Reactivity of indanedioneketene dimer with amines

The highly reactive indanedioneketene 5, resulting from the thermal decomposition of phenyliodonium ylide of 2-hydroxy-1,4-naphthoquinone (lawsone, 4), in the absence of nucleophiles dimerizes to the corresponding tetraoxo spiro oxetanone 6 in quantitative yield. This oxetanone exhibits an interesting reactivity toward amines.     

Monitoring and evaluation of dechlorination processes using compound-specific chlorine isotope analysis

A simple, quick and sensitive method for the compound-specific stable chlorine isotope analysis of chlorinated solvents by conventional quadrupole gas chromatography/mass spectrometry (GC/MS) is presented. With this method, compound-specific stable chlorine isotope ratios of typical chlorinated solvents like tetrachloroethene (PCE) and trichloroethene (TCE) can be determined quantitatively within 30 min by direct injection. The chlorine isotope ratios of target substances are calculated from the peak areas of several selected molecular ions and fragment ions of the substances, using a set of unique mathematical equations. The precision of the method was demonstrated through reproducibility tests. An internal precision of +/-0.4 per thousand to +/-1.1 per thousand was obtained when analyzing PCE and TCE in the 10-1000 pmol range. The validity of the method was further demonstrated by determining the chlorine isotopic fractionation factor during the reductive dechlorination of TCE in a batch experiment using zero-valent iron. The chlorine isotopic fractionation factor was calculated as 0.9976 +/- 0.0011 with a correlation coefficient of 0.9469 (n = 38). The high correlation coefficient indicates that compound-specific stable chlorine isotope analysis can be performed with sufficient accuracy using conventional quadrupole GC/MS when significant fractionation takes place during a reaction. For the first time, the chlorine isotope fractionation factor of TCE during an abiotic anaerobic dechlorination process was determined using quadrupole GC/MS, without offline sample preparation.     

Analysis of a chlorosulfolipid from Ochromonas danica by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (ToF) mass spectrometry (MS) is an established tool for analyzing high mass molecules, such as proteins, whereas it attracts far less interest in the field of lipid analysis. In the study reported here a new chlorosulfolipid (CSL), 3,8,12,15-tetrachloroeicosane-1,17,18-triyl tris(hydrogen sulfate), was identified from the alga Ochromonas danica and de novo characterized by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight (MALDI-QIT-ToF) MS in negative ion mode. This method provides an effective alternative for the analysis of compounds directly derived from organic cell extracts. For MALDI analyses several frequently used solid MALDI matrices as well as some ionic liquid matrices (ILMs) were tested to enhance the analyte response to UV-laser and its ionization. The molecular weight of the observed compound could be determined as Li-, Na- and K-adducts [M+Me-2H]-. The characteristic isotopic patterns of the measured ions and the well-allocated molecular fragments by MS1, MS2 and MS3 indicate the fourfold chlorination and threefold sulfation of the investigated compound. The MS fragmentation alongside of the chlorine-bearing C-atoms is accompanied by the generation of a double bond at the opposite fragment in MS1. This obtained fragmentation pattern provides an insight into the allocation of the chlorine-bearing C-atoms along the carbon chain.     

Influence of particle aspect ratio on the midinfrared extinction spectra of wavelength-sized ice crystals

We have used the T-matrix method and the discrete dipole approximation to compute the midinfrared extinction cross-sections (4500-800 cm(-1)) of randomly oriented circular ice cylinders for aspect ratios extending up to 10 for oblate and down to 1/6 for prolate particle shapes. Equal-volume sphere diameters ranged from 0.1 to 10 microm for both particle classes. A high degree of particle asphericity provokes a strong distortion of the spectral habitus compared to the extinction spectrum of compactly shaped ice crystals with an aspect ratio around 1. The magnitude and the sign (increase or diminution) of the shape-related changes in both the absorption and the scattering cross-sections crucially depend on the particle size and the values for the real and imaginary part of the complex refractive index. When increasing the particle asphericity for a given equal-volume sphere diameter, the values for the overall extinction cross-sections may change in opposite directions for different parts of the spectrum. We have applied our calculations to the analysis of recent expansion cooling experiments on the formation of cirrus clouds, performed in the large coolable aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe at a temperature of 210 K. Depending on the nature of the seed particles and the temperature and relative humidity characteristics during the expansion, ice crystals of various shapes and aspect ratios could be produced. For a particular expansion experiment, using Illite mineral dust particles coated with a layer of secondary organic matter as seed aerosol, we have clearly detected the spectral signatures characteristic of strongly aspherical ice crystal habits in the recorded infrared extinction spectra. We demonstrate that the number size distributions and total number concentrations of the ice particles that were generated in this expansion run can only be accurately derived from the recorded infrared spectra when employing aspect ratios as high as 10 in the retrieval approach. Remarkably, the measured spectra could also be accurately fitted when employing an aspect ratio of 1 in the retrieval. The so-deduced ice particle number concentrations, however, exceeded the true values, determined with an optical particle counter, by more than 1 order of magnitude. Thus, the shape-induced spectral changes between the extinction spectra of platelike ice crystals of aspect ratio 10 and compactly shaped particles of aspect ratio 1 can be efficiently balanced by deforming the true number size distribution of the ice cloud. As a result of this severe size/shape ambiguity in the spectral analysis, we consider it indispensable to cross-check the infrared retrieval results of wavelength-sized ice particles with independent reference measurements of either the number size distribution or the particle morphology.     

Microwave and quantum chemical study of propa-1,2-dienyl thiocyanate (H2C=C=CHSC triple bond N)

The microwave spectrum of propa-1,2-dienyl thiocyanate (H2C=C=CHSC triple bond N) has been investigated in the 24-40 and 50-80 GHz spectral regions. The spectrum of one conformer was assigned. This rotamer, which has a C-C-S-C dihedral angle of about 134 degrees from synperiplanar, is at least 2 kJ/mol more stable than any other form. Two vibrationally excited states assumed to belong to the first excited state of the C-S torsional vibration and to a low bending mode were assigned. Their frequencies were determined to be 62(20) and 155(30) cm-1, respectively. The microwave work has been augmented by ab initio calculations at the MP2/aug-cc-pVTZ and density functional theory calculations at the B3LYP/aug-cc-pVTZ level of theory. The B3LYP calculations are generally in better agreement with the observations than the MP2 calculations.     

A microwave and quantum chemical study of (trifluoromethyl)thiolacetic acid, CF3COSH, a compound with an unusual double-minimum potential

The microwave spectra of CF3COSH and one deuterated species, CF3COSD, have been investigated by Stark spectroscopy in the 40-80 GHz spectral range at -78 degrees C and by quantum chemical calculations using the HF, MP2, and B3LYP procedures with the aug-cc-pVTZ basis set. The microwave spectrum of one conformer was assigned. The conformations of the COSH and CF3 groups determine the overall conformation of this rotamer. It was not possible experimentally to find precise values for the associated dihedral angles, but it appears that the COSH group is distorted somewhat from an exact synperiplanar arrangement, while the CF3 group is rotated several degrees from a position where one of the C-F bonds eclipses the C-S bond. This rotamer tunnels through a transition state that has an exact Cs symmetry, where one C-F bond eclipses the C-S bond and the COSH group is synperiplanar. Relative intensity measurements yielded 28(15) cm-1 for the tunneling frequency. Two additional vibrationally excited states were assigned and their frequencies determined to be 94(30) and 184(40) cm-1, respectively. The theoretical calculations predict conflicting conformational properties for the identified rotamer. The B3LYP calculations find an exact synperiplanar arrangement for the COSH group, whereas the MP2 and HF calculations predict that this group is distorted slightly form this conformation. One of the C-F bonds is found to eclipse the C-S bond in the B3LYP calculations, while the MP2 calculations predict a slight deviation and the HF calculations a large deviation from the eclipsed position, as the corresponding F-C-C-S dihedral angle is calculated to be 0.9 degrees (MP2) and 27.6 degrees (HF). All three methods of calculations predict that a second rotamer coexists with the identified form but is several kJ/mol less stable. The spectrum of this form, which has overall Cs symmetry and is predicted to have an antiperiplanar conformation for the COSH group with one of the C-F bonds eclipsing the C=O bond, was not identified.     

Synthetic Processes toward Nitriles without the Use of Cyanide: A Biocatalytic Concept Based on Dehydration of Aldoximes in Water

While belonging to the most fundamental functional groups, nitriles represent a class of compound that still raises challenges in terms of an efficient, cost-effective, general and, at the same time, sustainable way for their synthesis. Complementing existing chemical routes, recently a cyanide-free enzymatic process technology based on the use of an aldoxime dehydratase (Oxd) as a biocatalyst component has been developed and successfully applied for the synthesis of a range of nitrile products. In these biotransformations, the Oxd enzymes catalyze the dehydration of aldoximes as readily available substrates to the nitrile products. Herein, these developments with such enzymes are summarized, with a strong focus on synthetic applications. It is demonstrated that this biocatalytic technology has the potential to “cross the bridge” between the production of fine chemicals and pharmaceuticals, on one hand, and bulk and commodity chemicals, on the other.     

Ultrasonic assistance syntheses of new nano-sized lead(II) coordination polymers: motifs for PbO preparation

Nanoparticles of two new coordination polymers, [Pb(5,5′-dm-2,2′-bpy)Cl₂] _n (1) and [Pb(5,5′-dm-2,2′-bpy)Br₂] _n (2), {5,5′-dm-2,2′-bpy = 5,5′-dimethyl-2,2′-bipyridine}, have been synthesized by ultrasonic assistance at different concentrations and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Metal oxide nanoparticles were prepared from thermal decomposition of compounds 1 and 2 at 600 °C under air atmosphere. Scanning electron microscopy images of the residue which are obtained from calcination of compounds 1, 2 show the formation of lead(II) oxide nanoparticles with an average diameter of about 80 and 90 nm for compounds 1 and 2, respectively.     

Silver(I) ions bridged by pyridazine: doubling the ligand functionality for the design of unusual 3D coordination frameworks

Nitrogen donor tetradentate ligands 4,4'-bipyridazine (bpdz) and pyridazino[4,5-d]pyridazine (pp) were prepared by inverse electron demand Diels-Alder cycloaddition reactions of 1,2,4,5-tetrazine. Examination of their behaviour towards silver(i) ions revealed a special potential of the ligands for the design of 3D coordination frameworks involving characteristic polynuclear and polymeric silver(i)-pyridazine motifs and multiple coordination of the ligands. Ag(4)(pp)(5)(ClO(4))(4) and Ag(4)(pp)(5)(SiF(6))(BF(4))(2).4H(2)O adopt a unique 3D trinodal 4,4,5-connected topology based upon five-fold coordination of the metal ions and tetradentate bridging function of the organic modules. Complexes Ag(3)(L)(3)(SO(3)CF(3))(3).nH(2)O and Ag(4)(L)(3)(X)(4).nH(2)O (L = bpdz, pp; X = BF(4)(-), 0.5SiF(6)(2-)) illustrate formation of highly-connected frameworks incorporating trinuclear clusters as an origin of the net connectivity. In the carboxylate complexes Ag(2)(L)(R(F)COO)(2) (R(F) = CF(3), C(2)F(5), C(3)F(7)) the pyridazine and acido ligands act as complementary linkers for generation of 3D frameworks involving helicate motifs. Fused bicyclic pyridazine pp is a unique system combining very efficient sigma(N)-donor ability and pronounced pi-acidity. The coordination frameworks commonly exhibit strong anion-pi interactions, including unprecedented examples of double anion-pi,pi binding that occur between pyridazino[4,5-d]pyridazine as a double pi,pi-receptor for geometry complementary SiF(6)(2-) anions.     

4,4'-Bipyridazine: a new twist for the synthesis of coordination polymers

A new polydentate ligand 4,4'-bipyridazine (4,4'-bpdz) was prepared by employing inverse electron demand cycloaddition of 1,2,4,5-tetrazine. A unique combination of structural simplicity, ampolydentate character and efficient donor properties towards Cu(I), Cu(II) and Zn(II) provide wide new possibilities for the synthesis of coordination polymers incorporating the 4,4'-bpdz module either as a bi-, tri- or tetradentate connector between the metal ions. 1D coordination polymers Cu(2)(4,4'-bpdz)(CH(3)CO(2))(4) x 4H(2)O and Zn(4,4'-bpdz)(NO(3))(2), and interpenetrated (4,4)-nets in [Cu(4,4'-bpdz)(2)(H(2)O)(2)]S(2)O(6) were closely related to 4,4'-bipyridine compounds. 1D "ladder-like" polymer Cu(2)(4,4'-bpdz)(3)(CF(3)CO(2))(4) and the unprecedented 3D binodal net ({8(6)}{6(3);8(3)}) in [Cu(3)(4,4'-bpdz)(6)(H(2)O)(4)](BF(4))(6) x 6H(2)O were based upon a combination of linear and angular organic bridges. Complex [Cu(3)(OH)(2)(4,4'-bpdz)(3)(H(2)O)(2){CF(3)CO(2)}(2)](CF(3)CO(2))(2) x 2H(2)O has a "NbO-like" 3D topology incorporating discrete dihydroxotricopper(II) clusters linked by tri- and tetradentate ligands. The tetradentate function of the 4,4'-bpdz ligand was especially relevant for copper(I) complexes, which adopt layered Cu(2)X(2)(4,4'-bpdz) (X = Cl, Br) or 3D chiral framework (X = I) structures based upon infinite (CuX)(n) chains. The electron deficient character of the ligand was manifested by short anion-pi interactions (O-pi 3.02-3.20; Cl-pi 3.35 A), which may be involved as a factor for controlling the supramolecular structure.