Reduktion 4-substituierter Acetophenone mittels Hefe

The velocity of reduction of 4-substituted acetophenones by baker's yeast is decreased by electron donating substituents. The steric course, however, is little influenced and (S)-1-arylethanols2 are generally formed with over 90% enantiomeric excess.

     

Complex formation between nickel(0) and a phosphaalkene: Influence of the second ligand on the η1- and η2-coordination mode

The η²-complex (bipy)Ni(XyPCPh₂) has been prepared and its structure determined by X-ray analysis. In contrast, Ni(CO)₄ forms η¹ -complexes by replacement of one or two CO ligands by XyPCPh₂.     

Organometallic Fluorides of Zirconium and Hafnium in the Synthesis of Carboxylate Complexes: Molecular Structures of [{(eta(5)-C(5)Me(5))ZrF(OCOCF(3))(2)}(2)] and [(eta(5)-C(5)Me(5))(2)Zr(OCOCF(3))(2)

The reaction of [(eta(5)-C(5)Me(5))ZrF(3)] and [(eta(5)-C(5)Me(5))HfF(3)] with Me(3)SiOCOCF(3) yields the dinuclear complexes [{(eta(5)-C(5)Me(5))ZrF(OCOCF(3))(2)}(2)] (1) and [{(eta(5)-C(5)Me(5))HfF(OCOCF(3))(2)}(2)] (2), regardless of the molar ratio employed. [(eta(5)-C(5)Me(5))(2)ZrF(2)] reacts with 1 and 2 equiv of Me(3)SiOCOCF(3) to form the mononuclear compounds [(eta(5)-C(5)Me(5))(2)Zr(OCOCF(3))(2)] (3) and [(eta(5)-C(5)Me(5))(2)ZrF(OCOCF(3))] (4), respectively. The molecular structures of 1 and 3 have been determined by single-crystal X-ray analysis: 1, triclinic, P&onemacr;, a = 9.508(3) ?, b = 11.002(4) ?, c = 17.528(3) ?, alpha = 78.55(4), beta = 76.80(2), gamma = 87.51(2) degrees, V = 1750(1) ?(3), Z = 2, R = 0.0378; 3, monoclinic, C2/c, a = 18.553(4) ?, b = 9.110(2) ?, c = 16.323(3) ?, beta = 114.88(3) degrees, V = 2503(1) ?(3), Z = 4, R = 0.0457. Compound 1 shows bridging bidentate and chelating carboxylate ligands as well as bridging fluorine atoms. The zirconium atoms are seven coordinated and have an 18-electron configuration. X-ray studies of 3 reveal two structural components where the carboxylate ligands coordinate in a monodentate (major component) and a chelating manner (minor component).     

The photolytic reaction between [ReN(H2O)(CN)4]2− and 1,2-ethanediamine. The crystal structure of tetraphenylphosphonium μ-1,2-ethanediamine-N,N′-bis[tetracyanonitridorhenate(V)] tetrahydrate

An aqueous solution of [ReN(H₂O)(CN)₄]^2– and 1,2-ethanediamine was irradiated in a photolytic reactor. The reaction product, which was isolated as yellow crystals suitable for X-ray structure determination, is a novel complex with the 1,2-ethanediamine acting as a bridge between two rhenium atoms. The crystal structure of (PPh₄)₄[{ReN(CN)₄}₂(-en)] · 4H₂O was determined from three-dimensional X-ray diffraction data. The [{ReN-(CN)₄}₂(-en)]^4– anion has a distorted octahedral geometry around both rhenium atoms with Re(1) displaced by 0.35 and Re(2) by 0.31 Å towards the respective nitrido ligands from the equatorial planes formed by the carbon atoms of the four cyano ligands of each rhenium atom.     

Interpretable molecular models for molybdenum disulfide and insight into selective peptide recognition

Molybdenum disulfide (MoS₂) is a layered material with outstanding electrical and optical properties. Numerous studies evaluate the performance in sensors, catalysts, batteries, and composites that can benefit from guidance by simulations in all-atom resolution. However, molecular simulations remain difficult due to lack of reliable models. We introduce an interpretable force field for MoS₂ with record performance that reproduces structural, interfacial, and mechanical properties in 0.1% to 5% agreement with experiments. The model overcomes structural instability, deviations in interfacial and mechanical properties by several 100%, and empirical fitting protocols in earlier models. It is compatible with several force fields for molecular dynamics simulation, including the interface force field (IFF), CVFF, DREIDING, PCFF, COMPASS, CHARMM, AMBER, and OPLS-AA. The parameters capture polar covalent bonding, X-ray structure, cleavage energy, infrared spectra, bending stability, bulk modulus, Young''s modulus, and contact angles with polar and nonpolar solvents. We utilized the models to uncover the binding mechanism of peptides to the MoS₂ basal plane. The binding strength of several 7mer and 8mer peptides scales linearly with surface contact and replacement of surface-bound water molecules, and is tunable in a wide range from −86 to −6 kcal mol⁻¹. The binding selectivity is multifactorial, including major contributions by van-der-Waals coordination and charge matching of certain side groups, orientation of hydrophilic side chains towards water, and conformation flexibility. We explain the relative attraction and role of the 20 amino acids using computational and experimental data. The force field can be used to screen and interpret the assembly of MoS₂-based nanomaterials and electrolyte interfaces up to a billion atoms with high accuracy, including multiscale simulations from the quantum scale to the microscale.

We introduce a cutting-edge force field for molybdenum disulfide and use it to uncover mechanisms of peptide recognition and design.     

Polymer mediated self-assembly of magnetic nanoparticles

We present a simple polymer-mediated process of assembling magnetic FePt nanoparticles on a solid substrate. Alternatively absorbing the PEI molecule and FePt nanoparticles on a HO-terminated solid surface leads to a smooth FePt nanoparticle assembly with controlled assembly thickness and dimension. Magnetic measurements show that the thermally annealed FePt nanoparticle assembly as thin as three nanoparticle layers is ferromagnetic. The magnetization direction of this thin FePt nanoparticle assembly is readily controlled with the laser-assisted magnetic writing. The reported process can be applied to various substrates, nanoparticles, and functional macromolecules and will be useful for future magnetic nanodevice fabrication.     

Enantioselectivity of epoxide hydrolase catalysed oxirane ring opening: a 3D QSAR study

A 3D QSAR analysis (quantitative structure activity relationships) of a set of 2,2-disubstituted epoxides, substrates for epoxide hydrolases originating from four different organisms, was conducted by CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis), with respect to the enantioselective ring opening to the corresponding vicinal diol. Structural variations of the substrates include alkyl chains of different lengths, unsaturated moieties ((E)- and (Z)-alkenyl, alkinyl, aryl) and electronegative groups (ether oxygens, halogen atoms) at different locations within the 2-substituent group. Generally, all four organisms, namely Rhodococcus ruber NCIMB 11216, Rhodococcus ruber DSM 43338, Rhodococcus ruber DSM 44540 and Rhodococcus ruber DSM 44539, preferentially react with the (S)-enantiomer of the epoxide. Enantioselectivities (enantiomeric ratio, lnE values) show a rather large variation, ranging from almost no (lnE<1) to nearly complete selectivity (lnE>5.3). In addition, the response of the epoxide hydrolases stemming from the four organisms towards structural modifications of the substrate is different. Models for the enantioselectivity (enantiomeric ratio, ln E values) obtained by CoMFA and CoMSIA are of different but reasonable predictive power, e.g., q² _CV=0.701 and r²=0.937 for the CoMFA model of Rhodococcus ruber DSM 43338. Enantiomeric ratios for the test molecules can be well predicted. Plots of steric and electrostatic CoMFA (CoMSIA) fields allow conclusions to be drawn for the choice of the most suitable organism for a specific type of substrate.     

Trace analysis of trichlorobenzenes in fish by microwave-assisted extraction and gas chromatography-electron-capture detection

An analytical method consisting of extraction, clean-up, and analysis by gas chromatography-electron-capture detection (GC-ECD) was developed for the determination of trichlorobenzenes (TCBs) in fish samples. Two extraction methods, saponification and liquid-liquid extraction (S-LLE), and microwave-assisted extraction (MAE), were evaluated. In both cases, n-pentane was used as the extraction solvent. For S-LLE, the recoveries ranged from 66.6+/-9.1% for 1-bromo-4-chlorobenzene (4-BCB) to 93.5+/-4.9% for 1,2,4-trichlorobenzene (1,2,4-TCB). The recoveries were significantly lower, between 31.0+/-3.9% for 1,2,3-trichlorobenzene (1,2,3-TCB) and 52.3+/-3.0% for 1,3,5-trichlorobenzene (1,3,5-TCB), in the absence of fish. Proteins and glycerides of the fish tissue seemed to compete with TCBs for the base, and hence decreased their decomposition rate. In the case of MAE, the recoveries were highly dependent on the pressure applied during extraction. At 5 bar, much higher recoveries were obtained, from 66.7+/-15.6% for 4-BCB to 79.9+/-13.6% for 1,2,4-TCB, than at 1 bar. Sulfur formation was, however, observed at 5 bar, and interfered with the GC-ECD analysis of TCBs. Sulfur was adequately removed by copper powder treatment, which was shown not to affect the recovery of analytes. The recoveries of target analytes by S-LLE and MAE did not differ statistically (t-test, alpha = 0.01). Both methods were appropriate for the detection of TCBs at concentration levels typically observed in marine biota, i.e. approximately 1 ng/g. S-LLE was, however, more time consuming, and required larger volumes of high-purity organic solvents than MAE.     

Improved phenotyping of alpha 1-antichymotrypsin (ACT) by isoelectric focusing and immunoprinting: first demonstration of a deficient protein variant in the ACT system.

Genetic variation of human alpha 1-antichymotrypsin (ACT) was investigated in sera using thin-layer polyacrylamide gel isoelectric focusing (pH range 4.0-6.5) followed by immunoprinting with a monospecific anti-human ACT antibody. Sialidase-treated samples showed a microheterogeneous banding pattern which consisted of two major and several additional minor components with isoelectric points between pH 5.0 and 5.3. A population study of 200 unrelated individuals from southern Germany revealed no genetic variation. In a clinical investigation, however, we found a unique banding pattern in a female patient suffering from chronic obstructive pulmonary disease. In comparison with the monomorphic normal type the detected variant phenotype shows two additional bands that have lower intensities and are located cathodically to their major bands. Inheritance of the deficient IEF variant "ACT Bochum" was confirmed by a family study. To our knowledge this is the first genetic ACT mutant to be observed at the protein level.