Enantioselective Alternating Olefin-Carbon Monoxide Copolymerization: A new concept for activity and stereoselectivity

Cationic Pd-complexes modified by dicyclohexyl{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}phosphine ( 1a ) give very active catalytic systems for the regioregular isotactic specific copolymerization of propene with CO. Other alk-1-enes also give stereoregular and regioregular copolymers, even if with lower productivity. The copolymers are isolated as poly(4-alkyl-tetrahydrofuran-2,2,5,5-tetrayl-2-oxy-2-methylenes) B in the solid state and give the isomeric poly(2-alkyl-1-oxopropane-1,3-diyls) A by dissolution in (CF₃)₂CHOH. Solid polymer A (R = Et) is formed back at least partially when the dissolved material is reprecipitated from MeOH. The use of the related (ferrocenyl)diphosphine ligands 1b ? e and 2 as the catalyst modifier shows that the presence of both elements of chirality and of large substituents on the P-atoms of the ligand is necessary to achieve good stereocontrol, and that the large difference in basicity between the two P-atoms is probably the reason for the good catalytic activity.     

The (3He,n) reaction on 16O and 18O

The (³He, n) reaction on ¹⁶O and ¹⁸O has been used to study low-spin states in ¹⁸Ne and ²⁰Ne up to E_x ≈ 8 and 20 MeV, respectively. The measured neutron angular distributions have been analysed using DWBA. By a comparison with shell-model calculations in the (s, d) shell it is found that most of the two-proton transfer strength can be explained within that shell. Important contributions, however, from the (f, p) shell in low-lying negative parity states are also present.     

Study of the 12C(12C,n)23Mg reaction around the resonance at Ecm = 19.3 MeV

A strong selectivity of the ¹²C(¹²C,n)²³Mg reaction is observed in a resonance at $\text{E}{}_{\mathrm{<mtext>cm</mtext>}}\text{(}{}^{12}\text{C) = 19.3}\text{MeV}$. The neutron spectra and n-γ coincidence measurements show evidence for population of high-spin members of the ground- state rotational band in ²³Mg.     

Two enantioselective syntheses of the diol precursor of the biologically most active isomer of an insect growth regulator

The diol precursor (R)-3 of the insect growth regulator 2 was synthesized enantioselectively by two different routes: a) via enantioselective hydrogenation of the -hydroxy-ketone 4, catalyzed by a Ru-BINAP-catalyst and b) via resolution of the enantiomers of glycerol using (−)-camphor-10-sulfonamide 7 as chiral auxiliary.     

Resotron: A Novel Tunable Millimeter and Submillimeter Wave Source of Radiation

The need for tunable radiation sources in the millimeter and submillimeter range for spectroscopic purposes is still a research area of great interest. The tunable radiation source, proposed in this paper, is a special free electron laser device with the prerequisite of low electron energy. The output power density in the millimeter (GHz)-range is of the order of MW/cm² and in the submillimeter (THz)-range of the order of kW/cm². The device consists of an electron source with electron optics, wiggler/microwiggler, and a longitudinal magnetic field. The wiggler for the THz-regime has a very short wiggler period of approximately 400 m and could be manufactured with laser micromachining techniques. The free electron laser operates in magnetoresonance and shows surprisingly stable electron orbits and therefore narrow output frequencies. Computational results of the temporal behavior of the output power done with a multi-frequency code are reported.     

Harn: Formoltitration

Ohne ZusammenfassungVergl. auch diese Zeitschrift47, 547;49, 66.     

Enzymatic modification of lignocellulosic substances for the production of fiberboards

The object of the research is the development of enzyme systems for the enzymatic modification of wood fiber materials as well as fiber materials from annual plants for the production of glue-free fiberboards. The project is aimed first at the process development for the enzymatic modification and second at the development of cellulase/hemicellulase complexes on the basis of stillage as a substrate and inducer for the enzymatic modification. The results demonstrate that it is possible to substitute synthetic resins by means of activation and biocatalytic cross-linking of fibers with hydrolytic enzyme systems, in particular, for the production of medium-density fiberboards. The article is published in the original.     

Optimized and far-red-emitting variants of fluorescent protein eqFP611

Fluorescent proteins (FPs) emitting in the far-red region of the spectrum are highly advantageous for whole-body imaging applications because scattering and absorption of long-wavelength light is markedly reduced in tissue. We characterized variants of the red fluorescent protein eqFP611 with bright fluorescence emission shifted up to 639 nm. The additional red shift is caused by a trans-cis isomerization of the chromophore. The equilibrium between the trans and cis conformations is strongly influenced by amino acid residues 143 and 158. Pseudo monomeric tags were obtained by further genetic engineering. For the red chromophores of eqFP611 variants, molar extinction coefficients of up to approximately 150,000 were determined by an approach that is not affected by the presence of molecules with nonfunctional red chromophores. The bright fluorescence makes the red-shifted eqFP611 variants promising lead structures for the development of near-infrared fluorescent markers. The red fluorescent proteins performed well in cell biological applications, including two-photon imaging.     

Simple synthesis of 2-C-branched glyco-acetic acids

Only three steps are required for the selective synthesis of 2-C-branched glyco-acetic acids from glycals by radical addition and decarboxylation.