnetism and the superexchange antiferromagnetism.     

Formation and characterization of carbon monoxide adducts of iron "twin coronet" porphyrins. Extremely low CO affinity and a strong negative polar effect on bound CO

The carbon monoxide (CO) adducts of iron "twin coronet" porphyrins (TCPs) are characterized by UV-vis, resonance Raman (RR), IR, and 13C NMR spectroscopies. A superstructured porphyrin, designated as TCP, was used as a common framework for the four different types of iron complexes. TCP bears two binaphthalene bridges on each side and creates two hydrophobic pockets surrounded by the bulky aromatic rings. In the CO-binding cavities, the hydroxyl groups are oriented toward the center above the heme. The iron complexes investigated are as follows: TCP (which is without a covalently linked axial ligand), TCP-PY (which has a linked pyridine ligand), and TCP-TB and TCP-TG (both of which have a linked thiolate ligand). These complexes were synthesized as ferric forms and identified by the various spectroscopic methods. The UV-vis spectra of TCP-CO and TCP-PY-CO exhibit lambda(max) at 432, 546 and 428, 541 nm, respectively. On the other hand, the CO adducts of TCP-TB and TCP-TG show typical hyperporphyrin spectra for a thiolate-ligated iron(II) porphyrin-CO complex. In the RR spectra, the nu(Fe-CO) bands were observed at 506, 489 cm(-1) (TCP), 465 cm(-1) (TCP-PY), 458, 437 cm(-1) (TCP-TG) and 429 cm(-1) (TCP-TB). Compared with the reported nu(Fe-CO) frequencies of hemoproteins and their model systems, these observed values are unusually low. Further, abnormally high nu(C-O) bands are observed at 1990 cm(-1) (TCP-CO) and 2008 cm(-1) (TCP-PY-CO) in IR spectra. The lower nu(Fe-CO) and the higher nu(C-O) frequencies can be ascribed to the strong negative polar effect caused by the vicinal hydroxyl groups in the cavity. This prediction is further supported by the observation of significant 13C shieldings exhibited by TCP-CO (delta = 202.6 ppm) and TCP-PY-CO (delta = 202.3 ppm), in comparison to hemoproteins and other heme models. The CO affinity of TCP-PY (P1/2CO = 0.017 Torr at 25 C) is unusually lower than other heme models. The unique behavior of these CO adducts is discussed in context of the TCP structures.     

High Resolution Structure of Bacteriorhodopsin Determined by Electron Crystallography

Abstract— Bacteriorhodopsin pumps protons from the cytoplasm to the outside of halobacteria, Halobacterium salinarium , by using absorbed light energy. The newly observed density map at 3 Å resolution clarified nearly the entire structure; the resolution in the direction perpendicular to the membrane surface is 3.2 Å. The new structure clearly indicates the proton transfer pathway in bacteriorhodopsin. In particular, the location of key aspartic acid and glutamic acid residues in the derived structural model suggested funneling structures with different designs for input and output of protons on the cytoplasmic and extracellular sides, respectively, of the protein. This paper describes the major differences between the model based on the new observation and the former model obtained through crystallographic refinement by Grigorieff et al . ( J. Mol. Biol 259; 393-421, 1996).     

Facile deallylation protocols for the preparation of N-unsubstituted triazoles and tetrazoles

Two facile deallylation protocols have been developed for the preparation of N-unsubstituted triazoles and tetrazoles. The first protocol is a direct deallylation using a combination of a catalytic amount of nickel complex, NiCl2(dppe), and a stoichiometric amount of Grignard reagent, tBuMgCl. The second protocol is a stepwise deallylation through consecutive reactions of isomerization and ozonolysis. The isomerization from N-allylazoles to N-vinylazoles is catalyzed by a ruthenium complex, HRuCl(CO)(PPh3)3, and the following ozonolysis of the derived N-vinyl intermediates affords N-unsubstituted azoles. These protocols can be used complementarily depending on the type of functional groups in the parent allylated azoles.