Gas chromatographic determination of aromatic amines in water samples after solid-phase extraction and derivatization with iodine: I. Derivatization

A new method for the selective determination of aromatic amines is presented, which is based on the solid-phase extraction at pH 9 and subsequent derivatization of the analytes to the corresponding iodobenzenes. These can selectively and sensitively be determined with gas chromatography and electron-capture detection. Separation of at least 30 compounds in a single chromatographic run in 30 min is possible. With this method, 56 aromatic amines were investigated, and only in six cases no derivatives were obtained. Limits of quantitation were between 0.5 and 8 μg l⁻¹, but may still be lowered with higher sample volumes or different injection techniques. The application to water samples revealed the suitability for the investigation of ground, leachate and wastewater.     

Catalytic-kinetic absorptiostat technique with the indigo carmine—hydrogen peroxide reaction as the indicator reaction

The absorptiostat method previously described is used for the catalytic-kinetic determination of sulphur compounds (sulphide, thioacetamide. thiourea and thiosulphate) in the micromolar range by means of their catalytic action for the indigo carmine—hydrogen peroxide indicator reaction. The thiosulphate catalyst is activated by iron(III) or aluminium(III); aluminium(III) is deactivated by fluoride. On this basis, iron(III) is determined in the ng range, and aluminium(III) and fluoride in the μg range.     

Synthesen und Reaktionen von Pyridazinderivaten, 11. Mitt.: 5-Acyl-4-pyridazincarbonsäurrester als „key intermediates” für 4-Acylpyridazine und 4-Alkyl-bzw. 4-Arylpyridazino[4,5-d]pyridazin-1 (2H) one

A convenient general method of preparing 4-acylpyridazines (4) is reported. It involves homolytic acylation of ethyl-4-pyridazinecarboxylate yielding ethyl-5-acyl-4-pyridazinecarboxylates (2) which easily can be converted to4 by alkaline hydrolysis followed by decarboxylation. The hitherto unknown pyridazino[4,5-d]pyridazine-1 (2H) ones bearing an alkyl- or arylsubstituent on C-4 (5a-g) were prepared in quantitative yields by reaction of2 with hydrazine.

10. Mitt.:G. Heinisch, A. Jentzsch undI. Kirchner, Tetrahedron Lett.1978, 619.     

Photoreactivity of psoralen derivatives in micelles: the roles of hydrophobicity and heavy atom substitution

Intersystem crossing quantum yields of two psoralen derivatives, bromopsoralen (BrMOP) and hexylpsoralen (8-HOP) were measured in ethanol and water by means of laser flash photolysis. Compared to 8-methoxypsoralen (8-MOP), the triplet quantum yields of BrMOP and 8-HOP in ethanol are increased by a factor of 5 and 30, respectively, while BrMOP in aqueous solution shows a twofold enhancement with respect to 8-MOP. Radical cations and hydrated electrons were generated by photoionization in micellar solution upon excitation at 266nm. A nonlinear relationship between transient yield and photon fluence was obtained for each compound, indicating that a two-photon mechanism is predominant in the photoionization of the sensitizers. The photoionization efficiencies are significantly higher in anionic sodium dodecyl sulfate (SDS) than in cationic cetyltrimethylammonium bromide (CTAB) micelles, reflecting the influence of micelle charge on the efficiency of the separation of the photoproduced charge carriers. The photoionization efficiencies of 8-HOP and 8-MOP are similar. It is concluded that the intersystem crossing properties of BrMOP show a substantial heavy atom effect, whereas the effects of hydrophobic substitution on photoionization efficiency are minor.     

Fragmentation of intra-peptide and inter-peptide disulfide bonds of proteolytic peptides by nanoESI collision-induced dissociation

Characterisation and identification of disulfide bridges is an important aspect of structural elucidation of proteins. Covalent cysteine-cysteine contacts within the protein give rise to stabilisation of the native tertiary structure of the molecules. Bottom-up identification and sequencing of proteins by mass spectrometry most frequently involves reductive cleavage and alkylation of disulfide links followed by enzymatic digestion. However, when using this approach, information on cysteine-cysteine contacts within the protein is lost. Mass spectrometric characterisation of peptides containing intra-chain disulfides is a challenging analytical task, because peptide bonds within the disulfide loop are believed to be resistant to fragmentation. In this contribution we show recent results on the fragmentation of intra and inter-peptide disulfide bonds of proteolytic peptides by nano electrospray ionisation collision-induced dissociation (nanoESI CID). Disulfide bridge-containing peptides obtained from proteolytic digests were submitted to low-energy nanoESI CID using a quadrupole time-of-flight (Q-TOF) instrument as a mass analyser. Fragmentation of the gaseous peptide ions gave rise to a set of b and y-type fragment ions which enabled derivation of the sequence of the amino acids located outside the disulfide loop. Surprisingly, careful examination of the fragment-ion spectra of peptide ions comprising an intramolecular disulfide bridge revealed the presence of low-abundance fragment ions formed by the cleavage of peptide bonds within the disulfide loop. These fragmentations are preceded by proton-induced asymmetric cleavage of the disulfide bridge giving rise to a modified cysteine containing a disulfohydryl substituent and a dehydroalanine residue on the C-S cleavage site.     

Structure determination of protein-ligand complexes by transferred paramagnetic shifts

Rational drug design depends on the knowledge of the three-dimensional (3D) structure of complexes between proteins and lead compounds of low molecular weight. A novel nuclear magnetic resonance (NMR) spectroscopy strategy based on the paramagnetic effects from lanthanide ions allows the rapid determination of the 3D structure of a small ligand molecule bound to its protein target in solution and, simultaneously, its location and orientation with respect to the protein. The method relies on the presence of a lanthanide ion in the protein target and on fast exchange between bound and free ligand. The binding affinity of the ligand and the paramagnetic effects experienced in the bound state are derived from concentration-dependent (1)H and (13)C spectra of the ligand at natural isotopic abundance. Combined with prior knowledge of the crystal or solution structure of the protein and of the magnetic susceptibility tensor of the lanthanide ion, the paramagnetic data define the location and orientation of the bound ligand molecule with respect to the protein from simple 1D NMR spectra. The method was verified with the ternary 30 kDa complex between the lanthanide-labeled N-terminal domain of the epsilon exonuclease subunit from the Escherichia coli DNA polymerase III, the subunit theta, and thymidine. The binding mode of thymidine was found to be very similar to that of thymidine monophosphate present in the crystal structure.     

Synthesis and Investigation of Advanced Energetic Materials Based on Bispyrazolylmethanes

Herein we present the preparation and characterization of three new bispyrazolyl‐based energetic compounds with great potential as explosive materials. The reaction of sodium 4‐amino‐3,5‐dinitropyrazolate ( 5 ) with dimethyl iodide yielded bis(4‐amino‐3,5‐dinitropyrazolyl)methane ( 6 ), which is a secondary explosive with high heat resistance (T_dec=310 °C). The oxidation of this compound afforded bis(3,4,5‐trinitropyrazolyl)methane ( 7 ), which is a combined nitrogen‐ and oxygen‐rich secondary explosive with very high theoretical and estimated experimental detonation performance (V_det (theor)=9304 m s^?1 versus V_det(exp)=9910 m s^?1) in the range of that of CL‐20. Also, the thermal stability (T_dec=205 °C) and sensitivities of 7 are auspicious. The reaction of 6 with in situ generated nitrous acid yielded the primary explosive bis(4‐diazo‐5‐nitro‐3‐oxopyrazolyl)methane ( 8 ), which showed superior properties to those of currently used diazodinitrophenol (DDNP).     

Chloride-catalyzed oxidation of phenol in pulsed-laser irradiation titanium dioxide sols

The kinetics of photolysis of phenol in presence of two kinds of TiO₂ colloid in acid aqueous solution medium was studied by transient absorption spectroscopy. The absorbance and quantum yield of the phenoxyl radicals is strongly influenced by the chloride ions. The process of laser flash photolysis of phenol in the presence of chloride has been discussed.