Untersuchungen an Hydriden im Bereich der Phase Ti2CO1—x Fe x (x=0–0,5)

The hydrogen absorption of the phase Ti₆₄Co_32–x Fe _x (x=0...16) and its influence on the magnetic properties have been investigated. Measurements of the vapour-pressure, wide-line NMR and magnetic susceptibility have been performed. Substitution of Co by Fe does not change the amount of absorbed hydrogen. However the reaction rate of hydriding process, the activation energy of diffusion and the magnetic quantities change upon this substitution.

     

Absolute configuration of C2-symmetric spiroselenurane: 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole

The enantiomers of 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole have been separated on a chiral preparative chromatographic column. The experimental vibrational circular dichroism (VCD) spectra have been obtained for both enantiomers in CH(2)Cl(2). The theoretical VCD spectra have been obtained by means of density functional theoretical calculations with the B3 LYP density functional. From a comparison of experimental and theoretical VCD spectra, the absolute configuration of an enantiomer with positive specific rotation in CH(2)Cl(2) at 589 nm is determined to be R. This conclusion has been verified by comparing results of experimental optical rotatory dispersion (ORD) and electronic circular dichroism (ECD) to predictions of the same properties using the B3 LYP functional for the title compound.     

Determination of aluminum in highly concentrated iron samples: Study of interferences using high-resolution continuum source atomic absorption spectrometry

High-resolution continuum source atomic absorption spectrometry (HR-CS AAS) has been used to investigate spectral and non-spectral interferences found with a conventional line source atomic absorption spectrometer in the determination of aluminum in pharmaceutical products containing elevated iron and sugar concentrations. A transversely heated graphite furnace was used as the atomizer in both spectrometers. The two most sensitive aluminum lines at 309.3 nm and 396.2 nm were investigated and it was found that an iron absorption line at 309.278 nm, in the vicinity of the aluminum line at 309.271 nm, could be responsible for some spectral interference. The simultaneous presence of iron and the organic components of the matrix were responsible for radiation scattering, causing high continuous and also structured background absorption at both wavelengths. The aluminum and iron absorption could not be separated in time, i.e., the iron interference could not be eliminated by optimizing the graphite furnace temperature program. However, an interference-free determination of aluminum was possible carrying out the measurements with HR-CS AAS at 396.152 nm after applying least squares background correction for the elimination of the structured background. Analytical working range and other figures of merit were determined and are presented for both wavelengths using peak volume registration (center pixel ± 1) and the center pixel only. Limits of detection and characteristic masses ranged from 1.1 to 2.5 pg and 13 to 43 pg, respectively. The method was used for the determination of the aluminum contamination in pharmaceutical formulations for iron deficiency treatment, which present iron concentrations from 10 to 50 g l^− 1. Spike recoveries from 89% to 105% show that the proposed method can be satisfactorily used for the quality control of these formulations.     

Highly Soluble and Green Indigo Dyes: 4,4′,7,7′‐Tetraalkoxy‐5,5′‐diaminoindigotins

Two new types of 4,4′,7,7′‐tetraalkoxyindigotins, 1a – f and 2a – f along with the new N‐substituted indigotins 4e – f , were synthesized from dinitrobenzaldehydes 5a – f , which were prepared from 2‐hydroxy‐5‐methoxybenzaldehyde ( 7 ) via dialkoxybenzaldehydes 6a – f (Scheme). The new dialkoxyindigotin 3g was obtained from dialkoxybenzaldehyde 6g via nitrobenzaldehyde 8g . The 1,4‐dialkoxy‐2,3‐dinitrobenzenes 9 were isolated as by‐products. The 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 are soluble in organic solvents, and their solutions are green, which is highly uncommon for indigotins and is primarily caused by electronic effects of substituents, steric effects playing a minor role. The indigotins 1 produce a strong red shift of the longest‐wavelength absorption and negative solvatochromism indicating the predominance of polar resonance structures in the ground state. Tautomeric structures were excluded. These indigotins are valuable compounds for technical applications, for synthetic purposes, and for analytical studies. SANS (Small‐angle neutron scattering) experiments showed that certain 4,4′,7,7′‐tetraalkoxy‐5,5′‐diaminoindigotins 1 form rod‐like aggregates in solution. The similarly substituted 4,4′,7,7′‐tetraalkoxy‐5,5′‐dinitroindigotins 2 are far less soluble. They produce red monoanions (preferably dimers) and bluish‐purple dianions in organic solvents.     

Carbohydrate-Based Antibiotics: A New Approach to Tackling the Problem of Resistance

Recent interest in the problem of antibiotic resistance has led to the identification of new targets and strategies for antibiotic discovery. Among these efforts, the development of small molecules as antibiotics to target carbohydrate receptors or carbohydrate-modifying enzymes represents a new direction. This review covers recent work in this regard and discusses the impact of each strategy on the development of drug resistance. Particularly interesting targets include unique cell-surface carbohydrates, the transglycosylase involved in peptidoglycan biosynthesis, and bacterial RNA. With a greater understanding of the genome of different bacteria as well as advances in functional genomics and proteomics, we can expect the discovery of a variety of targets for the development of novel antibiotics.     

Photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with acetylene: an effective method for the synthesis of 2-pyridines under mild conditions

The photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with 2 equiv of acetylene to 2-pyridines can be carried out under mild conditions and represents a valuable extension to common synthetical methods. For the ideal wavelength range (350-500 nm), lamps as well as sunlight can be used. Working at room temperature and in organic solvents such as toluene or hexane as well as in water gives satisfying results in many cases. However, it is also possible to vary the solvent and the reaction temperature of the photocatalyzed synthesis and to choose, with respect to the specific substrate, specific requirements for this particular reaction and general requirements of the method. This simple and selective method derives its potential mainly from the large variety of applicable nitriles. Suitable substrates include (functionalized) aliphatic and aromatic nitriles as well as cyanamides derived from secondary amines.     

Bildung oktaedrischer Komplexe durch cis-Addition an planar-quadratisches Bis(oxamidoximato)nickel(II): drei Strukturbeispiele

Formation of Octahedral Complexes via cis-Addition to Square Planar Bis (oxamideoximato)nickel(II): Three Structure Examples In the reaction of orange square planar bis(oxamide oximato)nickel(II) with acids, blue to blue-green octahedral complexes are formed with neutral oxamide oximide ligands and two acid anions in cis-positions. Three compounds are described: cis-dichlorobis(oxamide oxime)nickel(II) ( 1 ), NiCl₂(C₂H₆N₄O₂)₂, M_r = 365.81, monoclinic P2₁/n, a = 6.641(2), b = 14.086(4), c = 13.473(3) Å, β = 96.26(2)°, V = 1 252.8 ų, Z = 4, d_c = 1.94 gcm^?3, final R_w = 0.031 for 4090 reflections. In cis-di(sulfanilato)bis(oxamide oxime)nickel(II) dihydrate ( 2 ) one sulfanilic anion coordinates via the sulfonic acid group, the other one via the amino group; Ni(C₆H₆NO₃S)₂(C₂H₆N₄O₂)₂ · 2 H₂O, M_r = 675.30, monoclinic P2₁, a = 6.879(3), b = 14.305(5), c = 13.930(5) Å, β = 103.62(4)°, V = 1332 Å, Z = 2, d_c = 1.68 gcm^?3, R = 0.067 for 2693 reflections. In catena-μ-(phthalato)bis(oxamide oxime)nickel(II) tetrahydrate ( 3 ) bidentate bridging phthalate anions lead to chain formation; Ni(C₈H₄O₄)(C₂H₆N₄O₂)₂ · 4H₂O, M_r = 531.09, monoclinic P2₁/c, a = 10.633(8), b = 11.324(5), c = 17.680(14) Å, β = 98.25(7)°, V = 2107 ų, Z = 4, d_c = 1.67 gcm^?3. Final R = 0.110 for 3290 reflections.     

Dissoziative ionisierung von 2-trimethylsilyl-1-phenoxyethan. Nachweis des nicht-klassischen ethylen-trimethylsilanium-ions in der gasphase

The mass spectrometric investigation of specifically deuterium and ¹³C labelled 2-trimethylsilyl-l-phenoxyethanes proves that the dissociative ionization of β-silyl-substituted ethane derivatives (loss of PhO^?; p-CH₃C₆H₄O^?; and C₄H^?₉ from PhOCH₂CH₂SiMe₃, p-MeC₆H₄OCH₂CH₂SiMe₃ and CH₃CH₂CH(CH₃)CH₂-CH₂SiMe₃, respectively) yields the non-classical bridge ethylene trimethylsilanium ion and not the open-chain isomer. Other stable C₅H₁₃Si^+? ions, characterised by collisional activation mass spectrometry, are the dimethyl n-propyl silicenium ion and the l-trimethylsilyl ethyl cation, both generated from the molecular ions of CH₃CH₂CH₂Si(Cl)Me₂ and CH₃CH(Cl)SiMe₃ via unimolecular loss of Cl^?.