The mono- and bis-(trichloroacetic acid)-solvates of ferricenium trichloroacetate

Summary Inconsistent literature reports on the preparation of the mono- and bis-(trichloroacetic acid)-solvated ferricenium trichloroacetates, (1) and (2) have prompted a comprehensive investigation of the experimental conditions giving rise to the formation of the two ferricenium salts. In agreement with the majority of authors, (2) is reproducibly obtained from trichloroacetic acid and ferrocene in molar ratios of 3 and higher in benzene over a wide range of experimental variables in the presence of air or, preferably, under conditions of oxygen saturation. Treatment of aqueous ferricenium sulfate solutions with trichloroacetic acid in an acid/ferrocene ratio of 3 and above affords the di-solvate, whereas at lower reactant ratios, and under conditions of reduced acidity, formation of the mono-solvate prevails. More efficiently, and in a higher degree of purity, the latter salt is generated from the former by a controlled recrystallization from water. Representative spectroscopic features of the two salts are discussed.     

Determination of ephedra alkaloids by liquid chromatography/tandem mass spectrometry

In conjunction with an AOAC Task Group on dietary supplements, a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was validated for measurement of 6 major alkaloids in raw ephedra sinica herb, ephedra extracts, ephedra tablets, complex dietary supplements containing ephedra, and a high-protein drink mix containing ephedra. The amount of ephedrine-type alkaloids present was determined by LC with mass selective detection. Six replicates of each matrix were analyzed on 3 separate occasions. The presence of 6 ephedrine-type alkaloids was detected at a level > 0.5 microg/g based on a 0.5 g sample. The standard curve range for this assay is from 0.02 to 1.0 microg/mL. Appropriate dilutions covered a wide range of specific alkaloid concentrations. The calibration curves for all 6 analytes had correlation coefficients > 0.995.     

Nitrogen depth distribution, interface and structure analysis of SiNx layers produced by low-energy ion implantation

Thin silicon nitride (SiN _x ) layers with the stoichiometric N/Si ratio of 1.33 in the maximum of the concentration depth distributions of nitrogen were produced by implanting 10 keV¹⁵N ₂ ⁺ in 100 silicon at room temperature under high vacuum conditions. The depth distribution of the implanted isotope was measured by resonance nuclear reaction analysis (NRA), whereas the layer structure of the implanted region and the geometrical thickness of the layers were characterised by high resolution transmission electron microscopy (TEM). SiN _x layers with a thickness of about 30 nm were determined by NRA. Channeling Rutherford backscattering spectrometry was used to determine the disorder in the silicon substrate. Sharp interfaces of a few nanometers between the highly disordered implanted region and the crystalline structure of the substrate thickness were observed by TEM. The high thermal stability of SiN _x layers with N/Si ratios from under to over stoichiometric could be shown by electron beam rapid thermal annealing (1100 °C for 15 s, ramping up and down 5 °C/s) and NRA.     

4 + 2]-Cycloaddition Reactions between beta-Acceptor-Substituted Enamines and 2-Vinylindole Radical Cations Acting as Hetero-Dienes

[4 + 2]-Cycloaddition reactions between 2-vinylindoles acting as hetero-dienes and beta-acceptor substituted cyclic and acyclic enamines can be induced by formation of 2-vinylindole radical cations either via anodic oxidation or photoelectron transfer (PET) using catalytic amounts of triarylpyrylium tetrafluoroborates as sensitizers. In this way, pyrido[1,2-a]indoles or indolo[1,2-a]hexahydro-1,8-naphthyridines are formed in one step with complete regio- and stereochemical control.     

A new synthetic route to compounds of the AFDX-type with affinity to muscarinic M2-receptor

[3-(1,3-Dioxo-1,3-dihydroisoindol-2-yl)-propyl]dimethyl-{6-[(1-{2-[(6-oxo-5,6-dihydro-benzo[e]pyrido[3,2-b][1,4]diazepine-11-carbonyl)amino]ethyl}piperidin-2-yl-methyl)-propylamino]hexyl}ammonium bromide a hybride containing a fragment of the antagonist of muscarinic receptor AFDX-384 and a W84 moiety known as allosteric modulator of antagonist binding, was synthesized in a divergent synthesis starting from pipecolic acid, phthalic anhydride and 3-amino-2-chloropyridine. This new microwave assisted route is very convenient and allows to modify the piperidine ring, the benzodiazepine system, the phthalimide moiety and the chains connecting the ring systems. Yields and reproducibility were satisfying.     

Indirect Electroorganic Syntheses—A Modern Chapter of Organic Electrochemistry [New Synthetic Methods (59)]

The electrochemical formation and regeneration of redox agents for organic syntheses (indirect electrolysis) widens the potential of electrochemistry, as higher or totally different selectivities can often be obtained while at the same time the energy input can be lowered significantly. Higher current densities can also be obtained by preventing otherwise often encountered electrode inhibition. New types of redox catalysts can be formed in-situ and can be regenerated after reaction with the substrates. This principle is of increasing importance also for the application of already known redox agents with regard to environmental protection, since large amounts of a product can be generated in a closed circuit using only relatively small amounts of the redox reagent. Consequently the operation of such a process can be greatly simplified, and the release of ecologically objectionable spent reagents into the environment can be prevented. The broad spectrum of redox catalysts currently in use includes, inter alia, metal salts in very low or high oxidation states, halogens in various oxidation states, and, in particular, a wide variety of transition-metal complexes. A great deal of progress has recently been made in the application of organic electron transfer agents, since compounds have been found that are sufficiently stable in both the reduced as well as the oxidized state.     

Pulse Fourier Transform 13C-NMR Spectroscopy,Principles and Applications

As a result of the development of pulse Fourier transform NMR spectroscopy ¹³C resonance has become accepted as a means of elucidating the structures of organic compounds having the natural ¹³C abundance. Assignment of the signals is facilitated by broad-band and off resonance proton decoupling and by knowledge of longitudinal relaxation times. The pulse Fourier technique, which is more sensitive and faster than conventional NMR spectroscopy because of multi-channel excitation, allows ¹³C measurements within a short time even on dilute samples of high molecular weight compounds without prior enrichment in ¹³C.     

Silver Complexes with Cyanoguanidine: Preparation and Crystal Structures of [Ag(cgn)2]F and [Ag(cgn)2][BF4]

The silver cyanoguanidine complexes [Ag(cgn)₂]F ( 1 ), [Ag(cgn)₂][BF₄] ( 2 ), [Ag(cgn)₂][ClO₄] ( 3 ) and [Ag(cgn)][NO₃] ( 4 ) were obtained from aqueous solutions of the corresponding silver salts and cyanoguanidine. The crystal structures of 1 and 2 have been determined by single crystal X‐ray diffraction. 1 : Space group P1¯, Z = 2, cell constants at —65 °C: a =618.18(3), b = 761.49(8), c = 971.2(1) pm; α = 93.56(1), β = 97.439(8), γ = 97.376(9)β; R₁ = 0.0218 2 : Space group P1¯, Z = 2, cell constants at —65 °C: a = 549.79(9), b = 958.17(17), c = 1121.04(12) pm; α = 90.026(13), β = 102.520(11), γ = 95.937(14)°; R₁ = 0.0283.     

Synthesis of ‘difficult’ peptide sequences: application of a depsipeptide technique to the Jung-Redemann 10- and 26-mers and the amyloid peptide Aβ(1-42)

Recently a 26-mer peptide 1 incorporating Ser and Thr was described as a ‘difficult’ sequence that could not be synthesized by standard methods. If the first Ser residue was used to incorporate a depsipeptide unit, the resulting hybrid was readily assembled. The 26-mer ester was then converted to the native peptide by an O→N acyl shift. The technique may be general for other systems containing appropriate Ser and Thr units and was demonstrated here for the case of the amyloid peptide Aβ(1-42).     

Hydrogen exchange studies on Alzheimer's amyloid-beta peptides by mass spectrometry using matrix-assisted laser desorption/ionization and electrospray ionization

The conformation and aggregation behavior of synthetic Alzheimer's amyloid peptides (Abeta) has been investigated using hydrogen-deuterium exchange measured by electrospray ionization mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry. Mass spectrometric fragmentation of deuterated Abeta peptides was carried out by collision-induced dissociation, inlet fragmentation, and post-source decay. In contrast to the C-terminally truncated peptides Abeta(1-40) and Abeta(1-36) showing full hydrogen-deuterium exchange, Abeta(1-42) and the pyroglutamyl peptide Pyr(3)-Abeta(3-42) produced more complex signal patterns resulting from the formation of beta-sheet-structured oligomers having 18-20 strongly protected protons. Using mass spectrometric fragmentation the results show that the reduced isotope exchange of Abeta(1-42) can be attributed to the central part of the chain comprising residues 8-23. This confirms involvement of the hydrophobic binding domain LVFFA in the course of Abeta aggregation and demonstrates that hydrogen-deuterium exchange in combination with mass spectrometry is well suited for structural analysis of monomeric and reversibly associated amyloid peptides using picomole quantities of material.