Square‐Planar Carbonylchlororhodium(I) Complexes Containing trans‐Spanning Diphosphine Ligands as Catalysts for the Carbonylation of Methanol

The rhodium(I) complexes trans‐[Rh(diphos)(CO)Cl] 7 (diphos=pbpb), 8 (diphos=nbpb), and 9 (diphos=cbpb) were synthesized (Scheme 4) and used as catalysts for the carbonylation of MeOH to AcOH (Scheme 1). The trans coordination imposed by the rigid C‐spacer framework of the diphos ligands pbpb, nbpb, and cbpb, demonstrated by ³¹P‐NMR and IR spectroscopy of 7 – 9 and unambiguously confirmed by single‐crystal X‐ray structure analysis of 7 , improved the thermal stability of the rhodium(I) system under carbonylation conditions and, hence, the catalytic performance of the complexes. For the catalytic carbonylation of MeOH, the active catalyst could be prepared in situ from the mixture of [Rh(CO)₂Cl]₂ and the corresponding diphos ligand pbpb, nbpb, or cbpb, giving the same results as carbonylation in the presence of the isolated complexes 7, 8 or 9 (see Table). The highest activity was observed for complex 7 (or the mixture [Rh(CO)₂Cl]₂/pbpb, the catalytic turnover number (TON) being 950 after 15 min (170°, 22 bar).     

Fungicidal properties of meso-arylglycosylporphyrins: influence of sugar substituents on photoinduced damage in the yeast Saccharomyces cerevisiae

A series of neutral meso-arylglycosylporphyrins has been tested in order to evaluate their potency as antifungal agents against the yeast Saccharomyces cerevisiae. Photodynamic activity of these molecules results in intracellular damage as evidenced by the loss of clonogenicity and DNA fragmentation. The ability of these photosensitizers to permeate yeast cells is determined by microspectrofluorimetry and is correlated with their antifungal potency. Amphiphilic porphyrin derivatives are shown to exhibit the more pronounced photoactivity.     

Determination of various deformation processes in impact-modified PMMA at strain rates up to 105%/min

The deformation processes in impact-modified PMMA, which deforms homogeneously, were determined by means of the stress/strain experiment (, ) with simultaneous lateral strain measurement (_lat) in a wide range of strain rates () up to 10⁵%/min (impact stress). The elastic, plastic cavitation and plastic shear processes were determined as a function of strain. Therefore we calculated the elastic strain ( _el), the elastic volume expansion ( _{vol el}), the cavitation strain ( _cav), which is identical with the plastic volume expansion ( _{vol pl}), the shear strain ( _sh) and the energy densities (W_el, W_cav, W_sh) related to these three processes.For strains of 3 % onward it was found that plastic shear processes and plastic cavitation processes are responsible for a partial loss of elastically stored energy. Both plastic processes turn out to be mostly anelastic deformations, their amount depending strongly on the strain rate. The contributions of the processes to the total deformation of the unmodified PMMA in its strain range are similar to those of the impact-modified PMMA, and the high impact strength is caused by a shift of the catastrophic rupture to very high strains.     

Excess Molar Volumes and Liquid–Liquid Equilibria of the Ionic Liquid 1-Methyl-3Octyl-Imidazolium Tetrafluoroborate Mixed with Butan-1-ol and Pentan-1-ol

Experimental densities were measured for the system 1-methyl-3-octyl-imidazolium tetrafluoroborate [OMIM][BF₄] + butan-1-ol, + pentan-1-ol at 298.15 K and ambient pressure using a vibrating tube densimeter, taking into account the influence of the viscosity correction. Excess molar volumes V^E have been determined. V^E is quite small and negative in the alcohol-rich range of the mixture composition and positive in the alcohol-poor range. LLE data of [OMIM][BF₄] + pentan-1-ol have been measured using a laser light scattering cell for detecting cloud points at different compositions in the temperature range of 282–292 K. A miscibility gap with an upper critical solution temperature (UCST) of 292 K has been found.     

Analysis of post-translational modification and characterization of the domain structure of dynamin A from Dictyostelium discoideum

The post-translational modifications of the 96 kDa protein dynamin A from Dictyostelium discoideum were analyzed using Q-TOF mass spectrometry. The accurate molecular mass of the intact protein revealed a covalent modification causing an additional mass of 42 Da. The modification could be identified as N-terminal acetylation by tandem mass spectrometry. Extracted ion chromatograms for the a(1) and b(1) ion of the tryptic T1 peptide were used to detect the acetylated peptide within 54 nanoelectrospray ionization tandem mass spectra. Owing to the accurate molecular mass of the intact protein, additional covalent modifications could be excluded. In addition to the covalent modification, the domain structure of dynamin A was determined by applying a combination of limited proteolysis, sodium dodecylsulfate polyacrylamide gel electrophoresis, automated tandem mass spectrometry and protein database searching.     

Settling of paraffin crystals in cooled middle distillate fuels

The mechanism of action of additives that control the sedimentation of paraffin crystals after their crystallization in model diesel oil has been studied by means of a new experimental approach. The chemical analysis of the crystals and detailed measurements of the sedimentation phenomenon give new insights into this complex process. Thus, the wax antisettling additives used for preventing wax crystal sedimentation adsorb at the surfaces of wax particles and provide them with enhanced colloidal stability. The settling rate is not related to the size of the crystals or the viscosity of the liquid medium, but to the ability of the additives to prevent the aggregation of wax crystals. The reported methodology makes it possible to investigate the fundamental mechanisms, but also to evaluate structure-activity relationships of the various additives used in the petroleum industry.     

Synthesis of chiral N-protected 1,2-dihydro-quinoline-2-carbonitrile and 1,2-dihydro-isoquinoline-1-carbonitrile via an asymmetric Reissert reaction

Addition of cyanide ion to chiral N-acyl-quinolinium and N-acyl-isoquinolinium salts led selectively to 1,2-addition products. Removal of the chiral auxiliary affords the title compounds in pure enantiomeric form.     

Diaminocarbene- and Fischer-carbene complexes of palladium and nickel by oxidative insertion: preparation, structure, and catalytic activity

Oxidative insertion of [Pd(PPh3)4] or [Ni(cod)2]/PPh3 into the C-Cl bond of various 2-chloroimidazolinium- and other -amidinium salts affords metal-diaminocarbene complexes in good to excellent yields. This procedure is complementary to existing methodology in which the central metal does not change its oxidation state, and therefore allows to incorporate carbene fragments that are difficult to access otherwise. The preparation of a variety of achiral as well as enantiomerically pure, chiral metal-NHC complexes (NHC = N-heterocyclic carbene) and metal complexes with acyclic diaminocarbene ligands illustrates this aspect. Furthermore it is shown that oxidative insertion also paves a way to prototype Fischer carbenes of Pd(II). Since the required starting materials are readily available from urea- or thiourea derivatives, this novel approach allows for substantial structural variations of the ligand backbone. The catalytic performance of the resulting library of nickel- and palladium-carbene complexes has been evaluated by applications to prototype Suzuki-, Heck-, and Kumada-Corriu cross-coupling reactions as well as Buchwald-Hartwig aminations. It was found that even Fischer carbenes show appreciable catalytic activity. Moreover, representative examples of all types of neutral and cationic metal-carbene complexes formed in this study have been characterized by X-ray crystallography.     

A convenient synthesis of new aminomethylenedioxypyrroloindoles via an iminium salt

Cyclization of 2-(1-pyrrolyl)piperonylcarboxamide derivatives gave iminium perchlorates which afforded 9-(N-substituted-imino) and 9-(N-substituted amino)-6,7-methylenedioxypyrrolo[1,2-a]indoles.     

Crystal and molecular structures ofp-(1,1,3,3-tetramethylbutyl)calix[5]arene and its 1 : 1 complex with toluene

A cyclic pentamer was obtained fromp-(1,1,3,3-tetramethylbutyl) phenol. It crystallizes from a mixture of acetone and toluene at room temperature giving a 1 : 1 complex with toluene (compound A), whereas at 50°C the empty form (compound B) is obtained. Crystals of A are orthorhombic, space groupPna2₁,a = 20.083(2),b = 12.936(6),c = 28,423(1) Å,Z = 4, finalR value = 0.067. The empty form, B, is monoclinicP2₁/c,a = 18.695(2),b = 11.673(5),c = 35.100(4) Å, = 114.33(1),Z = 4, finalR value = 0.135. The macrocycle is in the cone conformation for both compounds; the toluene molecule lies in the cone as often found for calix[4]arenes.